In message <[email protected]> Juliusz Chroboczek writes: > > > Thought: In general, my feeling is that L2 link status is widely relied > > upon in commercial product/dpeloyments. If homenet feels it can not rely > > on it due to the non-commercial nature of its development platforms, > > thats an interesting aspect, especially because it could impact an IETF > > standard that we'd like to see commercially implemented and then the > > constraints could be different... > > Are you referring to the routing protocol comparison, or to something else? > > I have the impression that Babel and IS-IS behave essentially the same > wrt. L2 status -- they both converge fast enough after link status has > been established, and they essentially provide the same facilities for > application-layer link sensing (IMHO Babel's Hello/IHU subprotocol is > slightly more flexible, but that's probably not a big deal). > > As to wireless links -- as far as I'm aware, making efficient use of > wireless L2 information in a routing protocol is an open research problem.
Other than signal strength and collision rate, what L2 information is available? Per MAC information would be nice for the AP side or any node in mesh or adhoc mode but that isn't collected anywhere AFAIK. > -- Juliusz > > _______________________________________________ > homenet mailing list > [email protected] > https://www.ietf.org/mailman/listinfo/homenet ISPs mostly use Ethernet as point-to-point (PTP) links. Including using 100GbE as PTP. No switches. L2 Link down is one fast indicator of link down. But for Ethernet over transport gear (ie: OTN) BFD is almost always used. For short distances L2 over extended reach optics can be used, including colored optics and WDM. This is also PTP and in this case BFD should not be needed. To the extent that routers use SONET or OTN interfaces, these have fast L2 link down indication and are integrated with L3 link down detection. In all of these detection is on the order of 10 msec (geographic distance dependent), failover using FRR is under 50 msec, and IGP convergence is well under a second (typical 100-200 msec today AFAIK). L3 hellos are way too slow. BFD is not heavy weight. L3 hellos (OSPF, ISIS) can be set down to 1s with detection in 3s (too slow). BFD, Hellos, or any form of probe traffic over wireless has the speed of detection vs overhead issue. At nominal 10 Mb/s (low end today for wireless) a small probe would take about 0.1 msec (for example, 125 bytes including all overhead is about 1000 bits). Not bad if running 100 probes/sec (30 msec detection) unless there are a very large number of stations using the AP and doing the same thing. In that case 10 probes per second might be better. A very high collision rate (typically not due to probes, but to real traffic) might result in a link down indication. If that is the case, then moving to another AP would be a good thing. Flapping needs to be avoided if an alternate is available (ie: with 20% loss, in .2*.2*.2 = .008 = 0.8% of intervale a down indication would occur). If any packet received would bring it back up, then at 100 probes / sec, a change in IGP link state could occur about once a second on average. Remembering a link down and holding a down state for a (longish) while would be a good thing. If there is no alternate route, not probing at all and/or holding an up state would be good. OTOH- 20% loss borders on completely unusable. Curtis _______________________________________________ homenet mailing list [email protected] https://www.ietf.org/mailman/listinfo/homenet
