Refer to the exhibit.
All switches are Cisco switches. Assume that Cisco Discovery Protocol is enabled only on switches A
and C.
Which information is returned when you issue the command show cdp neighbors on switch C?
A.
a limited amount of information about switch B
B.
no neighbor details will be returned
C.
neighbor details for switch B
D.
neighbor details for switch A
E.
neighbor details for switch C
CDP is used to discover information on directly connected neighbors only, so in this case SwitchC
would only be able to obtain CDP information from SwitchB. However, since SwitchB is not
running CDP then no neighbor information will be seen on SwitchC. Same goes for Switch A also
in this topology.
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The reason the ‘All switches are Cisco switches’ line is important is that Cisco switches do not forward frames destined to the CDP MAC address (01:00:0c:cc:cc:cc) on to neighbors (i.e. TTL=1, kind of). However, you will sometimes run into other vendors switches or unmanaged switches which will forward CDP frames on.
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HP switches (5500, 5800, 5900, 125xx) forward CDP packets for sure.
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Thank you, Jordan! As I’ve just tested with three 3750Es, you are absolutely right.
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