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Pinging router to router

Unanswered Question
Jul 27th, 2003
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I was testing RIP with 4 routers daisy-chained via serial (2600 w/ 2 serial int and e0). I was having problems pinging from router to router. Some worked, some didn't. I was about to call it a night when I tried from the PCs attached to the net to the others attach to their net. That worked in all cases. Why would you be able to ping accross networks from PC to PC, but not from inside the router?

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hbaerten Sun, 07/27/2003 - 23:34
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When you ping from a router, it uses the address of the outgoing interface as the source address.

If the router that you are trying to ping, does not have a route back to this address, the ping will fail. I suspect this is your problem, so check this out.

If that's not it, please post the config of the routers that cannot ping each other and a description of your network layout.


hth

Herbert

ruwhite Mon, 07/28/2003 - 02:48
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It's possible that you have routes to the end destinations, but not the networks between the routers. For instance, if you have:


HA--RA--RB--RC--HB


It's possible to have, on RA, a route to HB, but not to RC. When RA receives traffic destined to HB, it will forwarded it along to the next hop it knows about, RB. If RB knows about the path to HB as well, then it will forward the traffic along as well.


If, however, RA has no path to the network between RB and RC, it will not even generate the traffic destined to this address, but will drop it, since it doesn't have a route to that destination. The only way to know for certain is to look at all of your routing tables, but I'd suspect a problem with route filtering, discontiguous subnets, or autsummarization.


Russ.W

dcianci Mon, 07/28/2003 - 23:01
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Thank you. I will try all of your suggestions.

I also wanted to add that I'm new to the forums and have been amazed at the courtesy and respect I've seen. Not the flamefests I've had to battle through in other groups.


Thanks again...

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