[libvirt-users] Problems setting up bridge

[Nataraj]

On 04/15/2011 01:13 PM, Alex wrote:
> Hi,
> I have a fc14 box with two interfaces that I'm having some difficulty
> setting up a bridge properly. I have a few kvm guests set up and
> running, but I've switched from using NetworkManager to using standard
> networking with a bridge. I've modified the ifcfg-eth0 and created
> ifcfg-br0 as per the standard documentation, but I think I'm having
> routing problems. This is what the network looks like:
>
> [root at fc14 ~]# route
> Kernel IP routing table
> Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
> 68.195.XXX.40   *               255.255.255.248 U     0      0        0 br0
> 192.168.1.0     *               255.255.255.0   U     0      0        0 eth1
> 192.168.125.0   *               255.255.255.0   U     0      0        0 virbr0
> link-local      *               255.255.0.0     U     1003   0        0 eth1
> link-local      *               255.255.0.0     U     1004   0        0 br0
> default         ool-44c3c129.st 0.0.0.0         UG    0      0        0 br0
>
> br0       Link encap:Ethernet  HWaddr 40:61:86:4E:84:09
>           inet addr:68.195.XXX.42  Bcast:68.195.XXX.47  Mask:255.255.255.248
>           inet6 addr: fe80::a0e7:ecff:fefd:340a/64 Scope:Link
>           UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
>           RX packets:3883 errors:0 dropped:0 overruns:0 frame:0
>           TX packets:3579 errors:0 dropped:0 overruns:0 carrier:0
>           collisions:0 txqueuelen:0
>           RX bytes:1818327 (1.7 MiB)  TX bytes:590720 (576.8 KiB)
>
> eth0      Link encap:Ethernet  HWaddr 40:61:86:4E:84:09
>           inet6 addr: fe80::4261:86ff:fe4e:8409/64 Scope:Link
>           UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
>           RX packets:3891 errors:0 dropped:0 overruns:0 frame:0
>           TX packets:3551 errors:0 dropped:0 overruns:0 carrier:1
>           collisions:0 txqueuelen:1000
>           RX bytes:1873169 (1.7 MiB)  TX bytes:588302 (574.5 KiB)
>           Interrupt:42
>
> eth1      Link encap:Ethernet  HWaddr 00:0E:0C:3B:36:F4
>           inet addr:192.168.1.1  Bcast:192.168.1.255  Mask:255.255.255.0
>           inet6 addr: fe80::20e:cff:fe3b:36f4/64 Scope:Link
>           UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
>           RX packets:7622 errors:0 dropped:0 overruns:0 frame:0
>           TX packets:6936 errors:0 dropped:0 overruns:0 carrier:0
>           collisions:0 txqueuelen:1000
>           RX bytes:1062687 (1.0 MiB)  TX bytes:4304984 (4.1 MiB)
>
> virbr0    Link encap:Ethernet  HWaddr E6:ED:D2:6E:58:5C
>           inet addr:192.168.125.1  Bcast:192.168.125.255  Mask:255.255.255.0
>           UP BROADCAST RUNNING MULTICAST  MTU:1500  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)
>
> vnet0     Link encap:Ethernet  HWaddr FE:54:00:67:2C:4C
>           inet6 addr: fe80::fc54:ff:fe67:2c4c/64 Scope:Link
>           UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
>           RX packets:5 errors:0 dropped:0 overruns:0 frame:0
>           TX packets:391 errors:0 dropped:0 overruns:0 carrier:0
>           collisions:0 txqueuelen:500
>           RX bytes:300 (300.0 b)  TX bytes:23358 (22.8 KiB)
>
> I've left out the loopback for simplicity. The problem is that I can't
> reach the br0 device from a server on the eth1 device (the 192.168.
> network).
Since the bridge is attached to the 68.195 network, you won't be able to
reach it from the 192.168.1 network unless this system (or another one)
is configured as a router.   To use it as a router you will need to
enable net.ipv4.ip_forward in /etc/sysctl.conf (echo '1' >
/proc/sys/net/ipv4/ip_forward) and then either run a dynamic routing
protocol or setup static routes on any other system that wants to reach
it from the 192.168.1 network.  The static routes for 68.195.xxx should
point at 192.168.1.1.

Nataraj
> Is this a routing issue? Should I also add the eth1 device to the
> bridge? If so, how would I do that?
>
> Also, can you explain under what circumstances a tun device would be
> used? Does that have any relation to bridging?
>
> Thanks,
> Alex
>
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