Warning
This post contains interactive examples. To visualize and interact
with them, you need to leave your RSS reader.
Imagine you rent office space for a three-day event. You quickly set up a few
Ethernet switches and tape some cables on the floor to get everyone online.
Unfortunately, Stan, your clumsiest coworker, kicks out a cable every time he
gets up for coffee. You could add extra cables, but then you d get a broadcast
storm: Ethernet packets that loop and multiply until nothing else gets through.
That s where the spanning tree protocol (STP) comes in. STP blocks just enough
of your spare cables to leave a loop-free tree. When Stan strikes again, it
rebuilds the tree in a second, leaving some time for Blobby, your one-person
support crew, to reconnect the cable.1 See for yourself: the diagram
below runs a real STP implementation in your browser!
:demo
A1 @0,0 prio=4096
A2 @0,1
A3 @0,2
A4 @0,3
B1 @1,0 prio=8192
B2 @1,1
B3 @1,2
B4 @1,3
C1 @2,0 prio=8192
C2 @2,1
C3 @2,2
C4 @2,3
A1 -- A2 hazard=0
A2 -- A3 hazard=0
A3 -- A4 hazard=0
B1 -- B2
B2 -- B3
B3 -- B4
C1 -- C2 hazard=0
C2 -- C3 hazard=0
C3 -- C4 hazard=0
A1 -- B1 cost=10
B1 -- C1 cost=10
A4 -- B4 cost=20
B4 -- C4 cost=20
Leo @-0.3,0.7 proto=none icon=
Mia @-0.3,1.3 proto=none icon=
Joy @0.3,0.7 proto=none icon=
Roy @0.3,1.3 proto=none icon=
A2 -- Leo hazard=0 A2:edge
A2 -- Mia hazard=0 A2:edge
A2 -- Joy hazard=0 A2:edge
A2 -- Roy hazard=0 A2:edge
Max @-0.3,1.7 proto=none icon=
Zoe @-0.3,2.3 proto=none icon=
Ada @0.3,1.7 proto=none icon=
Amy @0.3,2.3 proto=none icon=
A3 -- Max hazard=0 A3:edge
A3 -- Zoe hazard=0 A3:edge
A3 -- Ada hazard=0 A3:edge
A3 -- Amy hazard=0 A3:edge
Eli @0.7,0.7 proto=none icon=
Jay @0.7,1.3 proto=none icon=
Kai @1.3,0.7 proto=none icon=
Ben @1.3,1.3 proto=none icon=
B2 -- Eli hazard=0.2 B2:edge
B2 -- Jay hazard=0.2 B2:edge
B2 -- Kai hazard=0.2 B2:edge
B2 -- Ben hazard=0.2 B2:edge
Ava @0.7,1.7 proto=none icon=
Lea @0.7,2.3 proto=none icon=
Ivy @1.3,1.7 proto=none icon=
Rex @1.3,2.3 proto=none icon=
B3 -- Ava hazard=0.2 B3:edge
B3 -- Lea hazard=0.2 B3:edge
B3 -- Ivy hazard=0.2 B3:edge
B3 -- Rex hazard=0.2 B3:edge
Ana @1.7,0.7 proto=none icon=
Eve @1.7,1.3 proto=none icon=
Abe @2.3,0.7 proto=none icon=
Ian @2.3,1.3 proto=none icon=
C2 -- Ana hazard=0 C2:edge
C2 -- Eve hazard=0 C2:edge
C2 -- Abe hazard=0 C2:edge
C2 -- Ian hazard=0 C2:edge
Ned @1.7,1.7 proto=none icon=
Lou @1.7,2.3 proto=none icon=
Fay @2.3,1.7 proto=none icon=
Sue @2.3,2.3 proto=none icon=
C3 -- Ned hazard=0 C3:edge
C3 -- Lou hazard=0 C3:edge
C3 -- Fay hazard=0 C3:edge
C3 -- Sue hazard=0 C3:edge
Note
This article is also available as a video, but I advise you to
keep reading here to try the interactive demonstrations.
The basics
Designed in the 80s, the spanning tree protocol has evolved into a rapid
flavor (RSTP) and a VLAN-aware variation (MSTP).2 Any sound-minded
network engineer knows there are better alternatives, like BGP EVPN VXLAN.
Yet, because any switch speaks it, the venerable spanning tree protocol still
fills a niche.
We focus on RSTP: it replaced the original protocol in 2004. To eliminate
network loops, RSTP implements a complex state machine. Timers, link state
changes, and the link-local control frames a bridge receives from its neighbors
drive its transitions. These Ethernet frames are the Bridge Protocol Data
Units (BPDUs). You can watch them in action below: hit the Start button.
After some time, the topology converges to a tree: from the root
C11, there is a path to each bridge3 and no loop. In the upper right
corner, the interface displays a tree icon followed by the time it took to
reach this state. Cut a link and see how the protocol
finds an alternate path to reach C12 in less than a second. You can stop the
simulation, move it forward step by step, reset it to its initial state, or slow
it down with the snail mode . Don t worry about all the displayed
information: I explain it later.
All examples run in your browser, powered by MSTPD an open-source
user-space4 implementation of RSTP.5
Historical interlude
Radia Perlman, an inductee of the Internet Hall of Fame in 2014,
summarized the ancestor of STP she invented at DEC with this poem, later
included in a US patent:
I think that I shall never see
A graph more lovely than a tree.
A tree whose crucial property
Is loop-free connectivity.
A tree which must be sure to span
So packets can reach every LAN.
First, the root must be selected.
By ID, it is elected.
Least cost paths from root are traced.
In the tree, these paths are placed.
A mesh is made by folks like me,
Then bridges find a spanning tree.
Radia Perlman, Algorhyme.
Electing the root bridge
To build a tree, RSTP first elects the bridge with the lowest bridge
identifier as the root bridge. The bridge identifier combines the priority
and the MAC address: 8192.6e:2b:10:a0:5f:29.
In the example below, S1 and S2 have priorities of 4,096 and 8,192: S1 becomes
root. S4 has a priority of 12,288, while S3 keeps the default priority of
32,768:6 S4 becomes root. S5 and S6 don t have a specific priority, so
the lowest MAC address wins and S5 becomes root.
Each non-root bridge chooses its root port, the one with the lowest-cost
path to the root. Unless you override it, each bridge derives the link cost
from the speed: 20,000 for 1 Gbps. In case of equality, the lowest port
identifier wins.
Each remaining port becomes a designated port if the BPDU it sends is
better than the BPDU it receives. Otherwise, it becomes an alternate port.
Later, if the root port goes down, the best alternate port becomes the new
root port. The tiebreakers for the best BPDU are:
In the example above, after convergence, S1 is the root bridge
because it has a priority of 4,096, while the other bridges have a priority of
32,768. All its ports are designated ports because the accumulated cost to the
root is 0.
S2 s port facing S1 becomes a root port because it has the lowest accumulated
cost to the root 20,000 vs 40,000. S3 has two ports facing S1, and the one with
the lowest port identifier becomes the root port 0x8000 vs 0x8001. The other
candidate is an alternate port because the remote port on the link sends a
better BPDU, with an accumulated cost of 0. On the segment between S2 and S3,
S2 s port wins: while both bridges have the same accumulated cost to the root
(20,000), S2 s bridge identifier is smaller 32768.02:00:00:00:00:01 vs
32768.02:00:00:00:00:02.
