Hi Tom, I believe you are referring to section 4 of RFC8200 where it states:
"Extension headers (except for the Hop-by-Hop Options header) are not processed, inserted, or deleted by any node along a packet’s delivery path, until the packet reaches the node (or each of the set of nodes, in the case of multicast) identified in the Destination Address field of the IPv6 header." We copy SID[SL] in to DA as we pass through different segments along the path. EH manipulation is allowed as long as we do it at nodes identified by the DA (In SR case this node owns the SID[SL] of course). Am I missing anything? Arashmid -----Original Message----- From: dmm [mailto:dmm-boun...@ietf.org] On Behalf Of Tom Herbert Sent: 26 February 2018 15:24 To: Pablo Camarillo (pcamaril) <pcama...@cisco.com> Cc: satoru.matsush...@g.softbank.co.jp; cf(mailer list) <c...@cisco.com>; Miya Kohno (mkohno) <mko...@cisco.com>; dmm@ietf.org; Voyer, Daniel <daniel.vo...@bell.ca> Subject: Re: [DMM] SRv6 for Mobile User-Plane On Mon, Feb 26, 2018 at 12:05 PM, Pablo Camarillo (pcamaril) <pcama...@cisco.com> wrote: > Hello authors, DMM, > > > > I have reviewed your I-D on SRv6 for mobile user-plane and I would > like to make some proposals. I have already discussed and brainstormed > the details with some of the authors of the draft and they agree to > this changes, however I would like to get the WG feedback on it. > > > > Thank you, > > Pablo. > > > > I believe its straightforward to support IPv4 UE traffic by doing SRv6 > with T.Encaps behavior. Hence, I think this should be documented in the draft. > > The encapsulation behavior should be the default one, both for IPv4 > and IPv6 UE traffic. However, a specific provider is allowed to do SRH > insertion within a controlled domain > [draft-voyer-6man-extension-header-insertion-02] > for UE IPv6 traffic. Pablo, That draft received substantial pushback on 6man list. EH insertion is not allowed by RFC8200 and a host of points were raised why it shouldn't be allowed. The authors have not responded to this feedback yet. Also, IMO, the argument that it's okay to do this within a controlled domain is weak, such an argument could be used to pretty much justify anything one might do with protocols. Tom > > Also, in order to reduce overhead at the UPFs when using > encapsulation, I would replace the End.B6 function for a new End.MAP function. > > For example, if we consider the following topology: > > UE----gNB----UPF1----UPF2 > > > > Then the uplink packet flow for the basic mode would look like this: > > UE_out: (A, Z) > > gNB_out: (gNB, U1::1) (A, Z) -> T.Encaps <U1::1> > > UPF1_out: (gNB, U2::1) (A, Z) -> End.MAP > > UPF2_out: (A, Z) -> End.DT > > > > The End.MAP function is simply replacing the UPF1 SID for the UPF2 SID. > > > > Notice that using encapsulation, if you compare it with today > user-plane using IPv6/GTP, the result is that SRv6 is just adding 40B > of overhead (IPv6 header), while GTP over IPv6 is using 56B (IPv6, UDP, GTP). > > > > ======= > > > > With respect to the aggregation mode, aside from using the > encapsulation mode as described before, I would also like to add a > note on the I-D on the fact that we can support the aggregation mode > without changes in the N2 > interface: > > The current I-D for aggregation mode assumes that the gNB (uplink) has > knowledge of an SR policy that contains all the SIDs belonging to TE, > NFV and so on. Even though the I-D does not describe how the gNB is > retrieving this information, I would like to make a statement on the > fact that there are two alternatives: > > A. The N2 interface is modified in order to signal a SID list to the gNB. > > B. The N2 interface is not modified. In this case, we signal through > the N2 interface an SRv6 BindingSID, that the gNB is going to resolve > into a SID list via an SDN controller either using PCEP, reverse DNS lookup > or LISP. > > > > I’m aware that the I-D focuses on the user-plane, however I believe > it’s important to state this alternatives since it simplifies the > adoption and reduces