How Can This Be - HSRP & PING

All,

I have 2 x separate questions as follows:

1) Ping

Router -----DMVPN-----PIX----Internet

877 2801 515E-R

From my remote 877 DMVPN router I can ping my inside & outside 2801 DMVPN router without loss of a packet. Whenever I ping the inside of the PIX or beyond (the Internet) I get sporadic responses with Pings (some hits, some misses). There is a route on the PIX pointing at my 877's network via the

2801 (hence some ICMP packet hits) so I am sure the routing is OK. One caveat, if I set the size of the ping e.g 64 bytes, 1000 bytes 1400 bytes etc the response if 100% successful, if I set the size of the ping packet to the Cisco default 100 bytes it give me the hit / miss response.

On my DMVPN interface's I have tcp mss-adjust 1360 and MTU size of 1400 configured.

2) HSRP

A colleague has configured 2 x 3825 routers with an IP address on their Gig

0/0 ports with a 10.x.x.x /24 address. Under the same interface he has a standby IP address 62.x.x.x. His Gig ports connect to a switch and ultimately a Telco router that he runs eBGP with. He said that this allows him to provide resiliency to the Telco router.

I thought that the standby address had to be on the same subnet as the IP address coded under the port. He said the above works because the config provides resilience at layer 2 and not to get this confused with layer 3.

Anyone seen this before or have I go the wrong end of the stick.

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Posted 5 years ago by Darren Green in Cisco Systems

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