[H-GEN] dual homed isps

[Bruce Campbell]

(Note reply-to: being general at humbug.org.au vs Bruce Campbell <bc at thehub.com.au>)

On Thu, 13 May 1999, David Jericho wrote:

> (Note reply-to: being general at humbug.org.au vs David Jericho <davidj at in4free.com.au>)
> 
> On Thu, May 13, 1999 at 11:51:19AM +1000, David Jericho forgot to mention:
> > We want certain types of traffic, to certain destinations going out over
> > X, and the rest over Y. X and Y have their own C class ip address ranges.
> > 
> > It'd be easy if it were just based on ip addresses, but it's also based on 
> > either traffic types or ports.
> 
> What I ment by this, is something similar to BGP. I want the cheapest/quickest
> route to a destination.

It really does depend on exactly what you want to do.  If it was just for
exchanging IP route information, then I would suggest using BGP on one of
the links, and a default route on the other link (ie, you could get away
with using a private ASN for this).  If you feel like hurting yourself,
you could use a simplistic protocol such as RIP (Hello!  Here are *all*
the routes I know about.  Talk to you again in another 30 seconds) or a
more complicated protocol such as OSPF (Hello!  Heres the latest delta.
later) .

With trying to route based on traffic type (TCP/ICMP, src/dest port),
there is no 'cheap' method of doing this.  You could go for the 'poor mans
router', eg, a little unix box running IP Forwarding of choice with an
optomised ruleset (ie, you don't want to fully parse each packet), or you
could do this on your core router (which, unless you are a cheap ISP, is
not a little unix box ;) ). 

You can get around this by a bit of education of your users.  Its a lot
easier in configuring and on router cpu load to say block all web traffic
leaving your network except from your proxies and to educate your users as
to the benefits of using proxies, than it is to keep a overly complicated
transparent proxy working, or worse, to fault-find a setup where *certain*
types of traffic are taking different links to your normal traffic.[1]

Rethink what you are trying to do.

--==--
Bruce.

[1] You wouldn't think 4 bytes would affect anything, except when its a 4
    byte mismatch in MTU sizes on a link which is having web traffic
    dumped out, but nothing else.


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