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DLSW <-> Transparent Bridging via FE Subinterfaces?

Hi. I have a 7206 router connected with FE to a Catalyst 6509, via 802.1Q trunking. Two VLANs. The router supports DLSW to remote sites, and the switch transports SNA traffic to the router with transparent bridging through one of the FE subinterfaces.

What I'd like to do is establish DLSW peering between the router and another device on the local LAN -- in other words, also through the FE interface connected to the 6509. I don't have another physical FE interface on the router. Two questions:

1) Is there any reason I would run into difficulty setting up another VLAN on the switch and another FE subinterface in the router, and using the new VLAN/subinterface for DLSW, while keeping the other subinterface configured to use transparent bridging?

2) In that configuration, might there be any issue transporting SNA into and out of the router via the one FE subinterface configured with a bridge group and the other FE subinterface being used for the DLSW path? That is, I will need the router to decapsulate the SNA coming in via DSLW on one subinterface, and bridge it out the other subinterface, and vice-versa.

Thanks for any guidance.

4 REPLIES
New Member

Re: DLSW <-> Transparent Bridging via FE Subinterfaces?

I'm not sure how well I managed to explain the scenario in the previous post. An attempt to clarify:

VLAN1 -\ FE.Subinterface1

[6509] VLAN2 --> <=-802.1Q-=> FE.Subinterface2 [7206]

VLAN3 -/ FE.Subinterface3

6509

VLAN 1: bridge group 1

VLAN 2: bridge group 1

VLAN 3: L2-only VLAN (no definition in the MSFC). Used only to transport DLSW (and other IP) traffic to and from a router also running DLSW to FE.Subinterface3 on the 7206 through the 802.1Q trunk.

7206

FE.Subinterface1: bridge-group 1

FE.Subinterface2: bridge-group 1 (blocked by STP)

FE.Subinterface3: not in a bridge group. The interface through which the 7206 communicates with an internal router running DLSW (transporting SNA for a device directly connected to that internal router).

Traffic path

SNA must travel between the device the 7206 is DLSW peering with through FE.Subinterface3, and a device (a mainframe OSA Express interface) the 7206's SNA traffic can reach via transparent bridging through FE.Subinterface1.

The "steps": the 7206 uses FE.Subinterface3 to receive DLSW TCP/IP-encapsulated SNA traffic from the other DLSW router. The SNA traffic gets decapsulated in the 7206, and is bridged to the mainframe OSA Express interface via FE.Subinterface1. And of course the reverse, from the mainframe, transparently bridged into the 7206 through FE.Subinterface1 and sent via DLSW through FE.Subinterface3.

Do-able? Thanks!

New Member

Re: DLSW <-> Transparent Bridging via FE Subinterfaces?

Arg. The "ASCII art" came out badly due to the font change and space removals. Oh, well.

New Member

Re: DLSW <-> Transparent Bridging via FE Subinterfaces?

Hi Mitch,

This is just fine. In fact, there's no real need for separate VLANs. One traffic stream is IP and the other 802.3/802.2, so they wil never get mixed up.

Rgds, Dan

New Member

Re: DLSW <-> Transparent Bridging via FE Subinterfaces?

Thanks, Dan! Very helpful

Regarding the additional VLAN, yes, the IP just gets routed so no need for the additional VLAN. When I was whiteboarding the this, I actually wrote, "DLSW's IP is routed but add VLAN/subint anyway - no cost + simplicity." My relative DLSW inexperience was causing the odd notion of DLSW-in, decapsulated SNA back out the same interface via bridging to be cognitively stressful. :-)

But you're right, if the 7206 is happy, I guess I ought to be happy. It will be receiving the SNA for this host in TCP using DLSW through FE.Subinterface1 in bridge group 1, decapsulating it, then bridging it right back out FE.Subinterface1. And vice-versa. Even stranger than via separate subinterfaces from a simplistic traffic path perspective, but if it works it works!

Thanks, again.

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