Can't ping evvery machine across GRE Tunnel to remote subnet

[taufeeqrauf]

I have an GRE Tunnel across my head office and remote site with multiple subnets using cisco 1841 routers.I can ping most of  the devices on the remote side, but I can not ping certain devices. These  devices respond to ping requests on the local LAN, but not through the WAN link. If I change the IP of device than it start responding. I am using same gateway and mask on these devices. Any ideas. The remote site is running classic STP on switches with distribution switch being the root bridge. Any suggestions/ ideas?

[Richard Burts]

Is this just a regular GRE tunnel or is it GRE with IPSec or something ? Are there any access lists associated with the tunnel on either end? Are you running any routing protocol over the tunnel? After you change the address and a device starts to respond if you change it back to the original address does it respond still?

If we knew these things perhaps we could give you a better answer.

HTH

Rick

Sent from Cisco Technical Support iPhone App

[taufeeqrauf]

Its a regular GRE and OSPF is running on it. No access list associated either with physical interface and with Tunnel interface.

The device starts responding to ping rather randomly if I change the address it respond and if I change to its original address it sometimes respond for certain time and than again stop responding.

I have about 200 machine in that subnet and only 22 respond to ping addresses continously. From remote router I can ping every address but if I ping from my head office router I can get response from certain IP addresses.

After running debug ip packet on remote router I get  following response

Apr  8 22:27:11.409: IP: tableid=0, s=172.16.1.3 (Tunnel150), d=172.16.10.15 (FastEthernet0/0.1), routed via RIB
Apr  8 22:27:11.409: IP: s=172.16.1.3 (Tunnel150), d=172.16.10.15 (FastEthernet0/0.1), g=172.16.10.15, len 100, forward
Apr  8 22:27:11.413: IP: s=172.16.1.3 (Tunnel150), d=172.16.10.15 (FastEthernet0/0.1), len 100, encapsulation failed

It seems router loses layer 2 address rather randomly

-Taufeeq

[yashfaqu]

can u check the arp entry on the router, follow these steps:

show ip arp 172.16.10.15

ping 172.16.10.15

show ip arp 172.16.10.15

[taufeeqrauf]

Protocol  Address          Age (min)  Hardware Addr   Type   Interface

Internet  172.16.10.15             0   0015.6057.1bbb  ARPA   FastEthernet0/0.1

at remote router