Subject: RE: AII differences between PW routing and l2vpn signalling draftprovisionong methods.

From: "Florin Balus" <[email-masked]>
Date: Mon, 5 Dec 2005 08:53:36 -0500

I agree with Mustapha's proposal: we should just deprecate AII type 1
before people start implementing it. All its functionality could be
easily reproduced if need be using AII type 2: just set Global ID and
Prefix fields to zero. L2VPN Signaling itself proposes a similar
approach for the 32 bits field associated with AII type 1 when it comes
to BGP auto-discovery: i.e. just re-use 32 bits from the NLRI for BGP
VPLS SAFI and set the other unnecessary fields to zero...

Note that AII type 2 will be required for L2VPN addressing: all the Use
Cases (e.g. MAN-WAN, Inter-provider, Scalability, private PE addressing)
described in MS-PW requirements draft apply also for L2VPNs (PWs being
used as infrastructure). 

So there won't be a clear cut between the 2 cases outlined by Luca
below: there will be plenty of scenarios where 2 VSIs (VPLS)/Pools
(VPWS) will need to be connected via a MS-PW. 

Moreover there will be cases where the same PE will have to connect its
VSI to remote ones using both SS and MS-PWs. How does the PE choose when
to use one AII type versus the other? Definitely that should not happen
based on whether the PW goes one hop or multiple hops. 

Everybody will require sooner or later support for MS-PWs. So I think
it's a good idea to put in place early in the L2 build up, the L2
addressing that will easily accommodate the MS-PW expansion instead of
trying to live with 2 addressing plans: one unique per AGI (AII type 1),
one globally unique (AII type 2).

Focusing on one addressing format will maximize also technology re-use
(MS/SS-PWs transparently applicable to Individual VCs, VPWS, VPLS) and
will avoid interoperability issues between vendors and SPs.

Regards,
Florin 

>-----Original Message-----
>From: [email-masked] [mailto:[email-masked]]
>On Behalf Of Mustapha Aissaoui
>Sent: Friday, December 02, 2005 1:58 PM
>To: 'Luca Martini'; 'L2VPN'
>Cc: 'David McDysan'; [email-masked]
>Subject: RE: AII differences between PW routing and l2vpn 
>signalling draftprovisionong methods.
>
>
>Luca,
>I do not believe there is any substantial difference that
>warrants to standardize two different AII types. A MS-PW can 
>also terminate on a VSI, e.g., VPLS.
>
>The issue is to be able to encode the target termination
>interface: an endpoint for a p2p PW or a VSI for a VPLS in a 
>way such that it will work for both single hop PWs and MS-PWs. 
>Both types can be used for the various L2VPN applications.
>
>Pragmatically, the way to go is to deprecate the FEC 129 as
>defined in draft-ietf-l2vpn-signaling-06.txt (Type 1) and 
>extend the Type 2 to cover the various applications. One other 
>reason to deprecate Type 1 is that we do not want an 
>implementation to use different FEC 129 types for single-hop 
>PW and MS-PW. FEC 128 will be restricted to singe hop PW and 
>will be fine as long as we specify a way to reach U-PEs which 
>are on a FEC 129 Type 2 network.
>
>Mustapha.
>-----Original Message-----
>From: [email-masked] [mailto:[email-masked]]
>On Behalf Of Luca Martini
>Sent: Friday, December 02, 2005 1:09 PM
>To: L2VPN
>Cc: David McDysan; [email-masked]
>Subject: AII differences between PW routing and l2vpn 
>signalling draft provisionong methods.
>
>WG,
>
>After a good discussion with Bruce Davie,  we came up with the
>following explanation on why we need to have different AII 
>type int he PW setup and maintenance protocol. This note 
>explains why draft-ietf-l2vpn-signaling-06.txt (the L2VPN 
>Signaling draft) and 
>draft-balus-bocci-martini-dyn-ms-pwe3-00.txt (the MS PW
>draft) make use of different AII types, as defined in 
>draft-metz-aii-aggregate-01.txt.  In a nutshell, the two 
>drafts use different AII types because they are tackling 
>different problems. Specifically, L2VPN Signaling draft is 
>concerned with setting up all the PWs for a given L2VPN, while 
>the MS PW draft is concerned with setting up individual PWs.  
>Because it is concerned with building L2VPNs, the L2VPN 
>Signaling draft makes use of the AGI (the contents of which 
>effectively identify the
>VPN) plus the AII to identify a particular PW. Hence, the AII 
>only needs to identify a "pool" or a VSI relative to a 
>particular AGI. Hence a simple 32 bit AII is sufficient. By 
>contrast, because the MS PW draft is concerned with setting up 
>individual PWs, not L2VPNs, it has no use for the AGI - there 
>is no "group" concept. Hence it fully identifies the PW in the 
>AII. Because there may be many PWs connected to a given U-PE 
>device, it is necessary to identify the PWs relative to a 
>given U-PE. And it is necessary to identify the U-PE within 
>the AII so that the signaling message can be routed toward the 
>correct U-PE. Hence the requirements for the AII are quite 
>different, and it makes sense to use an AII type that is 
>designed to meet these requirements. It is obvious that the 
>simple AII type could be encoded in the more complex AII type 
>by leaving various fields set to zero, but this does not seem 
>to serve any useful purpose.
>
>Luca
>
>
>
>
>
>

---

From: Luca Martini <[email-masked]>
Date: Mon, 05 Dec 2005 10:25:38 -0700

Florin,

> Prefix fields to zero. L2VPN Signaling itself proposes a similar
Prefixing the fields to 0 just means that you really have encoded a new 
AII type , but you are hiding it.
What happens when a new provisioning model comes along ? do we put all 
the fields to 0xffff ?

> (VPWS) will need to be connected via a MS-PW. 
Yes , and this case is handled properly in the l2vpn-signaling draft.
For VPLS the PW-Switching point PE is a BGP speaker, hence it can 
advertise the VPLS with itself as a next hop. This will initiate the 
MS-PW segments correctly through the S-PE ( basically , the BGP speaker 
itself )

> based on whether the PW goes one hop or multiple hops. 
there is no need to choose. In this case , the BGP message contains 2 
piece of information: "please setup a PW to myself" , and " here is the 
VSI you should connect the PW to"

This is very different from the MS-PW BGP message that simply says "you 
can reach this PW AC address here" .

> will avoid interoperability issues between vendors and SPs.
The reason we had an AII type field is to allow different provisioning 
schemes ...
what would be the point to have only one AII type ?

Although I think this is fairly complicated, keeping the AII type 1 as 
is , ( which is used in a different context ) does not preclude any of 
the MS-PW technology from being used.
On the contrary , only using AII type 2 , precludes the autodiscovery 
methodology described in the l2vpn-signaling draft, unless most fields 
are set to 0 which gets us right back to AII type 1.

Thanks.
Luca