Subject: IPv6, gre tunnel to cisco and tcpdump
To: None <>
From: Mark Davies <>
List: current-users
Date: 06/20/2005 16:13:32
I'm trying to set up a gre tunnel between a 3.99.6 box and a cisco 7500 to 
throw IPv6 traffic over.

I seem to have the tunnel working and can ping6 (and bgp etc) over the link 
but if I try to see what is flowing over the gre0 interface using tcpdump it 
reports "wrong link-layer encapsulation" for all incoming packets:

16:06:06.050281 2001:4401::1011.65533 > 2001:4401::1010.bgp: P 380:399(19) ack 
46064 win 33120: BGP, length: 19 [flowlabel 0x931d4] [hlim 1]
16:06:06.063225 IP6 , wrong link-layer encapsulationbad-len 0
16:06:06.260229 2001:4401::1011.65533 > 2001:4401::1010.bgp: . ack 46083 win 
33120 [flowlabel 0x931d4] [hlim 1]
16:06:58.020214 IP6 , wrong link-layer encapsulationbad-hlen 0
16:06:58.020245 2001:4401::1011 > icmp6: echo reply seq 0

and poking at the packets more with ethereal I see that indeed in the 
"Null/Loopback" frame the family for the incoming packets is "IP" (2) rather 
than "IPv6" (24).

Anyone struck this before?  Know how to fix?