Subject: Re: Re: Who do VLAN translation in LDP-VPLS? PE-rs or MTU-s?

From: Du Wenhua <[email-masked]>
Date: Sat, 20 Mar 2004 10:10:10 +0800

Hi,Ali Sajassi,
   Thanks for your careful clarity.  
 
>-----Original Message-----
>From: Ali Sajassi <[email-masked]>
>Sent: 13:29:00,2004-03-19
>To: Ali Sajassi <[email-masked]>
>Subject: Re: Who do VLAN translation in LDP-VPLS? PE-rs or MTU-s?

>>> >If you want to use
>>> >a) Ethernet access network and
>>> >b) allow muxed UNI port and
>>> >c) don't restrict customer VLAN assignment,
>>> >then MTU-s need to support VLAN translation (e.g., based on 802.1ad). But
>>>PE-rs can do VLAN translation. MTU-s need not to do VLAN translation.
>>> >if you want to restrict customer VLAN assignment or use PW between your
>>> >u-PE and n-PE, then you don't need this feature.
>>> >
>>> >>    3)[PWE3-ETHERNET]<draft-ietf-pwe3-ethernet-encap-05.txt> defines the
>>> >> VLAN translation function for PW. <LSP-VPLS> say VPLS supports such PW
>>> >> defined by [PWE3-ETHERNET]. So I think PE-rs support VLAN translation 
>>> also.
>>> >
>>> >But for that you need MPLS access network and your u-PE needs to support
>>> >MPLS PW (e.g., your MTU-s becomes PE-r) and this is different from section
>>>I think you might have misunderstood what I mean.
>>>u-PE(MTU-s) is typical bridge, just carry  PDU over C-VLAN.
>>>n-PE(PE-rs) do C-VLAN tranlation when the PDU come into an VC(a.k.a PW).
>>>[PWE3-ETHERNET] defines the VLAN translation function for VC(PW).
>>
>>I think you are talking about a scenario in which the MTU-s (the bridge) 
>>is directly connected to the PE-rs without any Ethernet network in between 
>>(even a single bridge).  If that's the case, then yes you don't need to 
>>have VLAN translation at the MTU-S since each pair of port+vlan at the 
>>PE-rs is considered as an AC that can be associated with a given VSI. 
>>However, I was talking about the more general case of "Ethernet access 
>>network" in which MTU-S is connected via one or more provider bridges to 
>>the PE-rs. And in such general scenario, the VLAN translation must be done 
>>at the MTU-s since each provider VLAN represent a VPLS instance.
>
>I think I need to further clarify what I said earlier to ensure that there 
>is no ambiguity. In the above paragraph, I said that if the MTU-S is 
>directly connected to PE-rs, then you don't need to have VLAN translation 
>at the MTU-s; however, to be more precise, I should have said that if there 
>is no VLAN ambiguity within MTU-S, then there is no need for VLAN 
>translation and the PE-rs can resolve the VLAN ambiguity between different 
>MTU-s. 
true. I agree with you.
>However, for scenario where different ports of a MTU-s is connected 
>to different customers (and different customers use different VLAN 
>assignments to represent different services, then VLAN translation is still 
>needed in the MTU-s even though it can be directly connected to PE-rs or 
>else traffic from one customer can leak to another because of local 
>switching property of MTU-s. 
true. I agree with you.
>Another way of doing this is to use 
>encapsulate all the the VLANs from a given customer with a provider VLAN 
>tag and use double-tag lookup at the PE-rs. This method was explained in 
>detail in draft-sajassi-ppvpn-vpls-architectures. However, VLAN translation 
>is more general and covers more cases and thus it is the only method 
>mentioned in vpls-ldp draft.
So, we get two scenarios:
1) If there is no VLAN ambiguity within MTU-S, then there is no need for VLAN 
translation and the PE-rs can resolve the VLAN ambiguity between different MTU-s.
each pair of port+vlan at the PE-rs is considered as an AC that can be associated
with a given VSI.
2) If there is VLAN ambiguity within one MTU-S(to be more precise, within one 
Ethernet access network),then VLAN translation is still needed in the MTU-s.

