RFC L2 (switch) topology. Mainly off-topic.

[Stanley Hopcroft]

Dear Ladies and Gentlemen,

<this is at most marginally on topic>

I am writing to ask if there is any interest in using layer two 
topological information with Nagios.

Potential uses include (that I will not probably not contribute to)

. custom status maps that show the bridge/switch layout with respect to 
the spanning tree, which in many cases is the inter switch path viewed 
from the point of the root bridge.

This is perhaps less useful than it may seem because the status map 
would ideally show the relationship of the hosts to the switches and 
while this is doable, it is slow with more than a small number of 
switches (say less than 10).

. custom checks that analyse the spanning tree (and whine if the 
favourite/most powerful/least powerful/XP in bridge mode/some stray 
wireless node bridge is not or is the root bridge.

What you would get ?

1 Net::SNMP (an absolute joy of a Perl module) pollers that ascertain

  - bridge MAC addresses (for relating to name and or IP)
  - descendant bridges
  - the switch 'designated bridge'
  - nodes in a netblock that are switches (ie respond to the 
    dot1dBaseType with a value of 'transparent')

2 A Perl CGI that displays them (primitively) in a tree form with the
root at the top

This is the only application I have at the moment, although in 
principle, generating a dot map and having graphviz generate a .png for 
a better looking web display 'shouldn't be too hard' (TM).

Switch topology.

        SCBR21-C5K-2
                DBR21-C5K-1
                        DNGR21-C29-10
                                DNGR22-C28-11
                        DN1R21-C29-20
                                DN1R22-C28-21
                        DN1R23-C28-22
                                DN1R24-C28-23
                        DNR21-C29-30
                                DN2R23-C28-32
                                        DN2R24-C28-33
                        DN2R22-C28-31
                        DN3R21-C29-40
                                DN3R22-C28-41
                                        DN3R23-C28-42
                        DN3R24-C29-43
                        DN4R21-C29-50
                                DN4R22-C28-51
                                        DN4R23-C28-52
  .. snip ..

                SC1R41-C29-65
                        SC1R42-C28-66
                                SC1R43-C28-67
                SC1R44-C28-68
                SC1R45-C28-69
                SC1R46-C29-162

What about the bad bits ?

1 The pollers don't reliably discover switches since 

1.1 agents don't respond if they have better things to do

1.2 the switch discovery wants to be fast; I haven't bothered to retry 
the requests; maybe I should.

2 The code is not suitable for publication ie supportable or without 
known showstoppers (how can you have showstoppers in 300 lines of Perl ? 
well, I can).

In fact, there may even be conceptual flaws also.

3 It almost certainly doesn't scale.

At the moment the switch discovery and polling of ~ 80 switches in a /24 
takes less than 5 seconds - without connectivy or utilisation problems.

wins> /home/anwsmh/perl5/dotime 5 ./update_switch_topology
Running ./update_switch_topology 5 times
1 2 3 4 5 done
         Avg        1        2        3        4        5
      ------   ------   ------   ------   ------   ------
real   3.730     3.52     4.17     3.69     3.51     3.76
user   1.120     1.19     1.18     1.08     1.08     1.07
sys    0.062     0.07     0.07     0.07     0.04     0.06
wins> 


Please would you let me know if there is any interest or that

- this is stupid; L2 sucks (sure does)

- we already use big name product foo to do this and foo is great

- why would you want to do this

- we need it done for big_number k switches across n netblocks

- does it work for Cisco rapid spanning tree (probably not).


</this is at most marginally on topic>

Yours sincerely.

-- 
------------------------------------------------------------------------
Stanley Hopcroft
------------------------------------------------------------------------

'...No man is an island, entire of itself; every man is a piece of the
continent, a part of the main. If a clod be washed away by the sea,
Europe is the less, as well as if a promontory were, as well as if a
manor of thy friend's or of thine own were. Any man's death diminishes
me, because I am involved in mankind; and therefore never send to know
for whom the bell tolls; it tolls for thee...'

from Meditation 17, J Donne.


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