Why is Linux choosing the wrong source ip address

Posted by Scheintod on Server Fault See other posts from Server Fault or by Scheintod
Published on 2013-10-24T18:44:02Z Indexed on 2013/10/25 9:58 UTC
Read the original article Hit count: 179

Filed under:

linux

|

routing

|

kernel

|

openvz

and what to do to let it choose the right one?

This all happens inside an OpenVZ container:

The Host is Debian/Wheezy with Redhat/OpenVZ Kernel:

root@mycl2:~# uname -a
Linux mycl2 2.6.32-openvz-042stab081.5-amd64 #1 SMP Mon Sep 30 16:40:27 MSK 2013 x86_64 GNU/Linux

The container has two (virtual) network interfaces. One in public and one in private address-space:

root@mycl2:~# ifconfig
lo        Link encap:Local Loopback  
          inet addr:127.0.0.1  Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:16436  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0 
          RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)

venet0    Link encap:UNSPEC  HWaddr 00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00  
          inet addr:127.0.0.2  P-t-P:127.0.0.2  Bcast:0.0.0.0  Mask:255.255.255.255
          UP BROADCAST POINTOPOINT RUNNING NOARP  MTU:1500  Metric:1
          RX packets:475 errors:0 dropped:0 overruns:0 frame:0
          TX packets:775 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0 
          RX bytes:32059 (31.3 KiB)  TX bytes:56309 (54.9 KiB)

venet0:0  Link encap:UNSPEC  HWaddr 00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00  
          inet addr:80.123.123.29  P-t-P:80.123.123.29  Bcast:80.123.123.29  Mask:255.255.255.255
          UP BROADCAST POINTOPOINT RUNNING NOARP  MTU:1500  Metric:1

venet0:1  Link encap:UNSPEC  HWaddr 00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00  
          inet addr:10.0.1.29  P-t-P:10.0.1.29  Bcast:10.0.1.29  Mask:255.255.255.255
          UP BROADCAST POINTOPOINT RUNNING NOARP  MTU:1500  Metric:1

The route to the private network is set manually:

root@mycl2:~# route -n
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
10.0.0.0        0.0.0.0         255.0.0.0       U     0      0        0 venet0
0.0.0.0         0.0.0.0         0.0.0.0         U     0      0        0 venet0

Tring to ping others on the private network leads to the wrong source address been choosen:

root@mycl2:~# ip route get 10.0.1.26
10.0.1.26 dev venet0  src 80.123.123.29 
    cache  mtu 1500 advmss 1460 hoplimit 64

Why is this and what can I do about it?

EDIT:

If I create the route with (thanks to Joshua)

ip route add 10.0.0.0/8 dev venet0 src 10.0.1.29

it is working. But according to man ip-route the src parameter should only set the source-ip if this route is chosen. But if this route is chosen then the source-ip would be that anyway.

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