Global debug
When configuring Cisco routers, global and interface commands is very clear boundaries. In this case, we use "global" to identify those who can not be used for debugging interface, or a particular type of transmission medium and protocol debug command. For example, in the 2500 series routers, you can use debug commands of Cisco Discovery Protocol (Cisco Discovery Protocol, CDP). We telnet to the router via telnet. In default mode, the debug command output is sent to the console, telnet session if you are in, we can use the terminal monitor command to see the output.
Debug Interface
debug serial interface command is transmitted directly to the router interfaces and media types associated debug command. In the following example, serial interface with HDLC encapsulation. End of the HDLC packets to maintain an active exchange of one every 10 seconds. This indicates that the link operation and the second layer is working properly. show interface serial0 command line protocol that normally start. Use undebug all commands turn off all debugging.
YH-Router # debug serial interface
Serial network interface debugging is on
YH-Router #
Jun 1 21:54:55 PDT: Serial0: HDLC myseq 171093, mineseen 171093 *, yourseen 1256540, line up
Jun 1 21:55:05 PDT: Serial0: HDLC myseq 171094, mineseen 171094 *, yourseen 1256541, line up
Jun 1 21:54:15 PDT: Serial0: HDLC myseq 171095, mineseen 171095 *, yourseen 1256542, line up
YH-Router # undebug all
All possible debugging has been turned off
Protocol debugging
Below we give two examples of protocol debugging. Two examples are related to IP agreements. Of course, the debug command applies to all other protocols.
The first example (shown below) shows the ARP debugging. ARP debug start, and then clear the ARP cache, while producing the ARP request and response. First, we use the command clear the ARP cache of all routers, the routers connected to each LAN segment will generate ARP packets. Because we do not produce too many ARP packets, so the choice of the router is connected only with an Ethernet segment.
YH-Router # debug arp
ARP packet debugging is on
YH-Router # clear arp
YH-Router #
* Jun 1 21:57:36 PDT: IP ARP: sent req src 171.136.10.1 00e0.1eb9.bbcd
dst 171.136.10.34 00a0.24d1.5823 Ethernet0
* Jun 1 21:57:36 PDT: IP ARP: sent req src 171.136.10.1 00e0.1eb9.bbcd
dst 171.136.10.10 0080.5f06.ca3d Ethernet0
......
* Jun 1 21:57:36 PDT: IP ARP: rcvd req src 171.136.10.10 0080.5f06.ca3d, dst 171.136.10.1 Ethernet0
* Jun 1 21:57:36 PDT: IP ARP: creating entry for IP address: 171.136.10.10, hw: 0080.5f06.ca3d
......
The second example (shown below) shows the IP RIP debugging. In debugging the beginning, there was no clear router table, because the router automatically every 30 seconds a RIP update, so do not force the update. Similar with the first example, in access to enough information that it should close all the debugging.
YH-Router # debug ip rip events
RIP event debugging is on
YH-Router #
NOV 27 13:55:45 PST: RIP: sending v1 update to 255.255.255.255 via TokenRing1 / 0 (165.48.65.136)
NOV 27 13:55:45 PST: RIP: Update contains 25 routes
NOV 27 13:55:45 PST: RIP: Update queued
NOV 27 13:55:45 PST: RIP: Update contains 6 routes
NOV 27 13:55:45 PST: RIP: Update queued
NOV 27 13:55:45 PST: RIP: Update sent via TokenRing1 / 0
......