Speaking as an individual participant, as I understand it the
consideration is one of space vs state tradeoff. In the extreme, using
a binding MPLS SID at every hop is essentially classical MPLS, and needs
a means to create state in every node along the path to know how it
processes the binding SID (and communicate that to those will will use
the binding SID.) Conversely, pure SR withotu binding SID only requires
local state about local identities. But requires space in the packets
roughly corresponding to the abount of path control one is using.
(Flex-algo allows some alternatives in the trade space for some classes
of problems.)
Yours,
Joel
On 2/6/2024 12:15 AM, Gyan Mishra wrote:
Dear Spring WG
I have a ? related to the bottom of section 5 about how BSID label can
be used for compression of the label stack.
My understanding of BSID AFAIK is that the BSID can be static value or
auto generated value by the SR source node and is used to bind the
candidate path to the forwarding plane at which time the BSID is
popped off the label stack and the segment list specified by the BSID
is pushed onto the packet or SRV6 SRH or uSID carrier.
I am not aware that BSID can be used as a topological sid and is just
locally significant however the advertised with the VPN overlay BGP
prefix as informational only is my understanding.
If that is true I guess since the BSID contains the entire instruction
set for steering why not always use the BSID label and not the typical
prefix sid and adj sid label when steering. That would cut way down
on MSD down to a single label.
“In the SPRING architecture, Node SIDs or Binding SIDs can be used to
reduce the label stack size. As an example, to steer the traffic on
the same path as before, PE1 could use the following label stack:
<Node_P9, Node_P5, Binding_P5, Node_PE2>. In this example, we consider
a combination of Node SIDs and a Binding SID advertised by P5 that
will stitch the traffic along the path P10 -> P11 -> P12 -> P13. The
instruction associated with the Binding SID at P5 is thus to swap
Binding_P5 to Adj_P12-P13 and then push <Adj_P11-P12, Node_P11>. P5
acts as a stitching node that pushes additional labels on an existing
label stack; P5's MSD needs also to be taken into account and may
limit the number of labels that can be imposed.”
Question about adjacency set sid ?
7.2.2.2.<https://datatracker.ietf.org/doc/html/rfc8662#section-7.2.2.2>Adjacency-Set
SID
<https://datatracker.ietf.org/doc/html/rfc8662#name-adjacency-set-sid>
An adjacency-set is an Adj-SID that refers to a set of adjacencies.
When an adjacency-set segment is used within a label stack, an
implementation can deduce that load-balancing is expected at the node
that advertised this adjacency segment. An implementationMAYfavor the
insertion of an ELI/EL after the Adj-SID representing an
adjacency-set.¶
<https://datatracker.ietf.org/doc/html/rfc8662#section-7.2.2.2-1>
I don’t see any other SR document that talks about adjacency set sid.
Is this set sid part of the base SR architecture and as well is
another topological sid I don’t see defined anywhere?
Thank you
<http://www.verizon.com/>
*Gyan Mishra*
/Network Solutions A//rchitect /
/Email gyan.s.mis...@verizon.com//
/
/M 301 502-1347
/
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