netdev - Re: routing bug?

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Message-ID: <1321621796.3277.1.camel@edumazet-HP-Compaq-6005-Pro-SFF-PC>
Date:	Fri, 18 Nov 2011 14:09:56 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Sven-Haegar Koch <haegar@...net.de>
Cc:	Pozsár Balázs <pozsy@...linux.hu>,
	Linux-Kernel-Mailinglist <linux-kernel@...r.kernel.org>,
	Tamási János <janusz@...linux.hu>,
	netdev@...r.kernel.org
Subject: Re: routing bug?

Le vendredi 18 novembre 2011 à 13:48 +0100, Sven-Haegar Koch a écrit :
> Added netdev list to CC:, there you should have a higher chance of a
> usefull answer.
> 
> On Fri, 18 Nov 2011, Pozsár Balázs wrote:
> 
> > Hi all,
> > 
> > I have been struggling with this not easily reproducible issue since a while.
> > I am using linux kernel v3.1.0, and sometimes routing to a few IP addresses
> > does not work. What seems to happen is that instead of sending the packet to
> > the gateway, the kernel treats the destination address as local, and tries to
> > gets its MAC address via ARP.
> > 
> > For example, now my current IP address is 172.16.1.104/24, the gateway is
> > 172.16.1.254:
> > 
> > |# ifconfig eth0 eth0      Link encap:Ethernet  HWaddr 00:1B:63:97:FC:DC
> >           inet addr:172.16.1.104  Bcast:172.16.1.255  Mask:255.255.255.0
> >           UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
> >           RX packets:230772 errors:0 dropped:0 overruns:0 frame:0
> >           TX packets:171013 errors:0 dropped:0 overruns:0 carrier:0
> >           collisions:0 txqueuelen:1000
> >           RX bytes:191879370 (182.9 Mb)  TX bytes:47173253 (44.9 Mb)
> >           Interrupt:17
> > 
> > # route -n
> > Kernel IP routing table
> > Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
> > 0.0.0.0         172.16.1.254    0.0.0.0         UG    0      0        0 eth0
> > 172.16.1.0      0.0.0.0         255.255.255.0   U     1      0        0 eth0
> > |
> > 
> > I can ping a few addresses, but not 172.16.0.59:
> > 
> > |# ping -c1 172.16.1.254
> > PING 172.16.1.254 (172.16.1.254) 56(84) bytes of data.
> > 64 bytes from 172.16.1.254: icmp_seq=1 ttl=64 time=0.383 ms
> > 
> > --- 172.16.1.254 ping statistics ---
> > 1 packets transmitted, 1 received, 0% packet loss, time 0ms
> > rtt min/avg/max/mdev = 0.383/0.383/0.383/0.000 ms
> > root@...sybook:~# ping -c1 172.16.0.1
> > PING 172.16.0.1 (172.16.0.1) 56(84) bytes of data.
> > 64 bytes from 172.16.0.1: icmp_seq=1 ttl=63 time=5.54 ms
> > 
> > --- 172.16.0.1 ping statistics ---
> > 1 packets transmitted, 1 received, 0% packet loss, time 0ms
> > rtt min/avg/max/mdev = 5.545/5.545/5.545/0.000 ms
> > root@...sybook:~# ping -c1 172.16.0.2
> > PING 172.16.0.2 (172.16.0.2) 56(84) bytes of data.
> > 64 bytes from 172.16.0.2: icmp_seq=1 ttl=62 time=7.92 ms
> > 
> > --- 172.16.0.2 ping statistics ---
> > 1 packets transmitted, 1 received, 0% packet loss, time 0ms
> > rtt min/avg/max/mdev = 7.925/7.925/7.925/0.000 ms
> > root@...sybook:~# ping -c1 172.16.0.59
> > PING 172.16.0.59 (172.16.0.59) 56(84) bytes of data.
> > From 172.16.1.104 icmp_seq=1 Destination Host Unreachable
> > 
> > --- 172.16.0.59 ping statistics ---
> > 1 packets transmitted, 0 received, +1 errors, 100% packet loss, time 0ms
> > |
> > 
> > When trying to ping 172.16.0.59, I can see in tcpdump that an ARP req was
> > sent:
> > 
> > |# tcpdump -n -i eth0|grep ARP
> > tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
> > listening on eth0, link-type EN10MB (Ethernet), capture size 96 bytes
> > 15:25:16.671217 ARP, Request who-has 172.16.0.59 tell 172.16.1.104, length 28
> > |
> > 
> > and /proc/net/arp has an incomplete entry for 172.16.0.59:
> > 
> > |# grep 172.16.0.59 /proc/net/arp
> > 
> > 172.16.0.59      0x1         0x0         00:00:00:00:00:00     *        eth0
> > |
> > 
> > Please note, that 172.16.0.59 /is/ accessible from this LAN from other
> > computers.
> > 
> > 
> > Does anyone have any idea of what's going on? Thanks,
> > 
> > 
> > Balazs Pozsar
> > 
> > ps: I think it is related to this one: https://lkml.org/lkml/2011/11/16/292
> > 
> > --

Could you send us result of :

ip route get 172.16.0.59
ip route list cache match 172.16.0.59




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