From owner-freebsd-hackers  Wed Oct  6  0:54:14 1999
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From: Luigi Rizzo <luigi@labinfo.iet.unipi.it>
Message-Id: <199910060856.JAA12460@labinfo.iet.unipi.it>
Subject: Re: ARPs on a bridge
To: dennis@etinc.com (Dennis)
Date: Wed, 6 Oct 1999 09:56:37 +0100 (MET)
Cc: hackers@FreeBSD.ORG
In-Reply-To: <199910051825.OAA07146@etinc.com> from "Dennis" at Oct 5, 99 01:24:30 pm
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> >> Is there a way to force a Freebsd system to route to the same logican IP
> >> network rather than send a redirect?
> >> 
> >> The situation occurs with segmented bridges where customers on the same
> >> logical IP network are on separate bridge groups. When trying to reach one
> >> another, they are getting redirects however they are not permitted to arp
> >> across groups.
... (long explaination moved to the end)...

I think i don't understand the architecture of the system, so could you
explain a bit more about that -- i would like to learn more about
this. How many physical and logical interfaces does the FreeBSD
system see ?

From your description this is what i understand:

    customer ----[ DSL bridge ]------+----[ main router ]-- rest of net.
				     |
    customer ----[ DSL bridge ]------+
				     |
	 repeat 150 to 900 times     | shared frame relay without
				     | multicast/broadcast support
    customer ----[ DSL bridge ]------+

and the understanding is that the 'DSL bridge' is perhaps implemented
with a FreeBSD-based box with an ethernet on the customer side and a
suitable card on the other side.

Now if the DSL bridge is "almost" a bridge (in the sense that it filters
broadcast traffic) then your architecture "almost" works (except
when operation depends on traffic that you filter) and you need a
separate mechanism to implement the functionality killed by the
filtering. E.g. recognize that some broadcasts (e.g. ARP) are special
and need to be forwarded anyways...

	cheers
	luigi


> On a DSL bridge you have 150 to 900 customers bridged on a relatively low
> bandwidth line (frame relay in this case). Forwarding broadcast traffic is
> very undesireable as you have to replicate the packet 900 times, and since
> you know the IP assignement for the DLCI you dont need to forward it to
> everyone. Each customer is on a different bridge group so traffic cannot be
> bridged between them, so you have to route, but you dont want to have to
> allocate a subnet to each bridge group either. The problem is that, from
> the FreeBSD boxes view, you are routing to the same logical net (assuming
> that all of the bridge groups are in the same IP space.
> 
> We're not talking about bridging a couple of ethernets here.
> 
> Dennis
> 
> 
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