Spanning Tree Protocol Protocol Identifier: Spanning Tree Protocol (0x0000) Protocol Version Identifier: Rapid Spanning Tree (2) BPDU Type: Rapid/Multiple Spanning Tree (0x02) Root Identifier: 4096.02:00:00:00:00:00
Root Path Cost: 20000
Bridge Identifier: 32768.02:00:00:00:00:01
Port identifier: 0x8002
If you cut the active link between S1 and S3, S3 promotes
the best alternate port to root port. If you also disable the second
link, S3 chooses the remaining alternate port as a
root port. But if you disable the link between S1 and
S2, S2 needs a bit more work to elect a new root port
because it does not have an alternate port.
Unless a specific event happens, designated ports send BPDUs every 2
seconds.9 If a bridge does not
receive BPDUs from its neighbor for 3 consecutive hello periods, it considers
the neighbor dead and removes the port information.
Port state transition
Each port can have one of three states. The diagram displays a background color
for each state:
discarding (red),
learning (yellow), or
forwarding (green).
A root port transitions automatically to the forwarding state. An alternate
port stays in the discarding state. A designated port has two options to
transition from the discarding state to the forwarding state:
If the port is an edge port, either through configuration or because the
remote device does not speak any flavor of STP, the bridge assumes the device
won t participate in the protocol and cannot create a loop. In this case, the
designated port immediately transitions to the forwarding state.
Otherwise, it sends a proposal to its downstream neighbor. If the remote
bridge agrees that the received BPDU is better than any other BPDU stored
for other ports, it elects the receiving port as its root port and starts the
synchronization process: it transitions all non-edge non-synced designated
ports to the discarding state to avoid a loop. Then, it sends back an
agreement. Upon receiving the agreement, the peer designated port
transitions to the forwarding state.10
In the topology above, H1, H2, H3, and H4 are end devices not participating in
the protocol. We configure the ports they connect to as edge ports, so these
ports immediately move to the forwarding state.
Use the step button to move the simulation forward. The clock moves to 1
second. Step again and S1 and S2 send a proposal to
each other. Here is the proposal from S2:
Spanning Tree Protocol Protocol Identifier: Spanning Tree Protocol (0x0000) Protocol Version Identifier: Rapid Spanning Tree (2) BPDU Type: Rapid/Multiple Spanning Tree (0x02) BPDU flags: 0x4e, Agreement, Port Role: Designated, Proposal
0... .... = Topology Change Acknowledgment: No
.1.. .... = Agreement: Yes
..0. .... = Forwarding: No
...0 .... = Learning: No
.... 11.. = Port Role: Designated (3).... ..1. = Proposal: Yes
.... ...0 = Topology Change: No
Root Identifier: 32768.02:00:00:00:00:01
Root Path Cost: 0
Bridge Identifier: 32768.02:00:00:00:00:01
Port identifier: 0x8001
S1 ignores it: its own root identifier is lower. When S2 receives a similar
proposal from S1, it accepts S1 as its root bridge. It also elects the port to
S1 as the root port and starts the synchronization process. The two designated
ports are already discarding, so no change here. Step
again and S2 sends two BPDUs to S1. In one of them, the
agreement bit is 1 and the proposal bit is 0. It also shows that S2 accepted S1
as the root bridge and its root port is now in the forwarding state. When
receiving this BPDU, S1 transitions its own designated port to the forwarding
state. From this point, the link between S1 and S2 forwards user traffic.
Spanning Tree Protocol Protocol Identifier: Spanning Tree Protocol (0x0000) Protocol Version Identifier: Rapid Spanning Tree (2) BPDU Type: Rapid/Multiple Spanning Tree (0x02) BPDU flags: 0x79, Agreement, Forwarding, Learning, Port Role: Root, Topology Change
0... .... = Topology Change Acknowledgment: No
.1.. .... = Agreement: Yes
..1. .... = Forwarding: Yes
...1 .... = Learning: Yes
.... 10.. = Port Role: Root (2).... ..0. = Proposal: No
.... ...1 = Topology Change: Yes
Root Identifier: 4096.02:00:00:00:00:00
Root Path Cost: 20000
Bridge Identifier: 32768.02:00:00:00:00:01
Port identifier: 0x8001
Let s look at what happened to S5. Reset the simulation and step
twice. S5 exchanges BPDUs with both S3
and S6. Since S5 has a lower root identifier than S3 and S6, it stays the root
bridge, while S3 and S6 accept the proposal and elect their root ports. S3 and
S6 start the synchronization process. S6 s port to H4 keeps forwarding because
it is an edge port. Move one step. Both S3 and S6 send
an agreement back to S5, which transitions both designated ports to the
forwarding state. Yet, the link between S5 and S3 keeps discarding user traffic!
If you look carefully, S3 s port toward S5 is now a designated port, not a root
port. During the same step, S3 also receives a better BPDU
from S2 with S1 as the root bridge. It elects its port to S2 as the root port
and downgrades the port to S5 to a designated port, which stays in the
discarding state.
On the next step, things get a bit tricky. S3 sends a
proposal to S5:11
Spanning Tree Protocol Protocol Identifier: Spanning Tree Protocol (0x0000) Protocol Version Identifier: Rapid Spanning Tree (2) BPDU Type: Rapid/Multiple Spanning Tree (0x02) BPDU flags: 0x4f, Agreement, Port Role: Designated, Proposal, Topology Change
0... .... = Topology Change Acknowledgment: No
.1.. .... = Agreement: Yes
..0. .... = Forwarding: No
...0 .... = Learning: No
.... 11.. = Port Role: Designated (3).... ..1. = Proposal: Yes
.... ...1 = Topology Change: Yes
Root Identifier: 4096.02:00:00:00:00:00
Root Path Cost: 40000
Bridge Identifier: 32768.02:00:00:00:00:02
Port identifier: 0x8002
S5 elects S1 as its root bridge and the port toward S3 as its root port. It
starts its synchronization process, but the designated port to S6 does not
move into the discarding state. Why? That port stays a designated port and its
neighbor S6 has already sent an agreement on the link, so the port keeps its
synced status.
Now, let s step back to look at what happens to S6. At this point,
S6 believes S5 is the root bridge. Step once and S4 sends
a new proposal to S6. S6 accepts the proposal, elects S1 as the root bridge and
the port to S4 as its root port. The role of the port facing S5 changes: from a
root port, it becomes a designated port. Because its peer keeps advertising an
inferior BPDU on the link, this port becomes disputed and moves to the
discarding state. The root port transitions to the forwarding state and the link
starts forwarding immediately because S4 s designated port is already in the
forwarding state. If we step one more time, S5 and S6
exchange two BPDUs. The one from S5 is better because of its lower bridge
identifier. S5 s port stays a designated port, while S6 downgrades its own port
to an alternate port.
Let s rewind to the start one last time: cut the link between S1 and S2, run
the simulation until the topology is stable, stop the
simulation, and restore the link between S1 and S2. During the first
step, S1 and S2 exchange proposals. S2
elects S1 as the root bridge instead of S5 and the port to S1 as the root port.
It downgrades the previous root port to a designated port and moves it into the
discarding state. The other designated port stays synced and keeps its
forwarding state. At the next step, S2 sends
an agreement to S1 and the link between them starts forwarding user traffic. It
also sends a proposal to S3, but not to S4.