Let's review the 1st scenario. Give an example, if {port 3,VLAN 100} and {port 3, 
VLAN 200} of a PE-rs are considered as two ACs, are associated with one VSI. 
It become amusing, there are two idea not to be think about:
 1)PDU come into the PE-rs on {port 3, VLAN 100}, and leave out of the same PE-rs 
on {port 3, VLAN 200} when data exchanging between two ACs.
 2)In port 3 of the PE-rs, 2 VLANs map to 1 VSI. Here is C-VLAN, but have 
the same function as P-VLAN. This differs from the sentence in LDP-VLPS: 
"Therefore, there is a  one to one correspondence between a P-VLAN and a VPLS instance."

The above scenarios is not clear in the LDP-VPLS. 
My suggestion are: 
1)Both PE-rs and MTU-s can do VLAN translation. MTU-s do VLAN translation only when 
there is VLAN ambiguity in one Ethernet access networks.
2) In one port of a PE-rs, many P-VLAN can map to one VSI.

>
>-Ali
>
>
>>-Ali
>>
>>> >11.2 whose title is "H-VPLS model using Ethernet Access Network". Besides,
>>> >if you use MPLS PW between u-PE and n-PE, then you wouldn't need VLAN
>>> >traslation to begin with since each customer VLAN gets mapped to a
>>> >different PW.
>>> >
>>> >
>>> >>     In summary, I suggest to move the VLAN translation function from the
>>> >> MTU-s to PE-rs. PE-rs are more powerful and more expensive. PE-rs is more
>>> >> easy to do VLAN translation, which is defened in
>>> >> <draft-ietf-pwe3-ethernet-encap-05.txt>.
>>> >>     MTU-s is just a typical bridge, no additional UNI capability, no VLAN
>>> >> translation.
>>> >
>>> >I think you might have misunderstood the scenario for H-VPLS with Ethernet
>>> >access network. Hope the above explanation helps in clarifying it.
>>> >
>>> >-Ali
>>> >
>>> >
>>> >
>>> >>　　　　　　　　Yours
>>> >>
>>> >>　　　　　　　　Du Wenhua
>>> >>     　　　　　　　　　　2004-03-18
>>>= = = = = = = = = = = = = = = = = = = =
>>
= = = = = = = = = = = = = = = = = = = =

---

From: Ali Sajassi <[email-masked]>
Date: Fri, 19 Mar 2004 19:21:41 -0800

>"Therefore, there is a  one to one correspondence between a P-VLAN and a 

In your example, both VLAN 100 and 200 come through port 3 of PE-rs which 
means they come through the same MTU-s (since MTU-s is directly connected 
to PE-rs). What this implies is that if VLAN 100 and 200 are used by 
customer A connected to that MTU-s, then no other customers can use these 
VLANs (e.g., there is no VLAN ambiguity); however, this contradicts the 
initial premise that any customer can use any VLAN. Even if we go based on 
the assumption that the customer's VLAN-100 and 200 don't overlap with any 
other customer VLAN, there is no  P-VLAN in here !!! Because all you have 
done is to aggregate customer's VLANs (C-VLANs) and bring them to PE-rs.

>there is VLAN ambiguity in one Ethernet access networks.

In most applications you have VLAN ambiguity. In other words, as soon as 
you have two customers connected to a MTU-s, you can have VLAN ambiguity 
because the two customer's VLAN can overlap.

>2) In one port of a PE-rs, many P-VLAN can map to one VSI.

No. not P-VLAN. Multiple C-VLAN can map to one VSI but not multiple P-VLAN. 
P-VLAN is used in conjunction with Ethernet access network and it 
corresponds to a broadcast domain and thus to a VPLS instance.

-Ali