Subject: [MOBILE-IP] RFC 2002 (+bis) and the 'V' bit

From: "[email-masked]" <[email-masked]>
Date: Thu, 29 Jun 2000 12:01:16 -0700

All,

I am wondering if there are any Mobile IP implementations that support the 'V'
bit (Van Jacobson), and if so, whether they have ever had interoperability
with other implementations.

In the process of looking to 'V' bit, I noticed that one important parameter
that must be negotiated to setup VJ is never discussed in RFC 2002, which led
to my question. RFC 1144 states:

"  There are two configuration parameters associated with header
   compression:  Whether or not compressed packets should be sent on a
   particular line and, if so, how many state slots (saved packet headers)
   to reserve.  There is also one link-level configuration parameter, the
   maximum packet size or MTU, and one front-end configuration parameter,
   data compression, that interact with header compression.  Compression
   configuration is discussed in this section.  MTU and data compression
   are discussed in the next two sections."

Obviously, RFC 2002 does negotiate the first, but not the second parameter. So
either every implementation picked the same random number, or no
interoperability has ever been achieved.

If the latter is true, I would like to know whether it makes sense to remove
VJ compression from the standard. In most cases, VJ is run over PPP, so I
believe that most VJ compliant hosts actually negotiate it during PPP setup,
and not Mobile IP.

PatC

---

From: gab <[email-masked]>
Date: Thu, 29 Jun 2000 12:30:50 -0700

> believe that most VJ compliant hosts actually negotiate it during PPP setup,

i second that. besides, rfc2507 is preferrable to VJ, right? this wouldn't
be supported or negotiable via the V bit.
rather, one negotiates compression via NCP according to rfc's 2509,1332
and 2023.

---

From: Steven Glass - Solaris Software <[email-masked]>
Date: Thu, 29 Jun 2000 17:24:24 -0400

> rather, one negotiates compression via NCP according to rfc's 2509,1332

    I third this, and add that this is a link-layer specific bit that doesn't
belong here.

                              Cheers,
                                  Steve

---

From: Steven Glass - Solaris Software <[email-masked]>
Date: Thu, 29 Jun 2000 18:32:19 -0400

>     I third this, and add that this is a link-layer specific bit that doesn't

    Sorry, didn't mean link-layer (as strictly defined), meant a link-specific
bit, that is it's dependent on the link topology between the MN and FA.  As
Vipul points out, there are other ways to negotiate (IPhdr, VJ, etc)
compression, of which a single bit in the mip registrtion isn't going to be
complete enough, assuming such a thing belongs there.

                              Cheers,
                                  Steve

                              Cheers,
                                  Steve

---

From: "Kent K. Leung" <[email-masked]>
Date: Fri, 30 Jun 2000 11:37:58 -0700

> believe that most VJ compliant hosts actually negotiate it during PPP setup,

I agree with removal of V bit, which is not supported by Cisco
implementation.  Frees up a bit. :)

-- Kent --