DHCPv6总是给客户端分配一样的IPv6地址的问题，根据抓包分析，找到问题所在
1. CMTS发给dhcpv6 server的地址里面，relay头里面带的interface-id，填的都是同样的值 00000022
2. 根据itut的文档http://tools.ietf.org/html/draft-ietf-dhc-dhcpv6-ldra-03#page-6
         Servers MAY use the Interface-ID for parameter assignment policies.
   The format of the Interface-ID is outside the scope of this
   contribution.  The Interface-ID SHOULD be considered an opaque value,
   i.e. the server SHOULD NOT try to parse the contents of the
   Interface-ID option.  The LDRA SHOULD use the same Interface-ID value
   for a given interface, and this value SHOULD be retained across
   restarts.  This is because, if the Interface-ID changes, a server
   will not be able to use it reliably in parameter assignment policies.
3. 通过查看iscdhcpv6-src发现，根据interface-id去找cache的地址。造成客户端总是拿到同样的IPv6地址。
 
 
去isc的网站上看到，新版本解决了这个问题。请升级一下
 
1. cd /PATH/iscdhcpv6-src/
2. wget http://ftp.isc.org/isc/dhcp/4.2.4-P1/dhcp-4.2.4-P1.tar.gz
3. tar -zxvf dhcp-4.2.4-P1.tar.gz
4. mv /PATH/iscdhcpv6 /PATH/iscdhcpv6.old
5. ./configure --prefix=/PATH/iscdhcpv6
6. make
7. make install

And then restart DHCP server.