How to create a bridge interface for eth0?

Altiris · 07-24-2015, 07:30 PM

Ive been testing around Slackware 14.1 in a VM as preparing to move my server from CentOS to Slackware (thank god CentOS/RHEL don't touch upstream configuration...unlike other distros such as debian...transitioning is very easy because of this). Anyway, I am not entirely sure I can properly test a bridged interface in Virtualbox so I am looking for someone to provide me an example of briding the eth0 interface. The way I do it in CentOS 6.6 is as such (maybe it is similar?)

/etc/sysconfig/network-scripts/ifcfg-eth0

Code:

DEVICE="eth0"
BOOTPROTO=none
BRIDGE="br0"
IPV6INIT="yes"
IPV6_AUTOCONF="yes"
NM_CONTROLLED="no"
ONBOOT="yes"
TYPE="Ethernet"
UUID="UUIDHERE"
# Do not assign IP here when br0 is active
#IPADDR=192.168.1.10
PREFIX=24
GATEWAY=192.168.1.12
DNS1=104.237.144.172
DNS2=107.170.95.180
DEFROUTE=yes
IPV4_FAILURE_FATAL=yes
IPV6_DEFROUTE=yes
IPV6_PEERDNS=yes
IPV6_PEERROUTES=yes
IPV6_FAILURE_FATAL=no
NAME="eth0"
LAST_CONNECT=1419879599

I don't use IPV6, I don't know what most of the non-obvious parameters are either.

/etc/sysconfig/network-scripts/ifcfg-br0 (this is my bridged interface)

Code:

DEVICE="br0"
TYPE="Bridge"
BOOTPROTO="none"
ONBOOT="yes"
DELAY=0
DNS1=104.237.144.172
DNS2=107.170.95.180
IPADDR=192.168.1.10
GATEWAY=192.168.1.12

Obviously network configuration is different in Slackware, its in /etc/rc.d/rc.inet1 for Slackware I believe. I am just giving an example of how I do it in CentOS 6

allend · 07-24-2015, 07:54 PM

If you want the bridge to be set up at boot, then use/etc/rc.d/rc.inet1.conf. http://www.linuxquestions.org/questi...9/#post4803979
If you want to manually start the bridge before you start the VM, then you can use a little script. http://www.linuxquestions.org/questi...9/#post4804396

mralk3 · 07-24-2015, 07:58 PM

I believe you would want to edit /etc/rc.d/rc.local and create the bridge there at boot using the bridge-utils package. You use brctl command for this.

Here is some documentation from the Arch wiki:

https://wiki.archlinux.org/index.php...h_bridge-utils

EDIT: I think allend's way is better.

wildwizard · 07-27-2015, 02:48 AM

Just out of curiosity when you talk about a bridged interface are you talking about the option for your VM in the Virtualbox settings?

Because if that is all your doing then you don't need to set anything up it just works.

franzen · 04-06-2016, 04:22 AM

Quote:

Originally Posted by allend

If you want the bridge to be set up at boot, then use/etc/rc.d/rc.inet1.conf. http://www.linuxquestions.org/questi...9/#post4803979

I would like to set following in /etc/rc.d/rc.inet1.conf

Code:

IFNAME[0]="eth0"
IPADDR[0]="PUBLICADDRESS"
NETMASK[0]="255.255.255.0"
USE_DHCP[0]=""
DHCP_HOSTNAME[0]=""

# Config information for br0:
IFNAME[1]="br0"
BRNICS[1]="none"
IPADDR[1]="192.168.1.1"
NETMASK[1]="255.255.255.0"

GATEWAY="GATEWAY"

BRNICS[1]="none" is not supportet, but i want a bridge with seperate subnet, as i have a(only one) public ip-address on eth0.
Another solution could be to add a second address to br0, like
ip addr add 192.168.1.1/24 dev br0
But this also seems not to be supportet by /etc/rc.d/rc.inet1.conf

Alien Bob · 04-06-2016, 04:45 AM

It works a bit differently than you think.

Perhaps the first thing you need to to is draw your network topology, because I do not believe you have both a public IP on eth0 and an internal network segment attached at the same time. What is it that you want to bridge? You need two network devices for a working bridge.

kikinovak · 04-06-2016, 05:21 AM

Quote:

Originally Posted by Altiris

Ive been testing around Slackware 14.1 in a VM as preparing to move my server from CentOS to Slackware (thank god CentOS/RHEL don't touch upstream configuration...unlike other distros such as debian...transitioning is very easy because of this). Anyway, I am not entirely sure I can properly test a bridged interface in Virtualbox so I am looking for someone to provide me an example of briding the eth0 interface. The way I do it in CentOS 6.6 is as such (maybe it is similar?)

