[ale] failover planning

Chris Ricker kaboom at gatech.edu
Tue Nov 30 17:58:09 EST 2004


On Tue, 30 Nov 2004, Christopher Fowler wrote:

> Not fixed on 2.4.24
> 
> I configured the 2nd interface on one of our devices running 2.4.24 as
> 192.168.2.121 and there is no CAT-5 connected.
> 
> [cfowler at cfowler cfowler]$ ping 192.168.2.121
> PING 192.168.2.121 (192.168.2.121) 56(84) bytes of data.
> 64 bytes from 192.168.2.121: icmp_seq=1 ttl=64 time=0.405 ms
> 64 bytes from 192.168.2.121: icmp_seq=2 ttl=64 time=0.163 ms
> 64 bytes from 192.168.2.121: icmp_seq=3 ttl=64 time=0.167 ms
> 
> 
> I guess eth0 on 192.168.2.120 is responding for 192.168.2.121

That's what's supposed to happen. The easiest way to understand it is to
think of Linux IP addresses as being per machine, not per interface.

There are patches floating around to get you closer to the behavior you're
expecting (and long flame wars on linux-kernel about them ;-), but this is a
feature, not a bug....

Depending on kernel version, vendor, patches, etc., you may or may not have
sysctl values in your kernel which you can change to influence this. If you
have them, they may or may not work ;-). There are also user-space / 
quasi-user-space solutions you can use to help, such as the ip arp filtering 
commands.

<http://www.ssi.bg/~ja/> is the canonical source for patches, docs, etc. 
about this....

later,
chris



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