Echo Reply Never Received

[mmanning]

I have a 2611 Router with a T1 (S0) interface and 2 ethernet interfaces, E0 and E1.

E0 and S0 have NAT going. I can ping just fine anywhere through my E0 interface out to the internet.

When I try to ping a host on E1 from E0 (or vice versa), I never receive the reply. A sniffer shows that the Echo Request arrived, but the reply never comes.

When I ping the hosts from other hosts on the subnet, everything works. It is definitely only a problem when I go through the router.

I only have "In" rules at every interface and my "In" rule at E1 is wide open.

I've tried everything I know, but I am fairly new to routers. Any help will be greatly appreciated. (This is only step 1 in troubleshooting a bigger problem.)

Thanks,
Mark [sig][/sig]

 

[jeter]

what kind of routing are you set up for ( Rip , Igrp, Eigrp ect ) ? What are the ip's on E1 and e0 ? Also have you tried setting up a ( ip helper-address ) on E0 and E1 ? [sig][/sig]

 

[mmanning]

Jeter, thanks for the help.

I actually have no routing set up since all networks are connected to the router ( 3 networks, 3 interfaces.)

I'll bet you may have something when you ask what the addresses are. E1 is the 198.76.189.0 network, but E0 is the 192.168.0.0 (not a routable set of addresses.)

I think the mystery is solved. ( I only had the sniffer on the 198.76.189.0 network. The Echo request was detected, but the reply never got there - because the return address is not routable and NAT was not being done between the 2 networks.)

Unless you see a flaw in the logic I just wrote down, I'll assume you solved my problem.

Thanks again

Mark [sig][/sig]

 

[jroysdon]

First, 192.168.0.0 will route on a LAN the same as any other non-class D/E or loopback address. It may not route through your ISP across the internet, but that's only because the ISP is chosing to drop those packets (as the RFC's say those certain private address ranges shouldn't be routed).

Check that the node has a gateway set to the router's 198.76.189.0 address, that your masks are consistant between router and node, etc. Then ping the router's 198.76.189.0 interface, then attempt to ping the 192.168.0.0 interface. Make sure your are routing IP on the Cisco box ('ip routing,' but that's the default unless someone turned it off), and you should also try 'debub ip icmp' on the router (with 'terminal monitor' on if you're watching from a telnet). That debug command will let you see all icmp ping packets destined for your router. [sig][/sig]