Just one more point about using SR’s traffic steering capability described in our draft: when traffic between two end points (E1<-> E2) traverse a SR domain and there are multiple egress PEs (PE-a, PE-b, etc) to reach E2, it is relatively easy for SR to steer some flows towards egress PE-a and other flows towards egress PE-b.
Linda Dunbar From: Linda Dunbar Sent: Tuesday, July 03, 2018 3:09 PM To: 'Robert Raszuk' <[email protected]>; Jeff Tantsura <[email protected]> Cc: SPRING WG List <[email protected]> Subject: RE: [spring] solicit feedback on draft-dunbar-sr-sdwan-over-hybrid-networks-02 proposing SD-WAN source node using UDP port to indicate to SR ingress node how to map to appropriate Binding SID Robert, Jeff, Sasha, Jim, Lou, et al, Thank you very much for the feedback. The main attraction of SR is indeed its Traffic steering capability, especially when there are multiple egress PEs to reach the SD-WAN end points. SR can easily force a path to traverse the explicitly selected egress node or explicit segments through the SR Domain based on the applications need. If only using MPLS, quite some configurations are needed to force a flow to a specific egress PE. Linda From: [email protected]<mailto:[email protected]> [mailto:[email protected]] On Behalf Of Robert Raszuk Sent: Tuesday, July 03, 2018 3:08 AM To: Jeff Tantsura <[email protected]<mailto:[email protected]>> Cc: Linda Dunbar <[email protected]<mailto:[email protected]>>; SPRING WG List <[email protected]<mailto:[email protected]>> Subject: Re: [spring] solicit feedback on draft-dunbar-sr-sdwan-over-hybrid-networks-02 proposing SD-WAN source node using UDP port to indicate to SR ingress node how to map to appropriate Binding SID Hello Jeff, “What exactly do you call by "resource allocation" in WAN ?” – anything that is not “best effort”, BW reservation, protection type, number of hops, latency, you name it… Somehow, between ATM and now we managed to build a technology that would work in both, control and data planes 😉 TE with BW reservation is a working technology, with all the bugs, whether done as a soft state on a device and enforced in FW, aka RSVP-TE or computed on a controller and enforced by policing configuration out of band. We also know pretty well how to compute a constrain path that is loop free and with the constrains. Either way, working stuff. It has been nearly 20 years and it seems that some marketing slides from vendors are still in minds of many many people ... MPLS-TE does *NOT* do any data plane reservations nor any data plane resource allocation. It is all control plane game. Let me shock you even more today ... what we call "Guaranteed Bandwidth TE" also does *NOT* perform any data plane reservations. This up to current days is the most misunderstood element (or hidden secret) of one of the technologies which has been made available during the last two decades. If you signal MPLS TE LSP with 5M "reservation" to check if such a path in your network can be established such check is *ONLY* done at the control plane (RP/RE) pools of available bandwidth (per priority level) registers and physical interfaces nor any data plane queues are never aware of it. Now what is a direct consequence of this is if you like to really do control plane reservations and think of it as actual data plane you must do it in 1:1 fashion - again all done in control plane. That means that two fundamental conditions must be met: A) All traffic must be sent over MPLS-LSPs - be it IPv4, IPv6, multicast etc ... - even if I have seen 3 networks trying to do that for IPv4 no one did it for all traffic types. B) All traffic entering your network must be subject to very strict admission control and excess shaped or dropped which is very hard thing to do considering statistical multiplexing gains you count on in any IP network (Explanation: On any single ingress node you must apply strict CAC as you are not aware about what traffic is coming from other ingress nodes. So you may be dropping or shaping traffic which could flow through your network just fine end to end due to absence of competing class from different ingress). All RSVP-TE does is traffic steering in normal steady state or during protection. That's all. In the WAN's data plane it is all back to basic Diff Serve at each router's data plane. The only technology which does provide interface data plane reservation is RSVP IntServ - but I doubt anyone here or Linda in her draft meant to use such tool. Why am I jumping on this here in SPRING WG list ... Well few months ago I have witnessed a discussion where someone was arguing that SR is much worse then MPLS-TE as it does not provide any data plane reservations. When I tried to nicely and politely explain how confused the person is the look I got was comparable to those green folks walking down from just arrived UFO. So to conclude SR just like MPLS-TE does a good job in packet steering via your domain. (SR can do actually more via embedded functions/apps). But the fundamental difference is that SR does that steering without necessity of number of control plane protocols and their required extensions - so does simplify control plane significantly. Neither of those do any data plane reservations and all bandwidth contentions need to be resolved via classic QoS. Cheers, R.
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