[c-nsp] High CPU load from loose TE tunnels

[Anton Smith]

Hi all,

I am having a problem with high CPU load on a 7600 because of a downed 
TE tunnel that is configured to use a path that starts with a loose hop, 
followed by strict hops. The tunnel is down because one of the strict 
hops is not reachable (physical link down). The tunnel and path config 
are as follows:

interface Tunnel111
  description Tunnel111
  ip unnumbered Loopback1
  tunnel destination x.x.x.4
  tunnel mode mpls traffic-eng
  tunnel mpls traffic-eng autoroute announce
  tunnel mpls traffic-eng priority 2 2
  tunnel mpls traffic-eng path-option 1 explicit name path1
  tunnel mpls traffic-eng load-share 155

ip explicit-path name path1 enable
  index 2 next-address loose x.x.x.1
  next-address x.x.x.2
  next-address x.x.x.3
  next-address x.x.x.4


Other tunnels that are configured with paths that are very similar (and 
are fully up) do not cause this kind of CPU load. But when they go down, 
they also create the same kind of load.

The CPU histogram looks as follows:

       44444     44444     44444    444444444455555     44444
      233333     66666     7777788886666655555444441111166666
100
  90
  80
  70
  60
  50             *****     *****    ***************     *****
  40   *****     *****     *****    ***************     *****
  30   *****     *****     *****    ***************     *****
  20   *****     *****     *****    ***************     *****
  10   *****     *****     ************************     *****
     0....5....1....1....2....2....3....3....4....4....5....5....
               0    5    0    5    0    5    0    5    0    5

                CPU% per second (last 60 seconds)

And the process that seems to be causing the load is CEF scanner:

CPU utilization for five seconds: 44%/0%; one minute: 29%; five minutes: 18%
  PID Runtime(ms)   Invoked      uSecs   5Sec   1Min   5Min TTY Process
  114    43044320   1823442      23606 37.11% 21.28% 11.57%   0 CEF 
Scanner
....

If I admin shut the tunnel interface in question, the CPU load drops 
back to near zero.

I notice that when I run show mpls traffic-eng tunnels summary, the 
activations and deactivations numbers increment steadily every few 
seconds, as though the box is continually trying to bring up the tunnel 
(more often than it should?):

R1#show mpls traffic-eng tunnels summary
Signalling Summary:
     LSP Tunnels Process:            running
     Passive LSP Listener:           running
     RSVP Process:                   running
     Forwarding:                     enabled
     Head: 15 interfaces, 13 active signalling attempts, 13 established
           23356 activations, 23343 deactivations
     Midpoints: 0, Tails: 13
     Periodic reoptimization:        every 300 seconds, next in 213 seconds
     Periodic FRR Promotion:         Not Running
     Periodic auto-bw collection:    every 300 seconds, next in 269 seconds

I have another router (the tail), which has return tunnels built (also 
using a combination of loose and strict hops). This router also has a 
downed tunnel interface (for the same reason that the first router does 
- i.e. a downed physical link on a strict hop), but it does not exhibit 
high CPU load nor does it seem to be periodic. In addition, the 
'activations' and 'deactivations' counters do not increment. However, 
this other router is a 7301. The tunnels are not administratively shut 
on the 7301.

Does anybody have any ideas? How frequently does a 7600 attempt to bring 
up a tunnel interface? I imagine that the CPU load is coming from the 
CSPF calculation being run every few seconds in an attempt to find a 
path to the first (loose) hop. Is it possible to change this frequency? 
(I have tried changing the reoptimisation timers but I do not believe 
this is the problem, since they are by default 300 seconds - and I see 
high CPU load every few seconds).

Any help much appreciated :).

Regards,
Anton