Ping works but traceroute doesnt

[chocyman]

Hi folks...

Just before I start, I have posted this in the Cisco router section as well..just to try to get as much info as I can. Its really causing some grief for what seems like a so so simple problem.

Brief description

2 x 1720 routers connected via a frame.

Router A config :
F/E 0 = 192.0.0.1/24
Serial 0 = 192.168.200.2/30
F/E 0 connected to Cisco 2924 switch
Router A default gateway = 192.168.200.1
Router has RIP version 2 enabled with networks 192.0.0.0 and 192.168.200.0 being broadcast.

Router B config:-
F/E 0 = 192.168.1.1/24
Serial 0 = 192.168.200.1/30
F/E 0 connected to hub
Router default gateway = 192.168.200.2
Router has RIP version 2 enabled with networks 192.168.1.0 and 192.168.200.0 being broadcast.

Switch Config (located behind router A):-
Switch has IP address = 192.0.0.141
Switch default gateway = 192.0.0.1

Router A (via switch) workstation(s) config:-
default gateway = 192.0.0.141 (to the switch)

Router B workstation config:-
Default gateways set to 192.168.1.1 (have tried 192.168.200.1 as well)

OK (apologies for the lengthy detail)

From Router B I can ping router A and workstations beyond Router A
From Router B I can traceroute to workstations behind router A and the switch, which is good. To my thinking there is a route to and from Router B through Router A, through the switch, to the workstation and then back again.

Problem is from Router A..(and anything behind router A)
I can ping workstations beyond Router B (via the hub), but I cannot traceroute to any devices behind Router B.

Im struggling to see what the reason is. I understand ping is different to traceroute, but I can FTP to the devices I am trying to traceroute to..weird...
Its causing some problems with an application we are running where comms are OK between Router B to A...but fail from Router A to B ( well, the devices behind router B ).
I can traceroute to each one of the routers..the problems happen when I try to get to devices beyond router B.

Confused!!?? I am just reading this, but hopefully someone will be able to help.

BTW, the workstations in question (behind router B) are running DOS and TCP/IP (PCTCP)

Any ideas folks???

Really appreciate any assistance...

Andrew

**Update...I have narrowed it down to router B. I cannot traceroute from router B to any workstations behind it. There is a netgear hub (EN104) connecting a few workstations together to the router F/E 0. I can still ping though.

AGain..really really apprecite any help.

Andrew

 

[Morsing]

Ping isn't really different to traceroute, only the reply is slightly different. In the case of ping it's an icmp reply (don't know the excact name) and for traceroute it's an icmp network unreacheable. I won't make much difference.

What exactly happens?? Can you show us the output??

Cheers Henrik Morsing
IBM Certified AIX 4.3 Systems Administration

 

[chocyman]

Yeah..no problems..

I can remember what the output was. If I ping say one of the workstations lets say 192.168.1.100 from router A. I get responses back of < 80ms. All OK and no drops
Ok..from router A again (I mean telnetted into router A) if I try to traceroute to the same device (ie across the frame) I get the first hop of 192.168.200.1 shown up (so router B serial interface), and then nothing (* * *) for ever and ever.
Likewise if I telnet to router B, I can ping 192.168.1.100 (which hangs off its own F/E port) no problems. responses <10ms.WHen I try to traceroute from router B to the same device it fails (ie * * *). Its almost as though router B does not know it has the 192.168.1.x network off its own F/E port. There IS a route (show IP route) in it to point to it ( ie there is an entry C 192.168.1.1/24 is directly connected, FE0). Likewise, the workstation in question has its own gateway set to the FE0 port on the router (ie 192.168.1.1).
ALso..most confusing is that I can FTP to and from the workstation. FTP uses TCP/IP and I would have thought that if I can FTP then traceroute should be working.
THe only 'thought' Ive had is that this workstation uses an old DOS TCP module called PCTCP. There may be some bizarre way it handles requests and responses to traceroute. Dunno, but reading about it now. I would guess though that ping and traceroute are THE basic tools for diagnosing network problems. Cant imagine why it would work any differently to any other TCP modules (ie windows 98/95/SCO etc etc)

Like I say..stumped and causing me grief so really really appreciate help on this one!!

Andrew

 

[krr]

Just a stab in the dark: are there any filters/access-lists configured or is there a firewall in the path?

Ping sends ICMP Echo Request and gets back ICMP Echo Reply.

Tracert (as implemented in Windows) sends ICMP Echo Request and gets back ICMP TTL Expired from intermediate routers. This would break if ICMP TTL Expired is filtered somewhere, but should eventually give a response from the final destination (ICMP Echo Reply).

Traceroute (as implemented on UNIX) sends UDP packets - don't know which port is used - and gets back ICMP TTL Expired from intermediate routers. Same as above for ICMP TTL Expired, but in addition UDP might be blocked somewhere.

Cheers *Rob