The MPLS WG Archive

[Neeraja Jasty <neeru_mpls@yahoo.com>]

Hi,
  Hi have some doubts in MPLS fragmentation.

Section 3.4 of RFC says the following.

-----------------
If a labeled IPv4 datagram is "too big", and the DF
bit is not set in its IP header, then the LSR MAY
silently discard the datagram.

Note that discarding such datagrams is a sensible
procedure only if the "Maximum Initially Labeled IP
Datagram Size" is set to a non-zero value in every LSR
in the network which is capable of adding a label  
stack to an unlabeled IP datagram.
-----------------

I didn't understand this. In general, If the DF bit is
not set and the packet is too big, we fragment the
packet.

Can anyone explain this?


Next question
RFC says
------------
If the LSR chooses not to discard a labeled IPv4
datagram which is too big, or if the DF bit is set in
that datagram, then it MUST execute the following
algorithm:

1. Strip off the label stack entries to obtain the IP
datagram.

2. Let N be the number of bytes in the label stack
(i.e, 4 times the number of label stack entries).

3. If the IP datagram does NOT have the "Don't
Fragment" bit set in its IP header:
------------------

My question is, if the DF set, How can we fragment the
packet?

thanks
neeraja



         

__________________________________________________
Do You Yahoo!?
Check out Yahoo! Shopping and Yahoo! Auctions for all of
your unique holiday gifts! Buy at http://shopping.yahoo.com
or bid at http://auctions.yahoo.com