impact in the existing mobile architectures > (without going into the details on the mechanisms for each one of the > alternatives of LISP, PCEP, reverse DNS-lookup). > > > > ======= > > > > On the other hand, the current I-D proposes a mechanism for stateless > interworking with legacy access networks that doesn’t support SRv6 > (SGW and/or eNB). This mechanism presented in the I-D is limited to > IPv4/GTP legacy networks. I would like to propose a mechanism to > support interworking with legacy gNBs that does not support SRv6 but do > support IPv6/GTP. > > The main benefit comes from the fact that we can leverage an SRv6 > BindingSID to have remote classification and steering of the UE > traffic over an SR policy [draft-filsfils-spring-segment-routing-policy]. > > > > In this scenario, I propose that we add the notion of an SR GW -as the > current stateless interworking node in the I-D-. This SR GW can be > either a software based platform -e.g. VPP- or any existing router > -the mechanism is simple and can be supported in existing HW-. This SR > GW receives through the control plane the SR policies and installs the > required Binding SIDs. > > > > Then, for any UE connecting to a gNB, the N2 interface is going to > signal an > IPv6 address and a TEID. However, the difference is that with this new > mechanism the IPv6 address that we are going to signal is going to be > an > SRv6 BindingSID instantiated at the SR GW. > > > > The overall workflow is the following: > > > > Uplink > > Note: S1, S2 represent service functions and C1 represents a node for > TE purposes > > UE sends its packet (A, Z) on a specific wireless bearer to its gNB > > gNB’s CP associates the session from the UE (A) with IPv6 address B > and TEID T (N2 interface unchanged) > > gNB_out: (gNB, B) (GTP: TEID T) (A, Z) ;; Interface N3 > is unchanged > > SR_GW_out: (SRGW, S1) (U2::1, C1; SL=2)(A, Z) ;; new End.GTP.UP > > S1_out: (SRGW, C1) (U2::1, C1; SL=1)(A, Z) > > C1_out: (SRGW, U2::1) (A, Z) ;; > assuming PSP > > UPF2_out: (A, Z) ;; > End.DT > > > > Downlink > > UPF2_in: (Z, A) > ;; UPF2 maps the flow with SID list <C1, S1, SRGW::TEID, gNB> > > UPF2_out: (U2::1, C1) (gNB, SRGW::TEID, S1, SL=3) (Z, A) ;; T.Encaps > > C1_out: (U2::1, S1) (gNB, SRGW::T, S1, SL=2) (Z, A) > > S1_out: (U2::1, SRGW::TEID) (gNB, SRGW::T, S1, SL=1) (Z, A) > > SR_GW: (SRGW, gNB)(GTP: TEID=T)(Z, A) ;; > End.GTP.DN > > gNB_out: (Z, A) > > > > The key points are: > > - gNB is unchanged and encaps into GTP (N3 interface is not modified). > gNB only needs to support IPv6 which is currently common in existing > deployments. > > - 5G Control-Plane (N2 interface) is unchanged: 1! IPv6 address (i.e. > a BSID at the SR GW) > > - SR GW removes GTP, finds SID list related to IPv6 DA (BSID), add SRH > with SID list > > - Same TE, NFV and scale properties as Aggregation mode > > - There is NO state for the downlink at the SR gateway > > - There is simple state in the uplink at the SR gateway (notice that > since we are leveraging the aggregation mode, we expect few SR > policies on this node. SR policies are shared across UEs) > > - As soon as the packet leaves the gNB (uplink), the traffic is SR-routed. > This simplifies considerably network slicing. > [draft-hegdeppsenak-isis-sr-flex-algo]. > > - Traffic is already classified and steered into an SR policy when it > arrives to the SR GW. > > > > Finally, I believe that this mechanism is so simple, that it would be > trivial to implement it in VPP > [https://wiki.fd.io/view/VPP/What_is_VPP%3F] > . Hence if the working group believes that this is interesting work > and we add it to the I-D, I will analyse how to implement it in this platform. > > > _______________________________________________ > dmm mailing list > dmm@ietf.org > https://www.ietf.org/mailman/listinfo/dmm > _______________________________________________ dmm mailing list dmm@ietf.org https://www.ietf.org/mailman/listinfo/dmm _______________________________________________ dmm mailing list dmm@ietf.org https://www.ietf.org/mailman/listinfo/dmm
