10-15
Configuring for Network Management Applications
CDP
General CDP Operation
The switch stores information about adjacent CDP devices in a CDP Neigh-
bors table maintained in the switch’s MIB (Management Information Base).
This data is available to SNMP-based applications designed to read CDP data
from the MIB. For example:
Figure 10-5. Example of How the Switch Stores Data on Neighbor CDP Devices
Outgoing Packets
A Switch 2650 or 6108 running CDP periodically transmits a one-hop CDP
packet out each of its ports. This packet contains data describing the switch
and, if the one-hop destination is another device running CDP, the receiving
device stores the sending device’s data in a CDP Neighbors table. The receiving
device also transmits a similar one-hop CDP packet out each of its ports to
make itself known to other CDP devices to which it is connected. Thus, each
CDP device in the network provides data on itself to the CDP neighbors to
which it is directly connected. However, there are instances where a packet
is forwarded beyond the immediate neighbor, or simply dropped.
Switch "A"
with CDP Running
• The Neighbors table in switches "A", "B", and "D"
contain information on switch "C" only because
it is the only neighbor for these switches.
• The Neighbors table in switch "C" contains
information on switches "A", "B", and "D"
because all of these switches are neighbors of
switch "C".
Note: A given switch’s CDP Neighbor table
includes data only on neighbor CDP devices, but
not on that switch itself.
CDP Neighbor Table
Switch "C" data
Switch "B"
with CDP Running
CDP Neighbor Table
Switch "C" data
Switch "C"
with CDP Running
CDP Neighbor Table
Switch "A" data
Switch "B" data
Switch "D" data
Switch "D"
with CDP Running
CDP Neighbor Table
Switch "C" data
!Software.book Page 15 Thursday, October 10, 2002 6:10 PM
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