Apologies for asking this from naive perspective. For a system with two external DSL connections (different providers) I'm trying to work up a solution that combines dynamic DNS round robin (described by Leghart in the Nov. Sys Admin) with ip route on a 2.2.19 kernel with ipchains. The system runs DNS, Apache, and masqs an internal network. Since the DNS round robin should take care of bringing, for instance, http requests in on whichever line is up - or both if both lines are - what I want ip route to do is send the response back out on the same interface the request came in on. What's the easiest way to do that? Also, port forwarding is being used to an internal NT mail server. I'd like to handle redundancy to that by having a secondary MX on the second public interface, and also forwarding that to the server. Again, when the server comes back through the masq in negotiations I'd like it to connect out through whichever interface/IP it was connected to from. I've looked at the Linux 2.4 Advanced Routing HOWTO and Alexey's docs, and am having trouble identifying which capabilities I need to wrap my mind around - there's obviously a whole lot of stuff I don't need to learn, if I could only sort it out without learning it all first! The solution might be easier with 2.4 iptables, but I've got a complex set of ipchains rules and would prefer not having to translate it. Thanks for any advice. Some things in computing come easily to me - routing isn't one of them. But it seems like this might be reasonably simple: mark incoming traffic according to the interface it comes in on, route it out according to the mark. (Once this setup is working, I'll be working to add heartbeat so a backup server is ready to step in. If this all seems like a generically useful setup, I'd be happy to try to document it after it comes together - the hope is for reasonably good redundancy on the cheap.) Whit @transpect.com
