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Keep network access on device after it is attached to bridge
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syl22_00
n00b
n00b


Joined: 31 Aug 2011
Posts: 12

PostPosted: Thu Feb 21, 2013 10:14 am    Post subject: Keep network access on device after it is attached to bridge Reply with quote

Hi,

I am creating a bridge to be used as device for a XEN guest. My physical device is eth0 and the bridge is xenbr0. After I start xenbr0 I lose connectivity on eth0. Meanwhile, the guest can access the network.

Here is /etc/conf.d/net:

Code:

config_eth0="192.168.1.61 netmask 255.255.255.0 brd 192.168.1.255"
routes_eth0="default via 192.168.1.1"
dns_servers_eth0="192.168.1.14"

bridge_xenbr0="eth0"
config_xenbr0="dhcp"
routes_xenbr0="default via 192.168.1.1"
brctl_xenbr0="setfd 0
sethello 10
stp off"
rc_net_xenbr0_need="net.eth0"


I am quite confused whether I should turn on or off ip forwarding, in /proc/sys/net/ipv4/ip_forward or in /etc/sysctl.conf, and whether I should add entries to iptables. Any help would be very appreciated.
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AngelKnight
Tux's lil' helper
Tux's lil' helper


Joined: 14 Jan 2003
Posts: 118

PostPosted: Sun Feb 24, 2013 11:07 am    Post subject: Reply with quote

Hi,

This config exhibits conceptual errors with regard to what ethernet bridges in Linux are and how they work. Try this:

Code:
config_eth0="null"

bridge_xenbr0="eth0"
config_xenbr0="dhcp
192.168.1.61/24"
routes_xenbr0="default via 192.168.1.1"
brctl_xenbr0="setfd 0
sethello 10
stp off"

dns_servers_xenbr0="192.168.1.14" # This might bomb out if you require the DNS server provided by DHCP
rc_net_xenbr0_need="net.eth0"


The conceptual error is in thinking that an IP address belongs to a specific adapter. It doesn't; it belongs to the host. An IP was traditionally "bound" to a specific adapter in order to let the kernel know where the L3 network to which that address belongs belongs. (The previous sentence really does make sense; read it again.)
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