Subject: [Fwd: Comment for rfc3032 on TTL process]

From: "Patrick Lee" <[email-masked]>
Date: Wed, 31 Jan 2001 10:48:37 -0500

Subject: Comment for rfc3032 on TTL process
From: "Lee, Patrick [CAR:9Q17:EXCH]" <[email-masked]>
To: [email-masked]
Date: Tue, 30 Jan 2001 14:17:22 -0500

To whom it may concern,

On the draft for MPLS label stack encoding, section 2.4.3 has mentioned
about the processing of MPLS TTL field.

The last paragraph state that:
   It is recognized that there may be situations where a network
   administration prefers to decrement the IPv4 TTL by one as it
   traverses an MPLS domain, instead of decrementing the IPv4 TTL by the

   number of LSP hops within the domain.

That means IP packet with small TTL value can also go through the MPLS
domain since the MPLS domain is treated as 1 hop for IP forwarding.

But for the second paragraph on section 2.4.3 state that:
   When an IP packet is first labeled, the TTL field of the label stack
   entry MUST BE set to the value of the IP TTL field.  (If the IP TTL
   field needs to be decremented, as part of the IP processing, it is
   assumed that this has already been done.)

That means the first label stack entry's TTL value MUST be initialized
to the IP header's TTL value.

Imagine that an IP packet with TTL value 3 go into a LSP with 6 LSP
hops.
Although the network can view the MPLS domain as 1 IP forwarding hop,
the packet can not go through that 1 hop.

It seems to be NOT CONSISTENT for both paragraph.

Regards,
Patrick Lee

--
Passport Software Development (9Q17)
Multimedia Enterprise Division       ESN: 39-51213
P.O. Box 3511, Station C,          PHONE: (613)765-1213
Ottawa, Ontario, Canada, K1Y 4H7  E-MAIL: [email-masked]

---

From: "Andrew R Frame" <[email-masked]>
Date: Wed, 31 Jan 2001 08:53:55 -0800

The spec is not contradicting itself, the last paragraph is defining an
alternative behavior. If you would prefer for the make the LSP look like one
hop to tools like traceroute, or if you are trying to solve the situation
given by your example below, implementing the alternative behavior might be
a good idea.

-andrew

-----Original Message-----
From: [email-masked] [mailto:[email-masked]]On Behalf Of Patrick Lee
Sent: Wednesday, January 31, 2001 7:49 AM
To: [email-masked]
Subject: [Fwd: Comment for rfc3032 on TTL process]

To whom it may concern,

   When an IP packet is first labeled, the TTL field of the label stack b

That means the first label stack entry's TTL value MUST be initialized to
the IP header's TTL value.

Imagine that an IP packet with TTL value 3 go into a LSP with 6 LSP hops.
Although the network can view the MPLS domain as 1 IP forwarding hop, the
packet can not go through that 1 hop.

Regards,
Patrick Lee