Hi Sasha, Although I like your proposal for a reserved label, but if that is not agreeable then what is wrong with an LSP dedicated to PTP (call it PTP LSP)? Also why do you say that PTP FEC can't do FRR?
Thanks, Shahram From: [email protected] [mailto:[email protected]] On Behalf Of Alexander Vainshtein Sent: Monday, July 19, 2010 8:06 AM To: Tal Mizrahi Cc: [email protected] Subject: Re: [TICTOC] FW: 1588 over MPLS draft Tal, I think that we are in full agreement regarding a single-label GAL-only stack: It allows the LSRs to modify PTP packets (as TC must do), but it does not support forwarding (unicast and multicast). Hence it is useless. IMO GAL/G-ACH are a clear dead end in this discussion. If you have been following this list, I've suggested allocating a new reserved label which, at the top of the stack, would indicate PTP packets. IMHO this is the only method that would somehow accommodate TC (which is a layer violation, of course) without completely breaking MPLS data plane. However, this approach did not gain support on the list. "PTP FEC" IMO is also a dead end. E.g., you would not be able such popular recovery techniques as Facility FRR for this FEC, etc. At the same time, if TC support is not required, there is no need to invent any special encapsulation of PTP over MPLS. All the rest of the use cases can be easily accommodated with PTP/UDP/IP/MPLS without inventing new wheels. My 2c, Sasha From: Tal Mizrahi [mailto:[email protected]] Sent: Monday, July 19, 2010 5:55 PM To: Alexander Vainshtein Cc: [email protected] Subject: Re: [TICTOC] FW: 1588 over MPLS draft Hi Sasha, all, A couple of comments: 1. Generally, regarding using GAL+ACH: according to RFC 5586: "LSRs MUST NOT modify the G-ACh message, the ACH or the GAL towards the targeted destination". However, a PTP capable LSR that functions as a TC must modify the packet (including the correctionField and the UDP checksum). This means that if an LSR functions as a TC, either (a) the functionality in RFC 5586 must be enhanced to allow modification, or (b) the LSR terminates all incoming PTP messages, and then re-generates them, which may burden the control plane. 2. Sasha, regarding your option 1 below: if each packet has a label stack with 1 label (GAL), it raises the question how to distinguish between single-target and multi-target PTP packets. PTP calls for both multicast frames (e.g.), and unicast (e.g. Delay_Req). That's not to say I am against using the GAL, but it needs some further refinement. Tal. -----Original Message----- Yaakov and all, Please note that GAL and, by implication, the ACH header are only looked at by an LSTR if GAL happens to be the top label in the stack (either because it has been the top label in originally received packet, or because all the labels above it have been popped by this LSR). This leaves two options IMO: 1. You carry PTP directly across physical links using labeled packets that have a label stack of depth 1 containing GAL. In this case you can probably do want you want with the PTP packets' payload, (e.g., support TC), but you need some new mechanism for forwarding PTP packets along a multi-hop path. 2. You can carry PTP across any LSP using GAL at the bottom of the label stack. In this case only the tail end of the LSP will be PTP-aware, i.e., TC will not be supported with this option. I suggest taking a look at http://datatracker.ietf.org/doc/draft-ietf-mpls-tp-data-plane for details regarding MPLS (and MPLS-TP) data plane. Regards, Sasha -----Original Message----- From: tictoc-bounces at ietf.org [mailto:tictoc-bounces at ietf.org] On Behalf Of Yaakov Stein Sent: Monday, July 19, 2010 12:06 PM To: Mikael Abrahamsson Cc: tictoc at ietf.org Subject: Re: [TICTOC] FW: 1588 over MPLS draft No. Not a new Ethertype - we are talking about MPLS NOT Ethernet. There is a protocol type (it's actually called a "channel type") in the Ach control word. See RFC 4385. Right now only a few are defined (raw BFD, IPv4, IPv6). Y(J)S -----Original Message----- From: Mikael Abrahamsson [mailto:swmike at swm.pp.se] Sent: Monday, July 19, 2010 09:48 To: Yaakov Stein Cc: stbryant at cisco.com; tictoc at ietf.org Subject: Re: [TICTOC] FW: 1588 over MPLS draft On Sun, 18 Jul 2010, Yaakov Stein wrote: > 1) define a new protocol type (plenty of openings in THAT registry!) New protocol type on what level? Ethernet, so this would involve a new ethertype? If routers generally can look that far into the packet on the correct forwarding level (I doubt it though) then that would be the least intrusive, but having LSRs look for ethertype within MPLS labeled packets sounds kind of advanced to do that early in the receive path? Why not do it more like an MPLS L3 VPN terminated/routed by all involved&&aware routers, then it would signal special labels to its neighbours that would be local significance only? But now we're talking handling it like a tree and that would involve routing protocols as well... Basically this would be like multicast IP and could leverage all the multicast MPLS standards out there. -- Mikael Abrahamsson email: swmike at swm.pp.se _______________________________________________ TICTOC mailing list TICTOC at ietf.org https://www.ietf.org/mailman/listinfo/tictoc
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