Tag Archives: centos

Multiple interfaces in CentOS

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I had an issue with CentOS6.4 – two network interfaces were configured eth0 - 10.x.y.z and eth1 - 192.168.x.y. eth0 is being used for SSH access, but as soon as eth1 was brought up the node became unreachable from anything except the local subnet.

Source was 10.x.y.230 and they are on the same switch:

[root@controller etc]# ping 10.x.y.234
PING 10.3.8.234 (10.x.y.234) 56(84) bytes of data.
64 bytes from 10.x.y.234: icmp_seq=1 ttl=64 time=1.33 ms
64 bytes from 10.x.y.234: icmp_seq=2 ttl=64 time=0.298 ms
64 bytes from 10.x.y.234: icmp_seq=3 ttl=64 time=0.277 ms
64 bytes from 10.x.y.234: icmp_seq=4 ttl=64 time=0.270 ms

But ping from any other subnet and nothing… Turns out that you have to be very specific when configuring the default gateway in /etc/sysconfig/network. It seems that both the default gateway and the gateway interface are required, to get the route added properly.

[root@node-2 ~]# cat /etc/sysconfig/network
NETWORKING=yes
HOSTNAME=node-2.fqdn.net
GATEWAY=10.x.y.1
GATEWAYDEV=eth0

And now our route is correctly added

[root@node-2 ~]# route
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
10.x.y.0        *               255.255.255.0   U     0      0        0 eth0
192.168.1.0     *               255.255.255.0   U     0      0        0 eth1
link-local      *               255.255.0.0     U     1002   0        0 eth0
link-local      *               255.255.0.0     U     1003   0        0 eth1
default         10.x.y.1        0.0.0.0         UG    0      0        0 eth0