Re: [exim] SMTP Transport: Try different interfaces

Jan-Peter Koopmann wrote:

> On Thursday, January 20, 2005 10:16 PM exim-users-bounces@??? wrote:
>
>
>>Personally, I think this is silly.
>>
>>Sure, you can do it in Exim. But Exim's not the best tool.
>>
>>With Linux, the best tool would probably be advanced routing (using
>>the iproute2 package), getting subsystems closest to the
>>periodically available interfaces to manage it.
>
>
> Well. First of all we do not use Linux but FreeBSD.

There are differences in naming and configuration between Linux and
FreeBSD in this area, but their overall capabilities are essentially the
same - or certainly can be made to be with with available ports.

> Second, how would iproute2 help in this situation? This is the setup:

No time here to research and offer specifics, but the general gist of
the advice you were offered was to let filter and routing rules handle
the alt-routing/failover/route-selection outside of Exim.

Good advice, IMHO.

>
> First line pppoe connected directly to the firewall (which is doing pppoe).
> Second line connected via a seperate router to the firewall as well.
> Default route go out both lines with the first line having a better preference so all traffic usually goes out that way.
>
> If the first line goes down the interface goes down as well and all traffic uses the second line. So far so good. Only problem: The first line has a dial-up IP so that e-mail sending over it is a problem. We therefore configured the system using source routes so that exim always uses the second line for outgoing mail. Now what happens if the second line has a problem? The router will stay up and therefore the firewall will not take the corresponding interface down. Therefore the source route will still be active and exim will still try to deliver mail over the second line even though it has problems.
>
> Therefore I need exim to be able to try a second interface if the TCP connect on the first one is not successful.
>

This is a (failed/available) physical-layer and transport-layer issue,
so if Exim tries, instead, to use a singular 'virtual' interface that is
externally routed to whatever is 'best available', your Exim config can
remain simple. Handling this externally can also be more secure.

Sorry not to have time for specifics.. but we have used such techniques,
and it can be a good way to go

>
>>Just because a cheese grater is so flexible that you can use
>>one to shave your beard, doesn't mean it's the best way to do so. :-)

My cheese grater doesn't even do Cheddar all that well <g>

HTH,

Bill Hacker

>
>
> Tell me a different way for this problem and I will be grateful forever... :-)
>
> Kind regards,
> JP
>