Instead, it sends a regular BPDU to S4. S4
still elects S1 as its root bridge and the port to S2 as its root port. It
demotes its previous root port, the one to S3, to a designated port, which
transitions to the discarding state because of the root port change. The other
alternate port, to S6, also becomes a designated port and stays in the
discarding state. The new root port moves to the forwarding state. On the next
step, S4 s port to S3 settles as an
alternate port after receiving a better BPDU from S3.
RSTP is a giant state machine split into smaller ones: bridge detection, port
information, port protocol migration, port role selection, port role
transitions, port receive, port state transitions, port timers, port transmit,
and topology change. Some of them are per bridge, some per port. Each bridge
runs an instance. Time, operational port state changes, and the BPDUs it
receives from other instances drive the transitions. Being event-driven makes
RSTP more efficient but also more difficult to understand.
Placeholder for the Port Information state machine extracted from IEEE 802.1Q-2005, page 182. Pending IEEE authorization for reproduction, this is the blueprint for the Western Australian Government Railways class Msa Garratt articulated steam locomotive.
Topology change notification
A bridge populates a MAC address table: it associates each source MAC address
with the port that last received it. When forwarding an Ethernet frame, it looks
up this table to choose the right port.12 When a link fails, a connected
fridge reachable through one port may become reachable through another one. The
affected bridges should flush the MAC addresses they learned, because these
entries may now be wrong.
For this purpose, RSTP implements topology change notifications using a
flooding mechanism. When a non-edge port transitions to the forwarding state, a
bridge generates BPDUs with the topology change (TC) bit set. It sends them to
all the non-edge designated ports and to the root port. It also flushes the MAC
address table on these ports. When a bridge receives such a BPDU, it propagates
the notification to all non-edge designated ports and the root port, except the
one the notification came from. It also flushes the MAC address table on these
ports. In the examples, the BPDUs with the TC bit set to 1 have a red circle.
Start the simulation and wait a few seconds for the topology to
settle. Stop the simulation and disable the link between S2 and
S5. S5 elects the port facing S4 as the root port, which
transitions immediately to the forwarding state. Step
once and S5 emits a BPDU with the TC bit set to 1:
Spanning Tree Protocol Protocol Identifier: Spanning Tree Protocol (0x0000) Protocol Version Identifier: Rapid Spanning Tree (2) BPDU Type: Rapid/Multiple Spanning Tree (0x02) BPDU flags: 0x79, Agreement, Forwarding, Learning, Port Role: Root, Topology Change
0... .... = Topology Change Acknowledgment: No
.1.. .... = Agreement: Yes
..1. .... = Forwarding: Yes
...1 .... = Learning: Yes
.... 10.. = Port Role: Root (2).... ..0. = Proposal: No
.... ...1 = Topology Change: Yes
Root Identifier: 4096.02:00:00:00:00:00
Root Path Cost: 40000
Bridge Identifier: 32768.02:00:00:00:00:04
Port identifier: 0x8002
S4 receives this BPDU. It flushes the MAC address table on the port facing S1:
while LPT was previously reachable through this port, it is now reachable
through S5. Step once. S4 sends S1 a BPDU
with the TC bit set to 1. When S1 receives this BPDU, it flushes the MAC address
table on the ports facing S2 and S3. Step
once and S1 sends a notification to S2 and
S3. Step once again and S2 sends a notification to
S3, while S3 does nothing because the port toward S2 is an alternate port. S3
does not flush any MAC address table: LPT is still reachable through its port to
S1.
If you step a bit more, you will see that some of the
periodic BPDUs keep the TC bit set to 1. Each port runs a timer equal to the
hello timer plus one second.13 The timer starts when the port emits a
notification. Until it expires, the port sets the TC bit to 1 in every BPDU it
sends. You can also see some periodic BPDUs
without the TC bit: they originate from a port that only received a notification
and therefore did not arm its timer.
Security
RSTP is weak against configuration errors and malicious actors. A bridge not
talking RSTP can create a loop. An attacker can insert themselves into the
topology to disrupt the service, spy on the traffic, or alter it.
To mitigate such problems, you need to identify the edge ports. An edge port
connects to an end device, like a PC or a printer. Such devices do not generate
BPDUs and cannot create a loop. RSTP defines two related flags:
When true, AdminEdge initializes a port as an edge port. It defaults to
false.
When true, AutoEdge lets a port become an edge port when it does not
receive BPDUs for 3 seconds. It defaults to true.
If an edge port receives a BPDU, regardless of the values of these two flags, it
reverts to a non-edge port.
In the topology above, S1, S2, S3, S4, S5, and S6 act as bridges, while H1, H2,
H3, H4, H5, and H6 act as end devices:
S1 and H1 are on a port without a specific configuration: AutoEdge is true,
AdminEdge is false,
S2 and H2 are on a port where AdminEdge is true,
S3 and H3 are on a port where AutoEdge is false and AdminEdge is true,
S4 and H4 are on a port where AutoEdge is false.
If you start the simulation and wait about 20 seconds, links to S1,
S2, S3, S4, H1, H2, H3, and H4 eventually forward user traffic: none of the
flags matter.
But what about the two remaining pairs? S5 and H5 connect to a network port.
Such a port enables a non-standard feature: bridge assurance. The port
transmits BPDUs regardless of its role. If it does not receive BPDUs for 3
consecutive hello periods, it transitions to the discarding state. On the link
between R0 and S5, you can see BPDUs traveling in both
directions, unlike the other links, where only
designated ports send BPDUs.
S6 and H6 connect to a port where AdminEdge is true and BPDU guard is
enabled. This is another non-standard feature that shuts down a port if it
receives a BPDU.
In summary, if you expect a port to be an edge port, you should set AdminEdge
to true and enable BPDU guard. Otherwise, declare it as a network port.
Why RSTP today?
A compelling use case for RSTP today is an out-of-band network for a datacenter,
since you can tolerate an outage of a few seconds. The configuration is minimal
and you can use cheap switches, like a Cisco 2960X.14 You need two
switches acting as root bridges, and you build several loops to connect OOB
switches in each cabinet. This simple design survives one failure on each
loop.15
This topology converges in about 6 seconds. Each loop should stay
small (around 16 bridges) to reduce the probability of a double failure and to
avoid sharing too much bandwidth. The design can evolve a bit without adding too
much complexity: one VLAN per loop or one bridge domain per loop.
How large can a network be?
The maximum age, whose default value is 20, governs the maximum distance of a
bridge from the root. The topology below is too big for BPDUs from R1 to reach
beyond S20.16
Once the topology settles, part of the network considers R1 the
root, while the other votes for R2. At the boundary, S20 tries to start a
synchronization with S21 to move its designated port to the forwarding state.
