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Cisco 887VA VDSL with high CPU utilisation impacting performance

I have a Cisco 887VA router that has a working VDSL configuration. It syncs with an attainable rate of 48932 kbits/s and 13432 kbits/s. Speed tests max out around 38Mbits and I can get download speeds of 4.5MB/s but the CPU utilisation hits the roof. I'm trying to work through the process to determine exactly what is causing the high CPU utilisation. I'm guessing its related to a combination of NAT and/or the zone based firewall but would like to know exactly how I can find out what is causing this so I can look at my options to improve the performance. I would have thought the hardware could be able to cope with full VDSL speed even with NAT enabled. Unless my configuration is wrong somewhere.

I have run a "show process cpu sort" and get the following results:

=============================

sh proc cpu sort

CPU utilization for five seconds: 96%/87%; one minute: 79%; five minutes: 32%

PID Runtime(ms)     Invoked      uSecs   5Sec   1Min   5Min TTY Process

283      405388     4774710         84  6.79%  0.55%  0.21%   0 Per-Second Jobs

  92    71743328    23856936       3007  0.79%  1.38%  1.49%   0 COLLECT STAT COU

   5     6339528      739749       8569  0.71%  0.17%  0.12%   0 Check heaps

  98     1087752   611431395          1  0.15%  0.41%  0.26%   0 Ethernet Msec Ti

   2       88512      954882         92  0.07%  0.23%  0.07%   0 Load Meter

116     6286520     7952493        790  0.07%  0.15%  0.12%   0 IP Input

251       19372      764109         25  0.07%  0.00%  0.00%   0 PPPoE Background

295      118140   148952256          0  0.07%  0.05%  0.05%   0 PPP Events

   9          16         905         17  0.00%  0.00%  0.00%   0 WATCH_AFS

=============================

Now I understand that the reason why no process is showing with high CPU utilisation is because the usage is due to interrupt CPU utilisation. I have followed the guide for troubleshooting high CPU utilisation due to interrupts and got as far as looking at the "show cef not-cef-switched" after confirming that "ip cef" was enabled and active on the interfaces. 

=============================

sh cef not-cef-switched

% Command accepted but obsolete, see 'show (ip|ipv6) cef switching statistics [feature]'

IPv4 CEF Packets passed on to next switching layer

Slot  No_adj No_encap Unsupp'ted Redirect  Receive  Options   Access     Frag

RP         0       0        5211        0      293        0        0        0

=============================

sh ip cef switching statistics feature

IPv4 CEF input features:

       Feature                Drop    Consume       Punt  Punt2Host Gave route

       Dialer i/f overr          0     373876       1693          0          0

       NAT Outside               0          0          0       1583          0

Total                            0     373876       1693       1583          0

IPv4 CEF output features:

       Feature                Drop    Consume       Punt  Punt2Host    New i/f

       Post-routing NAT          0          0          0       1760          0

       Firewall (firewa          2          0          0         14          0

Total                            2          0          0       1774          0

IPv4 CEF post-encap features:

       Feature                Drop    Consume       Punt  Punt2Host    New i/f

Total                            0          0          0          0          0

IPv4 CEF for us features:

       Feature                Drop    Consume       Punt  Punt2Host    New i/f

       CCE Firewall            115          0          0          0          0

Total                          115          0          0          0          0

IPv4 CEF punt features:

       Feature                Drop    Consume       Punt  Punt2Host    New i/f

Total                            0          0          0          0          0

IPv4 CEF local features:

       Feature                Drop    Consume       Punt  Punt2Host Gave route

Total                            0          0          0          0          0

=============================================

Now from this information I don't know whether this is a problem or how big of a problem. I have looked at some stats from a "show ip nat stat" command but there aren't that many translations happening when the CPU is so high and the CEF translated packets looks much higher than the CEF punted packets.

=============================================

sh ip nat stat

Total active translations: 85 (0 static, 85 dynamic; 85 extended)

Peak translations: 91, occurred 00:12:08 ago

Outside interfaces:

  Dialer1, Virtual-Access3

Inside interfaces:

  Vlan5

Hits: 1483141  Misses: 0

CEF Translated packets: 1477467, CEF Punted packets: 5212

Expired translations: 576

Dynamic mappings:

-- Inside Source

[Id: 1] access-list 1 interface Dialer1 refcount 85

Total doors: 0

Appl doors: 0

Normal doors: 0

Queued Packets: 0

=============================================

Are there some other commands that I can run to get a better picture of the problem? I don't really want to have to resort to researching whether I can run the router in some bridge mode so NAT can be performed on my firewall that is 1 step behind the router. I only have 1 public IP address.

