NIDS/NIPS implications on HSRP

["Brian Blankenship" <security () packetinfo net>]

Greetings,

A potential problem with a NIPS installation has come up, and I am curious to 
what other people may have done in this situation.

Scenario:
(2) routers, (1) switch
Both routers have a fiber link to the switch, both routers run HSRP to float 
the default gateway for the switch.  There is also a routed link between the 
two routers directly.
Now insert an NIDS/NIPS device on each of the two links from the swtich.  In 
this case it is a TippingPoint, but I don't think that really matters.  

What will happen with HSRP if the primary router link fails between the NIPS 
device and the switch?  The HSRP primary router would still see the line 
protocol up since the NIPS device is still active.

> From what I have been reading, HSRP Hello packets are what determines a 
failover, and that those should only be flowing between the routers through 
the switch.  This would work fine.  Cisco says that if a device (such as an 
IDS/IPS) inline keeps the line protocol up, HSRP will not failover. 

This would seem to be a fairly common scenario.  Anyone have experience with 
this?

Thanks!
Brian

--
Opinions expressed are either that of my own, or someone else's.


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