Subject: unnum-02 comments

From: "Kullberg, Alan" <[email-masked]>
Date: Wed, 4 Oct 2000 13:21:05 -0400

I have read the latest Unumbered Links draft and have a question
and some suggestions.

From section 5, 2nd paragraph, 
   If the LSP is bidirectional, and the tail-end LSR (of the forward
   LSP) advertises the reverse LSP as an unnumbered Forwarding
   Adjacency, the tail-end LSR MUST allocate an interface ID to the
   reverse Forwarding Adjacency.

How does the tail-end LSR know that the bidirectional LSP is a
FA-LSP so that the reverse interface ID will be assigned?

In section 6.2, a comparison is made between the <PHOP, Interface ID>
tuple and the <Extended Tunnel ID, Tunnel ID> tuple.  CR-LDP does not
have a TLV in the REQUEST message that carries the PHOP information.
Actually, the Path Vector TLV carries the LSR ID of the previous hop.
But is the LSR ID the same as the Router ID?  If so, then the draft
could mandate the inclusion of the PV TLV when sending a Request
message containing an ER TLV with a 1st ER Hop of type Unnumbered
Interface ID.  Or should a new TLV be specified to carry the same
information as the PHOP in RSVP?

In section 5, CR-LDP needs a way to transmit the Reverse Interface
ID in the MAPPING message.  I took the liberty to suggest some text
for section 5 that adds a new TLV to CR-LDP and specifies how to
signal the information for CR-LDP.  <<<<< and >>>>> surround new and
changed parts of the text.

############################ start of changed section 5
5. Unnumbered Forwarding Adjacencies

   If an LSR that originates an LSP advertises this LSP as an unnumbered
   Forwarding Adjacency in IS-IS or OSPF [LSP-HIER], the LSR MUST
   allocate an interface ID to that Forwarding Adjacency.  Moreover, the
<<<<<
   Tunnel ID in the Session Object of the Path Message or the Local
   CR-LSP ID in the LSPID TLV of the Request Message for the LSP
   MUST be set to that interface ID, and the Extended Tunnel ID in the
   Session Object or the Ingress LSR Router ID in the LSPID TLV of the
   LSP MUST be set to the Router ID of the LSR that originates the LSP.

   If the LSP is bidirectional, and the tail-end LSR (of the forward
   LSP) advertises the reverse LSP as an unnumbered Forwarding
   Adjacency, the tail-end LSR MUST allocate an interface ID to the
<<<<<
   reverse Forwarding Adjacency.

   For RSVP, it MUST set the "Reverse
   Interface ID" field in the Filter Specification object in the flow
   descriptor list for this LSP to the reverse FA's interface ID (note
   that while in general there can be multiple Filter Specifications, it
   is expected in the case of point-to-point LSPs that there is only
   one).  To accommodate this, the LSP_TUNNEL_IPv4 Filter Specification
   Object's format is modified per Figure 1:

   Figure 1: LSP_TUNNEL_IPv4 Filter Specification Object

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   IPv4 tunnel sender address                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Reverse Interface ID      |            LSP ID             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   For CR-LDP, it MUST set the "Reverse Interface ID" field in the Reverse
   Interface ID TLV in the MAPPING message to the reverse FA's interface
   ID.  The Reverse Interface ID's format is shown in Figure 2:
 
   Figure 2: Reverse Interface ID TLV in CR-LDP

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |0|0|            Type           |            Length             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |            MUST be zero       | Reverse Interface ID (16 bits)|
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The Type is TBD (Reverse Interface ID) and the Length is 4.
############################ end of changed section 5

Note that all of the figure numbers following this (new) one must be
adjusted. 

Thanks,

Alan