From: Fred Ingham (fningham@xxxxxxxxxxxxxxxx)
Date: Sun Mar 17 2002 - 14:49:04 GMT-3
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!sometimes my leading lines get deleted.
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Bill: You can put a bridge statement on the hub but the bridge still
won't send a packet out the port it was received on.
Just to make sure we are talking about the same configuration:
R1 is a hub with a multipoint subinterface going to R2 and R3, and a
point-to-point
subinterface going to R4. R2, R3, R4 have physical interfaces. All are
using a single frame relay DLCI. All interfaces have a bridge-group
specified and the physical and multipoint interfaces have a frame-relay
map bridge DLCI br statement. IP addresses are not on any of these
interfaces. Either IP routing is disabled or bridge irb is configured
for the four routers so we are only bridging on these interfaces.
When you do a show span for R1 it shows two bridge ports, one for the
multipoint interface and one for the point-to-point interface.
So lets construct a test. Connect another router, R6, to R2 via
Ethernet and give the R6 interface an IP address (IP routing is on for
R6). Enable an Ethernet connection between R4 and R3 and on R3
configure a BVI in the same subnet as the R6 address. R3 now will have
IP routing and bridge irb enabled. For this test configure R1 as the
root of the spanning tree.
Now let's ping the R3 BVI address from R6. It will fail. The reason it
fails is that R6 first sends an ARP for the R3 MAC address to the
broadcast destination address. The ARP arrives at the R2 interface and
is forwarded on the other R2 bridge port to R1 via the serial line
DLCI. R1 receives the ARP request and forwards it out the other bridge
port to R4. R1 does not forward the ARP to R3 since R3 is on the same
bridge port as R2. This is a basic characteristic of a layer two
bridge. If all serial lines are configured with equal cost the Ethernet
link between R4 and R3 will be in a blocking state and the ARP packet
will die.
This is an exercise in the RS-NMC-1 course to show the same point that
was originally raised and to explore irb. Question: How do you get
the ping between R6 and R3 to succeed?
If you have a counter example I'd appreciate seeing it.
Cheers, Fred.
Bill Greenwood wrote:
>
> Yes you can, but you must put bridge statements on the hub as well as on the
> spokes.
> ----- Original Message -----
> From: "Fred Ingham" <fningham@worldnet.att.net>
> To: "Richard Wheat" <rwheat@ami.com.au>
> Cc: <ccielab@groupstudy.com>
> Sent: Sunday, March 17, 2002 12:55 PM
> Subject: Re: Transparent Bridge with FR hub & spoke
>
> > Richard: Your conclusion is correct. Each interface or sub-interface
> > is a port on the bridge and a bridge does not forward out a port the
> > packet was received on.
> > Therfore you cannot bridge spoke to spoke on a hub and spoke
> > configuration.
> >
> > HTH, Fred.
> >
> > Richard Wheat wrote:
> > >
> > > Hi there,
> > >
> > > This may sound very simple - but I just need a sanity check here ...
> > >
> > > Can someone please verify for me that it is not possible to
> > > transparently
> > > bridge from spoke to spoke (over frame relay) using a single multi-point
> > >
> > > interface (or sub-interface) on the hub? My understanding is that this
> > > is
> > > because the bridge will not forward a packet out of the interface it
> > > received
> > > it on (makes sense). I have to use two interfaces (or more likely two
> > > sub-interfaces) to get this to work? Or have I missed something?
> > >
> > > Tks,
> > > Richard.
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