awk '{IP[$NF]++}END{for (k in IP) print k,IP[K]}' access.log | sort -nrk2 | head
awk '{h[$NF]++}END{for(p in h)print p,h[p]}' access.log |sort -rnk2|head
awk '{print $NF}' access.log|sort |uniq -c|sort -rnk2|head