Hi Rajesh,

The prefix reachability is always signalled via the OSPFv2 Type 3/5/7 LSAs - 
this is required for Algo 0 and 1 but also for Flex Algo for basic 
reachability. These LSAs carry/include the IGP metric in them. The OSPFv2 
Extended Prefix TLV is used to carry the Prefix SIDs - both algo 0 and Flex 
Algos. The FAPM in the OSPFv2 Extended Prefix TLV enables the prefix metric 
specific to the FA to be also signalled with using FAD with M flag.

I am not sure if I understood your question correctly and if not please 
elaborate.

Thanks,
Ketan

From: Rajesh M <mraj...@juniper.net>
Sent: 07 August 2020 09:34
To: Peter Psenak (ppsenak) <ppse...@cisco.com>; Shraddha Hegde 
<shrad...@juniper.net>; Clarence Filsfils (cfilsfil) <cfils...@cisco.com>; 
Ketan Talaulikar (ketant) <ket...@cisco.com>; Gulko, Arkadiy (Refinitiv) 
<arkadiy.gu...@refinitiv.com>
Cc: SPRING WG <spring@ietf.org>
Subject: https://tools.ietf.org/html/draft-ietf-lsr-flex-algo-08 (OSPFv2 flex 
algo)


Note : Discussion is not about FAPM.

For flex algorithm (example take it as 128) OSPF Prefix (For summary/external 
prefixes),  how to get the prefix cost ? there is no prefix cost field in 
OSPFv2 Extended Prefix TLV.
Currently only way I can see is prefix needs to be advertised in flex algo 
zero(as summary or external prefixes in legacy ospf) as well as in flex algo 
128 (OSPFv2 Extended Prefix TLV)

Thanks
Rajesh




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