RSTP port question

This question is from the Hucaby BCMSN cd...

What 802.1w port type has a segment's best cost to reacg the root bridge?

a) Backup
b) Alternate
c) Designated
d) Forwarding
e) Disabled
f) Root

I do not see how the answer isn't f) Root, and yet David Hucaby suggests it's c.

From the answer's explanation:

Designated:
A designated port is the non-root port on a network segment with the lowest cumulative cost to the root bridge.

Root:
A root port is the port on a switch that has the lowest cumulative cost to the root bridge.

Help me understand... what's the difference? Why am I wrong thinking that the Root port is the right answer.

Thanks,
mike

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Comments

dtlokee

mikearama wrote:

This question is from the Hucaby BCMSN cd...

What 802.1w port type has a segment's best cost to reacg the root bridge?

a) Backup
b) Alternate
c) Designated
d) Forwarding
e) Disabled
f) Root

I do not see how the answer isn't f) Root, and yet David Hucaby suggests it's c.

From the answer's explanation:

Designated:
A designated port is the non-root port on a network segment with the lowest cumulative cost to the root bridge.

Root:
A root port is the port on a switch that has the lowest cumulative cost to the root bridge.

Help me understand... what's the difference? Why am I wrong thinking that the Root port is the right answer.

Thanks,
mike

The key is the question said "segment" not "switch". If ti were switch then I would agree it's the root port, but for a segment the designated port has the lowest cost to the root.

networker050184

Tricky question, don't expect anything less from Cisco

If you read that one too fast you will pick root port. I usually read the question twice to make sure.

mikearama

So a follow up question... is the connection from any switch to the root switch (assuming directly connected) not also called a segment?

networker050184

Yes, what is the port advertising the lowest root path cost? The port on the root (root path cost 0) which is the designated port for the segment.

mikearama

Ahhh... nice. Thanks.

dtlokee

Remember all the ports on the root switch will be designated (well except for the odd occurance where you connect a port on the root switch back to another port on the root switch.)