Force Users to Release or Renew their DHCP Addresses

[FAQ_User]

Article ID: 5277

Protocols/Features
DHCP

Goals
Force users to release DHCP address.
Force users to renew DHCP address.
Force a port to drop link.

Cause
It is occasionally desirable for a network administrator to

• Disable ports of misbehaving users, then force them to release their DHCP addresses
  -or-
  
• Leave user ports enabled, but force them to renew their DHCP addresses.

Solution
The key element in both of these goals is to force the client machine to "re-DHCP", by triggering temporary loss of ethernet link.

Matrix N-Series DFE

1. Upgrade to firmware 5.11.21 or higher, for support of the 'show | set | clear forcelinkdown' commands.
2. Issue the global 'set forcelinkdown enable' command, which forces disabled ports to drop link and not transmit auto-negotiation fast-link pulses.
3. Issue the 'set port disable <port_string>' command against the user port(s) in question, which will drop ethernet link.
4. As desired, issue the 'set port enable <port_string>' command against the same port(s), which will return functionality and trigger the DHCP process on attached DHCP clients.

SecureStack

1. Upgrade to firmware 1.00.80 (C3), 5.00.59 (C2), 1.00.74 (B3), or 4.00.60 (B2) or higher; which forces disabled ports to drop link and not transmit auto-negotiation fast-link pulses.
2. Issue the 'set port disable <port_string>' command against the user port(s) in question, which will drop ethernet link.
3. As desired, issue the 'set port enable <port_string>' command against the same port(s), which will return functionality and trigger the DHCP process on attached DHCP clients.

D-Series, G-Series, I-Series

1. Issue the 'set port disable <port_string>' command against the user port(s) in question, which will drop ethernet link.
2. As desired, issue the 'set port enable <port_string>' command against the same port(s), which will return functionality and trigger the DHCP process on attached DHCP clients.

Devices which do not force a drop of ethernet link on disabled ports

• If auto-negotiating port speed and duplex, clear all Auto-Negotiation "advertised abilities", then re-establish them.
• If hard-setting speed and duplex, cause a speed mismatch, then correct it. See 5298, for the relevant underlying MIBs.