Ping - no reply?

[louis0001]

This one is a little strange for me and I'm running out of ideas. This is over an MPLS network

Router A = 10.1.10.1

Host B = 10.1.28.132

Issue:

From host B, I can ping Router A. Wireshark on Host B shows it going out and a reply. ICMP debug on Router A show ICMP being recieved from Host B. All is well

From Router A to host B. No reply. Wireshark on host B shows ICMP being recieved from Router A and host B sending replies back to Router A. Router A shows no reply.

Router A can sucessfully ping some other hosts on the same subnet as Host B but only some ie it can ping Host B,C,D but not host X,Y,Z on the same /24 subnet

It's the strangest thing I've seen and not sure of what's going on. There are no ACL's or FW's involved here. Other routers on the same MPLS network can reach all hosts. Config is exactly the same on the routers apart from the peering addresses.

Amy ideas?

[Julio E. Moisa]

Hi

ICMP is reciprocal it means that if you send a packet you must receive a response, 2 ways. So if both Hosts have valid routes to each other and there are no ACLs on the ISP network or internal network, it could be pointing to the Host specifically, you could verify if the window firewall is disabled (if apply) or antivirus blocking ICMP. 

[louis0001]

I'm getting a little nearer.

Router A (CE) > Router B (PE) > MPLS > Router C (PE) > Router D (CE) > Host B /24

Router A ping Router B, C & D = ok

Router D ping Router C, B ok can't ping Router A (CE)

Now, let's choose a different host HOST C /24 (on same subnet as host B)

HOST C > Router D (CE) > Router C (PE) > MPLS > Router B (PE) > Router A (CE) = everything pings ok!

So you have to wonder why host C can ping router A but host B can't. Host B stops at Router B wheras Host C doesn't.

Trying it from the router:

Router D can't ping router A (it stops at Router B)

It's strange

[Julio E. Moisa]

Hi,

It looks like an ACL or filtering method on the ISP side. It is weird, the labels should be fine. Are you testing on GNS3 or with real devices?

[Georg Pauwen]

On a side note, what is host B, a Windows machine ? Compare the output of 'route print' of host B and host C, there might be an indication...

[paul driver]

Hello

software firewall on host B ?

res

paul