Subject: HopLimit for IPv6

From: "Lori Napoli" <[email-masked]>
Date: Wed, 9 May 2001 16:17:30 -0400

The Basic API RFC documents two ways an application can alter the hop limit
for a packet -- using setsockopt or ancillary data.  We have some
questions regarding this that are not covered in the RFC and I would like
your opinion on:

   If an adminstrator set up the stack to have a hoplimit of x.  Does this
   imply that any application, authorized and unauthorized, can override
   this value?  If the adminstrator only wanted packets sent from this
   stack to route through 10 hosts, an application can increase this?  Does
   it make sense to only allow the application to specify a hop limit that
   is lower than the configured hop limit for the stack?
   RFC 1122 states you MUST not send out a packet w/ a TTL of 0.  Does this
   mean that we shouldn't send out an IPv6 packet w/ hop limit = 0?  If so,
   why does the RFC state the valid values are 0 - 255?  Since the packet
   cannot be sent out using hop limit of 0, does it make more sense to fail
   a request to set it to 0?

Thanks!
Lori Napoli

z/OS Communications Server Development - TCP/IP Stack

919-254-6146   T/L 8-444-6146
E-mail: [email-masked]

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From: "Dave Thaler" <[email-masked]>
Date: Wed, 9 May 2001 14:47:56 -0700

Lori Napoli writes:
>    stack to route through 10 hosts, an application can increase this?

It's up to the implementation.  I think the usual answer would be "yes".

> Does

Not sure.

>    mean that we shouldn't send out an IPv6 packet w/ hop limit = 0?  

One shouldn't send an IPv6 packet out on the wire with hop limit = 0.

> If so,

No.  Packets with a hop limit of 0 can still be sent on the same
machine,
for example between different processes.

-Dave