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IETF90 Toronto July 20-25, 2014

This document addresses the challenges of offering a Layer 2 solution to the Satellite market, with a focus on minimizing bandwidth overhead and achieving quick convergence. It proposes the use of BFD (Bidirectional Forwarding Detection) as a solution, utilizing a proxy design to handle BFD sessions and control packets. The document also suggests improvements in BFD timers and the implementation of BFD Demand Mode.

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IETF90 Toronto July 20-25, 2014

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  1. BFD Proxy Connections over Monitored LinksBrian Snyderbsnyder@idirect.nethttp://tools.ietf.org/html/draft-snyder-bfd-proxy-connections-monitored-links-00 IETF90 Toronto July 20-25, 2014

  2. Problem • Offering a layer 2 solution to the Satellite market exposed new challenges. • L3 routing KA timer settings would result in tradeoff between convergence time versus bandwidth overhead. • Satellite bandwidth is very expensive, overhead needs to be minimized. (There could be thousands of modems in one network). • Customers are used to very quick convergence as we were previously directly attached L3 devices.

  3. Possible Solutions 1 • DLEP • Designed for MESH environments • Multicast complications • Not ubiquitous • Not a ratified standard • Can take time for vendors to implement • Limited L3 application support (ex: no BGP) • Scalability (<100 connections) • VLAN Trunking

  4. Possible Solutions 2 • BFD • Not as informative as DLEP (no link state). • Proxy design would break security extensions • Very “chatty”. Even more so then L3 hello timers.(*) • (*) No “deal breakers”… because…..

  5. Overview • The radio link state is monitored for station keeping purposes • “Chattiness” could be minimized by spoofing BFD messaging in the radio devices. • L3 KA timers can be pushed as high as possible. (Ideally they could be turned off). • Satellite outroutes are a broadcast channel, so IGP routing is a natural choice. • Asynchronous timer routing protocols are ideal as outroute and inroute have very different characteristics. • Inroute design decisions must scale to the thousands. • Therefore, one could rely on outroute HELLO packets to drive convergence and tune down inroute as low as possible. • Hence, EIGRP and IS-IS are ideal.

  6. Proxy Design Goals • The proxy can ‘sniff’ the traffic to auto-learn about BFD sessions. (0 config) • “Eat” all the KA BFD packets from external devices. This keeps all the BFD overhead off the monitored (and expensive) link. • Reply to all the KA packets to keep sessions alive. (If DUM is up) • Inject BFD control packets (state change events) to connected network equipment in order to communicate DUM status events.

  7. Proxy Details • Proxy must keep an OAM object per reachable neighbor. Demux by destination MAC. • Upon intercepting further BFD packets and locating OAM object (Plus internal checks) • If DUM is down, drop. • If state is : • ADMIN_DOWN: Forward on monitored link • DOWN: Reply with constructed BFD Packet (Clear your discriminator field) • INIT: Reply with constructed BFD Packet (Set state UP) • UP: Reply with constructed BFD Packet

  8. Constructed Reply Packets • Swap source and destination MAC addresses • Swap source and destination IP addresses • Swap discriminator fields • Set UDP checksum to 0 (optimization)

  9. Integration Improvements • BFD Timers: Allowing for connected equipment to configure a very high BFD interval value. This use case puts forth a useful situation where sub-second failure is not needed but where BFD is still very useful. Relaxing timer configuration strictness would help scale. • BFD Demand Mode implementation: Alternative to above, this would allow all the KA processing to disappear -> event driven is more scalable. • BFD Protocol: Adding the notion of a proxier could assist with enabling security support in this use case.

  10. Example Flow

  11. Questions??

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