[CentOS] Centos and Bridging

Robert Heller heller at deepsoft.com
Fri Nov 26 12:28:44 EST 2010


At Fri, 26 Nov 2010 12:15:51 -0500 CentOS mailing list <centos at centos.org> wrote:

> 
> 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

brctl addif br0 eth0

You need to add the physical interface(s) to the bridge interface.

You can set this up to go automagically like this:

sauron.deepsoft.com% cat /etc/sysconfig/network-scripts/ifcfg-eth0
# nVidia Corporation MCP77 Ethernet
DEVICE=eth0
BOOTPROTO=static
HWADDR=00:19:66:D6:ED:93
ONBOOT=yes
BRIDGE=br0

sauron.deepsoft.com% cat /etc/sysconfig/network-scripts/ifcfg-br0
DEVICE=br0
TYPE=Bridge
BOOTPROTO=static
BROADCAST=192.168.250.255
IPADDR=192.168.250.1
NETMASK=255.255.255.0
NETWORK=192.168.250.0
ONBOOT=yes

(change as needed to match your interaces and ipaddresses, etc.)

> > 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?
> 
> 

-- 
Robert Heller             -- 978-544-6933 / heller at deepsoft.com
Deepwoods Software        -- http://www.deepsoft.com/
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