Global, interface, and Protocol debugging for Cisco Routers

This article describes in detail how to configure Cisco routers in terms of global debugging, interface debugging, and Protocol debugging. I believe this article will help you.

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 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

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 commands 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 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 (as shown below) shows ip rip debugging. The vro table is not cleared at the beginning of the debugging. Because the vro performs a RIP update every 30 seconds, you do not need to update it forcibly. Similar to the first example, all debugging tasks should be disabled after sufficient information is obtained.

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
......
YH-Router # undeb all
All possible debugging has been turned off