I'm having a routing problem on CentOS 6.2 (kernel 2.6.32-220)
Here's the setup: One host is on my local network. It's talking to two nearly identical hosts at a remote location. The two remote hosts are on all the same networks, acting as redundant backups for each other.
I set up two GRE tunnels from the local host, one to each remote host:
ip tunnel add name tunnel1 mode gre local 10.2.1.2 remote 10.2.1.1 ip link set dev tunnel1 up ip route add 172.16.1.0/24 dev tunnel1 metric 101 ip tunnel add name tunnel2 mode gre local 10.2.1.4 remote 10.2.1.3 ip link set dev tunnel2 up ip route add 172.16.1.0/24 dev tunnel2 metric 102
Outgoing packets route properly, no problem. Incoming packets are weird. It appears that whichever tunnel has the route with the higher metric (tunnel2 in the example above) will ignore incoming packets. They come in all right, and can be seen on the local machine with 'tcpdump -i tunnel2', but they are not routed properly to the local networks. They're simply dropped. I can switch the two metrics, and then tunnel1 will drop all incoming packets. The tunnel with the lower route metric will route packets properly, both incoming and outgoing.
Is this "working as designed?" What I'd like to have happen, of course, is for all packets on both tunnels to be properly forwarded. Is this possible?
Quick update: One person suggested (I'm not sure why) adding 'key' parameters to the 'ip tunnel' commands. I tried this, both with different keys for each tunnel and with identical keys for both tunnels, but neither trial had no effect.