On Tue, Dec 10, 2019 at 12:18 PM Robert Raszuk <rob...@raszuk.net> wrote:
> Hi Erik, > > What you are proposing IMHO is not needed. > > Each SR node (Segment Endpoint) is effectively applying new IPv6 encap so > is already doing an insertion of new SRH while maintaining src address and > previous SRH content (modulo updating it). That is legally permitted > operation based on IPv6 tunneling RFC. > > The word insertion has been questioned in the context of adding SRH at non > SR midpoints (say for TI-LFA) into existing "private" IPv6 header. For this > sure one could think of more structure (bypass section) of original SRH > already present or addition of 2nd SRH. > If there were no resolution to the insertion question vis a vis RFC 8200, then would it then suffice to recommend that ingress nodes should include some padding for these non-SR midpoints to play with (iff. the network has such midpoints), and otherwise abide by RFC 8200? Thx > R. > > > > > > > On Tue, Dec 10, 2019 at 9:10 PM Erik Kline <ek.i...@gmail.com> wrote: > >> My apologies for raising something that might have already been discussed >> a rejected, but I'm finding it non-trivial to track this wide-ranging >> discussion across multiple mailing lists. >> >> Regardless of how SRv6 works now (using header insertion, as Darren said >> in Singapore), I'm wondering if it would suffice to say that the ingress >> encapsulation node could/should pad the SRH with an operationally >> determined amount of extra space to allow for header re-writing. >> >> This would effectively turn the SRH into a scratch space could be >> specified as able to be re-written by SR-aware nodes along the path. >> >> For example, if the ingress router new the SR domain's carefully curated >> path MTU, it could pad out the SRH to some fraction of that, a la: >> >> {segments_left=2, last_entry=5, [sr_rtr_3, sr_rtr_2, sr_rtr_1, ::0, >> ::0, ::0]} >> >> then permit intermediate SR routers to rewrite all of that scratch space >> for router insertion/deletion as needed. For example, if sr_rtr_1 needs to >> route around sr_rtr_2 via sr_rtr_4 and sr_rtr_5 it could rewrite this as: >> >> {segments_left=2, last_entry=5, [sr_rtr_3, sr_rtr_5, sr_rtr_4, >> sr_rtr_1, ::0, ::0]} >> >> If there's no scratch space left with which to fiddle then generate an >> ICMP error to the ingress router (ICMP source address selection aside). >> The rules for examining this header scratch space in the returned ICMP >> error might need to be suitably lax. >> >> I'm unsure of how this would interact with the HMAC bits, but overall, if >> this could work then perhaps we don't need to worry about insertion anymore. >> >> Yes, there's more overhead on each packet, but that should be tunable by >> the operator based on things like (1) operational path mtu in the SR >> domain, (2) operationally acceptable padding overhead, (3) expected space >> required for adding routers for re-routing or whatever... >> >> On Tue, Dec 10, 2019 at 11:45 AM Robert Raszuk <rob...@raszuk.net> wrote: >> >>> Brian, >>> >>> > Situation has changed since this email: the network programming draft >>>> has now removed text related to SRH insertion. >>>> > Please comment on the text if you see text related to SRH insertion. >>>> >>>> For example: >>>> >>>> https://tools.ietf.org/html/draft-ietf-spring-srv6-network-programming-05#section-8.2 >>>> >>>> Why would draft-voyer-6man-extension-header-insertion exists if the SRH >>>> proponents do not intend to perform SRH insertion? >>>> >>> >>> >>> What Bruno is describing is the new situation after removal of SRH >>> insertion at non SR midpoints from NP draft under last call... >>> >>> Section 8.2 is referring to SRH insertion at the SR encapsulation node >>> (for example ingress to the domain). >>> >>> draft-voyer-6man-extension-header-insertion is progressing as >>> recommended to relax the RFC8200 restricting EH insertion at any arbitrary >>> node - not necessarily segment endpoint. >>> >>> Regards, >>> R. >>> >>> >>> >>> >>> >>> >>> >>> -------------------------------------------------------------------- >>> IETF IPv6 working group mailing list >>> i...@ietf.org >>> Administrative Requests: https://www.ietf.org/mailman/listinfo/ipv6 >>> -------------------------------------------------------------------- >>> >> _______________________________________________ >> spring mailing list >> spring@ietf.org >> https://www.ietf.org/mailman/listinfo/spring >> >
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