> a)Advertise the “Area Prefix” in the Area Proxy TLV – much as we do a 
> router-id today in the Router-ID TLV.

This would make the Area Prefix mandatory for Area Proxy, which is not desired. 
 We would prefer it to remain optional and thus part of the Area SID sub-TLV.

> b)The remaining info (reachability and SID) can then be provided using 
> existing Prefix Reachability advertisements – no need for new sub-TLV for 
> “Area SID”. This eliminates any potential issues if the SID advertised by 
> “Area SID sub-TLV” were to differ from the SID advertised in Prefix 
> Reachability for the same prefix.

As we discussed privately, we view this as a non-issue.  The Area Leader is the 
one advertising both the Area SID sub-TLV and the Proxy LSP. If there’s a 
coding error, there’s a coding error. There is a single source of truth (the 
Area Leader’s config) and we cannot protect against every possible coding 
error.  Reconciling the prefix with a separate advertisement has a non-trivial 
chance of being broken too, and IMHO, much larger.

>  There then remains the question as to whether the “Area Prefix” is anycast 
> or unicast i.e., is it common to all IERs or is it unique to whomever gets 
> elected Area Leader?

Does it matter? We have no clear semantics for this prefix. A difference that 
makes no difference is no difference.


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