crazyscot: Selfie, with C, in front of an alpine lake (Default)
crazyscot ([personal profile] crazyscot) wrote2013-10-11 10:19 pm

Linux IP routing weirdness

OK, internets, help me out here, my google-fu is deserting me and possibly because I'm using the wrong terminology...

I have some regular weirdness with networking on my desktop PC at home. I regularly lose the ability to route packets to certain destinations. It tends to be the same destinations. For a long time it was feedproxy; now it's that and facebook. The interface remains up, and I can reach those destinations from the Linux PC that is the immediate router; just that those failing destinations seem to be blackholed on my desktop.

So it's obviously (?) entirely my machine at fault.

If I bounce the interface, it all works again. For a while, but it usually blackholes again soon.

It may be relevant that I am running the dreaded double NAT; once on my router/fileserver PC, and again on the DSL modem. I did briefly try to make the DSL modem not do NAT, but couldn't readily make it work. I suppose I ought to try again; and I could also try putting my PC outside the inner NAT to see if that makes a difference (though it wouldn't then be able to see the fileserver unless I reconfigured that *sigh*).

My googling did take me as far as a possible kernel bug to do with ARP caching and ICMP redirects and suggested echo 0 >/proc/sys/net/ipv4/conf/eth0/accept_redirects - but it hasn't helped. ip route list cache shows affected destinations as redirected, but I'm not entirely sure what that means or how I might prevent it. via dev eth0  src 
    cache   ipid 0xc125 rtt 206ms rttvar 67ms cwnd 10 from via dev eth0 
    cache   ipid 0xc125 rtt 206ms rttvar 67ms cwnd 10 is my desktop. is the DSL router.

Any ideas?