debug ip packet
debug ip packet [access-list-number]no debug ip packet [access-list-number]
(Optional) The IP access list number that you can specify. If the datagram is not permitted by that access list, the related debugging output is suppressed.
To display general IP debugging information and IP security option (IPSO) security transactions, use the
debug ip packet privileged EXEC command. The no form of this command disables debugging output.
If a communication session is closing when it should not be, an end-to-end connection problem can be
the cause. The debug ip packet command is useful for analyzing the messages traveling between the
local and remote hosts.
IP debugging information includes packets received, generated, and forwarded. Fast-switched packets
do not generate messages.
IPSO security transactions include messages that describe the cause of failure each time a datagram fails
a security test in the system. This information is also sent to the sending host when the router
configuration allows it.
Caution: Because the debug ip packet command generates a substantial amount of output, use it only when
traffic on the IP network is low, so other activity on the system is not adversely affected.
The following is sample output from the debug ip packet command:
Router# debug ip packet
IP: s=18.104.22.168 (Fddi0), d=10.125.254.1 (Serial2), g=22.214.171.124, forward
IP: s=126.96.36.199 (Ethernet4), d=10.36.125.2 (Serial2), g=188.8.131.52, forward
IP: s=184.108.40.206 (Ethernet4), d=255.255.255.255, rcvd 2
IP: s=220.127.116.11 (Ethernet4), d=18.104.22.168 (Fddi0), g=22.214.171.124, forward
IP: s=126.96.36.199 (Ethernet2), d=10.130.2.156 (Serial2), g=188.8.131.52, forward
IP: s=184.108.40.206 (Ethernet4), d=220.127.116.11 (Fddi1), g=18.104.22.168, forward
IP: s=22.214.171.124 (Ethernet4), d=126.96.36.199 (Fddi0), g=188.8.131.52, forward
IP: s=184.108.40.206 (Ethernet2), d=255.255.255.255, rcvd 2
IP: s=220.127.116.11 (Ethernet4), d=10.36.125.2 (Serial2), g=18.104.22.168, access denied
The output shows two types of messages that the debug ip packet command can produce; the first line
of output describes an IP packet that the router forwards, and the third line of output describes a packet
that is destined for the router. In the third line of output, rcvd 2 indicates that the router decided to receive
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