The BPDU looks like this:
Spanning Tree Protocol Protocol Identifier: Spanning Tree Protocol (0x0000) Protocol Version Identifier: Rapid Spanning Tree (2) BPDU Type: Rapid/Multiple Spanning Tree (0x02) BPDU flags: 0x4e, Agreement, Port Role: Designated, Proposal
Root Identifier: 4096.02:00:00:00:00:00
Root Path Cost: 400000
Bridge Identifier: 32768.02:00:00:00:00:15
Port identifier: 0x8002
Message Age: 20
Max Age: 20
S21 rejects it because the message age equals the maximum age. On the other
hand, the BPDU S21 sends to S20 looks like this:
Spanning Tree Protocol Protocol Identifier: Spanning Tree Protocol (0x0000) Protocol Version Identifier: Rapid Spanning Tree (2) BPDU Type: Rapid/Multiple Spanning Tree (0x02) BPDU flags: 0x7c, Agreement, Forwarding, Learning, Port Role: Designated
Root Identifier: 4096.02:00:00:00:00:01
Root Path Cost: 320000
Bridge Identifier: 32768.02:00:00:00:00:16
Port identifier: 0x8001
Message Age: 16
Max Age: 20
This is not enough to change S20 s root port because S20 has a lower root
identifier4096.02:00:00:00:00:00 vs 4096.02:00:00:00:00:01.
Fixing the link between R1 and R2 resolves the issue. The
maximum message age any packet carries is now 18, below the configured maximum
age. But it only works until another link breaks. A plausible fix is to increase
the maximum age to 40.17
How fast is RSTP?
RSTP usually converges in a couple of seconds at startup. It often repairs a
tree in less than a second. Even the 38-bridge topology takes less than 10
seconds to converge.18 Some topologies can take a bit more time to recover
when the root bridge becomes unavailable.19
In the topology above, start the simulation, wait for convergence,
hit stop, and cut the link between R0 and S1. The topology is
already optimal, but RSTP has a hard time converging again.
First, S1 loses its root port. It has no more information about R0 and elects
itself as the root bridge. It keeps its ports to S2 and S3 as designated ports
in the forwarding state. Step once and it
sends a BPDU to both S2 and S3 to let them know about the root change. When
receiving it, S2 accepts S1 as its root because it does not have a better root
on another port. It elects the port to S1 as its root port. The other port stays
a designated port. Both ports keep forwarding.
When receiving the BPDU from S1, S3 behaves differently: it knows R0 as a better
root than S1 through its alternate port to S2. It promotes this port to a root
port and demotes the port facing S1 to a designated port, which requires a new
agreement. Step once and S3 sends a proposal to
S1 with R0 as the root bridge. S1 elects R0 as the root bridge and promotes its
port to S3 as a root port.
During the same step, S3 also receives a BPDU from
S2 stating that S1 is the root bridge. Therefore, S3 has no port left with R0 as
the root bridge: it elects S1 as the root bridge and its port to S2 as the root
port. Step once and its next BPDU to S1 includes
this information: S1 elects itself again as the root bridge. But during the
same wave, S1 sends a proposal to S2 with R0 as
the root bridge. While S1 and S3 agree that S1 is the root bridge, S2 now
believes this is R0! In turn, S2 again convinces S3
that R0 is the root bridge, S3 convinces S1, S1 convinces S2, and S2 convinces
S3.
This could go on forever, but it does not. The BPDUs saying R0 is root
eventually age out when the message age goes past the maximum age. In the
example above, at the eleventh second, S2 sends a
BPDU to S3 with R0 as root, but S3 drops it because its message age reached the
maximum. With some luck, the topology can also converge faster if a port stops
transmitting new BPDUs after tripping the transmit hold count, whose default
value is 6 per second.
About MSTP
MSTP is the VLAN-aware version of RSTP: it runs several instances of RSTP and
lets the administrator map each VLAN to a specific instance. For example, you
can map VLANs 100 to 200 to a first instance, and 300 to 400 to a second
instance. The remaining VLANs map to a special instance named the Internal
Spanning Tree (IST). MSTP adds its own complexity, but the gist is that you have
several logical topologies acting independently. If you want to dig deeper, have
a look at MSTP Tutorial Part I: Inside a Region.
About the interactive examples
The interactive examples run MSTPD directly in your browser, compiled to
WebAssembly with emscripten. A C API replaces the code talking to the
Linux kernel: it manages bridges and ports, exports state as JSON, and drives
time deterministically. A JavaScript wrapper makes it more user-friendly:
importloadMSTPDfrom"./dist/mstpd.mjs";constmstp=awaitloadMSTPD();// Create 3 bridgesconsta=mstp.createBridge("A",priority:4096 );constb=mstp.createBridge("B",priority:8192 );constc=mstp.createBridge("C");// Each bridge has two portsconsta1=a.addPort("a-b",portno:1 );consta2=a.addPort("a-c",portno:2 );constb1=b.addPort("b-a",portno:1 );constb2=b.addPort("b-c",portno:2 );constc1=c.addPort("c-a",portno:1 );constc2=c.addPort("c-b",portno:2 );// Build a triangle topologymstp.link(a1,b1);mstp.link(a2,c1);mstp.link(b2,c2);// Enable all bridges and portsfor(constbrof[a,b,c])br.enable();for(constpof[a1,a2,b1,b2,c1,c2])p.enable();// Execute 40 seconds' worth of wall clock and display the topologymstp.step(40);console.log("Topology:",mstp.topology());
Several dozen unit tests explore the features of MSTPD and check that they work
correctly in this environment:
$ node--test*.test.mjs
two bridges: lower priority becomes root (41.657342ms) triangle loop: exactly one port blocks and all agree on the root (5.832ms) breaking the active link reconverges and restoring recovers (18.730753ms)[ ] tests 40 pass 40 fail 0[ ] duration_ms 396.190897
Additional JavaScript code looks for specific <pre> blocks containing a
topology definition and turns them into interactive widgets. You can inspect
and modify the definition by hitting the edit button.
There is also a cool trick to tell whether the topology has converged. After
each step, we save a snapshot of the simulation memory, play 50 seconds worth
of simulation to check if the topology is stable, and travel back in time by
restoring that snapshot.
The complete code lives on GitHub. I am happy with the result. It can be
difficult to follow everything happening during a single step, but stepping
forward and backward helps. I plan to use the same approach in future blog posts
about networking features.
Note
Michael Lynch reviewed a first draft of this article. He authored
Refactoring English, a book to sharpen your writing for blog posts,
documentation, commit messages, and tutorials. Any errors are still mine!
The sprites for Stan and Blobby come from Craftpix, the coffee
cups from Yanin.
The priority is a multiple of 4,096: with MSTP, the lower 12 bits
of the bridge priority encode the MST instance identifier, leaving only the
upper 4 bits for the configured priority.
To inspect the BPDUs crossing a link, select it, click the
Download packets button, and open the file with Wireshark.
A backup port only exists if the bridge has several ports on the same
collision domain. This should not happen in a switched network.
This is the value of the hello timer. It used to be configurable,
but IEEE 802.1Q-2005 pins it to 2. MSTPD does not allow another value.
If the peer port does not receive an agreement after the hello
timer elapses or the maximum age if the port has just come up it falls back
to the timer-based method for compatibility with STP: it transitions to
the learning state, waits again for the hello timer to expire, and
transitions to the forwarding state.
As in many proposals, S3 also sets the agreement bit to 1. The
proposal bit says I am the designated port on this link and I want to
transition to the forwarding state. The agreement bit says I am already in
sync with the rest of my bridge on this root information. Both can be true.
If it finds no entry, the bridge duplicates the Ethernet frame on all
ports, except the incoming one. The same happens if the destination MAC
address is the broadcast one (ff:ff:ff:ff:ff:ff). This behavior bootstraps
the learning process.
This timer makes RSTP resistant to packet loss.
You can get them for less than US$100 through a broker. All the ports
run PVST+ by default and automatically fall back to plain RSTP.
