Hi authors, all
As an individual contributor, please find below some feedback to trigger
discussion on the Preference Algorithm defined in ยง3.2.4.
> 1. Smaller range wins
Looks ok to me, as this gives preference to Prefix-SID advertisement from SR
routers which speaks for themselves/their own loopback/their own IP prefix
advertisement; rather than SRMS advertisement which speaker for others. IOW, to
know Brian's SID, I'd rather believe Brian himself rather than George.
Also, this gives preference to SR nodes rather than LDP nodes (SRMS entries).
Over the time/SR deployment, as more nodes gets SR, the number of nodes
negatively impacted by the wrong configuration change is reduced.
Alternatively, I'd be fine to prefer Prefix-SID advertisement over SRMS
advertisement. Actually, I'd propose to add this as rule 0. "0. Prefer
Prefix-SID Sub-TLV over SID/Label Binding TLV"
I've been told OSPF can't make the distinction, but I'm not sure to see the
issue.
> 4. Smaller prefix length wins
I'd rather have longer prefix length wins, and move this higher in position 3
(*). Indeed, we usually primarily care to reach a specific egress node i.e.
loopbacks destinations, which have the longest possible prefix length.
(*) It needs to be after IPv6 wins, to not conflict with it, as IPv6 have
longer prefixes.
> 3. Smaller algorithm wins
> 5. Smaller starting address (considered as an unsigned integer
value) wins
I'm fine with this order, to privilege prefix diversity (typically for algo 0
or 1) rather than algo diversity. (on the basis that to reach a node N, we need
a SID for this node, while to follow algo N, we can use a combinations of
segments from other algo).
So in summary, I'd propose discussing the following
OLD:
1. Smaller range wins
2. IPv6 entry wins over IPv4 entry
3. Smaller algorithm wins
4. Smaller prefix length wins
5. Smaller starting address (considered as an unsigned integer value) wins
6. Smaller starting SID wins
NEW:
0. Prefix-SID Sub-TLV wins over SID/Label Binding TLV
1. Smaller range wins
2. IPv6 entry wins over IPv4 entry
3. Longer prefix length wins
4. Smaller algorithm wins
5. Smaller starting address (considered as an unsigned integer value) wins
6. Smaller starting SID wins
Thanks,
Regards,
-- Bruno
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