[Lsr] Benjamin Kaduk's Discuss on draft-ietf-lsr-isis-rfc5306bis-07: (with DISCUSS and COMMENT)
Benjamin Kaduk via Datatracker <noreply@ietf.org> Thu, 19 September 2019 06:56 UTC
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Date: Wed, 18 Sep 2019 23:56:37 -0700
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Subject: [Lsr] Benjamin Kaduk's Discuss on draft-ietf-lsr-isis-rfc5306bis-07: (with DISCUSS and COMMENT)
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Benjamin Kaduk has entered the following ballot position for draft-ietf-lsr-isis-rfc5306bis-07: Discuss When responding, please keep the subject line intact and reply to all email addresses included in the To and CC lines. (Feel free to cut this introductory paragraph, however.) Please refer to https://www.ietf.org/iesg/statement/discuss-criteria.html for more information about IESG DISCUSS and COMMENT positions. The document, along with other ballot positions, can be found here: https://datatracker.ietf.org/doc/draft-ietf-lsr-isis-rfc5306bis/ ---------------------------------------------------------------------- DISCUSS: ---------------------------------------------------------------------- Section 3.2 notes that "the presence of [the Restart] TLV indicates that the sender supports the functionality defined in this document". But, while that was true for RFC 5306, I don't see how it can be true for the extended functionality that's new in this document. It seems on first look that the need for a PR to be acknowledged by a PA means that the routers in question will be able to properly determine full feature support at runtime, in which case this is essentially an editorial issue, but I would like to make sure it's received enough thought, so am raising it as a Discuss point to get the needed discussion. (We will still need to change this text to reflect reality, though.) It's also unclear to me if we need to give more description of the behavior when a router planning to restart does not receive (all) the necessary PAs -- does it cancel the planned restart? Fall back to the regular RR usage? It looks like there's an internal inconsistency between Section 3.2 ("[w]hen transmitting a TLV multiple flags MUST NOT be set.") and Section 3.3.2 ("the IIH is retransmitted with both RR and SA bits set"). ---------------------------------------------------------------------- COMMENT: ---------------------------------------------------------------------- Abstract Four paragraphs is perhaps pushing it a bit, for RFC style. It might also be nice to avoid starting two sentences with "This document additionally describes", e.g., as Barry suggests. It also seems a little mismatched to me to differentiate between "restart while maintaining forwarding plane state" and "restarting", since in Section 2 we make the convention that "restarting" means that forwarding state is maintained definitionally. Section 1 In the case of a restarting router process, the first of these is highly undesirable, but the second is essential in order to ensure synchronization of the LSP database. Is the convention introduced in section 2 about preserving forarding state intended to apply here? Section 3.2.3 Neighbors of the router which has signaled planned restart SHOULD maintain the adjacency in a planned restart state until it receives an IIH with the RR bit set, receives an IIH with both PR and RR bits clear, or the adjacency holding time expires - whichever occurs first. When might a router want to ignore the SHOULD (and how so)? c. on a Point-to-Point circuit, transmission of LSPs, CSNPs, and PSNPs MAY be suppressed. It is expected that the PDUs will not be received. Are there any security considerations here (e.g., a spoofed PR flag would cause suppression of updates and potentially DoS)? Section 4.1 I'm a little surprised to see "RX PA" under the "Running Router" table, since I thought the "running" categorization was supposed to imply that it was not going to restart (which would be a "restarting router"). If the categorizations are exclusive, then receiving PA would be an error condition. Section 6 I think we should go a bit further about the false-IIH with PR bit set, since there is not a protocol mechanism to apply any sanity check to the hold time that the recipient is obligated to apply (overriding local policy). Such spoofed values could be unreasonably large, and it may be prudent to have a policy filter that rejects implausible values. Even if such a policy is present, it seems that a series of spoofed IIHs with PR set could force an adjacency to be maintained (absent topology changes), by cancelling the PR-bit and then sending a new PR-bit in quick succession. Relatedly, Section 3.2.1's description of the RR/RA bits notes that: "This procedure allows the restarting router to cause the neighbor to maintain the adjacency long enough for restart to successfully complete, while also preventing repetitive restarts from maintaining an adjacency indefinitely." It doesn't seem that this property (preventing repetitive restarts from maintaining an adjacency indefinitely) still holds for PR/PA with a neighbor router that is (mis)behaving in a certain way. Explicitly noting this disparity seems reasonable to me.
- [Lsr] Benjamin Kaduk's Discuss on draft-ietf-lsr-… Benjamin Kaduk via Datatracker
- Re: [Lsr] Benjamin Kaduk's Discuss on draft-ietf-… Les Ginsberg (ginsberg)
- Re: [Lsr] Benjamin Kaduk's Discuss on draft-ietf-… Benjamin Kaduk
- Re: [Lsr] Benjamin Kaduk's Discuss on draft-ietf-… Les Ginsberg (ginsberg)
- Re: [Lsr] Benjamin Kaduk's Discuss on draft-ietf-… Benjamin Kaduk