coax mn1 also the bu received from mn1 100 must be verified based on this address consequently mn1 100 must be aware of coax mn1 and must calculate the bu authenticator based on coaxmn1 instead of coa mn1 in 306 for successful bu authentication also the bu message must contain coax mn1 instead of coa mn1 this requires modification of the mn implementation fig4 shows a variant which prevents this modification i e mn1 100 calculates the bu authenticator using coa mn1 as usual to allow a successful verification at cn ar1 200 recalculates the authenticator using coax mn1 and substitutes the authenticator in the bu messages 408 therefore ar1 200 needs to know home and care of keygen token which it can determine from the earlier received hot and cot messages 400 and 406 they are stored together with the corresponding hoas and coas the replacement of the coa can be done as in modified mn variant 402 404 410 412 and 414 fig7 shows the method of fig3 and 4 in form of a flow diagram in step 700 ar2 substitutes the care of address of mn1 in the source address field of the ip header of the coti message with coax of mn1 then in step 702 ar2 substitutes coax of mn1 in the destination address field of the ip header of the cot message with the coa.