DHCP Transaction ID生成和使用方法

    今天领导问了一下DHCP事务ID的问题。仔细研究了一下。

    下面三段摘录于rfc1541，大致解释了xid的生成和使用方法。
 
   The client generates and records a random transaction identifier and  inserts that identifier into the 'xid' field.  The client records its   own local time for later use in computing the lease expiration.  The   client then broadcasts the DHCPDISCOVER on the local hardware   broadcast address to 0xffffffff IP broadcast address and 'DHCP   server' UDP port.
   客户端生成一个随机数事务ID，并记录下来，然后把它插入到xid字段。客户端发送DHCP DISCOVER广播报文。
 
   The server inserts the 'xid' field from the DHCPDISCOVER message into  the 'xid' field of the DHCPOFFER message and sends the DHCPOFFER   message to the requesting client.
   服务器从DHCP DISCOVER消息解析得到xid值，把xid值插入到DHCP OFFER消息的xid字段，发送DHCP OFFER报文到请求客户端。
 
   If the 'xid' of an arriving DHCPOFFER message does not match the   'xid' of the most recent DHCPDISCOVER message, the DHCPOFFER message   must be silently discarded.  Any arriving DHCPACK messages must be   silently discarded.
   如果DHCP OFFER消息中的xid值与最近发送DHCP DISCOVER消息中的xid值不同，那么客户端必须忽略这个DHCP OFFER。接收到的任何DHCPACK必须悄悄地丢弃。