[Bier] Rtgdir last call review of draft-ietf-bier-te-arch-10
Yingzhen Qu via Datatracker <firstname.lastname@example.org> Sat, 21 August 2021 05:29 UTC
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Reviewer: Yingzhen Qu Review result: Has Nits I have been selected as the Routing Directorate reviewer for this draft. The Routing Directorate seeks to review all routing or routing-related drafts as they pass through IETF last call and IESG review, and sometimes on special request. The purpose of the review is to provide assistance to the Routing ADs. For more information about the Routing Directorate, please see http://trac.tools.ietf.org/area/rtg/trac/wiki/RtgDir <http://trac.tools.ietf.org/area/rtg/trac/wiki/RtgDir> Although these comments are primarily for the use of the Routing ADs, it would be helpful if you could consider them along with any other IETF Last Call comments that you receive, and strive to resolve them through discussion or by updating the draft. Document: draft-ietf-bier-te-arch-10 Reviewer: Yingzhen Qu Review Date: Aug 20th, 2021 Intended Status: Standards Track Summary: This document has some issues/nits that should be at least considered prior to publication. Comments: Typically when BIER-TE controller calculates BitStrings, the result “overlay” topology has to be trees, no circles. Then ring topology becomes a special case. This should be explained/stressed. Comments inline: [Line numbers from idnits] >From IDNITS: == The document seems to lack the recommended RFC 2119 boilerplate, even if it appears to use RFC 2119 keywords -- however, there's a paragraph with a matching beginning. Boilerplate error? RFC 8174, paragraph 11: The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here. ... text found in draft: The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119], [RFC8174] when, and only when, .....................................^ they appear in all capitals, as shown here. The extra “,” should be removed. 142 BIER-TE introduces a new semantic for bit positions (BP) that 143 indicate adjacencies, as opposed to BIER in which BPs indicate Bit- 144 Forwarding Egress Routers (BFER). With BIER-TE, the BIFT of each BFR 145 is only populated with BP that are adjacent to the BFR in the BIER-TE 146 Topology. Other BPs are empty in the BIFT. The BFR replicate and 147 forwards BIER packets to adjacent BPs that are set in the packet. 148 BPs are normally also cleared upon forwarding to avoid duplicates and 149 loops. This is detailed further below. [nits]: BIFT, BFR should be expanded the first time in this document. [nits]: detailed further below, may reference a section number. 359 BIER-TE is designed so that is forwarding plane is a simple extension [nits]: s/so that is/so that its 376 3. The supportable encapsulations, [RFC8296] or other (future) 377 encapsulations. [minor]: I don’t think you can say it works with “future” encapsulations. 388 1. In BIER, bits in the BitString of a BIER packet header 389 indicate a BFER and bits in the BIFT indicate the BIER 390 control plane calculated next-hop toward that BFER. In BIER- 391 TE, bits in the BitString of a BIER packet header indicate an 392 adjacency in the BIER-TE topology, and only the BFRs that are 393 upstream of this adjacency have this bit populated with the 394 adjacency in their BIFT. [nits]: The English language in this paragraph needs to be improved, especially whether it’s singular or plural. For example, bits in the BitString of a BIER packet header indicate BFERs. 430 4. BIER-TE forwarding does not use the BFR-id field of the BIER 431 packet header. [minor]: what’s BFR-id field? Do you mean BFIR-id? 443 2. BIER-TE deployments will have to assign BFR-ids to BFR and 444 insert them into the BFR-id field of BIER packet headers as [minor]: the BFR-id field? 512 1. During initial provisioning of the network and/or during 513 modifications of its topology and/or services: protocols and/or 514 procedures to establish BIER-TE BIFTs: [nits]: two “:” in a row. 523 BIER-TE headers on BFIR. Alternatively, bfir-id in BIER [nits]: s/bfir-id/BFIR-id as in RFC8296. 527 4. Install/update the BIFTs into the BFRs and optionally BFR-id 528 into BFIR. [minor]: “optionally BFR-id into BFIR” duplicates with point 3 above. 530 2. During operations of the network: Protocols and/or procedures to 531 support creation/change/removal of overlay flows on BFIR: [nits]: two “:” in a row. 553 BFR in step 1, such YANG/Netconf/RestConf. [nits]: s/ Netconf/Restconf /NETCONF/RESTCONF, also you may consider adding informative references YANG (RFC7950), NETCONF [RFC6241] and RESTCONF [RFC8040] 578 extending a Link-State-Protocol (LSP) based IGP into the BIER-TE [minor]: I’d suggest remove “LSP” abbreviation here. LSP means Link-State PDU in IS-IS. 600 models such as Netconf/RestConf/Yang/PCEP. Vendor-specific CLI on [nits]: s /Netconf/RestConf/Yang/ NETCONF/RESTCONF/YANG. They are used in multiple times in the draft, please fix all of them. 1016 AdjacentBits = Packet->BitString &= ~AdjacentBits[SI]; 1017 Packet->BitString &= AdjacentBits[SI]; [major]: I’m confused about these two lines of code. Can you please explain what it is trying to achieve? Packet->BitString got masked twice? 1047 4.5. Basic BIER-TE Forwarding Example 1049 [RFC Editor: remove this section.] [minor]: an example that matches the pseudocode would be helpful. Whether this example needs to be removed is up to the author. 1127 is in the BitString and this is an adjacency towards BFR3. BFIR2 1128 therefore clears p2 in the BitString and sends a copy towards BFR2. [major]: line 1128 should be “a copy towards BFR3” in case the example is kept. 1142 Further processing of the packet in BFR4, BFR5 and BFER2 accordingly. [major]: BFR4 sees BitStrings of p5, p10, p11 and p12, should it send the packet To BFER2 directly because of p10? I’m not sure whether p10 is adjacent to BFR4 in the figure 7. 1180 topologies with fewer bit positions (4.1, 4.3, 4.4, 4.5, 4.6, 4.7, 1181 4.8). [major]: the section numbers in “()” are not correct. 1209 A leaf BFERs is one where incoming BIER-TE packets never need to be [nits]: s/BFERs/BFER 1241 BFR1 1242 |p1 1243 LAN1-+-+---+-----+ 1244 p3| p4| p2| 1245 BFR3 BFR4 BFR7 1247 Figure 11: LAN Example [nits]: Please center this figure 1266 bit position on the hub's BIFT is set up with a list of 1267 forward_connected() adjacencies, one for each Spoke. [comments]: my understanding is that this optimization only works when the hub needs to forward a received packet to all spokes except the spoke sending the packet. Correct? 1326 5.1.7. Equal Cost MultiPath (ECMP) [minor]: How a hash function is chosen is up implementations. This section talks about “polarization” and how it can be avoided, personally I think it’s not relevant. 1475 segments: (1) BFR2 via link L1, (2) BFR2 via link L2, or (3) via 1476 BFR3. [nits]: I think it should be: (3) BFR3 L0. 1494 bit positions can be re-used across multiple BFR to minimize the [nits] s/bit/Bit, s/BFR/BFRs 1492 5.1.9. Reuse of bit positions (without DNC) [comments]: About the reuse of bit positions in this section, my understand is that this needs to be calculated carefully to meet condition (A) or (B). In case of new Multicast overflows added or topology changes, there are risks neither of these two condition holds any more, so the BP has to be reassigned hence BitStrings at BFIR and BIFTs.
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