Debugging problems

superduperlopez · ‎05-03-2006

Hi,

I am expereincing the following problem with a Cisco 1701, flash:c1700-advsecurityk9-mz.124-5.bin.

I telnet into the router, type the terminal monitor command and then the fun begins......

if I do a "debug ip icmp" and do a ping somewhere I get the following...

TEST#debug ip icmp

ICMP packet debugging is on

TEST#ping 66.249.93.99

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 66.249.93.99, timeout is 2 seconds:

!!!!!

Success rate is 100 percent (5/5), round-trip min/avg/max = 44/50/56 ms

TEST#

003201: May 3 13:45:56.140 London: ICMP: echo reply rcvd, src 66.249.93.99, dst 88.66.244.33

003202: May 3 13:45:56.192 London: ICMP: echo reply rcvd, src 66.249.93.99, dst 88.66.244.33

003203: May 3 13:45:56.252 London: ICMP: echo reply rcvd, src 66.249.93.99, dst 88.66.244.33

003204: May 3 13:45:56.296 London: ICMP: echo reply rcvd, src 66.249.93.99, dst 88.66.244.33

003205: May 3 13:45:56.348 London: ICMP: echo reply rcvd, src 66.249.93.99, dst 88.66.244.33

However, if I do a "debug ip packet" and ping again.......no thing happens....

TEST#debug ip packet

IP packet debugging is on

TEST#ping 66.249.93.99

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 66.249.93.99, timeout is 2 seconds:

!!!!!

Success rate is 100 percent (5/5), round-trip min/avg/max = 40/46/56 ms

TEST#

any ideas on why some debugging commands are working and others aren't???

Thank you

GRAEME DANIELSON · ‎05-04-2006

I think packets need to be process switched for "debug ip packet" to see them. You need to "no ip route-cache" on the interfaces passing your interesting traffic. But BEWARE of doing this on a highly utilised interface and/or a device with high avg CPU utilisation. Also use a tightly targeted ACL e.g. "debug ip packet 199" so you don't kill the router. And/or stop debug msgs going to the console with "logging console info" as each msg to console causes CPU interupt so a debug flood will kill you.

debug ip packet can be extremely helpful but be VERY CAREFUL how you use it on a box you care about.

...and remember to turn on the "ip route-cache [cef]" interface configs again when finished (: