I set up my BBB to static IP address like below:root@beaglebone:/var/log# cat /etc/network/interfaces# This file describes the network interfaces available on your system# and how to activate them. For more information, see interfaces(5).# The loopback network interfaceauto loiface lo inet loopback# The primary network interfaceauto eth0iface eth0 inet static    address 192.168.0.99    netmask 255.255.255.0    gateway 192.168.0.1# Example to keep MAC address between reboots#hwaddress ether DE:AD:BE:EF:CA:FE# WiFi Example#auto wlan0#iface wlan0 inet dhcp#    wpa-ssid essid#    wpa-psk  password# Ethernet/RNDIS gadget (g_ether)# ... or on host side, usbnet and random hwaddr# Note on some boards, usb0 is automaticly setup with an init script# in that case, to completely disable remove file [run_boot-scripts] from the boot partitioniface usb0 inet static    address 192.168.7.2    netmask 255.255.255.0    network 192.168.7.0    gateway 192.168.7.1And the DNS config of China like below:root@beaglebone:/var/log# cat /etc/resolv.confnameserver 202.96.128.86nameserver 202.96.134.33From 2015-12-15 17:04:33 to 2015-12-22 23:03:41, my BBB worked with static IP address 192.168.0.99 well. After that then, my BBB static IP address was changed strangely to 192.168.0.128:root@beaglebone:/var/log# ip addr show1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00    inet 127.0.0.1/8 scope host lo    inet6 ::1/128 scope host       valid_lft forever preferred_lft forever2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000    link/ether d0:5f:b8:e8:b3:86 brd ff:ff:ff:ff:ff:ff    inet 192.168.0.128/24 brd 192.168.0.255 scope global eth0    inet6 fe80::d25f:b8ff:fee8:b386/64 scope link       valid_lft forever preferred_lft forever3: usb0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc pfifo_fast state DOWN qlen 1000    link/ether ba:5c:46:47:5f:c1 brd ff:ff:ff:ff:ff:ff    inet 192.168.7.2/30 brd 192.168.7.3 scope global usb0And the /var/log/messages like below (Why?):Dec 22 23:03:41 beaglebone kernel: [626417.699238] libphy: 4a101000.mdio:00 - Link is DownDec 22 23:03:44 beaglebone kernel: [626420.411322] net eth0: initializing cpsw version 1.12 (0)Dec 22 23:03:44 beaglebone kernel: [626420.414330] net eth0: phy found : id is : 0x7c0f1Dec 22 23:03:44 beaglebone kernel: [626420.430487] IPv6: ADDRCONF(NETDEV_UP): eth0: link is not readyDec 22 23:03:45 beaglebone kernel: [626421.064855] net eth0: initializing cpsw version 1.12 (0)Dec 22 23:03:45 beaglebone kernel: [626421.067713] net eth0: phy found : id is : 0x7c0f1Dec 22 23:03:45 beaglebone kernel: [626421.083786] IPv6: ADDRCONF(NETDEV_UP): eth0: link is not readyDec 22 23:03:47 beaglebone kernel: [626423.075018] libphy: 4a101000.mdio:00 - Link is Up - 100/FullDec 22 23:03:47 beaglebone kernel: [626423.075152] IPv6: ADDRCONF(NETDEV_CHANGE): eth0: link becomes readyDec 22 23:03:51 beaglebone kernel: [626427.215227] net eth0: initializing cpsw version 1.12 (0)Dec 22 23:03:51 beaglebone kernel: [626427.218207] net eth0: phy found : id is : 0x7c0f1Dec 22 23:03:51 beaglebone kernel: [626427.234320] IPv6: ADDRCONF(NETDEV_UP): eth0: link is not readyDec 22 23:03:51 beaglebone kernel: [626427.637475] net eth0: initializing cpsw version 1.12 (0)Dec 22 23:03:51 beaglebone kernel: [626427.640382] net eth0: phy found : id is : 0x7c0f1Dec 22 23:03:51 beaglebone kernel: [626427.656675] IPv6: ADDRCONF(NETDEV_UP): eth0: link is not readyDec 22 23:03:53 beaglebone kernel: [626429.645608] libphy: 4a101000.mdio:00 - Link is Up - 100/FullDec 22 23:03:53 beaglebone kernel: [626429.645732] IPv6: ADDRCONF(NETDEV_CHANGE): eth0: link becomes readyMy uname -a as below:Linux beaglebone 3.8.13-bone47 #1 SMP Fri Apr 11 01:36:09 UTC 2014 armv7l GNU/LinuxNo one acessed the BeagleBone to change it's ip, Why the eth0 was down and up around 2015-12-22 23:03:41? Why the static ip address was changed after down and up ?PS.BeagleBone never rebooted all the timeI found a similar Q of Static IP address shifting to 192.168.1.251, it didn't helpI checked the command history, no commands was found around 2015-12-22 23:03:41UPDATE1 I found that hot-pluged the network cable would call the case mentioned above, and the dmesg appeared the same to above, but what was reason? Maybe my interchanger rebooted last night around 2015-12-22 23:03:41, i'm not suredUPDATE2root@beaglebone:~# ps ax | grep dhc 1132 ?        Ss     0:00 /usr/sbin/udhcpd -S /etc/udhcpd.conf10022 ?        Ss     0:00 /sbin/dhclient -v eth020352 pts/1    S+     0:00 grep dhc
BeagleBone Black static IP address was changed strangely
networking