NAS-Port attribute question

[Muhammad Tayseer Alquoatli]

Hi list:
I want your help to understand how freeradius uses NAS-Port attribute
within rlm_ippool module
I was looking for the interpretation of this attribute but i couldn't
find more that "it's the physical port from which the request has
come"
reading the rlm_ippool code I've found that freeradius is using
"NAS-IP, NAS-Port" pair as a key to search in the ippool file right ?
so my questions are:
1- what does it mean with ("rlm_ippool: Searching for an entry for
nas/port: %s/%u",key.nas,key.port)? does it mean that freeradius is
searching for entries reserved by this nas/port ? and if this was true
why it then set active entries to zero ? why it assume that this IP is
not in use "i assume that active ip entry means it's in use"?

2- regarding mppp, i assume that NAS-Port should be unique for all
sessions other that mppp sessions. those mppp sessions must share the
same NAS-Port. is this the right use of the NAS-Port attribute?

3- according to sum of my assumptions, all auth requests that will be
handled by the same rlm_ippool instance and that all have the same
NAS-IP, NAS-Port, CLI will certainly have the same ip address reserved
for them in the post_auth section, and any change in the triple
(nas-ip, nas-port, cli) will certainly cause them to have different ip
address assignment. is this true? please correct me?

any pointer will be very helpful, as i couldn't find helpful resources
Thanks in advance

-- 
Muhammad Tayseer Alquoatli