If you look closely at what happens at t=2s, you can see that R2 is
gaining popularity as root: S17 to S36 believe R2 is the root bridge. S16
does not follow because we hit the maximum age. Later, S17 to S20 reverse
their position. I ll let you explore the state of the various bridges to
understand the root cause.
When increasing the maximum age to 40, you also need to
increase the forward delay to 21 (:forward-delay 21), as the standard
enforces this condition: 2 (Forward Delay 1) Max Age. For this
specific topology, you could also increase the maximum age to 37 and
forward-delay to 20.
The simulation may seem slow, but it does not run in real time. Look at
the current timestamp in the upper right corner to know the wall clock, e.g.
t=8s. Once the topology stabilizes, the same corner shows the convergence
time, e.g. 2s.
Long-term Linux users may remember that Alan Cox used to write an online diary. This was before the concept of a "Weblog" had really become a thing, and there certainly weren't any expectations around what one was used for - while now blogging tends to imply a reasonably long-form piece on a specific topic, Alan was just sitting there noting small life concerns or particular technical details in interesting problems he'd solved that day. For me, that was fascinating. I was trying to figure out how to get into kernel development, and was trying to read as much LKML as I could to figure out how kernel developers did stuff. But when you see discussion on LKML, you're frequently missing the early stages. If an LKML patch is a picture of an owl, I wanted to know how to draw the owl, and most of the conversations about starting in kernel development were very "Draw two circles. Now draw the rest of the owl". Alan's musings gave me insight into the thought processes involved in getting from "Here's the bug" to "Here's the patch" in ways that really wouldn't have worked in a more long-form medium.
For the past decade or so, as I moved away from just doing kernel development and focused more on security work instead, Twitter's filled a similar role for me. I've seen people just dumping their thought process as they work through a problem, helping me come up with effective models for solving similar problems. I've learned that the smartest people in the field will spend hours (if not days) working on an issue before realising that they misread something back at the beginning and that's helped me feel like I'm not unusually bad at any of this. It's helped me learn more about my peers, about my field, and about myself.
Twitter's now under new ownership that appears to think all the worst bits of Twitter were actually the good bits, so I've mostly bailed to the Fediverse instead. There's no intrinsic length limit on posts there - Mastodon defaults to 500 characters per post, but that's configurable per instance. But even at 500 characters, it means there's more room to provide thoughtful context than there is on Twitter, and what I've seen so far is more detailed conversation and higher levels of meaningful engagement. Which is great! Except it also seems to discourage some of the posting style that I found so valuable on Twitter - if your timeline is full of nuanced discourse, it feels kind of rude to just scream "THIS FUCKING PIECE OF SHIT IGNORES THE HIGH ADDRESS BIT ON EVERY OTHER WRITE" even though that's exactly the sort of content I'm there for.
And, yeah, not everything has to be for me. But I worry that as Twitter's relevance fades for the people I'm most interested in, we're replacing it with something that's not equivalent - something that doesn't encourage just dropping 50 characters or so of your current thought process into a space where it can be seen by thousands of people. And I think that's a shame.
A few days ago
an
article in the Norwegian Computerworld magazine about how version
2.0 of
European
Interoperability Framework has been successfully lobbied by the
proprietary software industry to remove the focus on free software.
Nothing very surprising there, given
earlier
reports on how Microsoft and others have stacked the committees in
this work. But I find this very sad. The definition of
an
open standard from version 1 was very good, and something I
believe should be used also in the future, alongside
the
definition from Digistan. Version 2 have removed the open
standard definition from its content.
Anyway, the news reminded me of the great reply sent by Dr. Edgar
Villanueva, congressman in Peru at the time, to Microsoft as a reply
to Microsofts attack on his proposal regarding the use of free software
in the public sector in Peru. As the text was not available from a
few of the URLs where it used to be available, I copy it here from
my
source to ensure it is available also in the future. Some
background information about that story is available in
an article from
Linux Journal in 2002.
Lima, 8th of April, 2002
To: Se or JUAN ALBERTO GONZ LEZ
General Manager of Microsoft Per
Dear Sir:
First of all, I thank you for your letter of March 25, 2002 in which you state the official position of Microsoft relative to Bill Number 1609, Free Software in Public Administration, which is indubitably inspired by the desire for Peru to find a suitable place in the global technological context. In the same spirit, and convinced that we will find the best solutions through an exchange of clear and open ideas, I will take this opportunity to reply to the commentaries included in your letter.
While acknowledging that opinions such as yours constitute a significant contribution, it would have been even more worthwhile for me if, rather than formulating objections of a general nature (which we will analyze in detail later) you had gathered solid arguments for the advantages that proprietary software could bring to the Peruvian State, and to its citizens in general, since this would have allowed a more enlightening exchange in respect of each of our positions.
With the aim of creating an orderly debate, we will assume that what you call "open source software" is what the Bill defines as "free software", since there exists software for which the source code is distributed together with the program, but which does not fall within the definition established by the Bill; and that what you call "commercial software" is what the Bill defines as "proprietary" or "unfree", given that there exists free software which is sold in the market for a price like any other good or service.
It is also necessary to make it clear that the aim of the Bill we are discussing is not directly related to the amount of direct savings that can by made by using free software in state institutions. That is in any case a marginal aggregate value, but in no way is it the chief focus of the Bill. The basic principles which inspire the Bill are linked to the basic guarantees of a state of law, such as:
Free access to public information by the citizen.
Permanence of public data.
Security of the State and citizens.
To guarantee the free access of citizens to public information, it is indispensable that the encoding of data is not tied to a single provider. The use of standard and open formats gives a guarantee of this free access, if necessary through the creation of compatible free software.
To guarantee the permanence of public data, it is necessary that the usability and maintenance of the software does not depend on the goodwill of the suppliers, or on the monopoly conditions imposed by them. For this reason the State needs systems the development of which can be guaranteed due to the availability of the source code.
To guarantee national security or the security of the State, it is indispensable to be able to rely on systems without elements which allow control from a distance or the undesired transmission of information to third parties. Systems with source code freely accessible to the public are required to allow their inspection by the State itself, by the citizens, and by a large number of independent experts throughout the world. Our proposal brings further security, since the knowledge of the source code will eliminate the growing number of programs with *spy code*.
In the same way, our proposal strengthens the security of the citizens, both in their role as legitimate owners of information managed by the state, and in their role as consumers. In this second case, by allowing the growth of a widespread availability of free software not containing *spy code* able to put at risk privacy and individual freedoms.
In this sense, the Bill is limited to establishing the conditions under which the state bodies will obtain software in the future, that is, in a way compatible with these basic principles.
From reading the Bill it will be clear that once passed:
the law does not forbid the production of proprietary software
the law does not forbid the sale of proprietary software
the law does not specify which concrete software to use
the law does not dictate the supplier from whom software will be bought
the law does not limit the terms under which a software product can be licensed.
What the Bill does express clearly, is that, for software to be acceptable for the state it is not enough that it is technically capable of fulfilling a task, but that further the contractual conditions must satisfy a series of requirements regarding the license, without which the State cannot guarantee the citizen adequate processing of his data, watching over its integrity, confidentiality, and accessibility throughout time, as these are very critical aspects for its normal functioning.
