RTNETLINK answers: File exists

Wasn't sure where to post this one.

I was hit by this problem today. Normally this wouldn't be an issue but I guess the circumstances were right for this to happen. One of our routers had an issue and ended up being forcibly shut down. Not uncommon, done it before without a problem.

When I tried to bring the server up after I booted up the router, it wouldn't establish a link.

I kept doing:

service network restart

And this error was ocurring, and it was unable to bring up eth0:

RTNETLINK answers: File exists

I googled around and I believe the problem occurs when the routing table gets out of whack. I ran this command to look at it:

netstat -rn

The routing tables were messed up with incorrect routes.

The fix was:

service network restart
ifup eth0

I don't exactly know why it worked, but that cleaned the tables and brought up the device. It's worth nothing that I had to restart a switch that was connected to this machine as well. For some reason I think it poisoned both the switch and the direct links to one of our servers with this bad information. I also had to restart the switch to get that to work right, but that was trivial.

Anyone ever have this issue before / might be able to share some further insight?

hi:
I got the same message. I tried to migrate our current linux firewall to sl-6 yesterday. we have 9 ethernt interface in our machine and very complicated firewall rules. sl-6 connected to internet happily but it refuse to forware the packet for other machines. I check it for 1 hour but can not figure why and can only see some unusal "RTNETLINK answers: File exists".
I will setup a test machine and try to see what really happened with sl-6. but
it's good to know if anyone has experience with sl-6 firewall.

hi:
ok. I got my firewall problem solved. the root cause of my problem is the changed behavior of interface rp_filter settings. the internal design change is from kernel 2.6.31.

in my case, I use fwmark ip rule to do policy routing, and this kind of traffic will be filtered in SL6, because the default setting will enable rp_filter, and it didn't like fwmark policy routing. although the same setting disabled rp_filter in older kernels.

In my case I could not get any internet connection at all. There was just no link. Period. And my setup is not even complicated, it's just 1 crossover cable in a single NIC with a direct line to my firewall server. Doesn't even pass through a switch.

It was really frustrating but the method I posted worked just fine for me.

Interesting about the rp_filter but I'm not seeing that enabled on my machine by default unless I'm looking in the wrong place.

cat /proc/sys/net/ipv4/conf/all/rp_filter

returns a '0'

I should soon have a bash script to use to run to check for this problem and then issue the command if it's found. Should be as simple as trying to ping the gateway then doing an ifup eth0. Because it's really annoying.