Comments within and below.
> Does anyone have a router acting as a bridge in their lab
network?
Yes, a bunch of 2500s running everything from 12.09 to 12.2(3)
and experimental smokin IPv6 code. I also have a BFR (Cisco
7000) running 11.2(16)
> Cisco documentation claims that there is a "debug span"
command that
> shows
> BPDU frames in hex as they come in. Now, I think this is an
awful idea,
> since they come in every 2 seconds, but for a project I'm
working on I
> need
> to find out if the command really exists.
For starters, this appears to be one of those commands that has
been propagated over the years as a recurring mistake in the
command summaries. Just to let you know, this command first
appeared in IOS 8.3 (yes, you are reading that correctly :-)
http://www.cisco.com/univercd/cc/td/doc/product/software/ssr83/r
pc_r/53998.htm#xtocid1116650
Although the command was released in 8.3 code, very little was
mentioned about it in terms of what you should see and how to
interpret it. That appears to have been documented in IOS
9.21, which is shown here:
http://www.cisco.com/univercd/cc/td/doc/product/software/ssr921/
dcr/80432.htm#xtocid755369
It indicates the same sort of information that you read in the
12.2 command reference. My guess is that right about at that
time the Kalpana switches were becoming the rage, bridging was
taking a back seat to routing and the focus was on routing and
routing protocols. Although the functionality and debugs for
bridging did improve over the years, the documentation does not
appear to have kept up. For example, here is what my 12.2(3)
cisco 2511 has to say about the debugs available:
2511#debug spa?
spanning-tree
2511#debug spa
2511#debug spanning-tree ?
all All Spanning Tree debugging messages
bpdu Spanning tree bridge protocol data units
bpdu-opt Optimized BPDU handling
config Spanning tree config changes
etherchannel EtherChannel support
events Spanning tree topology events
exceptions Spanning tree exceptions
general Spanning tree general
pvst+ PVST+ events
root Spanning tree root events
snmp Spanning Tree SNMP handling
Just for grins, I turned them all on and configured an IEEE
bridge with routing disabled. Here is what I get:
2511#sh span
Bridge group 1 is executing the ieee compatible Spanning Tree
protocol
Bridge Identifier has priority 32768, address 0000.0c92.7624
Configured hello time 2, max age 20, forward delay 15
Current root has priority 32768, address 0000.0c83.e2d0
Root port is 3 (Serial0), cost of root path is 647
Topology change flag not set, detected flag not set
Number of topology changes 3 last change occurred 00:38:31 ago
from Serial0
Times: hold 1, topology change 35, notification 2
hello 2, max age 20, forward delay 15
Timers: hello 0, topology change 0, notification 0, aging 300
Port 3 (Serial0) of Bridge group 1 is forwarding
--More--
01:00:03: Returning spanning tree stats @ 5CEDA0
01:00:03: Returning spanning tree port stat Port path cost
647, Port priority
128, Port Identifier 128.3.
Designated root has priority 32768, address 0000.0c83.e2d0
Designated bridge has priority 32768, address 0000.0c83.e2d0
Designated port id is 128.6, designated path cost 0
Timers: message age 2, forward delay 0, hold 0
Number of transitions to forwarding state: 3
BPDU: sent 57, received 1502
Port 4 (Serial1) of Bridge group 1 is blocking
Port path cost 647, Port priority 128, Port Identifier 128.4.
Designated root has priority 32768, address 0000.0c83.e2d0
Designated bridge has priority 32768, address 0000.0c83.e2d0
Designated port id is 128.7, designated path cost 0
Timers: message age 2, forward delay 0, hold 0
Number of transitions to forwarding state: 1
BPDU: sent 56, received 1509
Here are the debugs:
2511#sh deb
Spanning Tree:
Spanning Tree general debugging is on
Spanning Tree Exceptions debugging is on
Spanning Tree BPDU debugging is on
Spanning Tree event debugging is on
Spanning Tree root changes debugging is on
Spanning Tree configuration debugging is on
Spanning Tree etherchannel support debugging is on
Spanning Tree PVST+ debugging is on
Spanning Tree uplinkfast debugging is on
Spanning Tree uplinkfast exceptions debugging is on
Spanning Tree backbonefast general debugging is on
Spanning Tree backbonefast detail debugging is on
Spanning Tree backbonefast exceptions debugging is on
Spanning Tree optimized bpdu handling debugging is on
Spanning Tree optimized bpdu handling detail debugging is on
Spanning Tree optimized bpdu handling packet level debugging
is on
Spanning Tree SNMP support debugging is on
Here is the output from the debugs after one minute:
nada...
I was prepared to give up, but on a whim I decided that
something just didn't "feel right". Why do we have debugs in
many cases? Usually to point out some sort of problem that
needs to be fixed. What sort of problem would need to be fixed
in a bridged environment? Yes, you guessed it - the bridge
loop. I tried to do this on my 2511 between the two serial
interfaces, but the router was too smart for that (it reported
that I has internally looped the two interfaces. So, I needed
a router that had two LAN interfaces. I decided to go back to
my BFR. I had a crossover cable ready and plugged it into E2/0
and E2/1. I then proceeded to turn on the debugs (same ones
you have - events and tree). here is what I saw:
ST: Ethernet2/1
0000000000008000000C00700000000000008000000C007000805B0000140002
000F00
ST: Ethernet2/1
0000000000008000000C00700000000000008000000C007000805B0000140002
000F00
ST: Ethernet2/1
0000000000008000000C00700000000000008000000C007000805B0000140002
000F00
When I broke the loop, the decode went away. It would appear
that this was designed to try and track down bridge loops. It
seems that the command evolved over time (as they usually do)
and different subcommands were put in to add granularity. The
base command however that gives the functionality you desire is:
debug spanning tree
and later,
debug spanning-tree bpdu
HTH,
Paul Werner
>
> My routers will not run IOS beyond 11.0. (Hey, they were
free! ;-) They
> do
> not support "debug span." They only support "debug span
events" which
> shows
> this:
>
> Albany#debug span events
> Spanning Tree event debugging is on
> Albany#
> ST: Topology Change rcvd on Ethernet0
> ST: Topology Change rcvd on Ethernet1
> ST: Topology Change rcvd on Ethernet0
> ST: Topology Change rcvd on Ethernet1
>
> I'm wondering 2 things:
>
> Does "debug span events" still exist? (It's not in the
documentation.)
>
> Does "debug span" exist? (It is in the documentation but
doesn't work on
> my
> routers.)
>
> Could anyone try it for me and send me output?
>
> By the way, if you don't have bridging working on your
routers, it's
> really
> easy to configure:
>
> bridge 1 protocol ieee
> int e0
> bridge-group 1
> int e1
> bridge-group 1
>
> THANK-YOU!!!!!!
>
> Priscilla
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