Re: [nvo3] New Version Notification for draft-fan-l2tp-vp-01.txt

["Carlos Pignataro (cpignata)" <[e-mail]>]

Frank, Tom,

Please find some additional comments inline, L2TPExt chair hat off.

On Apr 10, 2014, at 11:46 AM, Tom Herbert <[e-mail]<mailto:[e-mail]>> wrote:

On Wed, Apr 9, 2014 at 8:37 PM, Xialiang (Frank)
<[e-mail]<mailto:[e-mail]>> wrote:
Hi folks,
We have updated the L2TP-VP version -01 draft.
In the new version draft, we add the motivation of this draft and modification to the format of L2TP-VP header.
Welcome your comments and suggestions!

Hi Frank,

Thanks for posting. A few comments:

- This is so dramatically different from L2TP I wonder if it can still
honestly be called L2TP. Have you implemented this? How much of L2TP
stack can be leveraged?
- "Session ID is changed to a 31-bit field"-- doesn't this break L2TP then?

These two bullet points are critical. A "profile" of protocol is a constrained subset of it, within an applicability context. What this document shows is not a profile.

The most-significant bit of the Session ID being used for something else ("Modified bit") has two implications:

  1.  This is not a profile, it's an attempt to redefine L2TPv3.
  2.  This non-profile draft describes a non-backwards compatible protocol. Meaning, L2TPv3's Session ID allows for Session IDs with the MSB set. Consequently, a packet cannot be differentiated between L2TPv3 and this other protocol (which is not a profile).
  3.  It breaks L2TPv3.

OK, I lied, three (or possibly more) implications :-)

The remaining points are subordinate to this high-order bit (no pun intended).

- "Type field"-- I suspect this is meant to be an EtherType value.
Please be explicit about this.
- To get hashing (for ECMP, RSS, etc.) in the network we'd almost
certainly use L2TP over UDP, so L2TP-VP should probably have a format
defined for use with UDP.

There's also hashing for L2TPv3 directly over IP (e.g., RFC 5640)

Thanks,

Carlos.

- Even with Type field, this still suffers from the same problem L2TP
has that network devices won't be able to parse the packet beyond the
L2TP header (the cookie field makes the header variable length). This
eliminates the ability to implement the protocol with LRO for
instance. I suggest you take four or five bits from reserved section
for header length to resolve this (see example in GUE).
- Cookie mechanism is an advantage over VXLAN and nvgre I believe, but
why limit it to 32 bits? 64 bits is much stronger, and at some point
we might even want 128 bits to do strong authentication.

Some more general questions applicable to this and some other proposals.

- "TNI field"-- this seems to use the same 24 bit left shifted format
of nvgre and VXLAN. I still don't see the rationale for this! Why
can't the full 32 bit field be allocated for vni? A large deployment
will be using various levels of hierarchical allocation and possibly
obfuscation of vni (TNI). The nvo3 requirements on this are vague
("100's of thousands of virtual networks"), but they clearly don't
expect this the VNI to be a simple flat space either.
- "Outer Ethernet Header"-- showing the outer Ethernet header in L3
encapsulations examples is not necessary, use of Ethernet is not a
requirement, and this is potentially very misleading. For instance,
the outer Ethernet FCS does *not* protect the packet end to end in an
L3 routed network. Personally, I think it would be more illustrative
to show the IP packet in the inner Ethernet frame instead to see how
its alignment is affected.

Thanks,
Tom

B.R.
Frank

-----Original Message-----
From: [e-mail]<mailto:[e-mail]> [mailto:[e-mail]]
Sent: Thursday, April 10, 2014 11:22 AM
To: Xialiang (Frank); Zhen Cao; Fanduoliang; Zehn Cao; Namgon Kim; Namgon
Kim; Fanduoliang; Xialiang (Frank)
Subject: New Version Notification for draft-fan-l2tp-vp-01.txt


A new version of I-D, draft-fan-l2tp-vp-01.txt has been successfully submitted
by Liang Xia and posted to the IETF repository.

Name:         draft-fan-l2tp-vp
Revision:     01
Title:                L2TP-VP: Layer Two Tunneling Protocol - Virtualization Profile
Document date:        2014-04-10
Group:                Individual Submission
Pages:                9
URL:
http://www.ietf.org/internet-drafts/draft-fan-l2tp-vp-01.txt
Status:         https://datatracker.ietf.org/doc/draft-fan-l2tp-vp/
Htmlized:       http://tools.ietf.org/html/draft-fan-l2tp-vp-01
Diff:           http://www.ietf.org/rfcdiff?url2=draft-fan-l2tp-vp-01

Abstract:
  This document describes Layer Two Tunneling Protocol (L2TP)'s
  virtualization profile (L2TP-VP), which reuses session header of L2TP
  data message to securely support overlay networks for multiple
  tenants, and simplifies tunnel setup by disabling all kinds of L2TP
  control messages.




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