DHCP snooping

Unanswered Question
Oct 10th, 2007
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Trying to run DHCP snooping on a 2960. Using DOT1X to assign PC's into VLAN's for healthy, quarantine, guest etc but only VLAN 1 has an interface and IP address assigned.


When trying to use the "ip dhcp snooping vlan XXX" command the VLANs are shown in the config but doing a show ip dhcp snooping only ever shows VLAN 1.


Anyone aware of a way to resolve this apart from adding VLAN interfaces and possibly ip addresses to them?


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There's Dynamic VLAN membership DVMP.


http://www.cisco.com/univercd/cc/td/doc/product/lan/c2900xl/29_35sa6/eescg/mascvmps.htm


But remember, DVMP is used to ensure specific Layer 2 addresses are assigned to specific VLANS. And the VLANS have to exist. (Vlan 1 always exists).


If you are using multiple VLANS you might want to make 1 upsteam Layer 2 device a VTP domain server, there you would create all the vlan interfaces with you need, and use VTP clients to shake the vlans down to down-stream switches.


So to answer your question, yes a VLAN is a Layer 2 broadcast domain and must exist somewhere if it is to be used, you don't have to give it an IP address but I really can't imagine many reason I would keep things strictly at layer 2. That of course depends on your IP addressing schema and physical architecture.



Bill

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