うまくいってませんが、下記のような感じで良いのでしょうか？

http-client 1
request-timeout 10 retry 5
method 1 get url http://uuuuu:[email protected]/login.html i4 $i4
reference-interface pppoe 1
source-interface lan 1
logging error
exit

interface pppoe 1
ddns-client address ip action http-client 1 delay 30 interval 30