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felixg
Asked: 2012-03-08 00:01:07 +0800 CST

CentOS gateway setting on startup

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I'm running CentOS 6.2 on ESXi 5. The machine has 2 NICs, eth0 is connected to the Internet and eth1 to a LAN. eth0 has a single colo provided IP address, so the netmask is 255.255.255.255. The gateway is of course on a different subnet. After boot I've no Internet access, I'm solving it by running:

route add -host x.x.x.x dev eth0
route add default dev eth0 gw x.x.x.x

I want this to be automatic. Currently I've added these lines to the rc.local script. I've tried the recommended path of adding a route-eth0 script, but it doesn't work. I don't know what is correct syntax representing the route commands, nor how to see the errors my attempts generate. Can this be done via route-eth0 or some other expected CentOS way?

[Clarification]
My ifcfg-eth0:

DEVICE="eth0"
NM_CONTROLLED="yes"
ONBOOT=yes
HWADDR=xxx
TYPE=Ethernet
BOOTPROTO=none
IPADDR=82.166.38.XX
PREFIX=32
GATEWAY=82.166.190.YYY
DNS1=xxx
DOMAIN=xxx
DEFROUTE=yes
IPV4_FAILURE_FATAL=yes
IPV6INIT=no

Aseq's second scenario is very close, but the actual IP assignment is more complex. I got 82.166.38.XX, 82.166.38.XX+2 but they are reachable only through the 82.166.190.YYY, so if I put non 255.255.255.255 netmask those machine cannot communicate.

I think if I could translate the route syntax to ip addr syntax, it should work.

centos networking gateway

1 Answers

  1. Normally your ISP should have given you a /30, i.e. 192.0.2.49/30 Then you would for example use 192.0.2.49 as the gateway and 192.0.2.50 as the IP of eth0. Although if the ISP gave you one IP, say 192.0.2.80 then often the gateway would be 192.0.2.1.

    Using values in the first scenario, you need to edit /etc/sysconfig/network-scripts/ifcfg-eth0 and it would look something like:

    DEVICE=eth0
BOOTPROTO=static
ONBOOT=yes
IPADDR=192.0.2.50
NETMASK=255.255.255.252
GATEWAY=x.x.x.x

    Change GATEWAY:

    GATEWAY=192.0.2.49

    Second scenario:

    DEVICE=eth0
BOOTPROTO=static
ONBOOT=yes
IPADDR=192.0.2.80
NETMASK=255.255.255.0
GATEWAY=x.x.x.x

    Change GATEWAY:

    GATEWAY=192.0.2.1

    Run:

    /etc/init.d/network restart
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