Hi Santanu,
On 3/25/15 14:08 , Santanu Kar wrote:
Hi Authors
The Section 2, doesn't provide any clarification on the 'Instance' part
of the Link ID of
OSPFv2 Extended Prefix Opaque LSA.
Instance is an arbitrary number to make each OSPFv2 Extended Prefix
Opaque LSA's LSID unique, please see RFC5250, section abut Opaque-ID.
There can be two possible implementations
1) When a Segment routing enabled router is advertising multiple Ext
Prefix TLV, it can keep repacking it into a single Ext Prefix LSA, as
has been mentioned in end of section 2 and keep increasing the instance
. The lowest instance is taken. Higher instance from same router for
same prefix is ignored.
above only applies to the case where OSPFv2 Extended Prefix TLV is
advertised for the _same_ prefix in multiple different OSPFv2 Extended
Prefix Opaque LSAs, which is either an error or temporary condition.
2) Another possible way is, not to go for this repacking. Instead it
should be possible to originate separate Ext Prefix LSAs for every Ext
Prefix TLV, and only one TLV per LSA. The instance number or Opaque id
can be derived from the prefix/interface so as to ensure its unique for
every prefix originating from the same advertising router.
yes above is correct, but the draft allows to pack multiple Ext
Prefix TLVs in the single Extended Prefix Opaquer LSA if the
implementation prefers to do so.
The draft is not clear on whether (2) can be allowed. It hasn't
the draft says:
Multiple OSPF Extended Prefix TLVs MAY be advertised in each OSPFv2
Extended Prefix Opaque LSA."
That means it can be one or more.
mentioned that the instance is topology independent and dependent on how
we choose to implement it. The TE RFC however has a section devoted to this
https://tools.ietf.org/html/rfc3630#section-2.2
I can add a similar text to draft-ietf-ospf-prefix-link-attr.
thanks,
Peter
Please give your thoughts on this.
Regards
Santanu
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