Two Networks on one System

Damien Fleuriot ml at
Wed Jun 22 07:45:52 UTC 2011

On 6/22/11 9:16 AM, Bernt Hansson wrote:
> 2011-06-21 13:28, Martin McCormick skrev:
>>     Here is what the issue is right now. The remote campus
>> in question has been on number space that was part of our Class
>> B network. They got a block of subnets for their DNS's and
>> campus enterprises and work stations. We secured them their own
>> number space and they are migrating from their portion of our
>> network to their new network and both nets are presented
>> routable from the rest of the world.
>>     If you do a whois query for their domain, you get the
>> address on our network of their primary DNS. When one updates
>> the whois data, there is a lag of some hours until new queries
>> start going to the new address of their primary DNS. In the mean
>> time, we don't really care but we would like for the new
>> interface for the primary to be reachable so that the minute the
>> information changes, we're answering lookups. After that point,
>> we will permanently take down the old interface address on our
>> network and probably reboot with the normal configuration now
>> being the new IP address.
>>     The problem I have, probably due to a misunderstanding
>> of what I need to do, is easy to describe.
>>     The defaultrouter statement in rc.conf or
>> route add default x.x.x.x
> Have you tried route add netA netB or route add netB netA

No offense but please do not give random, untested advice.

What you just wrote reads as:
- if you want to go to network A, do that through network B
- if you want to go to network B, do that through network A

Now can you see some kind of a loop forming here ?

Solutions to the OP's problem have been given already:
- PF's "reply-to" option has been discussed at length.
- FreeBSD's own setfib was also briefly discussed

Note this requires a kernel option override as seen here:

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