Hi,
a few notes on current revision of ELSA draft (starting from
editorialgoing to more important).
Cosmetic notes:
6. OSPFv3 E-Inter-Area-Prefix-LSA
...
All LSA Header fields are the same as defined for the Network-LSA.
Should be IAP LSA.
Lindem, et al. Expires March 14, 2014 [Page 20]
Internet-Draft OSPFv3 LSA Extendibility September 2013
families as defined in [OSPFV3-AF]. The IPv6 Link-Local Address TLV
is only applicable to the E-Link-LSA. Inclusion in other Extended
LSAs MUST be ignored. Only a single instance of the IPv6 Link-Local
Address family SHOULD be included in the E-Link-LSA. Instances
preceding the first MUST be ignored.
It is probably meant to be "instances following the first ..."
Page 21:
Address family SHOULD be included in the E-Link-LSA. Instances
preceding the first MUST be ignored. For IPv6 address families as
defined in [OSPFV3-AF].
Incomplete sentence.
For simplicity and to avoid the scaling impact of maintaining both
TLV and non-TLV based versions of the same LSA within a routing
domain, the basic backward compatibility mode will not allow mixing
of LSA formats. Different formats could still be supported with
multiple OSPFv3 instances and separate OSPFv3 routing domains.
"Basic compatibility mode" is confusing name for a mode when instance
enabled with new functionality will not even talk to instance not
enabled for (or not supporting) it.
Notes to functionality:
Tag field in E-ASE-LSAs is made optional.
Subject of propagating tags together with Intra- and Inter- area routes
was raised more than once. It is very likely that sooner or later tag
sub-TLVs will be proposed for Intra- and Inter- Area E-LSA. In this case
implementations will have to deal with optional tag field in E-ASE LSA
and tag sub-TLV in Intra-/Inter- Prefix TLV. This is inconvenient. It is
better to avoid optional field in E-ASE-LSA and define tag sub-TLV for
External-Prefix TLV from the beginning.
In order to retain compatibility and semantics with the current
OSPFv3 specification, each LSA MUST contain a single Inter-Area
Prefix TLV. This will facilitate migration and avoid changes to
functions such as incremental SPF computation.
I appreciate ease of migration. OTOH, for better or worse but
E-Intra-Area-Prefix LSA can propagate multiple prefixes in single LSA.
So well-developed implementation will have to be able to work with an
LSA advertising multiple prefixes. It is a pity to restrict once and
forever Inter- and Ex- Prefix TLVs if Intra- does not have such limitation.
To give implementations possibility of future optimizations
(advertising multiple prefixes in single LSA) and still keep advantage
of faster standardization and deployment I propose:
- Allow Inter- and Ex- TLVs to be present more than once in respective LSAs
- Stipulate that routers running in any Migration mode MUST advertise
TLV only once per LSA.
Thanks,
Anton
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