Subject: [mpls] I-D Action: draft-kompella-mpls-larp-10.txt

From: [email-masked]
Date: Sun, 11 Jul 2021 19:22:39 -0700

A New Internet-Draft is available from the on-line Internet-Drafts directories.
This draft is a work item of the Multiprotocol Label Switching WG of the IETF.

        Title           : Label Distribution Using ARP
        Authors         : Kireeti Kompella
                          Balaji Rajagopalan
                          Reji Thomas
	Filename        : draft-kompella-mpls-larp-10.txt
	Pages           : 12
	Date            : 2021-07-11

Abstract:
   This document describes extensions to the Address Resolution Protocol
   to distribute MPLS labels for IPv4 and IPv6 host addresses.
   Distribution of labels via ARP enables simple plug-and-play operation
   of MPLS, which is key to deploying MPLS in data centers and
   enterprises.

The IETF datatracker status page for this draft is:
https://datatracker.ietf.org/doc/draft-kompella-mpls-larp/

There is also an htmlized version available at:
https://datatracker.ietf.org/doc/html/draft-kompella-mpls-larp-10

A diff from the previous version is available at:
https://www.ietf.org/rfcdiff?url2=draft-kompella-mpls-larp-10

Internet-Drafts are also available by anonymous FTP at:
ftp://ftp.ietf.org/internet-drafts/

---

From: Erik Auerswald <[email-masked]>
Date: Wed, 14 Jul 2021 13:13:43 +0200

Dear Authors,

thanks for sending an updated version of the L-ARP draft.

The L-ARP mechanism seems to be a nice and simple solution to extend an
MPLS fabric to hosts, e.g., for hypervisor based network virtualization
over MPLS.

I think that section 3, L-ARP Protocol Operation, could be made even
clearer with a few simple changes.  I'll first describe my suggested
changes, and then provide text for direct inclusion in the draft for
your convenience.

Section 3 illustrates L-ARP operation based on an example topology,
looking at egress, ingress, and data plane operation.  This uses four
named LSRs (T1 to T4), three named hosts (H1 to H3), two named transport
labels (L3 and TL3/L1/L), and one named VPN label (VL3).

I think it would be clearer and more consistent if a single name were used
for the second named transport label instead of three different names.

I would suggest to use "TL3," since this label is a transport label to
reach H3.  (Both "TL3" and "L1" are used thrice and thus require the same
amount of changes, but "TL3" corresponds better to "VL3".  Additionally,
one could assume "L1" to be a transport label allocated by T1 to reach
H1, just as "L3" is the transport label allocated by T3 to reach H3.)

Additionally, one sentence seems to have a typo in an LSR name, using
"T" instead of "T4".

Thus I would suggest the following text changes:

1. In the second paragraph of section 3 (on page 5) replate "T" with "T4":

  OLD:

   H1 might also want to talk to a member of the MPLS Fabric, say T.

  NEW:

   H1 might also want to talk to a member of the MPLS Fabric, say T4.

2. In enumeration point 2 in section 3.3 (on page 5) replace "L1" with "TL3":

  OLD:

   2.  if it does, T1 allocates a label TL3 to reach H3 (if it doesn't
       already have such a label) and installs an L-FIB entry to swap L1
       with the label (stack) to reach H3.

  NEW:

   2.  if it does, T1 allocates a label TL3 to reach H3 (if it doesn't
       already have such a label) and installs an L-FIB entry to swap TL3
       with the label (stack) to reach H3.

3. In enumeration point 3 in section 3.3 (on page 6) replace "L" with "TL3":

  OLD:

   3.  sends a (proxy) L-ARP reply to H1 with the Source Hardware
       Address (SHA) set to (L, M), where M is T1's metric to H3.  T1
       may also set some attribute bits in the SHA.

  NEW:

   3.  sends a (proxy) L-ARP reply to H1 with the Source Hardware
       Address (SHA) set to (TL3, M), where M is T1's metric to H3.  T1
       may also set some attribute bits in the SHA.

4. In the first paragraph of section 3.4 (on page 6) replace "L1" with "TL3":

  OLD:

   To send a packet to H3 over an MPLS tunnel, H1 pushes L1 onto the
   packet, sets the destination MAC address to M1 and sends it to T1.
   On receiving this packet, T1 swaps the top label with the label(s)
   for its MPLS tunnel to H3.  If T1's reachability to H3 is via a
   SPRING label stack, the label L1 acts as an implicit binding SID.

  NEW:

   To send a packet to H3 over an MPLS tunnel, H1 pushes TL3 onto the
   packet, sets the destination MAC address to M1 and sends it to T1.
   On receiving this packet, T1 swaps the top label with the label(s)
   for its MPLS tunnel to H3.  If T1's reachability to H3 is via a
   SPRING label stack, the label TL3 acts as an implicit binding SID.

Best regards,
Erik Auerswald
-- 
Dipl.-Inform. Erik Auerswald
Gesellschaft für Fundamental Generic Networking mbH
Geschäftsführung: Volker Bauer, Jörg Mayer
Gerichtsstand: Amtsgericht Kaiserslautern - HRB: 3630