Set Source

[Ondrej Zajicek]

On Fri, Dec 06, 2013 at 12:34:44PM +0200, Sergey Popovich wrote:
> ?? ???????????? ???? 6 ?????????????? 2013 02:28:32 ???????????????????????? Sargun Dhillon ??????????????:
> > So, from my understanding, routes in the Linux kernel have can have a
> > source associated with them.This is RTA_SRC attribute in netlink ( I
> > think ).
> 
> Maybe you mean RTA_PREFSRC attr? This is implemented and could be set/get
> withing BIRD filters using krt_prefsrc attribute without any problem.

Yes, krt_prefsrc should do the thing, but communication with directly
connected hosts would be handled by implicit device routes from kernel,
which wouldn't be changed by BIRD.

> > We basically want to ensure that when our routers get routes, locally
> > generated traffic comes from the loopback address.
> 
> Yes, setting krt_prefsrc whould help, but as for me there is no good reason
> to do this on router, as you loose troubleshooting hint on where packets 
> failed to deliver (for example TTL exceeded in transmit) should be delivered:
> you always get ansver from your router loopback.

There are some good reasons for such behavior, for example you could use
private addresses for inter-router networks, or even pseudo-link-local
ones (i.e. private addresses not propagated in OSPF area).

Another reason is that in some cases, an interface-attached address may
not be reachable, while the loopback address will be.

-- 
Elen sila lumenn' omentielvo

Ondrej 'SanTiago' Zajicek (email: santiago at crfreenet.org)
OpenPGP encrypted e-mails preferred (KeyID 0x11DEADC3, wwwkeys.pgp.net)
"To err is human -- to blame it on a computer is even more so."
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