That's the best way I found to see if GRE is up, just watching for two way "proto gre" traffic.
Here's how you can match the IP addresses *inside* the GRE packet, which you probably will want. Note that 0x0a050505 is hexadecimal for my desired IP address of 10.5.5.5: root@os-network:~# tcpdump -i eth1 'proto gre and ( ip[58:4] = 0x0a050505 or ip[62:4] = 0x0a050505 )' tcpdump: verbose output suppressed, use -v or -vv for full protocol decode listening on eth1, link-type EN10MB (Ethernet), capture size 65535 bytes 16:18:17.434378 IP os-network-d > os-compute-01-d: GREv0, key=0x0, length 110: IP opskzlp119.snops.net > 10.5.5.5: ICMP echo request, id 21321, seq 488, length 64 16:18:17.436190 IP os-compute-01-d > os-network-d: GREv0, key=0x0, length 110: IP 10.5.5.5 > opskzlp119.snops.net: ICMP echo reply, id 21321, seq 488, length 64 16:18:18.435750 IP os-network-d > os-compute-01-d: GREv0, key=0x0, length 110: IP opskzlp119.snops.net > 10.5.5.5: ICMP echo request, id 21321, seq 489, length 64 16:18:18.437798 IP os-compute-01-d > os-network-d: GREv0, key=0x0, length 110: IP 10.5.5.5 > opskzlp119.snops.net: ICMP echo reply, id 21321, seq 489, length 64 : On Thu, Mar 14, 2013 at 9:55 AM, Robert van Leeuwen < robert.vanleeu...@spilgames.com> wrote: > > Thanks for the reply. I have one more question. > > How we will check whether the tunneling is established or not? > > tcpdump can show you the GRE traffic: > tcpdump -i ethX proto gre > > Cheers, > Robert > _______________________________________________ > Mailing list: https://launchpad.net/~openstack > Post to : openstack@lists.launchpad.net > Unsubscribe : https://launchpad.net/~openstack > More help : https://help.launchpad.net/ListHelp >
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