参考官方文档（http://www.kernel.org/doc/Documentation/networking/ip-sysctl.txt），解释如下：
tcp_max_tw_buckets - INTEGER
Maximal number of timewait sockets held by system simultaneously.
If this number is exceeded time-wait socket is immediately destroyed
and warning is printed.
官方文档没有说明默认值，通过几个系统的简单验证，初步确定默认值是180000。
通过源码查看发现，这个选项比较简单，其实现代码如下：
=====linux-2.6.37 net/ipv4/tcp_minisocks.c 269======
void tcp_time_wait(struct sock *sk, int state, int timeo)
{
struct inet_timewait_sock *tw = NULL;
const struct inet_connection_sock *icsk = inet_csk(sk);
const struct tcp_sock *tp = tcp_sk(sk);
int recycle_ok = 0;
if (tcp_death_row.sysctl_tw_recycle && tp->rx_opt.ts_recent_stamp)
recycle_ok = icsk->icsk_af_ops->remember_stamp(sk);
if (tcp_death_row.tw_count < tcp_death_row.sysctl_max_tw_buckets)
tw = inet_twsk_alloc(sk, state);
if (tw != NULL) {
//分配成功，进行TIME_WAIT状态处理，此处略去很多代码
else {
//分配失败，不进行处理，只记录日志: TCP: time wait bucket table overflow
/* Sorry, if we're out of memory, just CLOSE this
* socket up. We've got bigger problems than
* non-graceful socket closings.
*/
NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPTIMEWAITOVERFLOW);
}
tcp_update_metrics(sk);
tcp_done(sk);
}
实测结果验证，配置为100，TIME_WAIT连接数就稳定在100，且不受组网和其它配置的影响。
官方手册中有一段警告：
This limit exists only to prevent
simple DoS attacks, you _must_ not lower the limit artificially,
but rather increase it (probably, after increasing installed memory),
if network conditions require more than default value.
基本意思是这个用于防止Dos攻击，我们不应该人工减少，如果网络条件需要的话，反而应该增加。
但其实对于我们的局域网或者公司内网应用来说，这个风险并不大。
tcp_max_tw_buckets - INTEGER
Maximal number of timewait sockets held by system simultaneously.
If this number is exceeded time-wait socket is immediately destroyed
and warning is printed.
官方文档没有说明默认值，通过几个系统的简单验证，初步确定默认值是180000。
通过源码查看发现，这个选项比较简单，其实现代码如下：
=====linux-2.6.37 net/ipv4/tcp_minisocks.c 269======
void tcp_time_wait(struct sock *sk, int state, int timeo)
{
struct inet_timewait_sock *tw = NULL;
const struct inet_connection_sock *icsk = inet_csk(sk);
const struct tcp_sock *tp = tcp_sk(sk);
int recycle_ok = 0;
if (tcp_death_row.sysctl_tw_recycle && tp->rx_opt.ts_recent_stamp)
recycle_ok = icsk->icsk_af_ops->remember_stamp(sk);
if (tcp_death_row.tw_count < tcp_death_row.sysctl_max_tw_buckets)
tw = inet_twsk_alloc(sk, state);
if (tw != NULL) {
//分配成功，进行TIME_WAIT状态处理，此处略去很多代码
else {
//分配失败，不进行处理，只记录日志: TCP: time wait bucket table overflow
/* Sorry, if we're out of memory, just CLOSE this
* socket up. We've got bigger problems than
* non-graceful socket closings.
*/
NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPTIMEWAITOVERFLOW);
}
tcp_update_metrics(sk);
tcp_done(sk);
}
实测结果验证，配置为100，TIME_WAIT连接数就稳定在100，且不受组网和其它配置的影响。
官方手册中有一段警告：
This limit exists only to prevent
simple DoS attacks, you _must_ not lower the limit artificially,
but rather increase it (probably, after increasing installed memory),
if network conditions require more than default value.
基本意思是这个用于防止Dos攻击，我们不应该人工减少，如果网络条件需要的话，反而应该增加。
但其实对于我们的局域网或者公司内网应用来说，这个风险并不大。
