Re: [spring] Question about SRv6 Insert function
Alexandre Petrescu <alexandre.petrescu@gmail.com> Thu, 19 December 2019 13:33 UTC
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From: Alexandre Petrescu <alexandre.petrescu@gmail.com>
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Date: Thu, 19 Dec 2019 14:33:18 +0100
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Subject: Re: [spring] Question about SRv6 Insert function
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Le 19/12/2019 à 12:52, Pablo Camarillo (pcamaril) a écrit : > Hi Alex. > > Please see inline. > > Many thanks, > > Pablo. > > ------------------------------------------------------------------------ > > > *From:*Alexandre Petrescu <alexandre.petrescu@gmail.com> *Sent:* > Monday, December 16, 2019 3:31 PM *To:* Pablo Camarillo (pcamaril) > <pcamaril@cisco.com>; ipv6@ietf.org <ipv6@ietf.org> *Subject:* Re: > [spring] Question about SRv6 Insert function > > Hi, SPRINGers, > > This is my first post to this list. > > This is about draft-ietf-spring-srv6-network-programming-06 more > precisely the T.Encaps section 5.2. > > Le 11/12/2019 à 21:05, Pablo Camarillo (pcamaril) a écrit : >> Alex, >> >> The precise definition T.Encaps is done in section 5.1 [5.2 now] of >> draft-ietf-spring-srv6-network-programming-06. If you have any >> comment on such definition please let me know -on a separate thread >> and directed to SPRING mailer-. > > Thank you for the reply. > > Please make the T.Encaps part of the draft easier for me to read, > e.g.: -expand what it means 'S01'; is it 'Step 01', like in BASIC > programming language? > > PC: Same format as in other documents (e.g. SRH). What is the other document SRH? > -clarify that the original packet in transit is not modified upon > transition (modulo the Hop Limit field and the Segments Left field if > present); new packet is created to carry the original packet - yes. > > PC: I have added a paragraph in the latest version of the draft to > capture your point. See rev07. Many thanks. I think you mean that you added this paragraph: > The T.Encaps received packet is encapsulated unmodified (with the > exception of the TTL or Hop Limit that is decremented as described in > [RFC2473]). I think it is good to say the packet is encapsulated unmodified. Indeed the Hop Limit is the sole exception. I think the TTL should not be mentioned. (side note: each IPv4 occurence should be dropped from everywhere in the document now :-) > -clarify what it means 'a packet (A, S2)(S3, S2, S1; SL=1)'; because > it is confusing in several ways; (A,S2) invites to think it is src > and dst addresses, but their place is switched (the normal order is > Source, Destination). S in 'S2' might mean a Source Address but > also might mean a Segment ID, or a Destination address. Confusion > should be avoided, at least in my mind. > > PC: This is explained in the terminology section of the draft (with > a detailed example). It is indeed in the terminology section. It clarifies many things to me. I am still left with the question: is a Segment Identifier an IPv6 address? (all the 128bits of it). I cant find an answer neither in this I-D neither in its reference RFC8402 "Segment Routing" terminology section. This is important to know, because in below the text says a destination address is an S1 (DA=S1) and it also says that S1 is part of a segment list. In a destination address field one cant have something else than an IPv6 address. But a segment identifier could be something else than an IPv6 address, if so it wanted. (somewhere else people talk about 'locator' being a 64bit value, I am not sure). About my initial worry - now T.Encaps cahnged its name into H.Encaps, right? It seems to not modify packets in transit, but to encapsulate them, which is ok. > Node N receives two packets P1=(A, B2) and P2=(A,B2)(B3, B2, B1; > SL=1). B2 is neither a local address nor SID of N. > > N steers the transit packets P1 and P2 into an SR Policy with a > Source Address T and a Segment list <S1, S2, S3>. > > The H.Encaps transit encapsulation behavior is defined as follows: > > S01. Push an IPv6 header with its own SRH (S3, S2, S1; SL=2) > S02. Set outer IPv6 SA = T and outer IPv6 DA = S1 > S03. Set outer payload length, traffic class and flow label > S04. Update the Next-Header value 'Update' or rather 'create'? I hope it is the next-header value of the outer IPv6 header; this is the first time to put something inside, so it is rather a creation. 'Updating' makes think that maybe the next header value of the inner (original) packet is updated from value x to y. Or? > S05. Decrement inner Hop Limit or TTL > S06. Submit the packet to the IPv6 module for transmission to S1 > > After the H.Encaps behavior, P1 and P2 respectively look like: > > - (T, S1) (S3, S2, S1; SL=2) (A, B2) > > - (T, S1) (S3, S2, S1; SL=2) (A, B2) (B3, B2, B1; SL=1) It looks ok - the P1 and P2 packets have not been modified in transit, but encapsulated. I wonder though about the 1 value for SL (SL=1) in P2 original and P2 transited. I wonder whether it should be decremented or not. I think it might complicated but I do not mind. Alex
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- Re: [spring] Question about SRv6 Insert function Pablo Camarillo (pcamaril)
- Re: [spring] Question about SRv6 Insert function Alexandre Petrescu
- Re: [spring] Question about SRv6 Insert function Alexandre Petrescu