Monday, July 4, 2011

Understanding the concept of CDP.

It is the Layer 2 protocol which is only used in the cisco routers and switches. The CDP is known as cisco discovery protocol.As the name indicated discovery protocol this protocol is used to find the neighbour cisco devices.
This CDP information will be send to the entire network by using the layer 2 multicast and in this we can set the time period for the hold on timer and intervals if we don’t specify the time period the default time will be set.The default time for the CDP message interval is 60 seconds and hold on timer will be 180 seconds.This protocol is very useful to find the down link in the network by this the Route poisoning will be avoided.Lets consider an example the CDP information; will be send to the neighbour devices if the information will be received then the devices are connected in the network and the routing table will be updated if not it states that the devices are down so the routing table is updated as the link is down.

This can enabled and disabled by using the command. By default the CDP will be enabled if we want to disable that we can execute the commad.The CDP information we can viewed by the following command.
Command :

Router_2#show cdp

   The interval timer and holdon timer can be set by using the following command
  Router_2#conf tEnter configuration commands, one per line.
End with CNTL/Z.
Router_2(config)#cdp timer 90
Router_2(config)#cdp holdtime 360

Though there are many security threats in enabling the CDP for this we can disable the CDP.Because the man in middle attack and the DOS attack can be occurred easily by using this protocol.For example if a hacker is in the network he can easily found the devices and componenets in the network and he can gain access and it may causes severe security threat.Because in the CDP protocol table it includes the interface number and device ID and holdon time and port ID. It can be disabled by using the following command.
Router_2#no cdp

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