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New Member

LNS IP fragmentation

I have LNS 7200 NPE-G2, which terminates around 2500 sessions. CPU load with 250Mbps, 30000pps is 95%

FYI: tcp mss is set to 1420, mtu on VAIs - 1492

My questions are

1) Is it better to fragment on PPP VAI or let Cisco do it on L2TP level.

Currently Cisco fragments L2TP packets.

2) What impact would be if I start getting unfragmented incoming L2TP packets (

2036989 local destination, 2024412 reassembled). It's still 1/4 of total outgoing fragmented packets, but maybe reassembling is more CPU intensive.

3) Is it worth to move this LNS into VAI-subinterface mode? what improvements I can expect?

4) it doesn't relate to this disccustion. But why I can make VAI-subinterfaces only for L2TP/PPP sessions and can't make them for PPPOE sessions.

aaa policy interface-config allow-subinterface is present on both BRASes.

#sh ip traffic

IP statistics:

  Rcvd:  6099983 total, 2036989 local destination

         0 format errors, 0 checksum errors, 3359 bad hop count

         0 unknown protocol, 0 not a gateway

         0 security failures, 0 bad options, 0 with options

  Opts:  0 end, 0 nop, 0 basic security, 0 loose source route

         0 timestamp, 0 extended security, 0 record route

         0 stream ID, 0 strict source route, 0 alert, 0 cipso, 0 ump

         0 other

  Frags: 2024412 reassembled, 8278 timeouts, 0 couldn't reassemble

         8140471 fragmented, 61 couldn't fragment

  Bcast: 0 received, 0 sent

  Mcast: 5793 received, 1278 sent

  Sent:  440099 generated, 283269053 forwarded

  Drop:  0 encapsulation failed, 0 unresolved, 0 no adjacency

         0 no route, 0 unicast RPF, 0 forced drop, 0 unsupported-addr

         0 options denied, 0 source IP address zero

1 REPLY
New Member

LNS IP fragmentation

By eliminating l2tp reassembling and fragmentation CPU Interrupts load dropped by 15%.

But still getting weird ignored errors.

cisco#sh int gi0/1 | incl errors|Input

  Input queue: 0/4096/0/0 (size/max/drops/flushes); Total output drops: 0

     248852 input errors, 0 CRC, 0 frame, 0 overrun, 248852 ignored

     0 output errors, 0 collisions, 0 interface resets

cisco#sh buffers | incl fail

     31266 failures (0 no memory)

     18358 failures (0 no memory)

     4336 failures (0 no memory)

     3080 failures (0 no memory)

     2594 failures (0 no memory)

     2382 failures (0 no memory)

     0 failures (0 no memory)

     0 failures (0 no memory)

     0 failures (0 no memory)

     0 failures (0 no memory)

     0 failures (0 no memory)

     0 failures (0 no memory)

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