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Webcast-Catalyst9k
New Member

A weird issue with PING

I have two Cisco 2501 routers connected together by their serial interfaces(Lab-D via s0 and Lab-E via s1). Everything is working properly.

Now I configured an access-list on Lab-D denying any traffic that comes in from Lab-E's IP address.

Lab-D serial 0 = 214.16.4.1

Lab-E serial 1 = 214.16.4.2

On router Lab-D:

access-list 1 deny host 214.16.4.2

access-list 1 permit any

On int s0 of Lab-D:

ip access-group 1 in

---------

So, when trying to ping from Lab-E router to IP address 214.16.4.1, I get a U.U.U answer to my ping query... which is normal !

But, if I ping from that same Lab-E router to IP address 214.16.4.2, I also get the U.U.U answer... which does not sound too normal to me.

My question is: How can this happen? How is my Lab-E's serial interface from the router itself affected by Lab-D's access-list?

Thanks..

2 REPLIES
New Member

Re: A weird issue with PING

When you ping your own serial interface, the frames are actually sent on the wire and the remote router sends them back. Since you have a access on the remote router, the frames are not getting back.

New Member

Re: A weird issue with PING

Thanks alot. That explains everything. And a quick answer too.

Thanks!

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