Can't connect to Internet(network). Why is route (default gateway) deleted when DHCPDISCOVER happens ?

Issue

I can not connect to Internet(network) when the following messages appear

Dec 21 12:33:37 HOST-A dhclient[1142]: DHCPREQUEST on eth0 to 192.168.1.1 port 67 (xid=0x25c2f67e)
Dec 21 12:33:37 HOST-A dhclient[1142]: DHCPNAK from 192.168.1.1 (xid=0x25c2f67e)
Dec 21 12:33:37 HOST-A dhclient[1142]: DHCPDISCOVER on eth0 to 255.255.255.255 port 67 interval 5 (xid=0x140685d3)
Dec 21 12:33:37 HOST-A dhclient[1142]: DHCPOFFER from 192.168.1.1
Dec 21 12:33:37 HOST-A dhclient[1142]: DHCPREQUEST on eth0 to 255.255.255.255 port 67 (xid=0x140685d3)
Dec 21 12:33:37 HOST-A dhclient[1142]: DHCPACK from 192.168.1.1 (xid=0x140685d3)
Dec 21 12:33:38 HOST-A ntpd[2012]: Deleting interface #7 eth0, 192.168.1.42#123, interface stats: received=0, sent=0, dropped=0, active_time=1282 secs

When these messages happens, it seems that route (default gateway) is deleted so you can not connect the network.