Re: [LARTC] Dual Redundant Network routing [Question]

[Jose Luis Domingo Lopez <lartc@24x7linux.com>]

On Tuesday, 18 May 2004, at 13:36:21 -0700,
Daniel Chemko wrote:

> If you're rolling your own, the most well used technique to detect a
> dead link is pinging static hosts located on each network segment. Since
> you are dual-redundant of the same network, you'll need top do a little
> source routing. If you have a ping with the -j or the -I options, you
> can cheat and socket bind ping to each physical network segement to test
> the common IP's.
> 
In the past I have implemented a Linux policy router with link failure
detection, but instead of "pinging" a remote host I use "hping" to make
a TCP connection request to a remote IP at port 80. If this remote IP
address is known to be always up (for example, www.google.com's IP) this
can be a good level-7 health check.

Yo can do this from the router itself on any number of links. Just make
sure you understand Linux policy routing, and just before sendind the
probe packets make them go trhough the link you are trying to test.

Couple the above with a "state machine" to prevent considering a link
down when just one probe fails, and to make a link up again when it has
been so for long enough.

> Once you detect a failure, you need to handle the outage. This can be
> done with marking a route dead or changing the default route to the
> other interface. This shouldn't be too hard.
> 
In my setup I have a routing table for each link to the Internet, each
table with just a default route to the Internet through this link. So
when I detect the link has gone down, I just make a "ip route change
table linkX default via ..." to reroute all traffic to another link.

Hope this helps.

-- 
Jose Luis Domingo Lopez
Linux Registered User #189436     Debian Linux Sid (Linux 2.6.6)
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