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New Member

Can traceroute but can't ping.

Hi experts,

I want to share a problem I encounter. What is a possible causes if I can trace an IP (server) from a branch to HQ, but I can't ping it and use it. This occur only for 1 branch during an ISDN call, other branch are OK even when it using ISDN. Can somebody help. Thanks.



Re: Can traceroute but can't ping.

Hi Azmir,

Good Day! This maybe because PING or TELNET is not allowed on the server. The server might have an active firewall the does not allow these services. Another is the router might have access lists configured that also does not allow them. Try to ping the router closest to the server, if this is successful then the first reason could be the case.

Hope this helps.



New Member

Re: Can traceroute but can't ping.

Hi Albert,

Thanks for your prompt reply. If I not mistaken, the server allow PING because, other branches router can ping it even when using ISDN. For the trouble branch, when it are on Lease Line (thru MPLS), the server are pingable.




Re: Can traceroute but can't ping.


This has got a little complicated. Try doing a trace from the server to your host and vise versa. This might show if the ICMP packets gets lost on its return path.



New Member

Re: Can traceroute but can't ping.


Yeah, its a lil complicated. I've done a few troubleshooting step including enable show ip icmp command. What I can seee is, the trouble router did't get the ICMP replies from the server, its only state that it can reach to HQ LAN Ip..


Hall of Fame Super Silver

Re: Can traceroute but can't ping.


I do not believe that we have enough information yet to find the answer to your problem. I agree with Albert that it seems likely that there is some configuration issue (most likely an access list issue or perhaps some ISDN issue) which is causing this. Perhaps you can post the configuration of the router and then we might be better able to help find an answer to your problem.



New Member

Re: Can traceroute but can't ping.


Scenario understanding is as following :

. There are several branches with primary connectivity and ISDN connectivity

. All branches are working fine with Primary connecitivity

. One - branch B is not able to ping and use when connected on ISDN

. Branch B is able to trace the server.( trace completes)


Please reply for following :

1> All these sites are connected on Point to Point link to Hub site ( carrying server ) for primary and ISDN link or is it via some ISP ?

2> ISDN call connects and all three layers are active , calls establishes for branch B

3> is unnumbered interface is being used or new IP is received when connected on ISDN ?

4> if same IP is provided to ISDN interface once connected , then please disconnect the primary link and trace the Branch B IP from Server and share the log

5> In both the situation,- a) keepin primary off and b) keeping primary on share the trace towards the server from the Branch B router

6> Please provide the debug ip icmp output from branch B for step 5

Please correct my assumptions on scenario , so that i can change my questions accordingly to resolve this issue.



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