User manual

Publication 1783-UM003D-EN-E - December 2009 81
Chapter 3
The following figure and chart illustrate DHCP persistence behavior.
FA1
FA2
FA3
FA7
FA4
FA5
FA6
FA8
Switch 1
Switch 2
If Then
• Switch 1 has ports FA1…FA3 in its persistence
table
• Switch 2 has ports FA4, FA5, FA6 and FA8 in its
persistence table
• Reserve Only is not selected and DHCP snooping is
off
A new device connected to switch 1 FA1 receives an IP address from the Switch 1
persistence table. A broadcast request is also sent across the network. Switch 2
will respond if there is an unassigned address in its pool. This may override the
assignment made by switch 1.
• Switch 1 has ports FA1…FA3 in its persistence
table
• Switch 2 has ports FA4, FA5, FA6 and FA8 in its
persistence table
• Reserve Only is selected in both switches and
DHCP snooping is off
A new device connected to switch 1 FA1 receives an IP address from the switch 1
persistence table. A broadcast request is also sent across the network. Switch 2
will not respond to the request. Note that if the device is connected to FA7 of
switch 1, it will not receive an IP address from the switch pool, since it is not
defined in the persistence table, and unused addresses in the pool are blocked.
• Switch 1 has ports FA1…FA3 in its persistence
table
• Switch 2 has ports FA4, FA5, FA6 and FA8 in its
persistence table
• Reserve Only is selected in switch 1 and DHCP
snooping is off, but not switch 2 when DHCP
snooping is off
A new device is connected to FA1 receives an IP address from the persistence
table. A broadcast request is also sent across the network. Switch 2 will not
respond to the request. In addition, a device connected to FA4 receives an IP
address from the switch 2 persistence table. A broadcast request is sent out, and
switch 1 responds with an unused IP address from its pool.This may override the
assigned port.
• Switch 1 has ports FA1…FA3 in its persistence
table
• Switch 2 has ports FA4, FA5, FA6 and FA8 in its
persistence table
• DHCP Snooping is selected
• Reserved only is selected
A new device connected to switch 1 FA1 receives an IP address from the Switch 1
persistence table. A broadcast request is not sent across the network, therefore
Switch 2 will not respond. Note that if a device is connected to FA7 (not defined in
the DHCP persistence table) of Switch 1, it will not receive an IP address from the
switch pool, since it is not defined in the persistence table, and unused addresses
in the pool are blocked.
• Switch 1 has ports FA1…FA3 in its persistence
table
• Switch 2 has ports FA4, FA5, FA6 and FA8 in its
persistence table
• DHCP Snooping is selected
• Reserved only is not selected
A new device connected to switch 1 FA1 receives an IP address from the Switch 1
persistence table. A broadcast request is not sent across the network, therefore
Switch 2 will not respond. Note that if a device is connected to FA7 (not defined in
the DHCP persistence table) of Switch 1, it will receive an unassigned IP address
from the Switch 1 pool.