Abhijit,
In section 4.3:
A link may cease participating in the default topology if
DefaultExclusionCapability is set to enabled. In this state, a
router will only form adjacency with routers that set the MT-bit in
their Hello packets. This will ensure that all routers have
DefaultExclusionCapability enabled before the default topology can be
disabled on a link.
thanks,
Peter
Abhijit Chaudhary wrote:
I have a question Regarding Section 5 of OSPF-MT
< RFC SNIPPET>
5. Interoperability between MT-Capable and Non-MT-Capable Routers
The default metric field is mandatory in all LSAs (even when the
metric value is 0). Even when a link or prefix does not exist in the
default topology, a non-MT router will consider the zero value in the
metric field as a valid metric and consider the link or prefix as
part of the default topology.
In order to prevent the above problem, an MT-capable router will
include all links as part of the default topology. If links need to
be removed from the default topology, an MT-capable router must be
configured in DefaultExclusionCapability mode. In this mode, routers
will ensure that all other routers in the area are in the
DefaultExclusionCapability mode before considering the MT-ID#0 metric
in the SPF calculation. Only then can the TOS 0 metric field in
Router-LSAs be safely ignored during the default topology SPF
computation.
</RFC SNIPPET>
Now, how does an MT-capable router automatically ensure that all other
routers in the same area are also in DefaultExclusionCapability mode?
If I understand correctly, one solution can be for the calculating
router to ensure that the router-LSAs from all other routers in the area
have the MT Option set. But then, it is not mandatory that router-LSAs
MUST have MT-bit set.
Is there any other solution?
Thanks,
- Abhijit
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