Can someone please provide some help or direction in how I can get to the bottom of this? Configuration is attached.

3 REPLIES
Cisco Employee

Cisco 887VA VDSL with high CPU utilisation impacting performance

You have NAT plus ZBFW configured on the router and then another firewall behind the router? Why the need for two firewalls?

High CPU due to interrups is almost always a combination of traffic and features configured. Remove the firewall config and either the cpu will go down or the performance will improve.

New Member

Cisco 887VA VDSL with high CPU utilisation impacting performance

Thanks for replying George. I had the ZBFW enabled mainly for learning purposes, I don't need it on. I thought I might be able to run some commands in order to see which features are having the most impact on the router. I wanted to go through the process of finding out the problem using show commands before turning them off to see the impact. Turning off the ZBFW does drop it down to 70 - 75% CPU utilisation.

New Member

I'm using the same router

I'm using the same router with ADSL2+ Annex A. I don't have the same CPU problem but my router causes a lot of latency even while idle. My router has only a basic configuration as I only just got it connected and functioning. Since swapping to this router I've noticed my connection latency has increase by an average of 5ms which is significant when the latency was 12ms previously. There was no change in line speed, only latency.

Is this router just under-powered?

============================================================================

Cisco_887#sh ip nat stat
Total active translations: 243 (2 static, 241 dynamic; 243 extended)
Peak translations: 1334, occurred 01:59:15 ago
Outside interfaces:
  Dialer1, Virtual-Access2
Inside interfaces:
  Vlan1
Hits: 13635094  Misses: 0
CEF Translated packets: 13530513, CEF Punted packets: 104584
Expired translations: 87257
Dynamic mappings:
-- Inside Source
[Id: 1] access-list 1 interface Dialer1 refcount 240
Appl doors: 0
Normal doors: 0
Queued Packets: 0
Cisco_887#

============================================================================

Cisco_887#sh proc cpu sort
CPU utilization for five seconds: 5%/0%; one minute: 6%; five minutes: 6%
 PID Runtime(ms)   Invoked      uSecs   5Sec   1Min   5Min TTY Process
  70    11391512   1707939       6669  3.43%  3.31%  3.31%   0 COLLECT STAT COU
   1          52       175        297  0.00%  0.00%  0.00%   0 Chunk Manager
   2         208     68272          3  0.00%  0.00%  0.00%   0 Load Meter
   3           4         2       2000  0.00%  0.00%  0.00%   0 VTEMPLATE Backgr
   4      303508     40606       7474  0.00%  0.08%  0.06%   0 Check heaps
   5           8        76        105  0.00%  0.00%  0.00%   0 Pool Manager
   6           0         2          0  0.00%  0.00%  0.00%   0 Timers
   7          68         2      34000  0.00%  0.00%  0.00%   0 License Client N
   8          20         2      10000  0.00%  0.00%  0.00%   0 Image License br
   9      183604      5687      32284  0.00%  0.06%  0.03%   0 Licensing Auto U
  10           0         1          0  0.00%  0.00%  0.00%   0 Crash writer
  11       19808    104223        190  0.00%  0.06%  0.01%   0 ARP Input
  12          96    355850          0  0.00%  0.00%  0.00%   0 ARP Background
  13           0         2          0  0.00%  0.00%  0.00%   0 ATM Idle Timer
  14           0         2          0  0.00%  0.00%  0.00%   0 AAA high-capacit
  15           0         1          0  0.00%  0.00%  0.00%   0 AAA_SERVER_DEADT
  16           0         1          0  0.00%  0.00%  0.00%   0 Policy Manager
  17         116     11365         10  0.00%  0.00%  0.00%   0 DDR Timers
  18           0         2          0  0.00%  0.00%  0.00%   0 Entity MIB API
  19           4        79         50  0.00%  0.00%  0.00%   0 EEM ED Syslog
  20         260     69310          3  0.00%  0.00%  0.00%   0 HC Counter Timer
 --More--

 

============================================================================

Cisco_887#sh cef not-cef-switched
% Command accepted but obsolete, see 'show (ip|ipv6) cef switching statistics [feature]'

IPv4 CEF Packets passed on to next switching layer
Slot  No_adj No_encap Unsupp'ted Redirect  Receive  Options   Access     Frag
RP         0       0      251946       10   100011        0        0        0
Cisco_887#

==========================================================================

 

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