Re: routing bug?

Re: routing bug?

[Sven-Haegar Koch]

[-- Attachment #1: Type: TEXT/PLAIN, Size: 3834 bytes --]

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@pozsybook:~# 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@pozsybook:~# 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@pozsybook:~# 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
> 
> --
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at  http://www.tux.org/lkml/
> 
> 

-- 
Three may keep a secret, if two of them are dead.
- Ben F.

Re: routing bug?

[Eric Dumazet]

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@pozsybook:~# 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@pozsybook:~# 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@pozsybook:~# 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

Re: routing bug?

[Pozsár Balázs]

On 2011-11-18 14:09, Eric Dumazet wrote:
> 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@pozsybook:~# 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@pozsybook:~# 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@pozsybook:~# 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
>    

I did not tell you in my first mail, that some times different hosts are 
reachable and unreachable. I will try to not confuse you :)
As of now, 172.16.0.59 is OK, and 172.16.0.37 is NOT OK.
Also, 172.16.0.64 is OK now, and 172.16.0.42 is NOT OK now.

The two commands you have requested give the following output for these 
IP addresses:

These are OK:

# ip route get 172.16.0.64
172.16.0.64 via 172.16.1.254 dev eth0  src 172.16.1.22
     cache
# ip route get 172.16.0.59
172.16.0.59 via 172.16.1.254 dev eth0  src 172.16.1.22
     cache

These are NOT OK:

# ip route get 172.16.0.37
172.16.0.37 dev eth0  src 172.16.1.22
     cache <redirected>  ipid 0x97a4
# ip route get 172.16.0.42
172.16.0.42 dev eth0  src 172.16.1.22
     cache <redirected>  ipid 0x0d21

These are OK:

# ip route list cache match 172.16.0.59
172.16.0.59 via 172.16.1.254 dev eth0  src 172.16.1.22
     cache
# ip route list cache match 172.16.0.64
172.16.0.64 via 172.16.1.254 dev eth0  src 172.16.1.22
     cache

These are NOT OK:

# ip route list cache match 172.16.0.37
172.16.0.37 dev eth0  src 172.16.1.22
     cache <redirected>  ipid 0x97a4
172.16.0.37 from 172.16.1.22 dev eth0
     cache <redirected>  ipid 0x97a4
172.16.0.37 from 172.16.1.22 dev eth0
     cache <redirected>  ipid 0x97a4
# ip route list cache match 172.16.0.42
172.16.0.42 dev eth0  src 172.16.1.22
     cache <redirected>  ipid 0x0d21
172.16.0.42 from 172.16.1.22 dev eth0
     cache <redirected>  ipid 0x0d21


How can I fix this?

Thanks!

Re: routing bug?

[Eric Dumazet]

Le vendredi 18 novembre 2011 à 14:23 +0100, Pozsár Balázs a écrit :
> On 2011-11-18 14:09, Eric Dumazet wrote:
> > 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@pozsybook:~# 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@pozsybook:~# 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@pozsybook:~# 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
> >    
> 
> I did not tell you in my first mail, that some times different hosts are 
> reachable and unreachable. I will try to not confuse you :)
> As of now, 172.16.0.59 is OK, and 172.16.0.37 is NOT OK.
> Also, 172.16.0.64 is OK now, and 172.16.0.42 is NOT OK now.
> 
> The two commands you have requested give the following output for these 
> IP addresses:
> 
> These are OK:
> 
> # ip route get 172.16.0.64
> 172.16.0.64 via 172.16.1.254 dev eth0  src 172.16.1.22
>      cache
> # ip route get 172.16.0.59
> 172.16.0.59 via 172.16.1.254 dev eth0  src 172.16.1.22
>      cache
> 
> These are NOT OK:
> 
> # ip route get 172.16.0.37
> 172.16.0.37 dev eth0  src 172.16.1.22
>      cache <redirected>  ipid 0x97a4
> # ip route get 172.16.0.42
> 172.16.0.42 dev eth0  src 172.16.1.22
>      cache <redirected>  ipid 0x0d21
> 
> These are OK:
> 
> # ip route list cache match 172.16.0.59
> 172.16.0.59 via 172.16.1.254 dev eth0  src 172.16.1.22
>      cache
> # ip route list cache match 172.16.0.64
> 172.16.0.64 via 172.16.1.254 dev eth0  src 172.16.1.22
>      cache
> 
> These are NOT OK:
> 
> # ip route list cache match 172.16.0.37
> 172.16.0.37 dev eth0  src 172.16.1.22
>      cache <redirected>  ipid 0x97a4
> 172.16.0.37 from 172.16.1.22 dev eth0
>      cache <redirected>  ipid 0x97a4
> 172.16.0.37 from 172.16.1.22 dev eth0
>      cache <redirected>  ipid 0x97a4
> # ip route list cache match 172.16.0.42
> 172.16.0.42 dev eth0  src 172.16.1.22
>      cache <redirected>  ipid 0x0d21
> 172.16.0.42 from 172.16.1.22 dev eth0
>      cache <redirected>  ipid 0x0d21
> 
> 
> How can I fix this?
> 
> Thanks!

