12-23
Configuring for Network Management Applicati ons
CDP
Monitoring and Managing
the Switch
For example, if the switch’s transmit interval for CDP packets was set to a
non-default value, you would use this command to reset it to one minute:
Switch 4108GL(config) cdp timer 60
Changing the Hold Time (CDP Packet Time-To-Live) for a Switch’s
CDP Packet Information. The default hold time for the switch’s CDP
packet information in the CDP Neighbor s table of another CDP device is 180
seconds (range: 5 - 254). This parameter is controlled in the transmitting
switch, and applies to all outbound CDP packets the switch transmits.
Syntax: cdp holdtime <5 . . 254>
For example, to configure a switch’s outbound CDP packets to live for one
minute in the CDP Neighbors table of neighboring CDP devices:
Switch 4108GL(config) cdp holdtime 60
Effect of Spanning Tree (STP) On CDP Packet Transmission
If STP has blocked a port on the switch, that port does not transmit CDP
packets. However, the port still receives CDP packets if the device on the other
end of the link has CDP enabled. Thus, for example, if switch "A" has two ports
linked to switch "B" (which is a CDP neighbor and also the STP root device)
and STP blocks traffic on one port and forwards traffic on the other:
Figure 12-14. Example of STP Effect on CDP Packet Transmission
Switch "A"
CDP Enabled
CDP Neighbor Table
Port | Data
------|------------------
A3 | Switch "B"data
C5 | Switch "B" data
Switch "B"
CDP Enabled
STP Root Device
CDP Neighbor Table
Port | Data
------|------------------
B1 | Switch "A" data
STP block on port C5 of switch "A" blocks
outbound transmission of CDP packets from
switch "A", but does not block inbound
packets to switch "A" from switch "B".
Port A3
Port C5
CDP Packets from Switch "A" to Switch "B"
Port B1
Port D8
CDP Packets from
Switch "B" to Switch "A"