From: Thomas Alexander (talexander1@xxxxxxxxxxxxx)
Date: Sat Jan 15 2000 - 01:24:50 GMT-3
Atif,
Let me put down my interpretation of Transparent Bridging.
If we were to take a very simple examlple of 2-port transparent
bridge. Eth LAN A------trans. brige------Eth LAN B
The function here is to bridge Ethernet packets from
from Ethernet LAN A to B or vice-versa. Now lets move
this functionaly over a WAN. The function of the TB has
been moved across 2 physical boxes, thus each box doing
half of the function, even sometimes called a half-bridge:
Eth LAN A------trans. brige-----trans. bridge------Eth LAN B
The objective here again here is to transparently bridge from LAN
A to LAN B. I hope the above explains why bridging over WAN goes
in pairs. I have no idea why transparent bridging works when
only router's WAN interface is configured for TB ? (Cisco bug or
feature ??) But just to cross-check, I did the same configure but
the WAN interfaces configured as PPP, where I could clearly
see when I did a "SH INT" that BRIDGECP was not negotiated
thru PPP, so router B would drop bridged packets originating from
Ethernet interface with the message:
Outbound bridge packet dropped, BNCP state is Listen
This proves the point that bridging should be enable on both sides
of a WAN link. Again, a more common configuration would be
if the TB would be configured to bridge remote LANs.
But with IRB enabled, the BVI interface becomes the kind of
virtual LAN interface. Again, with IRB, BVI is a routed interface, so
traffic coming into BVI may come bridged and then gets routed
to other IPX networks connected to router C or vice-versa.
Hope this helps.
Thomas Alexander
----- Original Message -----
From: "Atif Awan" <atifawan@hotmail.com>
To: <talexander1@austin.rr.com>; <ccielab@groupstudy.com>
Sent: Sunday, December 24, 2000 1:33 AM
Subject: Re: IPX bridging problem
>
> Well definitely router B is the culprit in this case but why this odd
> behaviour and why do you say that it is a requirement for WAN interfaces
> that bridging should be enabled on both ends ?
>
> this is confsing .. i will try it with configuring IRB on Router_C but
even
> if it works there has to be a logical explanation for this anomaly in the
> bridge's behaviour.
>
> Atif
>
> >From: "Thomas Alexander" <talexander1@austin.rr.com>
> >Reply-To: "Thomas Alexander" <talexander1@austin.rr.com>
> >To: "Atif Awan" <atifawan@hotmail.com>, <ccielab@groupstudy.com>
> >Subject: Re: IPX bridging problem
> >Date: Fri, 14 Jan 2000 17:03:53 -0600
> >
> >Atif,
> >
> >The problem is that no bridging in configured on Router_C.
> >Briding on WAN usually goes in pairs, ie both sides of a WAN link should
be
> >configured for bridging. In your case, only routerB serial 0 is
configured
> >for bridging.
> >I have done a quick test in my lab, and ofcourse there is no problem for
a
> >IPX/RIP
> >traffic originating from rtr A as it gets bridged from Router B and gets
> >forwarded to
> >Router C. Router B since it has bridging enable on S0, will forward the
> >bridged packet to Router C.
> >I am not sure how Router C accepts the bridge packet, may be it can
support
> >both bridge and routed
> >packets. But when IPX/RIP traffic orignates from Rtr C, RTR B is
expecting
> >a
> >bridged packet, instead
> >received a normal packet to be routed, and it drops the packets. This can
> >be
> >confirmed if you do a
> >"show bridge verbose". Under Flood ports, you will see zero bridged
packets
> >as being received from
> >Router C. If the connection to router C were to be Ethernet (or LAN) like
> >router a, this would would just
> > work fine. So for example:
> > Router_A(et0/0) --- (etH0)Router_B(s0) --- (s1)Router_X---(eth0)Routerc
> > IPX routing TB
> >TB IPX routing
> >
> >The other option is to enable IRB on Router C, so that it bridges IPX on
> >the
> >serial
> >interface to routerB and routes from all other interfaces.
> >
> >Hope this helps..
> >
> >Thomas Alexander
> >
> >----- Original Message -----
> >From: "Atif Awan" <atifawan@hotmail.com>
> >To: <ccielab@groupstudy.com>
> >Sent: Saturday, December 23, 2000 10:06 AM
> >Subject: IPX bridging problem
> >
> >
> > >
> > > i was working ipx ( my weak spot :) ) when i encountered a strange
> >problem
> > > that i cannot seem to solve. The relevant setup is like this :
> > >
> > > Router_A(ether0/0) --- (ether0)Router_B(serial0) --- (serial1)Router_C
> > >
> > > All the 3 routers are routing IP. Router_A and Router_C have ipx
routing
> > > turned on too but Router_B does not have ipx routing turned on.
> >Router_A's
> > > ethernet0/0 and Router_C's serial 1 both have the same IPX network
> >number.
> > > Router_B has bridge-group 1 statements on both ether0 and serial 0.
> > >
> > > IPX RIP routes from Router_A are seen successfully in the ipx routing
> >table
> > > of Router_C. However, updates from Router_C are not reaching Router_A.
> >When
> > > i turn on debugging on Router_C it says that it is broadcasting
updates
> >out
> > > serial 1 but these never reach Router_A. I dont think i need IRB
> >anywhere
> > > here ... why is this happening that one way traffic is going through
> > > successfully and the other way its not ??? Rest assured there are no
IPX
> > > access-lists anywhere ...
> > >
> > > TIA
> > > Atif Awan
> > >
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