[TriLUG] Multiple Public Interfaces == routing confusion

[Aaron Joyner via TriLUG]

For smokeping, most probes have a way to bind to an interface.  For
example, with curl it's explicit:
https://oss.oetiker.ch/smokeping/probe/Curl.en.html

... but depending on what you're doing you might also want to specify
--dns-interface:
https://curl.se/docs/manpage.html

with ICMP the smokeping probe doesn't support it directly, but you could
probably use extraopts to specify -I:
https://oss.oetiker.ch/smokeping/probe/EchoPing.en.html
https://linux.die.net/man/8/ping

For changing the ip rules when a DHCP lease changes, check out the dhclient
hooks (or it's equivalent for your OS and distribution):
https://netbeez.net/blog/linux-dhcp-hooks-network-engineers/

For Apache, you might consider just constraining VirtualHost stanzas on
name-based directives (ServerName) instead of constraining on IP with Listen
?  As for other services that expect to listen on specific IP addresses,
putting the above concepts together is left as an exercise for the reader.
  There has to be some mystery left in the universe?  The fun is in the
journey?  :)

Best wishes,
Aaron S. Joyner

On Wed, Jun 11, 2025 at 1:48 PM Brian via TriLUG <trilug at trilug.org> wrote:

> On 6/9/25 20:23, Mauricio Tavares wrote:
> >        Sounds like an interesting topic for a talk...
>
> Yeah, it probably could be.  There are some new tricky bits I need to
> work out before I would be interested in sharing the knowledge, mainly
> being how to set up services that only know how to identify interfaces
> by their IP addresses, when those interfaces have IP addresses that
> might change.  The ip rules themselves are one important thing that need
> to stay in sync with DHCP lease renewals.  Apache is one (I want it to
> serve one particular virtualhost only to requests that come in on a
> specific interface) and smokeping is another (I want to ensure it pings
> out through specific interfaces).
>
> Once I get those things figured out, yeah, that'd be a nice little
> package to serve as a topic for a talk.
>
> -B
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