Tethering技术在移动平台上已经运用的越来越广泛了，它可以把移动设备当做一个接入点，其它的设备可以通过Wi-Fi，USB或是Bluetooth等方式连接到此移动设备。
最近在Telechips的TCC8900开发板上调试网络设备，需要在Linux下实现简单的Tethering，通过Wi-Fi的Ad-hoc 模式，将网络连接共享给其它设备。开发板上一个有线网卡(eth1)，一个无线网卡(eth0)，eth1连接到外网，eth0作为AP共享给另一台装了无线网卡的PC，使得PC可以通过开发板连接到外网。(内网的ip地址为192.168.0.*)
分析下来需要实现以下几个简单的功能：1. Wi-Fi的Master或Ad-hoc模式配置2. NAT3. DHCP服务器
Wi-Fi模式设置随开发板提供的是AR6102，一个SDIO接口的Wi-Fi，从硬件说明上看，这个Wi-Fi只支持Ad-hoc的点对点的模式，而无法支持AP，因此使用iwconfig将它设置成Ad-hoc模式
1iwconfig eth0 mode ad-hoc 2iwconfig eth0 enc s:12345 3iwconfig eth0 essid "tcc8900" 4ifconfig eth0 up 5ifconfig eth0 192.168.0.1NAT使用iptables实现iptables可以实现地址翻译，防火墙，端口过滤等功能，这里只用到了最基本的地址翻译，使得PC可以访问外网
1iptables -t nat -A POSTROUTING -o eth1 -s 192.168.0.0/24 -j MASQUERADE 2echo "1" > /proc/sys/net/ipv4/ip_forwardDHCP服务使用udhcpd搭建需要新建一个配置文件，默认为/etc/udhcpd.conf，另外需要一个lease（租约）的记录文件，默认为/etc/udhcpd.leases，可以用dumpleases命令来查看已连接的客户端的租约情况。
1touch /etc/udhcpd.leases 2udhcpd -S /etc/udhcpd.conf提供一个udhcpd.conf的例子。
01# Sample udhcpd configuration file (/etc/udhcpd.conf) 02# The start and end of the IP lease block 03start 192.168.0.2 04end 192.168.0.100 05 06# The interface that udhcpd will use 07interface eth0 #default: eth0 08 09# The maximim number of leases (includes addressesd reserved 10# by OFFER's, DECLINE's, and ARP conficts 11max_leases 20 #default: 254 12 13# If remaining is true (default), udhcpd will store the time 14# remaining for each lease in the udhcpd leases file. This is 15# for embedded systems that cannot keep time between reboots. 16# If you set remaining to no, the absolute time that the lease 17# expires at will be stored in the dhcpd.leases file. 18remaining yes #default: yes 19 20# The time period at which udhcpd will write out a dhcpd.leases 21# file. If this is 0, udhcpd will never automatically write a 22# lease file. (specified in seconds) 23auto_time 7200 #default: 7200 (2 hours) 24 25# The amount of time that an IP will be reserved (leased) for if a 26# DHCP decline message is received (seconds). 27decline_time 3600 #default: 3600 (1 hour) 28 29# The amount of time that an IP will be reserved (leased) for if an 30# ARP conflct occurs. (seconds) 31conflict_time 3600 #default: 3600 (1 hour) 32 33# How long an offered address is reserved (leased) in seconds 34offer_time 60 #default: 60 (1 minute) 35 36# If a lease to be given is below this value, the full lease time is 37# instead used (seconds). 38min_lease 60 #defult: 60 39 40# The location of the leases file 41lease_file /etc/udhcpd.leases 42 43# The remainer of options are DHCP options and can be specifed with the 44# keyword 'opt' or 'option'. If an option can take multiple items, such 45# as the dns option, they can be listed on the same line, or multiple 46# lines. The only option with a default is 'lease'. 47 48#Examples 49opt dns 8.8.8.8 8.8.8.4 50option subnet 255.255.255.0 51opt router 192.168.0.1