[CentOS] Centos and Bridging

Robert Spangler mlists at zoominternet.net
Fri Nov 26 12:15:51 EST 2010


Hello,

Presently I am running CentOS release 5.5 (Final).  I am looking to setup 
bridging as I would like to setup some KVM virtual hosts on my system as a 
test lab.  I am following the the instruction at this site

> http://tldp.org/HOWTO/BRIDGE-STP-HOWTO/index.html

but I cannot figure out where I am going wrong and would be thankful if 
someone could point me in the right direction.

Here is what I have done:

Check bridge information with the following:

> ~ $ modprobe -v bridge

No issues or errors

> ~ $ cat /proc/modules | grep bridge
> bidge 91889 0 - Live 0xffffffff89247000

Check to ensure forwarding is turned on:

> ~ $ cat /proc/sys/net/ipv4/ip_forward
> 1

Checked that my interface are up and running
(Was sure of this but did the check anyway):

> ~ $ ifconfig
> eth0      Link encap:Ethernet  HWaddr 48:5B:39:2A:07:D5
>           inet addr:192.168.1.100  Bcast:192.168.1.255  Mask:255.255.255.0
>           inet6 addr: fe80::4a5b:39ff:fe2a:7d5/64 Scope:Link
>           UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
>           RX packets:1059 errors:0 dropped:0 overruns:0 frame:0
>           TX packets:1080 errors:0 dropped:0 overruns:0 carrier:0
>           collisions:0 txqueuelen:1000
>           RX bytes:454226 (443.5 KiB)  TX bytes:120584 (117.7 KiB)
>           Interrupt:90 Base address:0x8400
> 
> 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:92 errors:0 dropped:0 overruns:0 frame:0
>           TX packets:92 errors:0 dropped:0 overruns:0 carrier:0[Thu Nov 25 

So now I begin to create the bridge form CLI as I want to make sure everything 
works before committing it to the config:

> brctl addbr br0
> ifconfig eth0 down
> ifconfig br0 192.168.1.100 up
> ifconfig eth0 0.0.0.0 up
> route add default gw 192.168.1.254

I check my interfaces and routing:

> ~ $ ifconfig
> br0       Link encap:Ethernet  HWaddr 00:00:00:00:00:00
>           inet addr:192.168.1.100  Bcast:192.168.1.255  Mask:255.255.255.0
>           inet6 addr: fe80::200:ff:fe00:0/64 Scope:Link
>           UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
>           RX packets:0 errors:0 dropped:0 overruns:0 frame:0
>           TX packets:5 errors:0 dropped:0 overruns:0 carrier:0
>           collisions:0 txqueuelen:0
>           RX bytes:0 (0.0 b)  TX bytes:398 (398.0 b)
> 
> eth0      Link encap:Ethernet  HWaddr 48:5B:39:2A:07:D5
>           inet6 addr: fe80::4a5b:39ff:fe2a:7d5/64 Scope:Link
>           UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
>           RX packets:64662 errors:0 dropped:0 overruns:0 frame:0
>           TX packets:63301 errors:0 dropped:0 overruns:0 carrier:0
>           collisions:0 txqueuelen:1000
>           RX bytes:17699194 (16.8 MiB)  TX bytes:7958063 (7.5 MiB)
>           Interrupt:90 Base address:0x8400
> 
> 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:211 errors:0 dropped:0 overruns:0 frame:0
>           TX packets:211 errors:0 dropped:0 overruns:0 carrier:0
>           collisions:0 txqueuelen:0
>           RX bytes:17346 (16.9 KiB)  TX bytes:17346 (16.9 KiB)


> ~ $ route -n
> Kernel IP routing table
> Destination     Gateway         Genmask         Flags Metric Ref    Use 
Iface
> 192.168.1.0     0.0.0.0         255.255.255.0   U     0      0        0 br0
> 0.0.0.0         192.168.1.254   0.0.0.0         UG    0      0        0 br0

Time to test if ping works:

> ~ $ ping -c3 192.168.1.254
> PING 192.168.1.254 (192.168.1.254) 56(84) bytes of data.
> ping: sendmsg: Operation not permitted
> ping: sendmsg: Operation not permitted
> ping: sendmsg: Operation not permitted
> 
> --- 192.168.1.254 ping statistics ---
> 3 packets transmitted, 0 received, 100% packet loss, time 2000ms

I know the firewall is causing this issue so I stop the firewall:

> ~ $ service iptables stop
> Flushing firewall rules:                                   [  OK  ]
> Setting chains to policy ACCEPT: nat filter                [  OK  ]
> Unloading iptables modules:                                [  OK  ]

Time to try ping again:

> ~ $ ping -c3 192.168.1.254
> PING 192.168.1.254 (192.168.1.254) 56(84) bytes of data.
> From 192.168.1.100 icmp_seq=1 Destination Host Unreachable
> From 192.168.1.100 icmp_seq=2 Destination Host Unreachable
> From 192.168.1.100 icmp_seq=3 Destination Host Unreachable
> 
> --- 192.168.1.254 ping statistics ---
> 3 packets transmitted, 0 received, +3 errors, 100% packet loss, time 1999ms

To back out all I needed to do was:

> ifconfig br0 down
> brctl delbr br0
> service iptables start
> service netowrk restart

Everything is back to normal.  I cannot figure out what am I missing here?  
Interfaces and routing look to be setup correctly.  Is there something else I 
need to be looking at?


-- 

Regards
Robert

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