Some help with broadcasts through a Linux system

Dan Kaminsky effugas at
Wed Feb 3 22:05:41 GMT 1999

>>     Is it always bad to bridge broadcasts between subnets?  Yes, it's
>                          ^^^^^^
> bridge or route.. different stuff
>As far as I know you can't ask Linux 2.2 to forward directed broadcasts
>but you'd need to confirm that with ANK. Its been a while since I was
>in IP internals


Actually isn't there a bit of ambiguity there?  When one bridges two network
segments together, all packets on segment A exist on segment B.  When one
creates a route from segment A to segment B, only those packets from one
segment destined for the other will travel the route.  Broadcasts throw this
rule out the window, since all packets of a certain type are destined for
the other network yet the same packet is utilized on both network.

One might argue that by this logic, one doesn't route multicast packets, one
bridges them, except for the fact that multicasted packets will only go to
those connected networks that are known a priori to require the packet.
Bridged broadcasts just fly around.

The key terminological determinant here, I think, is can we envision a
difference between *routing* a broadcast packet vs. *bridging* the broadcast
packet.  Routing would imply a priori knowledge, i.e. the router, seeing a
broadcast packet requesting computer FOO, would send the broadcast to the
last known subnet of computer FOO.  Bridging implies a lack of intelligence,
as some people will say using broadcasts implies anyways.

Thank you.  We now return you to your regularly scheduled SMB packets.

More information about the samba-technical mailing list