RFC-2283 question

["Rijsman, Bruno" <[e-mail]>]

RFC-2283 contains the following paragraph (which was not present in
draft-ietf-idr-bgp4-multiprotocol-v2-03.txt) at the bottom of page 2: 

The [MP_REACH_NLRI] attribute contains ONE OR MORE triples <Address Family
Information, Next Hop Information, Network Layer Reachability Information>,
..."

The encoding of the MP_REACH_NLRI attribute contains fields for 
* length of the next hop network address, 
* the number of SNPAs
* the length of each SNPA
* the length of each prefix

However, the encoding of the MP_REACH_NLRI attribute does NOT contain a
field for the number of prefixes (i.e. the number of prefixes and hence the
total length of the NLRI field is implicit).

My question is: if the MP_REACH_NLRI contains MORE THAN ONE triple <Address
Family Information, Next Hop Information, Network Layer Reachability
Information>, how do I know where one triple ends and the next begins? In
other words, how can I find out what the number of prefixes is in a given
triple?

It seems to me that in the absence of a "number of prefixes" field, we can
only have ONE triple per MP_REACH_NLRI attribute and therefor only ONE type
of NLRI (i.e. address family) per UPDATE message (since dupplicate
attributes are not allowed). Either that or we must include a "number of
prefixes" field in the MP_REACH_NLRI attribute...

Bruno Rijsman
Unisphere Solutions