Subject: Some general concerns/issues

From: Larry Samberg <[email-masked]>
Date: Fri, 25 Jun 93 12:59:00 EST

Now that I have had a few days to immerse myself in DLSw related issues,
I have a number general concerns/questions. I would appreciate any answers,
information, concurrence, or indication that any of these aren't really
problems:

1. Support for duplicate TIC addresses in 3745s - Our first release
of PIR chose one TIC and just used it until it died and then switched to the
other. We were beat up by our customers who wanted to preserve the
load-balancing effects of dual TICs. My perception is that unless the
two TICs are reachable through the same DLS switch, DLS suffers the same
problem. Yes?  (note: PIR is CrossComm's technique for routing SNA).

2. Are the MAC addresses stored in SSP message canonical or in Token
Ring format? Have the tranlational bridging issues been addressed?

3. The spec doesn't discuss configuration very much. I infer that the
virtual ring alluded to must be unique on each switch. Am I correct?

4. As was pointed out in some other mail (Mr. Shu I believe) not propagating
the RIF/LF bits back to the source can result in a partitioning of the
network.

5. The lack of dynamic discovery scares me. I can't imagine a customer
configuring 60 (or even 30) switches correctly (and independently).

6. I haven't worked this out, but are there any possibilities of unnecessary
looping of SRB/ARB frames (or more politically correct STE/ARE frames) if
there are two DLS paths in parallel or a DLS path and an SR Bridge path?
How does DLS interact with the spanning tree setup for STE frames?

- Larry Samberg

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From: [email-masked] (Himanshu C. Shah)
Date: Fri, 25 Jun 93 14:11:41 EDT

Although I am not a SIG 'electorate', I love to indulge into technical
discussion. Forwarned, I am still a grasshopper.

1. Support for duplicate TIC addresses in 3745s - Our first release
of PIR chose one TIC and just used it until it died and then switched to the
other. We were beat up by our customers who wanted to preserve the
load-balancing effects of dual TICs. My perception is that unless the
two TICs are reachable through the same DLS switch, DLS suffers the same
problem. Yes?  (note: PIR is CrossComm's technique for routing SNA).
------
1) Duplicate MAC addresses in TKR environment risiding on differnet
rings (Of course, IEEE802.5 MAC will not even allow you to join the
ring with dupplicate address) can happen only in Source Routing Bridge (SRB)
environment. In transparent bridge environment, traffic will fluctuate
from one ring to other ring as bridge keeps learning from differnt
interfaces. 

In the SRB environment, source station selects the route. For example,
if DLS is initiating the connection on DLC_START_DL command, DLS is
responsible to select a route to destination which could be upto 14
hops away. Once, you select the route, all LLC2 frames will use the
same RIF (including the ones DLS doesn't know about, e.g. RR frames).

Unless you device your own mechanism to detect a failed route and
start using the alternate route or do reexploring without breaking the
data link connection, there is no information/guidelines in RFC.

Hence, even if the same DLS is reachable to two TICs, the problem
exist. If two TICs are directly connected to DLS, they are visible via
different interfaces and hence you still need some mechanism to detect
the unreachability and switch over.
-----------

	Current RFC assumes token ring and source routing environment. Hence I
will assume the address in non-canonical (token ring format) format.

-----------

3) 3. The spec doesn't discuss configuration very much. I infer that the
virtual ring alluded to must be unique on each switch. Am I correct?

No. As a matter of fact the virtual ring denoted to DLS cloud MUST
be unique in all the DLSs. If not, you may risk looping and/or traffic
reentering the DLS cloud by parallel DLS. 

I believe that RFC should accomodate a mechanism to ensure the virtual
ring number integrity amongst the participating DLSs.

------------

4) 4. As was pointed out in some other mail (Mr. Shu I believe) not propagating
the RIF/LF bits back to the source can result in a partitioning of the
network.

That is Himanshu and not Mr. Shu..(ask Nick Grewal for
pronounciation..)

I agree.

----------

5)5. The lack of dynamic discovery scares me. I can't imagine a customer
configuring 60 (or even 30) switches correctly (and independently).

Multicast OSPF??

Also, if you have client-server network, only at server site DLS, you
have to configure all the client IP addresses. At all client site DLS,
all you need to configure is server side DLS IP address only.
------
6)6. I haven't worked this out, but are there any possibilities of unnecessary
looping of SRB/ARB frames (or more politically correct STE/ARE frames) if
there are two DLS paths in parallel or a DLS path and an SR Bridge path?
How does DLS interact with the spanning tree setup for STE frames?

Not really. Work it out with (3) in mind and the fact that SRBs sheds
frames with Duplicate LOUTs in the frame.

Himanshu.