Le 27/04/2011 01:39, Reddy, Joseph a écrit :
Hi Thomas
Since RPL protocol is intended to operate in networks with
constrained devices and lossy, low-bandwidth links, there is a
desire to not require IP-in-IP tunnelling that is usually used for
inserting routing headers.
Hm?
IP-in-IP tunnelling is not used to insert routing headers.
(do you mean that because of some perception tunnels are too big for
low-bandwidth links and hence Routing Headers should be used? In terms
of bytecount I think a Routing Header takes about the same number of
bytes than adding a Base Header (i.e. use IP-in-IP tunnelling).)
This is detailed in the draft
http://tools.ietf.org/html/draft-hui-6man-rpl-headers-00
The draft says:
However, where LLNs are severely constrained in resources, IP-in-IP
tunneling may not be the most favorable solution. Use of IP-in-IP
requires datagrams to carry two IPv6 headers, increasing header
overhead and associated communication and memory requirements.
Try to evaluate how much overhead is that: compare the size in bytes of
one (not two) Base Headers (40bytes) to the size of a Routing Header
containing one address (24bytes).
HEaders of an IP-in-IP packet vs RH packet are like this:
Base+IP-in-IP: 80bytes.
Base+RH: 64bytes.
-----------------------
16bytes difference, potentially saved by preferring RH.
Minimal MTU is 1280bytes. Saving 16byte is little worth the trouble.
Alex
but I realize now this draft expired recently. Perhaps this can be
revived as it is helps to improve the applicability of RPL protocol.
-Joseph
-----Original Message----- From: Thomas Narten
[mailto:nar...@us.ibm.com] Sent: Tuesday, April 26, 2011 5:57 AM To:
Reddy, Joseph Cc: Jonathan Hui; 'ipv6@ietf.org' Subject: Re: Comment
on rpl-routing-header draft
In the most common usage of this header, the border router inserts
a source routing header with the full set of intermediate nodes
before forwarding it towards the destination within the RPL
network.
and then.
Yes, we do not use IP-in-IP tunneling and instead simply insert
the RH head= er in the packet.
What specification are you following that says do this?
Routing headers (as designed and specified) are inserted by an
originating node (whether the original sender or a tunnel entry
point). If you have a middle node insert this header to an existing
packet, no suprise things are not going to work.
Thomas
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