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From: "Lee, Patrick [CAR:9Q17:EXCH]" <patlee@americasm01.nt.com>
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Date: Tue, 30 Jan 2001 14:17:22 -0500
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Organization: Nortel Networks
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X-Mozilla-Status2: 00000000
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: patlee@nortelnetworks.com