Cannot ping local ethernet interface

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Nov 15th, 2006
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hey there,


having an issue where i cant ping the local gateway. here are the details


New site - 805 rtr with 12.3 img IP Plus

E0 ip address -172.26.12.X/28

SER - 172.26.12.X/30

EIGRP 1

NETWORK 172.26.0.0

NO AUTO-SUM


thats it basically. i have WAN connectivity but here is the thing. i connect my computer directly to the LAN interface of the 805. press switch to allow for straight thorough connectivity. i attempt to ping the local ethernet IP that is directly connected and I CANT. request timeout. if i change the ip scheme to something other than 172.26.12.X i can ping. MEANING, i changed the ethernet interface to 10.0.0.1 and that worked. if i reinsert the orgnial ip, i cant ping, but when i remove EIGRP i can, however,the serial goes down.


To me it makes no sense so im hoping that you guys can assist.


Thanks

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Richard Burts Wed, 11/15/2006 - 13:31
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Arvind


There are a couple of obvious things to check: will you verify the IP address configured on your PC, the mask configured on the PC, and the gateway configured on the PC?


I am quite puzzled at the part of your post that says that if you remove EIGRP then the serial interface goes down and you can ping. What would make the serial interface go down if you remove EIGRP? Perhaps you can post some config details to help us see what is going on there?


HTH


Rick

a.gooding Wed, 11/15/2006 - 13:40
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exactly, it really makes no sense. i have left the customer site with my head down and will post configs tomorrow. remember, if i change the ip add on the e0 to another that does not belong to EIGRP network, i can ping. PC and related configuration is fine. And that last issue with the frame link, is really puzzling.


Basically, no matter what, i should be able to ping my local LAN IP. routing protocol or not. and the serial should never have gone down.

cfolkerts Wed, 11/15/2006 - 13:45
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Would you be able to post your config? Your serial interface and ethernet interface may overlap.


Example

Ethernet interface

network 172.16.12.0/28

hosts on this network can be 172.16.12.1 through 172.16.12.14


Serial interface

Network 172.16.12.8/30

ip address 172.16.12.9 and 172.16.12.10 are eligible.


These two networks overlap.

a.gooding Wed, 11/15/2006 - 13:57
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this is what i have


E0 172.26.12.225 255.255.255.240

S0.1 - 172.26.12.206 255.255.255.252

Richard Burts Wed, 11/15/2006 - 14:14
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Arvind


Is it possible that the EIGRP was advertising a subnet of 172.26.12.224 with a subnet mask greater than 240 (for example 172.16.12.224 255.255.255.252)? In making routing decisions the router always prefers the longest match. So if there is a /28 for the local interface and a /30 (or a /29) learned by EIGRP over the serial then the router will attempt to get to the address by forwarding over the serial. And if the serial went down (or EIGRP was stopped) then the longer prefix would no longer be in the table and the interface access would be normal.


HTH


Rick

a.gooding Wed, 11/15/2006 - 14:23
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makes a lot of sense.i'd probably say yes if it were that i was another end of the network trying to access the LAN VIA the WAN. but, im a directly connected client that is not using any routing protocol to my local gateway. i was concerned about the IP Scheme so i went and did paper calulations for the network addresses. Im not seeing an overlap, however, there is something up with EIGRP and this E0. So then, other than changing the IP scheme, which i cant at this point, what might be a resolution to the issue?

Richard Burts Wed, 11/15/2006 - 18:52
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Arvind


I would suggest that when you can get back to this router that you bring up the serial interface, enable EIGRP, do a show ip route and post the output so that we can see it.


I accept your point that your client is directly connected and sends the ping packet directly to the router. I ask you to think about how the router responds to you and how it decides where to send the response packet. What if there is an overlapping more specific subnet that includes the address of your PC? One way to test this would be to assign your PC the address of 172.26.12.226 (if the router is 225 they will be in the same /30 and if my theory is right the ping should work).


HTH


Rick

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