DHCP on NW5.1 SP5 :

let's say I have two segment :
A) 10.10.10.0/24 (pool from 10.10.10.70 -> 10.10.10.130) on ServerA
(site A)
B) 10.10.20.0/24 (pool from 10.10.20.70 -> 10.10.20.130) on ServerB
(site B)
a user A (from site A)is defined in pool A to receive an address
"assignment type :Manual, Mac Type: 1 Ethernet 10", everything is ok,
here.
When the user move to site B, the user does not receive any IP
address,
until I create a manual assignemt for that Mac Address in that pool.
Even if forcing with "IPCONFIG /RELEASE /RENEW /PLEASE" ... etc

why ?
what did I did wrong ?

thanks
Pascal