Why is Linux choosing the wrong source ip address
- by Scheintod
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.