[c-nsp] L2TP problem with 7301

[Srdjan Simic]

Hello,

We stumbled into a strange problem with a brand new 7301. It is used as a
LNS for L2TP VPDN termination (ADSL). When a tunnel is cleared and a lot of
connections start coming in, router works normally up to the point where it
stops accepting sessions into tunnels (that number can be 100, or 1000). All
sessions are in wt-con state, there are a lot of unsent packets (Unsent
queuesize 7370, max 7370). The number of unsent packets keeps going up, and
only when we stop directing customers to that router, it slowly reduces
unsent queue and wt-con session slowly disappear.

What is strange is when we slowly direct customers (few at the time) all is
ok. We tried with ios 12.3(5a)B5 and 12.3(10) IP Plus. What is recommended
IOS for VPDN termination only, and what are limits for 7301 in terms of
number of VPDN users?

Best regards Srdjan

P.S. Here is show tunnel:

Tunnel id 15715 is up, remote id is 8853, 898 active sessions
  Tunnel state is established, time since change 04:00:23
  Remote tunnel name is xxxx
    Internet Address x.x.x.x, port 1701
  Local tunnel name is xxxx
    Internet Address x.x.x.x, port 1701
  Tunnel domain unknown
  VPDN group for tunnel is 2
  59448609 packets sent, 52585920 received
  390127877 bytes sent, 1334732326 received
  Last clearing of "show vpdn" counters 03:31:24
  Control Ns 10191, Nr 25808
  Local RWS 8, Remote RWS 8
  Tunnel PMTU checking disabled
  Retransmission time 1, max 8 seconds
  Unsent queuesize 0, max 737
  Resend queuesize 0, max 8
  Total resends 1508, ZLB ACKs sent 16622
  Current nosession queue check 0 of 5
  Retransmit time distribution: 0 0 24 0 8 0 0 0 176