We agree, Mr. Gonzalez, that information and communication technology have a significant impact on the quality of life of the citizens (whether it be positive or negative). We surely also agree that the basic values I have pointed out above are fundamental in a democratic state like Peru. So we are very interested to know of any other way of guaranteeing these principles, other than through the use of free software in the terms defined by the Bill.
As for the observations you have made, we will now go on to analyze them in detail:
Firstly, you point out that: "1. The bill makes it compulsory for all public bodies to use only free software, that is to say open source software, which breaches the principles of equality before the law, that of non-discrimination and the right of free private enterprise, freedom of industry and of contract, protected by the constitution."
This understanding is in error. The Bill in no way affects the rights you list; it limits itself entirely to establishing conditions for the use of software on the part of state institutions, without in any way meddling in private sector transactions. It is a well established principle that the State does not enjoy the wide spectrum of contractual freedom of the private sector, as it is limited in its actions precisely by the requirement for transparency of public acts; and in this sense, the preservation of the greater common interest must prevail when legislating on the matter.
The Bill protects equality under the law, since no natural or legal person is excluded from the right of offering these goods to the State under the conditions defined in the Bill and without more limitations than those established by the Law of State Contracts and Purchasing (T.U.O. by Supreme Decree No. 012-2001-PCM).
The Bill does not introduce any discrimination whatever, since it only establishes *how* the goods have to be provided (which is a state power) and not *who* has to provide them (which would effectively be discriminatory, if restrictions based on national origin, race religion, ideology, sexual preference etc. were imposed). On the contrary, the Bill is decidedly antidiscriminatory. This is so because by defining with no room for doubt the conditions for the provision of software, it prevents state bodies from using software which has a license including discriminatory conditions.
It should be obvious from the preceding two paragraphs that the Bill does not harm free private enterprise, since the latter can always choose under what conditions it will produce software; some of these will be acceptable to the State, and others will not be since they contradict the guarantee of the basic principles listed above. This free initiative is of course compatible with the freedom of industry and freedom of contract (in the limited form in which the State can exercise the latter). Any private subject can produce software under the conditions which the State requires, or can refrain from doing so. Nobody is forced to adopt a model of production, but if they wish to provide software to the State, they must provide the mechanisms which guarantee the basic principles, and which are those described in the Bill.
By way of an example: nothing in the text of the Bill would prevent your company offering the State bodies an office "suite", under the conditions defined in the Bill and setting the price that you consider satisfactory. If you did not, it would not be due to restrictions imposed by the law, but to business decisions relative to the method of commercializing your products, decisions with which the State is not involved.
To continue; you note that:" 2. The bill, by making the use of open source software compulsory, would establish discriminatory and non competitive practices in the contracting and purchasing by public bodies..."
This statement is just a reiteration of the previous one, and so the response can be found above. However, let us concern ourselves for a moment with your comment regarding "non-competitive ... practices."
Of course, in defining any kind of purchase, the buyer sets conditions which relate to the proposed use of the good or service. From the start, this excludes certain manufacturers from the possibility of competing, but does not exclude them "a priori", but rather based on a series of principles determined by the autonomous will of the purchaser, and so the process takes place in conformance with the law. And in the Bill it is established that *no one* is excluded from competing as far as he guarantees the fulfillment of the basic principles.
Furthermore, the Bill *stimulates* competition, since it tends to generate a supply of software with better conditions of usability, and to better existing work, in a model of continuous improvement.
On the other hand, the central aspect of competivity is the chance to provide better choices to the consumer. Now, it is impossible to ignore the fact that marketing does not play a neutral role when the product is offered on the market (since accepting the opposite would lead one to suppose that firms' expenses in marketing lack any sense), and that therefore a significant expense under this heading can influence the decisions of the purchaser. This influence of marketing is in large measure reduced by the bill that we are backing, since the choice within the framework proposed is based on the *technical merits* of the product and not on the effort put into commercialization by the producer; in this sense, competitiveness is increased, since the smallest software producer can compete on equal terms with the most powerful corporations.
It is necessary to stress that there is no position more anti-competitive than that of the big software producers, which frequently abuse their dominant position, since in innumerable cases they propose as a solution to problems raised by users: "update your software to the new version" (at the user's expense, naturally); furthermore, it is common to find arbitrary cessation of technical help for products, which, in the provider's judgment alone, are "old"; and so, to receive any kind of technical assistance, the user finds himself forced to migrate to new versions (with non-trivial costs, especially as changes in hardware platform are often involved). And as the whole infrastructure is based on proprietary data formats, the user stays "trapped" in the need to continue using products from the same supplier, or to make the huge effort to change to another environment (probably also proprietary).
You add: "3. So, by compelling the State to favor a business model based entirely on open source, the bill would only discourage the local and international manufacturing companies, which are the ones which really undertake important expenditures, create a significant number of direct and indirect jobs, as well as contributing to the GNP, as opposed to a model of open source software which tends to have an ever weaker economic impact, since it mainly creates jobs in the service sector."
I do not agree with your statement. Partly because of what you yourself point out in paragraph 6 of your letter, regarding the relative weight of services in the context of software use. This contradiction alone would invalidate your position. The service model, adopted by a large number of companies in the software industry, is much larger in economic terms, and with a tendency to increase, than the licensing of programs.
On the other hand, the private sector of the economy has the widest possible freedom to choose the economic model which best suits its interests, even if this freedom of choice is often obscured subliminally by the disproportionate expenditure on marketing by the producers of proprietary software.
In addition, a reading of your opinion would lead to the conclusion that the State market is crucial and essential for the proprietary software industry, to such a point that the choice made by the State in this bill would completely eliminate the market for these firms. If that is true, we can deduce that the State must be subsidizing the proprietary software industry. In the unlikely event that this were true, the State would have the right to apply the subsidies in the area it considered of greatest social value; it is undeniable, in this improbable hypothesis, that if the State decided to subsidize software, it would have to do so choosing the free over the proprietary, considering its social effect and the rational use of taxpayers money.
In respect of the jobs generated by proprietary software in countries like ours, these mainly concern technical tasks of little aggregate value; at the local level, the technicians who provide support for proprietary software produced by transnational companies do not have the possibility of fixing bugs, not necessarily for lack of technical capability or of talent, but because they do not have access to the source code to fix it. With free software one creates more technically qualified employment and a framework of free competence where success is only tied to the ability to offer good technical support and quality of service, one stimulates the market, and one increases the shared fund of knowledge, opening up alternatives to generate services of greater total value and a higher quality level, to the benefit of all involved: producers, service organizations, and consumers.
It is a common phenomenon in developing countries that local software industries obtain the majority of their takings in the service sector, or in the creation of "ad hoc" software. Therefore, any negative impact that the application of the Bill might have in this sector will be more than compensated by a growth in demand for services (as long as these are carried out to high quality standards). If the transnational software companies decide not to compete under these new rules of the game, it is likely that they will undergo some decrease in takings in terms of payment for licenses; however, considering that these firms continue to allege that much of the software used by the State has been illegally copied, one can see that the impact will not be very serious. Certainly, in any case their fortune will be determined by market laws, changes in which cannot be avoided; many firms traditionally associated with proprietary software have already set out on the road (supported by copious expense) of providing services associated with free software, which shows that the models are not mutually exclusive.
