Subject: Doubts related to draft-ietf-l3vpn-rfc2547bis-03.txt

From: Swati Gupta SBBD <[email-masked]>
Date: Thu, 7 Jul 2005 11:23:05 +0530

Hi,

I was going through IETF draft for L3 VPN - " 
draft-ietf-l3vpn-rfc2547bis-03.txt " and in that i am having some doubts.

1. Section 4.3.2  - Route distribution Among PEs by BGP

        In this on Page 20, it talks about assigning labels. So, in the 
2nd point i.e. assigning a label per Outgoing Attachment Circuit (AC), it 
says that no VRF                lookup is required but  ARP lookup will be 
done for data link encapsulation. This ARP lookup is needed in all the 3 
cases to get the MAC address of         the attached CE device ?  So, in 
this case, from Label Information Base, we can directly get attachment 
circuit and data link encapsulation information. 
        Please correct me if i am wrong somewhere.

2. Section 5 - Forwarding

        On page 25, regarding forwarding, it discusses 2 cases- (1) 
ingress & egress attachment circuits are on the same PE and associated 
with the same   VRF and  (2) both are associated with different VRFs. 
        I am not able to make out how this comes about.

Please clarify. Its urgently required

Thanks in advance

Swati

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From: Robert Raszuk <[email-masked]>
Date: Wed, 06 Jul 2005 23:20:01 -0700

Hey Swati,

> 2nd point i.e. assigning a label per Outgoing Attachment Circuit (AC), 
> it says that no VRF                 lookup is required but  ARP lookup 
> will be done for data link encapsulation. This ARP lookup is needed in 
> all the 3 cases to get the MAC address of         the attached CE device 
> ?  So, in this case, from Label Information Base, we can directly get 
> attachment circuit and data link encapsulation information.

ARP will be needed in all three cases. The difference is that in first 
and third case other system components are responsible for it. I think 
authors just listed the directly involved system components in the draft.

>         I am not able to make out how this comes about.

Oh that is very simple :) It basically describes the case where the 
result of your best IP lookup in the incoming vrf indicated that the 
packet needs to be switched back to the some local attachment circuits 
in the same vrf or in any other vrf of the same PE. Essentially it means 
that there are deployment scenarios where you don't need to impose any 
labels on the packets to switch between VPN sites attached to a given 
PE. Notice that is also says that it is an implementation choice if the 
egress vrf needs to do any lookup or not if we are doing local vrf to 
vrf switching within the same PE.

Let me know if you have any more questions ..

Cheers,
R.