neighbor cache 3 a in the mr 3 the mr 3 does not however forward the neighbor advertisements from the mnns 7 to the access network 4 instead the mr 3 sends a neighbor advertisement to the access network 4 on behalf of the mnns 7 the neighbor advertisement in this case contains the mapping between the coa of each mnn 7 and the lla_mr which are recorded in the neighbor cache 5 a of the ar 5 when a downlink packet one directed towards a mnn 7 reaches the ar 5 the ar 5 checks its neighbor cache 5 a and obtains the lla of the mr 3 by using the coa of the mnn 7 that is carried in the ip layer destination address field of the downlink packet that is the ar 5 indexes into the neighbor cache 5 a using the coa to look up the corresponding lla_mr of the mr 3 associated with the monet 1 that contains the mnn 7 the ar 5 then transmits the downlink packet s in the l2 frame to the correspondent mr 3 using the lla_mr after receiving the l2 frame from the ar 5 the mr 3 checks its neighbor cache 3 a and obtains the lla of the correspondent mnn 7 based on the coa carried in the ip layer destination address of the arriving packet s then transmits the packet s to the mnn 7 using lla of the.