working

root@OpenWrt:~# reset; \
> NET_IF="wan"; \
> NET_DEV="$(uci get network.${NET_IF}.ifname)"; \
i> ifup "${NET_IF}"; sleep 10; \
> tcpdump -v -n -i "${NET_DEV}" udp port 67 or udp port 68 & \
> ip address show dev "${NET_DEV}"; \
> kill -SIGUSR2 "$(pidof udhcpc)"; sleep 10; \
> ip address show dev "${NET_DEV}"; \
> kill -SIGUSR1 "$(pidof udhcpc)"; sleep 10; \
> ip address show dev "${NET_DEV}"; \
> killall tcpdump

10: eth1.2@eth1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP qlen 1000
    link/ether 24:f5:a2:c4:7a:d0 brd ff:ff:ff:ff:ff:ff
    inet 162.211.151.92/24 brd 162.211.151.255 scope global eth1.2
       valid_lft forever preferred_lft forever
    inet6 fe80::26f5:a2ff:fec4:7ad0/64 scope link
       valid_lft forever preferred_lft forever
tcpdump: listening on eth1.2, link-type EN10MB (Ethernet), capture size 262144 bytes
10: eth1.2@eth1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP qlen 1000
    link/ether 24:f5:a2:c4:7a:d0 brd ff:ff:ff:ff:ff:ff
    inet 162.211.151.92/24 brd 162.211.151.255 scope global eth1.2
       valid_lft forever preferred_lft forever
    inet6 fe80::26f5:a2ff:fec4:7ad0/64 scope link
       valid_lft forever preferred_lft forever
10: eth1.2@eth1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP qlen 1000
    link/ether 24:f5:a2:c4:7a:d0 brd ff:ff:ff:ff:ff:ff
    inet 162.211.151.92/24 brd 162.211.151.255 scope global eth1.2
       valid_lft forever preferred_lft forever
    inet6 fe80::26f5:a2ff:fec4:7ad0/64 scope link
       valid_lft forever preferred_lft forever

0 packets captured
0 packets received by filter
0 packets dropped by kernel