Hi All, On devices like the ASR9000s and ASR920s we have hardware acceleration for BFD echo mode and this works as expected. On platforms that do not have hardware support for BFD echo mode such as the ME3600X/ME3800X/7600 I am confused as to how I am getting low BFD interval times.
Enabling echo mode gives poor performance: the BFD echo packets are originated by the local peer at the configured interval rate from software, even though the remote peer loops them back in hardware, upon return they are then checked in software, so all local actions are happening in software. BFD control packets are sent at the rate of "slow-timers" which is much slower and of no real concern here since it is a fraction of the rate the echo packets are sent at. With echo mode disabled the local (and remote) peer sends BFD control packets at the rate it would have sent echo packets (the configured BFD interval) and no echo packets are sent (so control packets are sent at the rate of echo packets, instead of echo packets). But we must have hardware accelerated support in order for these control packets to be checked at the required rate to give fast failure detection. From the Cisco docs: http://www.cisco.com/c/en/us/td/docs/switches/metro/me3600x_3800x/software/release/15-3_3_S/configuration/guide/3800x3600xscg/swiprout.html#82479 "BFD is supported on physical interfaces that are configured as routing interfaces." I have been searching and only for the ME3600-24CX can I find this snippet "The switch [ME3600-24CX] supports BFD only in Asynchronous mode or no echo mode". I am guessing the statement above from the ME3600X/ME3800X page "means" the same thing as the statement from the ME3600X/ME3800x page, we do have hardware acceleration for BFD but it is only in "no echo mode". Surprise surprise, the documentation is not clear so I want to make sure I have fully understood this. Running BFD in echo mode between two ME switches the average interval is very high and varies a lot: Rx Count: 72, Rx Interval (ms) min/max/avg: 1/4976/4323 last: 2348 ms ago Tx Count: 74, Tx Interval (ms) min/max/avg: 1/4968/4217 last: 1436 ms ago Running BFD in no echo mode (which is what I usually do) we see the average interval is a lovely 47ms (but I've never had 100% clarification of why): Rx Count: 3314443, Rx Interval (ms) min/max/avg: 1/72/47 last: 36 ms ago Tx Count: 3310865, Tx Interval (ms) min/max/avg: 1/72/47 last: 40 ms ago Cheers, James. _______________________________________________ cisco-nsp mailing list [email protected] https://puck.nether.net/mailman/listinfo/cisco-nsp archive at http://puck.nether.net/pipermail/cisco-nsp/
