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user76678
Asked: 2012-12-13 13:31:56 +0800 CST

VIP and private IP on same NIC

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Is it possible to configure in the same NIC a VIP and a private IP (different) and both be enabled/accesible?
If yes, is there a guarantee that the communication path for these 2 IPs will be exactly the same?
Update: If this is possible, if I e.g. do a ping (or traceroute) from a specific machine will I always have the same route for both these 2 IPs?

linux

2 Answers

  1. You can have as many virtual IPs on the same physical device. On Linux you can create virtual interfaces for an IP (mostly) like this:

    ifconfig eth0:0 10.10.10.42 netmask 255.255.255.0 up

    or via /etc/network/interfaces

    The route for every IP can be determined independently. Every IP can have a different default route. But you can ping in and out from every of this IPs

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  2. Having multiple IPs on a NIC is not an issue at all. You can use regular tools like ip addr add 1.2.3.4/24 dev eth0 and a configuration file would be distribution dependent.

    The switch where your nic is connected will broadcast a "who has IP a.b.c.d" and your NIC will respond if it is one of the IPs it has. Receiving packets is not an issue.

    The outgoing packets, however, are a different story. In response to a ping, the outgoing packet's source IP will be determined from the routing table (ip route show). This will be most likely based on the destination IP, and depending on which IP got pinged, you could have problems.

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