We are working on it (see threads in netdev)

You can in the meantime 

echo 0 >/proc/sys/net/ipv4/conf/eth0/accept_redirects

Re: routing bug?

[Pozsár Balázs]

On 2011-11-18 14:33, Eric Dumazet wrote:
> Le vendredi 18 novembre 2011 à 14:23 +0100, Pozsár Balázs a écrit :
>    
>> On 2011-11-18 14:09, Eric Dumazet wrote:
>>      
>>> 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@pozsybook:~# 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@pozsybook:~# 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@pozsybook:~# 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
>>>
>>>        
>> I did not tell you in my first mail, that some times different hosts are
>> reachable and unreachable. I will try to not confuse you :)
>> As of now, 172.16.0.59 is OK, and 172.16.0.37 is NOT OK.
>> Also, 172.16.0.64 is OK now, and 172.16.0.42 is NOT OK now.
>>
>> The two commands you have requested give the following output for these
>> IP addresses:
>>
>> These are OK:
>>
>> # ip route get 172.16.0.64
>> 172.16.0.64 via 172.16.1.254 dev eth0  src 172.16.1.22
>>       cache
>> # ip route get 172.16.0.59
>> 172.16.0.59 via 172.16.1.254 dev eth0  src 172.16.1.22
>>       cache
>>
>> These are NOT OK:
>>
>> # ip route get 172.16.0.37
>> 172.16.0.37 dev eth0  src 172.16.1.22
>>       cache<redirected>   ipid 0x97a4
>> # ip route get 172.16.0.42
>> 172.16.0.42 dev eth0  src 172.16.1.22
>>       cache<redirected>   ipid 0x0d21
>>
>> These are OK:
>>
>> # ip route list cache match 172.16.0.59
>> 172.16.0.59 via 172.16.1.254 dev eth0  src 172.16.1.22
>>       cache
>> # ip route list cache match 172.16.0.64
>> 172.16.0.64 via 172.16.1.254 dev eth0  src 172.16.1.22
>>       cache
>>
>> These are NOT OK:
>>
>> # ip route list cache match 172.16.0.37
>> 172.16.0.37 dev eth0  src 172.16.1.22
>>       cache<redirected>   ipid 0x97a4
>> 172.16.0.37 from 172.16.1.22 dev eth0
>>       cache<redirected>   ipid 0x97a4
>> 172.16.0.37 from 172.16.1.22 dev eth0
>>       cache<redirected>   ipid 0x97a4
>> # ip route list cache match 172.16.0.42
>> 172.16.0.42 dev eth0  src 172.16.1.22
>>       cache<redirected>   ipid 0x0d21
>> 172.16.0.42 from 172.16.1.22 dev eth0
>>       cache<redirected>   ipid 0x0d21
>>
>>
>> How can I fix this?
>>
>> Thanks!
>>      
> We are working on it (see threads in netdev)
>
> You can in the meantime
>
> echo 0>/proc/sys/net/ipv4/conf/eth0/accept_redirects
>    

Unfortunately it does not solve the problem for me, I have have these 
"cache <redirected>" entries even after that echo command.

Re: routing bug?

[Eric Dumazet]

Le vendredi 18 novembre 2011 à 14:38 +0100, Pozsár Balázs a écrit :

> Unfortunately it does not solve the problem for me, I have have these 
> "cache <redirected>" entries even after that echo command.
> 

Its a problem with a cached value.

You must reboot to flush it.

It was already discussed yesterday on netdev.