Re: [nsp] ATM interface bridging

From: William Chu (wwwchu@itsd.gcn.gov.hk)
Date: Mon Nov 15 1999 - 23:04:50 EST


Dear Steven:

You will need to place each ATM PVC on separate subinterfaces because of the
"split horizon" rule. That is, a packet received on an interface cannot be
transmitted out the same interface even if the packet is received and
transmitted on different virtual circuits. Here is a working config from my
7513 (with non-relevant details removed) for your reference:

[snip]
!
bridge irb
!
[snip]
interface ATM9/0/0.1 point-to-point
 description WT14_to_GH6
 mtu 1584
 no ip directed-broadcast
 pvc WT14_2a-GH6 1/301
  encapsulation aal5snap
  ubr 1536
 !
 bridge-group 1
!
interface ATM9/0/0.2 point-to-point
 description WT14_to_GH7
 mtu 1584
 no ip directed-broadcast
 pvc WT14_2a-GH7 1/302
  encapsulation aal5snap
  ubr 1536
 !
 bridge-group 1
!
interface ATM9/0/0.3 point-to-point
 description WT14_to_GH8
 mtu 1584
 no ip directed-broadcast
 pvc WT14_2a-GH8 1/303
  encapsulation aal5snap
  ubr 1536
 !
 bridge-group 1
!
interface ATM9/0/0.4 point-to-point
 description WT14_to_GH9
 mtu 1584
 no ip directed-broadcast
 pvc WT14_2a-GH9 1/304
  encapsulation aal5snap
  ubr 1536
 !
 bridge-group 1
!
[snip]
interface BVI1
 description Routed interface for GH
 mtu 1500
 ip address 10.99.18.1 255.255.255.0
 no ip redirects
 no ip unreachables
 no ip directed-broadcast
 no ip proxy-arp
!
bridge 1 protocol ieee
 bridge 1 route ip
!
[snip]

By using subinterfaces, the router creates a "multi-port" bridge and
hence overcomes the split-horizon problem for layer-2 bridging.

HTH,

William Chu
Technical Manager, CCIE #1247
Network Infrastructure
Information Technology Services Department
E-mail: wwwchu@itsd.gcn.gov.hk

At 05:37 PM 1999/11/15 -0600, Steven Saner wrote:
>I am trying to setup a bridged interface with multiple ATM PVCs on a
>7206 for the purpose of provisioning ADSL. Below are the relavent
>configuration snipits. My problem is this: I have two PVCs defined to
>two different DSL circuits. The IPs at the remote ends of these
>circuits is 206.53.111.1 and 206.53.111.2. I can ping both of theses
>ip addresses from my 7206. I also have connectivity from each remote
>machine to the 7206 and to the outside world. I do not, however, have
>connectivity between the two remote machines. If I do a "debug arp" on
>the 7206, I see arp requests comming from one of the remote machines,
>but that request is never sent to the other one. I presume that the
>solution is some kind of proxy arp or something, but I have not found
>the answer. Can someone help?
>
>Thanks
>
>
>bridge irb
>!
>interface ATM6/0
> mtu 1500
> no ip address
> no ip directed-broadcast
> no ip mroute-cache
> no atm scrambling sts-stream
>!
>interface ATM6/0.1000 multipoint
> description ADSL Shared Interface
> ip directed-broadcast
> no ip proxy-arp
> atm pvc 1001 3 33 aal5snap 6144 6144
> atm pvc 1002 3 34 aal5snap 1536 1536
> bridge-group 1
>!
>interface BVI1
> description Interface for Shared ADSL
> ip address 206.53.111.6 255.255.255.248
> ip directed-broadcast
>!
>bridge 1 protocol ieee
> bridge 1 route ip
>
>==================================================================
>Steven Saner SouthWind Internet Access, Inc.
>ssaner@southwind.net Systems/Network Administrator
>http://www2.southwind.net/~ssaner http://www.southwind.net
> 263-7963 Wichita (800)525-7963
>
>
>



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