[ns] Question about meaning of ppagts in mip-reg.cc

[gmc50 <gmc50@it.canterbury.ac.nz>]

Hi,

I am trying to understand the Mobile IP code in mip-reg.cc but I cannot 
understand the following:

1) What is ppagts used for in:

case MIPT_ADS:
	  {
	    AgentList **ppagts = &agts_, *ptr;


	    while (*ppagts) {
	      if ((*ppagts)->node_ == miph->coa_) break;
	      ppagts = &(*ppagts)->next_;
	    }
	    if (*ppagts) {


(what is this while loop doing and what is the meaning of the if condition 
above?). I have looked at the Mobile IP chapter of the ns manual but could not 
find an answer to this.
 
Thank you very much for any clarification you may be able to provide me.

cheers,

Gustavo.