Re: [trill] [TRILL FGL] A question about RFC7172

Donald Eastlake <d3e3e3@gmail.com> Wed, 28 May 2014 16:37 UTC

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From: Donald Eastlake <d3e3e3@gmail.com>
Date: Wed, 28 May 2014 12:37:19 -0400
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To: Zouwenyu <zouwy@h3c.com>
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Subject: Re: [trill] [TRILL FGL] A question about RFC7172
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Hi Wenyu,

On Sun, May 25, 2014 at 10:29 PM, Zouwenyu <zouwy@h3c.com> wrote:
> Hi Donald,
> ________________________________________
> From: Donald Eastlake [d3e3e3@gmail.com]
> Sent: Saturday, May 24, 2014 22:31
> To: zouwenyu 06026
> Cc: trill@ietf.org
> Subject: Re: [trill] [TRILL FGL] A question about RFC7172
>
>>Hi Wenyu,
>
>>On Sat, May 24, 2014 at 4:00 AM, Zouwenyu <zouwy@h3c.com> wrote:
>>> Hi Donald,
>>>
>> >    In RFC7172, there are three types of RBridge: VL RBridge, FGL-safe
>> >RBridge and FGL RBridge.
>>>
>>>    As specified in [RFC7172], Section 8.2, the flag 1 in the TRILL-VER
>>> sub-TLV should be set to indicate that a RBridge is FGL-safe.
>>>
>>>     For FGL-edge RBridge, the Interested Labels and Spanning Tree Roots
>>> Sub-TLV which is specified in [RFC7176], Section 2.3.8, could indicate that
>>> a RBridge is FGL RBridge.
>>>
>>>     But how to decide whether a RBridge is FGL or not, which is only a
>>> transit FGL RBridge? I have not seen any TLV or flags to indicate that.
>
>>Generally all FGL RBridges are also FGL-safe. The only difference is
>>that an FGL RBridge can ingress a native frame to an FGL TRILL data
>>packet and it can egress an FGL TRILL data packet to a native frame.
>
>>If an FGL RBridge is a transit RBridge, then it is not ingressing or
>>egressing, so why would any other RBridge in the TRILL campus care if
>>it is an FGL RBridge or not? As long as the other RBridges know that
>>it is FGL-safe, they know they can route TRILL data through it.
>
> In [RFC7172], Section 4.1.1, it says this words, "Ingress as a TRILL
> multi-destination data packet (TRILL Header M bit = 1) on a
> distribution tree rooted at a nickname held by an FGL RBridge or by
> the pseudonode of an FGL link. ". In this descriptions, does the FGL
> RBridge mean both FGL RBridge and FGL-safe RBridge? In this way, for
> a native multi-destination frame which is FGL ingressed, the ingress
> RB must select a tree root held by a RBridge whose flag 1 in the
> TRILL-VER sub-TLV is set, and do not care whether a RBridge is FGL
> or FGL-safe.

Right. As long as the root of the distribution tree is FGL or
FGL-safe, you are OK.

As long as the root of the distribution tree knows about FGL, then one
of the following two cases will apply:

  If you are using Step (B) in Section 5.1, then the distribution
  tree will be restricted to a contiguous area of TRILL Switches that
  can safely handle FGL.

  If you are using Step (A) in Section 5.2, then the distribution tree
  will have a core of TRILL switches that can safely handle FLG
  although it can have branches extending into areas of VL TRILL
  switches. But other provisions of Step (A) will cause any FGL TRILL
  Data packets to be discarded before they could be seen by any VL
  TRILL switches.

> Does it work like this?

Yes.

Thanks,
Donald
=============================
 Donald E. Eastlake 3rd   +1-508-333-2270 (cell)
 155 Beaver Street, Milford, MA 01757 USA
 d3e3e3@gmail.com

> Thanks.
> Regards,
> wenyu
>
>>Presumably the network manager knows because the network manager knows
>>what the equipment they are managing can do. So if some FGL-safe
>>RBridge is not advertising interest in any FGL labels in an Interested
>>Labels sub-TV, the network manager would know if it could be
>>configured to ingress/egress to/from FGL -- and if it was so
>>configured it would then start advertising interest in one or more FGL
>>labels with the Interested Labels sub-TLV.
>
>>Does this answer your question?
>
>>Thanks,
>>Donald
>>=============================
>> Donald E. Eastlake 3rd   +1-508-333-2270  (cell)
>> 155 Beaver Street, Milford, MA 01757 USA
>> d3e3e3@gmail.com
>
>>> Thanks.
>>> Regards,
>>> wenyu