Hi Tom, thank you for your feedback and the suggestion. In proposing the use of 20 bits-long SID we've followed the existing IGP-SR extensions. Both draft-ietf-ospf-segment-routing-extensions and draft-ietf-isis-segment-routing-extensions advertisement of 4 octets-long SIDs as well as 20 bits-long (the latter as 20 rightmost bits in 3 octets-long field). Though the proposal to using 20 bits-long SIDs in IPv6 SR EH may be considered as duplication of the draft-ietf-mpls-sr-over-ip, SR EH has very useful property, for example in OAM, of preserving the SR path. I think that we can expand the length of the field in SR EH to support 16 and 64 bits-long SIDs in addition to ones being proposed in the draft. Much appreciate your comments.
Regards, Greg On Sat, Apr 20, 2019 at 12:50 PM Tom Herbert <[email protected]> wrote: > > > On Fri, Apr 19, 2019, 5:54 PM Greg Mirsky <[email protected]> wrote: > >> Hi Tom, >> in draft-mirsky-6man-unified-id-sr >> <https://tools.ietf.org/html/draft-mirsky-6man-unified-id-sr-02> we've >> proposed the use of 20 and 32 bits-long SIDs in SR EH. Two bits-long field >> also defined in the Flags to identify the length of SID element in the SR >> EH: >> 0b00 - 128-bits SID; >> 0b01 - 20-bits SID; >> 0b10 - 32-bits SID >> 0b11 - reserved for future use. >> > > Hi Greg, > > 20 bit fields in a list seems a little odd; how is this packed in a > packet? It's more typical to have byte alignment at least and if the fields > hold numerical values they would usually be bytes, words, double words, > etc. with natural alignment maintained. In a two bit representation of > length, I think best possibilities are 16, 32, 64, and 128 bits. > > Tom > > >> Much appreciate your comments on that draft, suggestions. >> >> Regards, >> Greg >> >> >> On Fri, Apr 12, 2019 at 3:09 PM Tom Herbert <[email protected]> wrote: >> >>> On Fri, Apr 12, 2019 at 1:48 PM Mark Smith <[email protected]> >>> wrote: >>> > >>> > Hi Tom, >>> > >>> > On Sat, 13 Apr 2019 at 00:26, Tom Herbert <[email protected]> wrote: >>> > > >>> > > On Sun, Mar 31, 2019 at 7:40 AM Robert Raszuk <[email protected]> >>> wrote: >>> > > > >>> > > > Hi Mark, >>> > > > >>> > > > > As MPLS SR SIDs are 20 bits, then rounding up to an octet >>> boundary and a 32 bit alignment, >>> > > > > I'd think 32 bit SIDs would be adequate to perform SR in an IPv6 >>> network. >>> > > > > >>> > > > > As 32 bit SIDs are also the same size as IPv4 addresses, that >>> may also create some opportunities to >>> > > > > leverage IPv4 support in existing protocols to suite carrying >>> and processing 32 bit SIDs with some, possibly >>> > > > > slight, modification. For example, perhaps IPv4 Address Family >>> support in OSPFv3 (RFC 5838) could be >>> > > > > somehow leveraged to suit SR. >>> > > > >>> > > > >>> > > > Thank you for describing your understanding of fundamentals of SR. >>> > > > >>> > > > I think SR while indeed started with the story of "less control >>> plane is good for you" now clearly has evolved into not only reduction of >>> control plane but what can be even more important to some users ability to >>> request specific behavior via programmed functions of network elements on a >>> per flow basis without actually per flow or per path signalling or state. >>> > > > >>> > > > Yes for some it may be very useful feature and I am sure some will >>> call it overload of data plane or . There is no one size fits all. >>> > > > >>> > > > With that let's observe that till today SR did not require any new >>> mapping plane to be distributed in control plane and to be inserted into >>> data plane. This is clearly a precedent. >>> > > > >>> > > > Furthermore as we see in companion documents all additional >>> network functionality is being taken away from SRH and is being shifted to >>> Destination Options . >>> > > > >>> > > > As far as mapping plane I already pointed out in my Vector Routing >>> proposal that we have one already it is called BGP. One needs to also >>> observe that we as industry worked number of years of protocol suite called >>> LISP allowing not only very good mapping plane, but also data plane >>> integration. CC-ing lisp authors for their comments. Note also work for >>> integrating SRv6 with LISP which is already is published. >>> > > > >>> > > > Since