Ethernet Encapsulation Failure

[sgrizzle]

Lab set up. Back-to-back Cisco routers through Serial ports. (with the correct serial cables). Both routers rev. 12.2 (T). Laptop connected to ethernet port on one side, rest of network (including Internet access through PIX 506E) on the other side through other ethernet port. All attempts to access Internet with Laptop fail. Debug reveals that traffic passing through 1st router fine to far side Serial port. However, far side Ethernet port is showing "Encapsulation Errors", and all data packets are dropped. Encapsulation on all Serial ports is HDLC, encapsulation on all Ethernet ports is ARPA. Routing protocol is OSPF. What is wrong?

Here is debug output from encapsulation failure:

14:09:50: IP: s=192.168.2.2 (Serial1), d=207.46.134.222 (Ethernet0), g=207.46.134.222, len 48, forward

14:09:50: TCP src=1748, dst=80, seq=1245146744, ack=0, win=8192 SYN

14:09:50: IP: s=192.168.2.2 (Serial1), d=207.46.134.222 (Ethernet0), len 48, encapsulation failed

14:09:50: TCP src=1748, dst=80, seq=1245146744, ack=0, win=8192 SYN

14:09:53: IP: s=192.168.2.2 (Serial1), d=207.46.134.222 (Ethernet0), g=207.46.134.222, len 48, forward

14:09:53: TCP src=1748, dst=80, seq=1245146744, ack=0, win=8192 SYN

14:09:53: IP: s=192.168.2.2 (Serial1), d=207.46.134.222 (Ethernet0), len 48, encapsulation failed

14:09:53: TCP src=1748, dst=80, seq=1245146744, ack=0, win=8192 SYN

14:09:59: IP: s=192.168.2.2 (Serial1), d=207.46.134.222 (Ethernet0), g=207.46.134.222, len 48, forward

14:09:59: TCP src=1748, dst=80, seq=1245146744, ack=0, win=8192 SYN

14:09:59: IP: s=192.168.2.2 (Serial1), d=207.46.134.222 (Ethernet0), len 48, encapsulation failed

14:09:59: TCP src=1748, dst=80, seq=1245146744, ack=0, win=8192 SYN

14:10:11: IP: s=192.168.2.2 (Serial1), d=207.46.134.222 (Ethernet0), g=207.46.134.222, len 48, forward

14:10:11: TCP src=1748, dst=80, seq=1245146744, ack=0, win=8192 SYN

14:10:11: IP: s=192.168.2.2 (Serial1), d=207.46.134.222 (Ethernet0), len 48, encapsulation failed

14:10:11: TCP src=1748, dst=80, seq=1245146744, ack=0, win=8192 SYN

14:10:35: IP: s=192.168.2.2 (Serial1), d=207.46.134.190 (Ethernet0), g=207.46.134.190, len 48, forward

14:10:35: TCP src=1749, dst=80, seq=1245191730, ack=0, win=8192 SYN

14:10:35: IP: s=192.168.2.2 (Serial1), d=207.46.134.190 (Ethernet0), len 48, encapsulation failed

14:10:35: TCP src=1749, dst=80, seq=1245191730, ack=0, win=8192 SYN

14:10:38: IP: s=192.168.2.2 (Serial1), d=207.46.134.190 (Ethernet0), g=207.46.134.190, len 48, forward

14:10:38: TCP src=1749, dst=80, seq=1245191730, ack=0, win=8192 SYN

14:10:38: IP: s=192.168.2.2 (Serial1), d=207.46.134.190 (Ethernet0), len 48, encapsulation failed

14:10:38: TCP src=1749, dst=80, seq=1245191730, ack=0, win=8192 SYN

14:10:44: IP: s=192.168.2.2 (Serial1), d=207.46.134.190 (Ethernet0), g=207.46.134.190, len 48, forward

14:10:44: TCP src=1749, dst=80, seq=1245191730, ack=0, win=8192 SYN

14:10:44: IP: s=192.168.2.2 (Serial1), d=207.46.134.190 (Ethernet0), len 48, encapsulation failed

14:10:44: TCP src=1749, dst=80, seq=1245191730, ack=0, win=8192 SYN

[deilert]

Encap failed basically means that the routing process does not know what layer 2 wrapper to put on it , what does a sh ip route to 207.46.134.190 on the far side show ? is it a static or is it learned dynamically ?

[mark-obrien · Accepted solution]

In the router connected to the PIX, make sure that the default route points to the PIX's IP address rather than to the ethernet interface of the router.

HTH

Mark

[sgrizzle]

Mark's 'default route' pointing to the PIX was right on! Can he give an explanation as to why?

[mark-obrien]

I assume that you previously had the default route pointed to the router's ethernet interface. If that is the case, the router would send an ARP for the destination IP address out that interface, and the PIX was not responding with proxy-ARP replies, thus the encapsulation failures. When you set the default route to be the PIX's IP address, the router ARPs for that address and, it being the PIX's own address, the PIX responds with its MAC address. The router sends the packet in a frame destined for the PIX's MAC address, and the PIX handles it from there.

HTH

Mark