Cisco router global, interface, protocol debugging guide (1)

Global debugging

When configuring a Cisco router, the boundaries between global and interface commands are obvious. In this case, we use "Global" to identify commands that cannot be used for interface debugging or specific transmission media types and Protocol debugging. For example, in vrouters 2500, you can use Debugging commands to analyze the Cisco Discovery Protocol (CDP ). We remotely log on to the vrotelnet through telnet. By default, the output of the DEBUG command is sent to the console. If it is in a telnet session, we can use the terminal monitor command to view the output.

Interface debugging

The debug serial interface command is a debugging command directly related to the router interface and transmission media type. In the following example, the serial interface is encapsulated by HDLC. End-to-End HDLC keeps Active packets exchanged every 10 seconds. This indicates that the link operation is normal and the Layer 2 operation is normal. The show interface serial0 command indicates that the line protocol is started normally. Use the undebug all command to disable all debugging tasks.

YH-Router#debug serial interfaceSerial network interface debugging is onYH-Router#Jun 1 21:54:55 PDT:Serial0: HDLC myseq 171093, mineseen 171093*, yourseen 1256540,line upJun 1 21:55:05 PDT:Serial0: HDLC myseq 171094, mineseen 171094*, yourseen 1256541,line upJun 1 21:54:15 PDT:Serial0: HDLC myseq 171095, mineseen 171095*, yourseen 1256542,line upYH-Router#undebug allAll possible debugging has been turned off

Protocol debugging

The following are two examples of protocol debugging. Both examples are related to the IP protocol. Of course, the DEBUG command applies to all other protocols.

The first example (as shown below) shows ARP debugging. ARP Debugging starts, then clears the ARP cache, and generates ARP requests and responses. First, we use the command to clear all ARP caches on the vro. Therefore, each LAN segment connected to the vro。 generates an ARP packet. Because we do not need to generate too many ARP packets, the selected router is connected to only one Ethernet segment.

YH-Router#debug arpARP packet debugging is onYH-Router#clear arpYH-Router#*Jun 1 21:57:36 PDT: IP ARP: sent req src 171.136.10.1 00e0.1eb9.bbcddst 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.bbcddst 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......