Commit ea94022a authored by Robert Ricci's avatar Robert Ricci
Browse files

Added some notes about debugging high CPU usage.

parent 5ab4b005
......@@ -300,3 +300,30 @@ ID Name Members of VLAN
set port channel 2/9-12 mode on
... of course, use the actual ports that your channel runs on.
19. Useful commands for debugging high CPU usage on routers (IOS)
show proc cpu - shows %ages of CPU used by various processes. If CPU usage
is high, and process usage doesn't add up to total usage, then the
extra time is in interrupt handlers, where 'fast path' forwarding
(and other things) take place
show ip traffic - show router-wide stats on traffic, including the reasons
for dropping packets. 'Encapsulation failed' (for drops) typically
means that the router wasn't able to ARP for the destination
show ip interface - will tell you more about the options, such as fast
switching, enabled on an interface. You definitely want fast switching
enabled, probably want CEF switching if your device supports it, and
might want 'flow' or 'netflow' if you are using big ACLs (since it
effectively caches firewall decisions)
show ip cache flow - shows the contents of the 'newflow' per-flow routing
cache, including an interesting histogram of packet sizes. If you want
to look at entries for a particular host, you can use '| include <IP>'
Cisco page about troubleshooting high CPU utilization:
http://www.cisco.com/en/US/products/hw/routers/ps133/products_tech_note09186a00800a70f2.shtml
If it's from interrupts:
http://www.cisco.com/en/US/products/hw/routers/ps359/products_tech_note09186a00801c2af0.shtml
More about performance tuning, the various switching paths, etc:
http://www.cisco.com/en/US/products/sw/iosswrel/ps1831/products_tech_note09186a00800a7306.shtml
Pasting the output of these commands into Cisco's Output Interpreter tool
(on the web, registered users only) is very helpful
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