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CISCO 2960 allows you to configure so-called Port-Based address allocation. It makes the switch to associate IP address it is giving out via DHCP with port-identifier, which is random, switch created identifier. In practice it means that any machine connected to such configured port will always get the same IP address, regardless of what that machine's MAC address is. I want to have that feature configured on --some ports-- only. But no matter what commands I try it seems that this can only be done for all ports, all for none. Even though CISCO manual seems to indicate there's both global and per-port command to enable that. Here are relevant commands from CISCO manual:

  • configure terminal

  • ip dhcp use subscriber-id client-id
    (this configures the DHCP server to globally use the subscriber ID as the client ID on all incoming DHCP messages)

  • interface FastEthernet0/1

  • ip dhcp server use subscriber-id
    client-id

    (Optional: Configures the DHCP server to use the subscriber ID as the client ID on all incoming DHCP messages on the interface)

but it appears if I configure only per-interface than there's no effect at all, if I configure globally and per interface - CISCo behaves as if all ports were configured to use that feature. Any ideas?

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3 Answers

I've made some tests. I think that as interface is intended the interface of the DHCP server that give the DHCP offer. In my setup I use vlans for different DHCP pools. So, in my case, I have to configure:

interface vlan n

ip dhcp server use subscriber-id client-id

It works but in my configuration I had to create dedicated vlans only for DHCP port based!

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Hopefully, this will help you Port Based Address Allocation

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You need an IOS that supports DHCP Server Port-Based Address Allocation on your switch; you also must issue DHCP from your switch. Assume that you have got Fa1/0/1 and Fa1/0/2 in Vlan120.

ip dhcp use subscriber-id client-id
ip dhcp subscriber-id interface-name
ip dhcp excluded-address 192.0.2.1 192.0.2.10
!
ip dhcp pool VLAN120
   network 192.0.2.0 255.255.255.0
   default-router 192.0.2.1
   dns-server 192.0.2.5
   reserved-only
   address 192.0.2.101 client-id "Fa0/1" ascii
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