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How to Determine the failed port with DHCP Snooping

Posted on 2014-10-07
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Last Modified: 2014-10-12
If I understand DHCP snooping is used to prevent usage of Rogue DHCP servers in the Network.
Let 's say someone has plugged a Rogue DHCP server in the Network and DHCP snooping has detected it. in This case how do you tell which port on the switch that the Rogue DHCP server is connected to.

If I am not wrong, Network Admins document each user Network Drop and map it to the Switch name, location and port number.

I am not sure if show DHCP snooping will show the port number that has failed, it will show just the Mac address of the device that has attempted the DHCP client request.


Thank you
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Question by:jskfan
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by:eeRoot
eeRoot earned 167 total points
ID: 40367321
It depends on the make and model of your switch, but there should be some variant of the "show dhcp snooping" command that shows ports, mac address, and stats for blocked traffic.  Also, your switch may have an option to send an alert to a syslog server when rogue DHCP servers are detected, which can be manually checked or set to email the alerts.
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by:Aaron Tomosky
Aaron Tomosky earned 333 total points
ID: 40367396
you should be able to look up a mac address and what port it's connected to easily.

In one of my brocade switches the command is (yes you have to put the dots in those spots):
show mac-address-table address xxxx.xxxx.xxxx

it returns the vlan, port, and some other info
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Author Comment

by:jskfan
ID: 40368936
I do not see this Option:

show mac-address-table address xxxx.xxxx.xxxx
Switch#sh mac-address-table ?
  dynamic     dynamic entry type
  interfaces  interface entry type
  static      static entry type
  <cr>

*** For Alerting System , it is  good idea...I wonder in the real world what they use ?
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LVL 39

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by:
Aaron Tomosky earned 333 total points
ID: 40369201
all switches are a little different, I was just giving you an example from my brocade vdx6740 I happened to have available to me.

In your example, the correct choice is probably dynamic.
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Author Closing Comment

by:jskfan
ID: 40375875
Thank you Guys!!!
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