[c-nsp] WG: SUP720 - 12.2(18)SXF17

[Marcus.Gerdon]

Hi Drew!

Unfortunately not. I've been through that discussion initially about 2 years back.

The initial state had been 5min-average cpu runing at 60-70% at SXE, lowering to 40-50% after upgrade to SXF10 (the peer-group not working bug of SXE had been one of the heavier culprits) which is still far too much (approx. 100 bgp sessions at that time). I didn't find the cpu graph from that time back anymore but only an email regarding the results from the following discussion regarding the traceroute results. Reconfiguring the 'TTL expired's from no limit down to 100 per sec gained another 15-25% of cpu (dependent on the number of subscribers connected to the attached access systems). I've actively seen that across reconfiguration under load.

First we've got a bunch of discussions about the rate-limit and resulting 'poor' presentation traceroutes gives after limiting it but they only pop up occasionally (once a month or so) nowadays. Most I like 'it's no traceoute, my mtr shows there's packet loss' - nothing to comment on that.

Despite the discussions it's been definitely worth the trouble.

The bgp scanner issue eating up 100% cpu every 60s is something that's seen at all platforms, just that the lc's in really active systems like the gsr aren't effected by the engine cpu. I think this is some process-priority/queing-topic somewhere inside.

One interesting thing I've seen then was that the bgp scanner seemingly doesn't go along with maximum priority in the process chain. After limiting the TTL's the time taken by the scanner to be completed also reduced by a few seconds. This suggests that processing of packets in RP or at least generating the ICMP's picks some cpu time off the bgp scanner process.

If you've a larger number of residential access flowing through your network you just might want to give the limiters a try and see how cpu changes (never seen any service affecting issue when configuring those under load).



regards,

Marcus

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