OT Having your routing protocol monitor reachability of routers (OSPF, EIGRP, BGP etc).

[Stanley Hopcroft]

Dear Folks,

Routing protocols like OSPF maintain neigbour relationships with other
routers in the area by exchanging periodic hello messages.

This can be used as a means of very quickly detecting router
reachabily failures because the hello messages typically occur several
times a minute and a failure is detected in less than a minute.

OSPF routers report a neighbour failure with messages like

155795 bar syslog-notice 2006-08-02 01:40:49 134777: %OSPF-5-ADJCHG:
Process 1, Nbr baz on Tunnel0 from FULL to DOW
N, Neighbor Down: Dead timer expired

155796 foo syslog-notice 2006-08-02 01:40:49 231: Aug 1 15:40:49:
%OSPF-5-ADJCHG: Process 1, Nbr baz on Tunnel0 fro
m FULL to DOWN, Neighbor Down: Dead timer expired

In this case, there is an OSPF broadcast network with DRs bar and foo.
The Neighbour baz is reported as having failed to respond to poll
(after 10 failures to respond ie 40 seconds). The DRs both report the
failure within 30 seconds of each other.

The way to to detect such failures in real time is with an event
correlation tool like SEC. A very good introduction to the challenges
of event correlation and how to deal with them using SEC is John
Rouillards paper at http://www.cs.umb.edu/~rouilj/sec/sec_paper.pdf

In this case the challenges include

1 detecting the pair of messages within a time interval of each other

2 allowing a delay interval for the neighbour to recover before notifying

3 notifying on recovery.

SEC allows a rich set of actions to be performed when it detects an
event. These include running programs such as a mail client or ssh to
submit a passive service check result.

Yours sincerely.

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