Home » Cisco » 350-080 » What’s the cause of this issue?
Refer to the exhibit.
During troubleshooting of Virtual PortChannel (vPC), it is observed that Virtual PortChannel 2 is in a down state. What’s the cause of this issue?
A. Virtual PortChannel is down because LACP is not enabled on the remote switch.
B. Virtual PortChannel is down because of a VLAN mismatch.
C. Virtual PortChannel is down because of an MTU mismatch.
D. Virtual PortChannel is down because of VLAN and MTU mismatch.
Correct Answer: C
Explanation/Reference:
Explanation:
Virtual Port Channels are actually a big part of the Networkers presentation I have done for the last 2 years, so I am familiar with a lot of the issues people have with them.
I have heard issues you raise discussed before, and we are working on making it better. I think some of the newer features would help your reader.
The consistency checker exists to keep bad things from happening on your vPC port-channel (like “unexplained” packet drops). There are two types of consistency check failures. The ones that will bring down the entire port-channel (these are type 1s) and the ones that will only cause an error, or keep a single or group of VLANs from becoming active on the port-channel (type 2).
Decisions for what a type 1 and 2 are were made by the engineering team.
For example the MTU mismatch will bring your vPC port-channel down, and it does so in a non vPC port-channel as well. I am sure that you can see the types of issues that having a link with a MTU of 9000 and one of 1500 can cause for a port-channel.
Reference: http://blog.ipspace.net/2011/11/nexus-vpc-and-consistency-checker.html
