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A Script for the “Troubleshooting” Section?

386 Words. Plan about 2 minute(s) to read this.

The lab exam might have a troubleshooting section. NMC DOiT labs did not cover troubleshooting, so I never developed a habit for quickly identifying issues. The IEWB Vol.3 series features troubleshooting sections. I’m trying to nail down a simple script that I can run against the rack to find common problems quickly. Here’s a summary of the “troubleshooting” problems I recall seeing thus far:

  • Incorrect IP address.
  • Incorrect subnet mask.
  • Rouge secondary IP address.
  • Incorrect SVI vlan number.
  • Rogue routing protocol.

A simple command set to ferret these out could be this:

show run | include interface|ip address
!
show ip protocols summary

You might have to do one command at a time, if the device has a lot of interfaces. The output will show you the interface with assigned IP addresses and masks. A “show ip interface brief” won’t show you secondary IPs or masks. Let’s focus on Fa0/0.13 in this example.

Rack1R1#conf t
Rack1R1(config)#interf fa0/0.13
Rack1R1(config-subif)#ip address 1.2.3.4 255.0.0.0 secondary

Rack1R1(config-subif)#^Z
Rack1R1#show ip interface brief | e unassigned
Interface IP-Address OK? Method Status Protocol
FastEthernet0/0.13 204.12.1.1 YES manual up up
FastEthernet0/0.16 145.1.16.1 YES manual up up
FastEthernet0/0.136 145.1.136.1 YES manual up up
Loopback0 150.1.1.1 YES manual up up
Rack1R1#show run | include interface|ip address
interface Loopback0
ip address 150.1.1.1 255.255.255.0
interface FastEthernet0/0
no ip address
interface FastEthernet0/0.13
ip address 1.2.3.4 255.0.0.0 secondary <== There’s the rogue IP address…
ip address 204.12.1.1 255.255.255.0

interface FastEthernet0/0.16
ip address 145.1.16.1 255.255.255.0
interface FastEthernet0/0.136
ip address 145.1.136.1 255.255.255.0
interface FastEthernet0/1
no ip address

You’ll also get a breakdown of routing protocols running on the router. If there are no rogue routing protocols enabled, your output should look similar to the following:

Rack1R1#show ip protocols summary
Index Process Name
0 connected
1 static
Rack1R1#

To compare, see the output when I enable some routing protocols:

Rack1R1#conf t
Enter configuration commands, one per line. End with CNTL/Z.
Rack1R1(config)#router rip
Rack1R1(config-router)#exi
Rack1R1(config)#router ospf 1
Rack1R1(config-router)#exi
Rack1R1(config)#router eigrp 1
Rack1R1(config-router)#exi
Rack1R1(config)#router bgp 1
Rack1R1(config-router)#exi
Rack1R1(config)#exi
Rack1R1#show ip protocols summary
Index Process Name
0 connected
1 static
2 rip
3 ospf 1
4 eigrp 1
5 bgp 1

Rack1R1#

What else could you add to my little script from your dealings with troubleshooting sections?