[c-nsp] Monitoring L3 link status

Brad Henshaw brad.henshaw at qcn.com.au
Wed Dec 13 20:48:48 EST 2006


Hi Frank,

> Thanks for checking the BGP4-MIB angle.  I am avoiding the SNMP trap
angle because
> I believe that SolarWind's Orion doesn't support receiving SNMP traps.


I haven't dealt with traps in Orion so I'm not sure.

> Correct me if I'm wrong, but a change in BGP state many not
*necessarily* indicate
> that the far end router is not accessible, right?

If a BGP peer goes down, then traffic won't route directly via that peer
- hence traffic won't flow over the B-D link, assuming B only peers with
D and not also with E. If this is the case, then it a state change at
least means that D isn't reachable via B's link into W, which is
probably what you're trying to watch?

> I'm also wondering if something can't be done with IOS scripting/Tcl
shell to check
> every 30 seconds and then set an SNMP value (http://tinyurl.com/v6vos)
that could be read via SNMP.

Possibly. I'm not sure if the 3750ME supports TCL.

> Another person recommended using static routes for B to D and C to E,
and then making
> sure that I have a higher cost route to null for the case when the
interface is down. 

You could do this with a specific loopback address of D & E, or the
address on the interface facing your switches if appropriate - but this
could cause troubleshooting mess later on. I prefer to steer clear of
hacks to support other requirements (such as polling) where possible,
but sometimes there's no other reasonable option.

Regards,
Brad


-----Original Message-----
From: cisco-nsp-bounces at puck.nether.net
[mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of Frank Bulk
Sent: Thursday, 14 December 2006 8:36 AM
To: Cisco-NSP Mailing List
Subject: [c-nsp] Monitoring L3 link status

We're using two Cisco 3750-ME routers (B & C) that are connected to our
upstream service provider's routers (D & E).  We started using ping
checks to D & E from our server running SolarWinds, but because our
internet traffic runs primarily over B-D or C-E it's not really a good
link test.  If our traffic runs over C-E then ping checks to D run over
C, E, and then on to D.  Link B-D could fail and we wouldn't know.

           |---OSPF---[B]---BGP---[W]---[EoS]---[EoS]---[D]
           |           |                     / \         |
server ----A         OSPF                   |   |       BGP
           |           |                     \ /         |
           |---OSPF---[C]---BGP---[X]---[EoS]---[EoS]---[E]

This can't be a new issue -- what's the easiest way to test L3
connectivity between B-D and C-E?  All our connections internally and to
our upstream provider are Ethernet, transport is Ethernet over SONET)
and testing for interface status is not reliable enough as our demarc
with our upstream provider is a Cisco 2950 (W & X).  I believe our
upstream provider uses Juniper routers.

Regards,

Frank




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