With this bill the State is deciding that it needs to preserve certain fundamental values. And it is deciding this based on its sovereign power, without affecting any of the constitutional guarantees. If these values could be guaranteed without having to choose a particular economic model, the effects of the law would be even more beneficial. In any case, it should be clear that the State does not choose an economic model; if it happens that there only exists one economic model capable of providing software which provides the basic guarantee of these principles, this is because of historical circumstances, not because of an arbitrary choice of a given model.
Your letter continues: "4. The bill imposes the use of open source software without considering the dangers that this can bring from the point of view of security, guarantee, and possible violation of the intellectual property rights of third parties."
Alluding in an abstract way to "the dangers this can bring", without specifically mentioning a single one of these supposed dangers, shows at the least some lack of knowledge of the topic. So, allow me to enlighten you on these points.
On security:
National security has already been mentioned in general terms in the initial discussion of the basic principles of the bill. In more specific terms, relative to the security of the software itself, it is well known that all software (whether proprietary or free) contains errors or "bugs" (in programmers' slang). But it is also well known that the bugs in free software are fewer, and are fixed much more quickly, than in proprietary software. It is not in vain that numerous public bodies responsible for the IT security of state systems in developed countries require the use of free software for the same conditions of security and efficiency.
What is impossible to prove is that proprietary software is more secure than free, without the public and open inspection of the scientific community and users in general. This demonstration is impossible because the model of proprietary software itself prevents this analysis, so that any guarantee of security is based only on promises of good intentions (biased, by any reckoning) made by the producer itself, or its contractors.
It should be remembered that in many cases, the licensing conditions include Non-Disclosure clauses which prevent the user from publicly revealing security flaws found in the licensed proprietary product.
In respect of the guarantee:
As you know perfectly well, or could find out by reading the "End User License Agreement" of the products you license, in the great majority of cases the guarantees are limited to replacement of the storage medium in case of defects, but in no case is compensation given for direct or indirect damages, loss of profits, etc... If as a result of a security bug in one of your products, not fixed in time by yourselves, an attacker managed to compromise crucial State systems, what guarantees, reparations and compensation would your company make in accordance with your licensing conditions? The guarantees of proprietary software, inasmuch as programs are delivered AS IS'', that is, in the state in which they are, with no additional responsibility of the provider in respect of function, in no way differ from those normal with free software.
On Intellectual Property:
Questions of intellectual property fall outside the scope of this bill, since they are covered by specific other laws. The model of free software in no way implies ignorance of these laws, and in fact the great majority of free software is covered by copyright. In reality, the inclusion of this question in your observations shows your confusion in respect of the legal framework in which free software is developed. The inclusion of the intellectual property of others in works claimed as one's own is not a practice that has been noted in the free software community; whereas, unfortunately, it has been in the area of proprietary software. As an example, the condemnation by the Commercial Court of Nanterre, France, on 27th September 2001 of Microsoft Corp. to a penalty of 3 million francs in damages and interest, for violation of intellectual property (piracy, to use the unfortunate term that your firm commonly uses in its publicity).
You go on to say that: "The bill uses the concept of open source software incorrectly, since it does not necessarily imply that the software is free or of zero cost, and so arrives at mistaken conclusions regarding State savings, with no cost-benefit analysis to validate its position."
This observation is wrong; in principle, freedom and lack of cost are orthogonal concepts: there is software which is proprietary and charged for (for example, MS Office), software which is proprietary and free of charge (MS Internet Explorer), software which is free and charged for (Red Hat, SuSE etc GNU/Linux distributions), software which is free and not charged for (Apache, Open Office, Mozilla), and even software which can be licensed in a range of combinations (MySQL).
Certainly free software is not necessarily free of charge. And the text of the bill does not state that it has to be so, as you will have noted after reading it. The definitions included in the Bill state clearly *what* should be considered free software, at no point referring to freedom from charges. Although the possibility of savings in payments for proprietary software licenses are mentioned, the foundations of the bill clearly refer to the fundamental guarantees to be preserved and to the stimulus to local technological development. Given that a democratic State must support these principles, it has no other choice than to use software with publicly available source code, and to exchange information only in standard formats.
If the State does not use software with these characteristics, it will be weakening basic republican principles. Luckily, free software also implies lower total costs; however, even given the hypothesis (easily disproved) that it was more expensive than proprietary software, the simple existence of an effective free software tool for a particular IT function would oblige the State to use it; not by command of this Bill, but because of the basic principles we enumerated at the start, and which arise from the very essence of the lawful democratic State.
You continue: "6. It is wrong to think that Open Source Software is free of charge. Research by the Gartner Group (an important investigator of the technological market recognized at world level) has shown that the cost of purchase of software (operating system and applications) is only 8% of the total cost which firms and institutions take on for a rational and truly beneficial use of the technology. The other 92% consists of: installation costs, enabling, support, maintenance, administration, and down-time."
This argument repeats that already given in paragraph 5 and partly contradicts paragraph 3. For the sake of brevity we refer to the comments on those paragraphs. However, allow me to point out that your conclusion is logically false: even if according to Gartner Group the cost of software is on average only 8% of the total cost of use, this does not in any way deny the existence of software which is free of charge, that is, with a licensing cost of zero.
In addition, in this paragraph you correctly point out that the service components and losses due to down-time make up the largest part of the total cost of software use, which, as you will note, contradicts your statement regarding the small value of services suggested in paragraph 3. Now the use of free software contributes significantly to reduce the remaining life-cycle costs. This reduction in the costs of installation, support etc. can be noted in several areas: in the first place, the competitive service model of free software, support and maintenance for which can be freely contracted out to a range of suppliers competing on the grounds of quality and low cost. This is true for installation, enabling, and support, and in large part for maintenance. In the second place, due to the reproductive characteristics of the model, maintenance carried out for an application is easily replicable, without incurring large costs (that is, without paying more than once for the same thing) since modifications, if one wishes, can be incorporated in the common fund of knowledge. Thirdly, the huge costs caused by non-functioning software ("blue screens of death", malicious code such as virus, worms, and trojans, exceptions, general protection faults and other well-known problems) are reduced considerably by using more stable software; and it is well known that one of the most notable virtues of free software is its stability.
You further state that: "7. One of the arguments behind the bill is the supposed freedom from costs of open-source software, compared with the costs of commercial software, without taking into account the fact that there exist types of volume licensing which can be highly advantageous for the State, as has happened in other countries."
I have already pointed out that what is in question is not the cost of the software but the principles of freedom of information, accessibility, and security. These arguments have been covered extensively in the preceding paragraphs to which I would refer you.
On the other hand, there certainly exist types of volume licensing (although unfortunately proprietary software does not satisfy the basic principles). But as you correctly pointed out in the immediately preceding paragraph of your letter, they only manage to reduce the impact of a component which makes up no more than 8% of the total.
You continue: "8. In addition, the alternative adopted by the bill (I) is clearly more expensive, due to the high costs of software migration, and (II) puts at risk compatibility and interoperability of the IT platforms within the State, and between the State and the private sector, given the hundreds of versions of open source software on the market."
Let us analyze your statement in two parts. Your first argument, that migration implies high costs, is in reality an argument in favor of the Bill. Because the more time goes by, the more difficult migration to another technology will become; and at the same time, the security risks associated with proprietary software will continue to increase. In this way, the use of proprietary systems and formats will make the State ever more dependent on specific suppliers. Once a policy of using free software has been established (which certainly, does imply some cost) then on the contrary migration from one system to another becomes very simple, since all data is stored in open formats. On the other hand, migration to an open software context implies no more costs than migration between two different proprietary software contexts, which invalidates your argument completely.
