答复: 答复: [rbridge] Call for draft-tissa-trill-cmt-00 to WG draft

[[e-mail]]

See in-line,pls.



Thanks,
Zhai Hongjun
""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
 Protocol Development Dept.VI, Central R&D Institute, ZTE Corporation
 No. 68, Zijinghua Road, Yuhuatai District, Nanjing, P.R.China, 210012
 
 Zhai Hongjun
 
 Tel: [phone]
 Email: [e-mail]
"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""





Mingui Zhang <[e-mail]> 
发件人:  [e-mail]
2012-03-28 17:10

收件人
Radia Perlman <[e-mail]>, "Tissa Senevirathne (tsenevir)" 
<[e-mail]>
抄送
"[e-mail]" <[e-mail]>
主题
答复: [rbridge] Call for draft-tissa-trill-cmt-00 to WG draft






Hi Radia,

It is a good idea to list the Pros and Cons of each solution. There are 
three candidate solutions for the same RPFC problem: PN, CMT and MTRA 
(Multi-Topology TRILL for RBridge Aggregation). Let me compare them in the 
following dimensions.

1. Whether the solution is incrementally deploy-able.

PN: YES.
CMT: NO.
MTRA: YES.

2. Use only existing silicons. 

PN: NO. New silicon is necessary to support "tunneling" or else MAC 
addresses may flip-flop.
----[Zhai Hongjun] I do not agree to this result. In PN, "tunneling" of 
taffice is not necessary. If each member RB in an RB group can get a DTree 
,PN works well on existing silicon . If an member can not get any DTree, 
it can remain passive. In the both cases, PN can use the existing 
silicons. So we should not give such a result to PN at this point.
CMT: YES.
MTRA: Currently NO. But after multi-topology is supported by TRILL, it is 
a "YES".

3. Multi-cast traffic up from RBv can be load-balanced.

PN: NO.
----[Zhai Hongjun] In PN draft, whether using one member RB or all member 
RBs to forward traffic for an end system, it depends on in which scenario 
the pseudo-nickname is used. Because of the AF, only one RB forward 
multi-cast traffic on a shared link. But in LAG, the concept of AF is not 
required, so load-balance of multi-cast traffic is OK for PN.
CMT: YES.
MTRA: YES.

4. Multi-cast traffic down to RBv can be load-balanced.

PN: NO.
----[Zhai Hongjun] See answer to #3.
CMT: YES.
MTRA: YES.

5. Fast convergence on failure recovery. We know that resilience is one of 
the two main purposes of "aggregation". This dimension discusses whether 
the solution offers a way to do fast failure recovery when there is a 
failure of an aggregated RBridge or link. 

PN: NO. The new distribution tree need to be recomputed.
CMT: NO. A overall re-configuration is necessary.
MTRA: YES. 

The following table lists all above comparisons (A jpg version is also 
attached just in case.). MTRA is always YES. I think it deserves our 
follow-up. 

+--------+------------+-----------+----------+------------+-------------+
|Solution|Incre-Deploy|Old Silicon|LB Upwards|LB Downwards|Fast Converge|
+--------+------------+-----------+----------+------------+-------------|
|PN      |YES         |NO         |NO        |NO          |NO           |
+--------+------------+-----------+----------+------------+-------------|
|CMT     |NO          |YES        |YES       |YES         |NO           |
+--------+------------+-----------+----------+------------+-------------|
|MTRA    |YES         |YES(will)  |YES       |YES         |YES          |
+--------+------------+-----------+----------+------------+-------------+

Thanks,
Mingui




发件人: [e-mail] [[e-mail]] 代表 Radia 
Perlman [[e-mail]]

发送时间: 2012年3月28日 12:52

到: Tissa Senevirathne (tsenevir)

Cc: [e-mail]

主题: Re: [rbridge] Call for draft-tissa-trill-cmt-00 to WG draft









It is my understanding that

a) CMT does require changing all the RBs in the campus

b) CMT requires there be at least as many trees as there are active/active 
RBs on any link

 

Of course, no solution is ideal.  It might have been nice to write up all 
the proposed solutions to this and pros/cons. Maybe it's

still worth doing.

 

So from memory...other proposals for allowing R1, R2, and R3 to be 
active/active/active on a link:

 

First note: regardless of whether their port to the link is in a tree, 
unicast works, and they can use the pseudonode

nickname when encapsulating unicast.

 

Also, if Ri's port to the link is in at least one tree, Ri can use the 
pseudonode nickname for that link when encapsulating

multidestination frames for ingress, and the RPF check will work without 
any problems.

 

However, if Ri's port to the link is not in any of the trees,

here were some of the proposed solutions.  So, let's say that R1 and R2's 
port to the shared link is in at least one tree, and R3's

port to the link is not in any of the trees, and R3 needs to encapsulate a 
multidestination frame:

 

1) R3 could tunnel it to one of {R1, R2}, and let them inject the packet 
(with pseudonode nickname) into the campus.

 

Pro: Doesn't affect any RBs other than the ones on the link; backwards 
compatible.  Con: more hops, might be difficult

in some implementations for R3 to forward by tunneling, might be difficult 
for R2 to accept a tunneled packet.

 

2) R3 could use its own nickname instead of the pseudonode nickname in 
this case

 

Pro: Doesn't affect any RBs other than the ones on the link; backwards 
compatible.  Con: MAC learning in distant RBs will have

frequent learning changes of the source MAC S between being on the 
pseudonode nickname (whenever S sends unicast,

or multicast through R1 or R2), or being on R3 (when R3 has to encapsulate 
a multidestination frame from S).

 

------

There might have been some other proposals, but they wound up not to work.

 

Personally, I don't love the CMT thing because of the two disadvantages I 
mentioned above, but I can live with it.

 

Radia 





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