[NTLUG:Discuss] Dual Nic's

[Chris Cox]

Paul Drew wrote:
> Howdy Guys,
> I have a quick question I was hoping that I could get some information 
> from you guys on. We currently have a Redhat proxy server running on a 
> Penguin Computing 1U rack mount case. It is sitting RIGHT next to the 
> networking switches. Recently the switch it was plugged into died, and 
> so no one could get to the website, and made things messy around here.
> 
> What I am curious about is, dual ethernet cards. I was wondering what 
> the possiblity of having both nic's plugged in and used. What I would 
> like to do it have both ip's in the same subnet, and have DNS somehow 
> failover to the other incase 1 went down. I thought it would be a nice 
> way to at least take 1 potential failure out of the loop. Having each 
> nic go to a different switch.
> 
> Let me know if this is possible, or if its a no-brainer, or if I am 
> smoking crack. To be honest I have not put much thought into it, but I 
> wanted to run this by you guys to see if you are doing something of the 
> sort already. Thanks for your time, and suggestions. Have a great day, 
> and take care.

Anything is possible.  Ideally, use dynamic DNS, detect the failure, rip
and replace the DNS entry. (to do at you have stated)

Obviously, this isn't good for internet side DNS because of propagation
TTL delays.  So... a better solution, IMHO, though it's more network
related is to quickly reroute through another switch (thus preserving
the IP).  If the system thinks the switch is down, it shuts down
the primary interface and brings up the secondary one with the
same IP info.... depending upon your routing discovery methodology,
things may just start working as new routes are made to the
new path (I'm not a routing guru though).

Some router/switch architectures may allow you to have some sort of
bonding/trunking of the two cards so they can be live at the same
time and handle things "correctly" when one path goes out.  I would
think there would be something on the network side that could handle
something like this.  With that said, bonding the NICs on the Linux
side is a Linux thing.  I haven't tried it and don't know what happens
on the Linux side if a path goes out (regardless if the switches
and routers get it right).

Okay.. maybe I just created more questions than answers...