Subject: Small comment on draft-ietf-6man-rpl-routing-header-02

From: Alexandru Petrescu <[email-masked]>
Date: Sun, 27 Mar 2011 19:58:50 +0200

Hello 6man,

I know this is late about the draft-ietf-6man-rpl-routing-header-02, but
allow me a small comment, thank you.

>> Third, to avoid some attacks that lead to the deprecation of RH0,
                                       led(?)

>> The Routing for Low Power and Lossy Networks (RPL) protocol can be
>> used in some deployments to store most, if not all, routes on one
>> (e.g. the Directed Acyclic Graph (DAG) root) or few routers and
>> forward the IPv6 datagram using a source routing technique to
>> avoid large routing tables on memory constrained routers.

If I understand correctly, the advice is to use a form of routing header
in order to avoid maintaining large routing tables in the routers.  But
I think that sometimes the routing table is larger if using routing
header; in these cases the rt table is smaller when using a prefixed dst
entry rather than a set of addresses (RH contents) per non-prefixed dst.

Besides, I believe the smallest routing tables are realized when only a
default route is used.  Or, this is already the case with RPL, i.e. a
leaf router only sends packest "up" to "parent" until it reaches the
Border Router.

This border router seems to be a very capable device, memory-rich, thus
not needing to reduce its tables.  Fortunately, this seems to
accommodate the use of Routing Headers, because it can accommodate
larger routing tables.

For the nodes which are memory-constrained, it is better to use default
routes if need to reduce the storage requirements, rather than RH.  In
some cases.

If you are comparing host-based routes vs prefixed routes - then yes:
using host-based routes implies there's going to be more entries in the
routing tables, hence larger.

In order to use prefix-based routes instead of host-based routes it is
sufficient to have a link layer having link multicast capabilities.
802.15.4 is one of them, when reading the spec.

Just some thought,

Alex