date: 2007-10-05 19:56:50+00:00

DHCP snooping on Cisco Catalyst 2950

categories: - Hardware - Networks - Security

I'll explain the few commands used to enable DHCP snooping on our Catalyst switch at work. The users aren't really tech savvy or anything, but it is painless to configure so it is worth having it enabled.

switch1>enable

First, we need to know which VLAN the DHCP server belongs to, "show arp" has that info :

switch1#show arp Protocol Address Age (min) Hardware Addr Type Interface Internet 192.168.1.3 1 0004.75XXXXXX ARPA Vlan1

Then we enable configuration mode :

switch1#conf term

Enabling DHCP snooping on VLAN 1 :

switch1(config)#ip dhcp snooping switch1(config)#ip dhcp snooping vlan 1 switch1(config)#ip dhcp snooping information option

The DHCP server is connected to the second port, we will add that interface to the trusted list :

switch1(config)#interface fastEthernet 0/2 switch1(config-if)#ip dhcp snooping trust

Let's review the config :

switch1#show ip dhcp snooping Switch DHCP snooping is enabled DHCP snooping is configured on following VLANs: 1 Insertion of option 82 is enabled Interface Trusted Rate limit (pps) ------------------------ ------- ---------------- FastEthernet0/2 yes unlimited

DHCP snooping is enabled on VLAN 1 for interface 2 !

Saving the config :

switch1#copy running-config startup-config