You can use IGPs to
signal the MSD of a node or link to a centralized controller by:
Element Protocol (PCEP) SR extensions signal MSD in SR PCE capability TLV and
metric object. However, if PCEP is not supported/configured on the head-end of
a SR tunnel or a binding-SID anchor node and controller does not participate in
IGP routing, it has no way to learn the MSD of nodes. BGP-LS defines a way to
expose topology and associated attributes and capabilities of the nodes in that
topology to a centralized controller. Typically, BGP-LS is configured on a
small number of nodes that do not necessarily act as head-ends. In order for
BGP-LS to signal MSD for all the SR capable nodes in the network, MSD
capabilities should be advertised by every IGP router in the network.
Readable Label Depth
Capability (RLDC) is used by a head-end to insert Entropy Label (EL) at
appropriate depth, so it could be read by transit nodes. MSD in contrary
signals ability to push SID's stack of a particular depth.
MSD of type 1 (IANA
registry) is used to signal the number of SIDs a node is capable of imposing to
be used by a path computation element/controller. It is only relevant to the
part of the stack created as the result of the computation. MSD advertises the
total number of labels that a node is capable of imposing regardless of the
number of service labels.