you correctly observed that now SID can be 32 bit and that >>> is similar to the size of IPv4 my fundamental question is why not use >>> something which already exists instead of defining some sort of new from >>> scratch ? >>> > > > >>> > > Robert, >>> > > >>> > > I don't see in the SRH draft where 32 bit SIDs are defined. Can you >>> > > please provide a reference? >>> > > >>> > >>> > To clarify, I've been thinking about the idea of a smaller SID size >>> > for IPv6 for a while now (since inserting EHs came up), and thought >>> > about what would be a generic single size that might suit SR that >>> > wasn't the same size as an IPv6 address. 32 bits seemed suitable to >>> > me, although if people wanted bigger, I'd be suggesting 64 bits (not >>> > entirely coincidentally the common IID size.) >>> > >>> > Ron and others have written this draft, which supports SIDS of various >>> > sizes - 8, 16 or 32 bits - that triggered this discussion. >>> > >>> Mark, >>> >>> Why not just put a SID length field in the header (like RFC6554 but >>> more generic). That would allow lengths of 1-16 bytes. Additional >>> flags could be used to indicate the semantics of the entries. For >>> instance, they might be actual addresses (128 bits for IPv6, 32 bits >>> for IPv4), parts of addresses (prefixes of suffixes like in RFC6554) >>> where the rest of the address can be inferred, indices into a table, >>> labels, etc. >>> >>> Tom >>> >>> > "The IPv6 Compressed Routing Header (CRH)" >>> > https://tools.ietf.org/html/draft-bonica-6man-comp-rtg-hdr-03 >>> > >>> > Regards, >>> > Mark. >>> > >>> > >>> > > As for trying to use something that already exists, why does SR used >>> a >>> > > fixed size format for SIDs instead of a variable length format like >>> > > that described in RFC6554? Similarly, why does SR define it's own TLV >>> > > format instead of using Hop-by-Hop and Destination Options defined in >>> > > RFC8200? >>> > > >>> > > Tom >>> > > >>> > > > It will be perfectly fine to have full proper SRv6 with SRH and >>> LISP or Vector Routing as an alternative options. I really do not see a >>> room or need for yet one more mapping plane. What problem does it solve >>> which would not be already solved elsewhere ? >>> > > > >>> > > > Kind regards, >>> > > > Robert >>> > > > >>> > > > >>> > > >>> 2) Is there an agreement that solutions which require additional >>> per SR path state in both control plane and now in data plane are really >>> something we should be endorsing here ? >>> > > >> >>> > > >> >>> > > >> I think so. >>> > > >> >>> > > >> My understanding of what SR is fundamentally about is to reduce >>> control plane state and processing. The trade-off for reduced control plane >>> state and processing is to instead carry and encode most or all of that >>> information or its semantics as per-packet overhead. >>> > > >> >>> > > >> If the per-packet overhead becomes too large and expensive, then >>> pushing some of that information and processing back into the control plane >>> should be ok, as long as there is still a beneficial overall reduction in >>> control plane state and processing. >>> > > >> >>> > > >> As MPLS SR SIDs are 20 bits, then rounding up to an octet >>> boundary and a 32 bit alignment, I'd think 32 bit SIDs would be adequate to >>> perform SR in an IPv6 network. >>> > > >> >>> > > >> As 32 bit SIDs are also the same size as IPv4 addresses, that may >>> also create some opportunities to leverage IPv4 support in existing >>> protocols to suite carrying and processing 32 bit SIDs with some, possibly >>> slight, modification. For example, perhaps IPv4 Address Family support in >>> OSPFv3 (RFC 5838) could be somehow leveraged to suit SR. >>> > > >> >>> > > >> Regards, >>> > > >> Mark. >>> > > > >>> > > > >>> -------------------------------------------------------------------- >>> > > > IETF IPv6 working group mailing list >>> > > > [email protected] >>> > > > Administrative Requests: >>> https://www.ietf.org/mailman/listinfo/ipv6 >>> > > > >>> -------------------------------------------------------------------- >>> >>> _______________________________________________ >>> spring mailing list >>> [email protected] >>> https://www.ietf.org/mailman/listinfo/spring >>> >>
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