Linux – multiple IP addresses bound – which one is used for outgoing packets

iptableslinuxnetworkingshorewall

Using IP aliasing a linux box has bound multiple ip addresses from the same subnet on the same NIC. So ifconfig shows up device eth0 with , eth0:1 with and eth0:2 with .

How does Linux determine the IP source address used for outgoing ip traffic? Is there a way to define what source IP address certain outgoing traffic should use?

Best Answer

I'm not sure why he posted his answer as a comment, but David Schwartz is correct, you should set a netmask of 255.255.255.255 on the 'secondary' addresses, and you should not set gateway addresses on them. You put the correct netmask on the main address, and give it the correct gateway address.

Related Solutions

Nat – Windows Server 2008: specifying the default IP address when NIC has multiple addresses

With Server 2008 Service Pack 2 (not R2), or Vista SP2 and MS hotfix KB975808 there is a solution, although a bit clumsy. You would remove all the addresses you DON'T want as a source, then re-add each one at the command line using

Netsh int ipv4 add address <Interface Name> <ip address> skipassource=true

The hotfix enables the "Skip As Source" flag.

For a deeper dive on how different Windows versions select source IPs, see this TechNet blog post.

Linux Networking – Two Network Interfaces and Two IP Addresses on the Same Subnet in Linux

Yes, the better way is to build a proper business case, and have them relax the rules on the switches so that you can have multiple IPs on one NIC.

Best Answer

Related Solutions

Nat – Windows Server 2008: specifying the default IP address when NIC has multiple addresses

Linux Networking – Two Network Interfaces and Two IP Addresses on the Same Subnet in Linux

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