Secondary IP CANNOT ping

[ReneeLiuSong]

Hi guys, I have 2 IP for my fastethernet interface in Cisco router 2621. The primary one can work well to ping the other clients in the same IP range. But the secondary IP never works. Another client in the same range with the second IP can ping the router, while the router cannot ping the client. I have exchanged the two IPs to make sure the problem lie in the secondary IP.

Please help me to figure out what's the reason to it.

Thanks in advance!

[Edison Ortiz]

When you ping from the router by using a secondary IP address, you must use an extended ping.

When pinging to/from a client, the client needs to have either the default gateway pointint to the device holding the secondary IP or the default gateway needs to have a route to the device holding the secondary IP.

Please rate helpful posts.

Thanks

[ReneeLiuSong]

Yeah, it works.

I find some tips for extended ping in the internet, it says "When a normal ping command is sent from a router, the source address of the ping is the IP address of the interface that the packet uses to exit the router. "

Could you please tell me this kind of activity is special in Cisco router or is a common protocol problem.

I'm really a newbie. Thanks for your kind help!

[vijayasankar]

Hi,

This is not an indication of a problem. This is the way it works.

When you initiate a ping from the router, the router selects an exiting interface based on the routing table, and it sets the source ip address as the exiting interface ip address.

This is by default.

If you want manipulate this behavior, you have to use the extended ping and set the source ip address.

HTH

-VJ

[Edison Ortiz]

It's not a protocol problem, it's an expected behavior and it holds true on all IP equipments I've worked on, Cisco and non-Cisco.

[ReneeLiuSong]

OK. I've got it. Thanks all!