The second argument refers to "problems in interoperability of the IT platforms within the State, and between the State and the private sector" This statement implies a certain lack of knowledge of the way in which free software is built, which does not maximize the dependence of the user on a particular platform, as normally happens in the realm of proprietary software. Even when there are multiple free software distributions, and numerous programs which can be used for the same function, interoperability is guaranteed as much by the use of standard formats, as required by the bill, as by the possibility of creating interoperable software given the availability of the source code.
You then say that: "9. The majority of open source code does not offer adequate levels of service nor the guarantee from recognized manufacturers of high productivity on the part of the users, which has led various public organizations to retract their decision to go with an open source software solution and to use commercial software in its place."
This observation is without foundation. In respect of the guarantee, your argument was rebutted in the response to paragraph 4. In respect of support services, it is possible to use free software without them (just as also happens with proprietary software), but anyone who does need them can obtain support separately, whether from local firms or from international corporations, again just as in the case of proprietary software.
On the other hand, it would contribute greatly to our analysis if you could inform us about free software projects *established* in public bodies which have already been abandoned in favor of proprietary software. We know of a good number of cases where the opposite has taken place, but not know of any where what you describe has taken place.
You continue by observing that: "10. The bill discourages the creativity of the Peruvian software industry, which invoices 40 million US$/year, exports 4 million US$ (10th in ranking among non-traditional exports, more than handicrafts) and is a source of highly qualified employment. With a law that encourages the use of open source, software programmers lose their intellectual property rights and their main source of payment."
It is clear enough that nobody is forced to commercialize their code as free software. The only thing to take into account is that if it is not free software, it cannot be sold to the public sector. This is not in any case the main market for the national software industry. We covered some questions referring to the influence of the Bill on the generation of employment which would be both highly technically qualified and in better conditions for competition above, so it seems unnecessary to insist on this point.
What follows in your statement is incorrect. On the one hand, no author of free software loses his intellectual property rights, unless he expressly wishes to place his work in the public domain. The free software movement has always been very respectful of intellectual property, and has generated widespread public recognition of its authors. Names like those of Richard Stallman, Linus Torvalds, Guido van Rossum, Larry Wall, Miguel de Icaza, Andrew Tridgell, Theo de Raadt, Andrea Arcangeli, Bruce Perens, Darren Reed, Alan Cox, Eric Raymond, and many others, are recognized world-wide for their contributions to the development of software that is used today by millions of people throughout the world. On the other hand, to say that the rewards for authors rights make up the main source of payment of Peruvian programmers is in any case a guess, in particular since there is no proof to this effect, nor a demonstration of how the use of free software by the State would influence these payments.
You go on to say that: "11. Open source software, since it can be distributed without charge, does not allow the generation of income for its developers through exports. In this way, the multiplier effect of the sale of software to other countries is weakened, and so in turn is the growth of the industry, while Government rules ought on the contrary to stimulate local industry."
This statement shows once again complete ignorance of the mechanisms of and market for free software. It tries to claim that the market of sale of non- exclusive rights for use (sale of licenses) is the only possible one for the software industry, when you yourself pointed out several paragraphs above that it is not even the most important one. The incentives that the bill offers for the growth of a supply of better qualified professionals, together with the increase in experience that working on a large scale with free software within the State will bring for Peruvian technicians, will place them in a highly competitive position to offer their services abroad.
You then state that: "12. In the Forum, the use of open source software in education was discussed, without mentioning the complete collapse of this initiative in a country like Mexico, where precisely the State employees who founded the project now state that open source software did not make it possible to offer a learning experience to pupils in the schools, did not take into account the capability at a national level to give adequate support to the platform, and that the software did not and does not allow for the levels of platform integration that now exist in schools."
In fact Mexico has gone into reverse with the Red Escolar (Schools Network) project. This is due precisely to the fact that the driving forces behind the Mexican project used license costs as their main argument, instead of the other reasons specified in our project, which are far more essential. Because of this conceptual mistake, and as a result of the lack of effective support from the SEP (Secretary of State for Public Education), the assumption was made that to implant free software in schools it would be enough to drop their software budget and send them a CD ROM with Gnu/Linux instead. Of course this failed, and it couldn't have been otherwise, just as school laboratories fail when they use proprietary software and have no budget for implementation and maintenance. That's exactly why our bill is not limited to making the use of free software mandatory, but recognizes the need to create a viable migration plan, in which the State undertakes the technical transition in an orderly way in order to then enjoy the advantages of free software.
You end with a rhetorical question: "13. If open source software satisfies all the requirements of State bodies, why do you need a law to adopt it? Shouldn't it be the market which decides freely which products give most benefits or value?"
We agree that in the private sector of the economy, it must be the market that decides which products to use, and no state interference is permissible there. However, in the case of the public sector, the reasoning is not the same: as we have already established, the state archives, handles, and transmits information which does not belong to it, but which is entrusted to it by citizens, who have no alternative under the rule of law. As a counterpart to this legal requirement, the State must take extreme measures to safeguard the integrity, confidentiality, and accessibility of this information. The use of proprietary software raises serious doubts as to whether these requirements can be fulfilled, lacks conclusive evidence in this respect, and so is not suitable for use in the public sector.
The need for a law is based, firstly, on the realization of the fundamental principles listed above in the specific area of software; secondly, on the fact that the State is not an ideal homogeneous entity, but made up of multiple bodies with varying degrees of autonomy in decision making. Given that it is inappropriate to use proprietary software, the fact of establishing these rules in law will prevent the personal discretion of any state employee from putting at risk the information which belongs to citizens. And above all, because it constitutes an up-to-date reaffirmation in relation to the means of management and communication of information used today, it is based on the republican principle of openness to the public.
In conformance with this universally accepted principle, the citizen has the right to know all information held by the State and not covered by well- founded declarations of secrecy based on law. Now, software deals with information and is itself information. Information in a special form, capable of being interpreted by a machine in order to execute actions, but crucial information all the same because the citizen has a legitimate right to know, for example, how his vote is computed or his taxes calculated. And for that he must have free access to the source code and be able to prove to his satisfaction the programs used for electoral computations or calculation of his taxes.
I wish you the greatest respect, and would like to repeat that my office will always be open for you to expound your point of view to whatever level of detail you consider suitable.
Cordially,
DR. EDGAR DAVID VILLANUEVA NU EZ
Congressman of the Republic of Per .
With all the news about Sun being cool etc., here's one for you: get them to
release their stuff under a GPL compatible license. Java is very high profile,
and it's not yet licensed under a fully open license. They reportedly said
they want to, though. And Microsoft says it works in our best interest and
cares about interoperability.
Why am I bringing this up? I've just read that some folks where discussing
Sun's ZFS in
the context of Linux. KernelTrap quotes Alan Cox and Theodore T'so
heavily doubting Sun's sincerity about Free Software issues, given that ZFS is
CDDL-licensed and heavily encumbered with patents. (note: I'm just quoting the
KernelTrap blog, and this is not an area I'm familiar with.)
Placeholder for the Port Information state machine extracted from IEEE 802.1Q-2005, page 182. Pending IEEE authorization for reproduction, this is the blueprint for the Western Australian Government Railways class Msa Garratt articulated steam locomotive.
Long-term Linux users may remember that