CCIE Pursuit Blog

August 11, 2007

Interpreting Tasks

Filed under: CCIE Lab Workbooks,Cisco,Cisco Certification,Lab Tips,Switching — cciepursuit @ 6:06 am

I have been working though the Internetwork Expert Volume I labs.  One of the switching labs asks you to complete the following task: 

Configure an etherchannel between sw1 and sw2 without using negotiation protocols. [both switches are 3560s – should not matter for etherchannel].

Interesting…the question states “without using negotiation protocols”.  Does this just mean the etherchannel negotiation (PAgP or LACP) or does this extend to the trunk negotation as well?  What about speed/duplex?  Do we need to hardset the speed and duplex so that we don’t auto-negotiate this parameters as well?  This would be an excellent question to clarify with the proctor.

Also, do we NEED to trunk across the etherchannel?  We could just create the etherchannel as an access port as this would disable DTP negotiation.  If the two switches are 3560s, no trunking is established. BUT if there’s a 3550 in the mix, then the default DTP mode is “dynamic desirable” and trunking will negotiate.  AND although a trunk does not establish between two 3560s, trunking negotiation IS still on by default (see this post for details):

Name: Po1
Switchport: Enabled
Administrative Mode: dynamic auto
Operational Mode: static access
Administrative Trunking Encapsulation: negotiate
Operational Trunking Encapsulation: native
Negotiation of Trunking: On

In order to meet the requirements of the task, it looks like we would need a configuration like the following on both switches:

Without trunking: 
interface FastEthernet0/13
 switchport mode access
 speed 100
 duplex full
 channel-group 1 mode on

With trunking:
interface FastEthernet0/13
 switchport trunk encapsulation isl
 switchport mode trunk
 switchport nonegotiate
 speed 100
 duplex full
 channel-group 1 mode on

This is the type of task that could turn up in your exam after you’ve already been tasked with configuring trunking.  I could see the following tasks being on the test but not right after each other:

Task 1: Configure an ISL trunk between sw1 and sw2 on ports fa0/13.
Task 9: Configure an etherchannel between sw1 and sw2 on ports fa0/13 without using negotiation protocols.

In this case the second task would affect how you configure the first task.  While you could accomplish the first task in a number of different ways (see details in this post), the second task would limit you to configuring both sides of the link with “switchport nonegotiate”.  As mentioned before, you would also want to check with the proctor about disabling auto-negotiation of speed and duplex.

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