Ccna Certification: Three Occasions To Reload Or Reopen A Cisco Router Interface

In a previous tutorial, I showed you how to configure an Etherchannel. You have to place each port into the Etherchannel with the channel-group command, and if you do so individually, some of the ports may go into error-disabled state, or "err-disable". This can also happen as a result of port security enforcement. You can see this with the show interface command:

sw1#show int fast 0/1

FastEthernet0/1 is down, line protocol is down (err-disabled)

A syslog message putting that port into err-disabled state will look like this:

04:10:23: %PM-4-ERR_DISABLE: channel-misconfig error detected on Po1, putting Fa0/1 in err-disable state

If this happens during an Etherchannel configuration, just finish the config and then shut and reopen the ports in err-disabled state. They'll come back up and be placed into the Etherchannel.

Finally, our old friend the SPID often makes us shut and reopen the BRI interface. If the BRI interface is open and you configure SPIDs on it, the SPID can be absolutely correct and you'll still see this in the output of show isdn status:

spid1 configured, spid1 NOT sent, spid1 NOT valid

At least the Cisco router puts "NOT" in caps, right? It's easier to see that way! With SPIDs, before you call the service provider or check the SPID you entered about 40 times, just shut and reopen the interface. That usually does the trick.

When you earn your CCNA certification, that means that you know what you're doing instead of hoping that you do - and part of that is knowing when a simple reload or open/shut will take care of the issue.

Chris Bryant, CCIE #12933, is the owner of The Bryant Advantage, home of over 200 free certification exam tutorials, including CCNA certification training articles. His exclusive CCNA study guide is also available! Visit his blog and sign up for Cisco Certification Central, a daily newsletter packed with CCNA, Network+, Security+, A+, and CCNP certification exam practice questions! A free 7-part course, “How To Pass The CCNA”, is also available, and you can attend an in-person or online Cisco CCNA training boot camp with The Bryant Advantage!

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