Bridging interfaces and the internet

Nigel Wade nmw at ion.le.ac.uk
Tue Nov 1 10:12:14 UTC 2005


Justin Willmert wrote:
> I just set up a desktop with two network cards and have got a bridge 
> working between the two. That is not what my problem lies in though. I 
> would like for the box to be able to connect to the internet also, but 
> if I understand what I've set up correctly, I can't do that with my 
> current setup. When I've tried to give one of the network cards an IP 
> address, nothing but lo works, so I know there's something missing. I'll 
> add my configuration at the bottom, but shortly, br0 is configured with 
> an IP address, and eth0 and eth1 have none. Now, I know br0 is capable 
> of at least a network connection because as I type this, I'm currently 
> SSHed into into the box, but if I try to ping anything, all the packets 
> are lost.
> 
> OK, so here are some of my thoughts and possible hints to a solution:
>    1) My routing tables need another route, so I just figure out how to 
> configure that and add a route.
>    2) br0, eth0, and eth1 are incapable of an internet connection, in 
> which case I need to create a virtual interface that can connect as if 
> it were a separate interface that does the internet connecting.

br0 is the network interface of the system. eth0 and eth1 are part of a bridge 
and therefore completely transparent in the network.

>    3) (Very unsure, but...) use a alias interface to allow both eth0 
> without an IP address to make br0 happy and give eth0:0 an IP address to 
> allow me to connect to the internet.
> 
> Thanks for any help,
> Justin Willmert
> 
> 
> ===================== ifcfg-br0 =====================
> DEVICE=br0
> TYPE=Bridge
> BOOTPROTO=static
> IPADDR=192.168.2.75
> NETMASK=255.255.255.0
> ONBOOT=yes
> DELAY=0
> STP=off
> 
> 
> ===================== ifcfg-eth0 =====================
> DEVICE=eth0
> BOOTPROTO=static
> HWADDR=00:04:5A:50:A6:38
> ONBOOT=yes
> TYPE=Ethernet
> BRIDGE=br0
> 
> 
> ===================== ifcfg-eth1 =====================
> DEVICE=eth1
> BOOTPROTO=static
> HWADDR=00:04:5A:4E:BC:02
> ONBOOT=yes
> TYPE=Ethernet
> BRIDGE=br0
> 
> 
> ===================== static-routes =====================
> any: net 127.0.0.0 netmask 255.0.0.0 dev lo
> any: net default gw 192.168.2.2 dev br0
> 
> 
> ===================== output of `route` =====================
> Kernel IP routing table
> Destination     Gateway         Genmask         Flags Metric Ref    Use 
> Iface
> 192.168.2.0     *               255.255.255.0   U     0      0        0 br0
> 169.254.0.0     *               255.255.0.0     U     0      0        0 br0
> 127.0.0.0       *               255.0.0.0       U     0      0        0 lo
>             ===== 10 second or so delay here =====
> default         192.168.2.2     0.0.0.0         UG    0      0        0 br0


You haven't set a netmask on the default route. It should be 255.255.255.0 to 
match the network segment.



-- 
Nigel Wade, System Administrator, Space Plasma Physics Group,
             University of Leicester, Leicester, LE1 7RH, UK
E-mail :    nmw at ion.le.ac.uk
Phone :     +44 (0)116 2523548, Fax : +44 (0)116 2523555




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