I mean local clients (servers) behind the router cannot ping the router (gateway).When you say "clients cannot ping the router", do you mean clients at your local network or clients elsewhere on the internet?
ND is disabled.So that could be an ND issue... Check what is happening in IPv6->Neighbors
(interestingly, the menus "ND" and "Neighbors" are swapped in IPv6)
# cat cron_fix_ipv6.sh #!/bin/sh for i in `seq 1 55` do ip nei flu all ping -6 ipv6gw -c 1 sleep 1 done