Bridging works fine in VirtualBox. Just configure your VM with Networking > Bridged and use your guest as any real host in the LAN.

On the other hand, if you use KVM, you'll have to define a bridge on your host system. Here's how I do it in rc.inet1.conf:

Code:

# Config information for br0::
IFNAME[0]="br0"
BRNICS[0]="eth0"
IPADDR[0]=""
NETMASK[0]=""
USE_DHCP[0]="yes"
DHCP_HOSTNAME[0]=""

# Config information for eth0:
#IPADDR[0]=""
#NETMASK[0]=""
#USE_DHCP[0]="yes"
#DHCP_HOSTNAME[0]=""

Cheers,

Niki

franzen · 04-06-2016, 06:09 AM

Quote:

Originally Posted by Alien Bob

It works a bit differently than you think.

Perhaps the first thing you need to to is draw your network topology, because I do not believe you have both a public IP on eth0 and an internal network segment attached at the same time. What is it that you want to bridge? You need two network devices for a working bridge.

Here is my current setup.

network topology:

Code:

eth0 public-ip     br0 192.168.1.1    lxc1 192.168.1.2
                                      lxc2 192.168.1.3
                                      ...

rc.firewall

Code:

/usr/sbin/iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE

rc.inet1.conf

Code:

IPADDR[0]="PUBLICADDRESS"
NETMASK[0]="255.255.255.0"
USE_DHCP[0]=""
DHCP_HOSTNAME[0]=""

# Config information for br0:
IFNAME[1]="br0"
BRNICS[1]="br0"
IPADDR[1]="192.168.1.1"
NETMASK[1]="255.255.255.0"

GATEWAY="GATEWAY_FROM_PROVIDER"

BRNICS=br0 is surly not ok, but this way my lxc-containers have access to the internet.
the lxc-containers use 192.168.1.1 as gateway.

Code:

brctl show
bridge name     bridge id               STP enabled     interfaces
br0             8000.xxxxxxxxxxxxx      no              lxc1
                                                        lxc2
                                                        ...

This setup works, i'm posting because it seems it's not the way configured it should be.

Alien Bob · 04-06-2016, 06:30 AM

Quote:

Originally Posted by kikinovak

Bridging works fine in VirtualBox.

You are responding to the wrong post... Altiris was the OP but the thread has been hijacked by franzen.

franzen · 04-06-2016, 06:34 AM

Quote:

Originally Posted by kikinovak

Code:

# Config information for br0::
IFNAME[0]="br0"
BRNICS[0]="eth0"
IPADDR[0]=""
NETMASK[0]=""
USE_DHCP[0]="yes"
DHCP_HOSTNAME[0]=""

This is fine if your in a lan, and the vm's are all in the same lan/subnet.
But i have to deal with *one* public ip-address, and have to create the lan within my host for the lxc-containers.

Alien Bob · 04-06-2016, 06:35 AM

Quote:

Originally Posted by franzen

Here is my current setup.

network topology:

Code:

eth0 public-ip     br0 192.168.1.1    lxc1 192.168.1.2
                                      lxc2 192.168.1.3
                                      ...

...

This setup works, i'm posting because it seems it's not the way configured it should be.

Have a look at ponce's old article on Linux Containers, it has good information on connecting your containers using bridging. The way you do it, is not correct, and I think it works by sheer luck.

franzen · 04-06-2016, 06:45 AM

Quote:

Originally Posted by Alien Bob

Have a look at ponce's old article on Linux Containers, it has good information on connecting your containers using bridging. The way you do it, is not correct, and I think it works by sheer luck.

I did follow Ponce's advices:

Quote:

containers on a natted private network

In this case the script to bring up the private network is this

/sbin/brctl addbr br0
/sbin/brctl setfd br0 0
/sbin/ifconfig br0 192.168.2.1 netmask 255.255.255.0 promisc up

I have the same setup, there is no eth0 assigned to br0, it's all working fine.
But, i can't find a way to accomplish this with rc.inet1.conf(in a correct way).