ipv6中获得ip的几种方式：
1. 手动配置，命令：ipv6 address xxxx:xxxx:xxxx:xxxx:xxxx:xxxx:xxxx:xxxx/nn
2. stateless autoconfiguration，过程如下：(假设r1已经在与host1互联的接口上配置好了一个global unicast address)
a. host1通过r1的RA发现这条链路上的prefix
b. host1生成一个interface id，并添加在prefix的后面
c. host1通过DAD判断这个地址是否唯一，如果唯一则使用次地址。
cisco的路由器可以通过关闭RA来禁止stateless autoconfiguration，命令：ipv6 nd suppress-ra，默认这个命令是关闭的。
由于有了stateless autoconfiguration，那么一个企业更换sp的时候就不需要手动在每台pc上更换地址，而只要将路由器上每个接口的prefix改掉就可以了。并且cisco还提供了一个接口级的命令：ipv6 nd prefix at ，这样就可以设置在某一时间自动更改接口的prefix。(注，这个命令需要时间的准确性，可惜的是cisco的设备还不支持ipv6的ntp)
3. stateful dhcp，功能较强两种方式都更为强大。默认情况下，cisco路由器使用RA发送有关stateless autoconfiguration的信息，如果想只使用stateful dhcp，那么需要输入接口命令：ipv6 nd managed-config-flag(但不推见这样做)
4. dhcp-pd(dhcp prefix delegation)，地址委派。在pe-ce的简单环境下，只需要在pe配置好ipv6的地址和ipv6 dhcp池，那么ce就可以直接通过dhcp获得接口地址，并且在其下联接口上仍然可以获得dhcp池中的地址。这样做也是为了方便用户更换sp。
*但在实际的运营中，还是第一种方法最为可靠保险。
dhcp-pd和stateless autoconfiguration的配置
R1
hostname R1
!
ipv6 unicast-routing
!
interface Ethernet1/1
no ip address
duplex full
ipv6 address test ::C800:5AFF:FE3F:1D/64
ipv6 enable
!
interface Ethernet1/2
duplex full
ipv6 address autoconfig default
ipv6 enable
ipv6 dhcp client pd test
R2
hostname R2
!
ipv6 unicast-routing
ipv6 dhcp pool test
prefix-delegation pool test
!
interface Ethernet1/1
duplex full
ipv6 address 2001::C800:5AFF:FE40:1D/64
ipv6 enable
ipv6 dhcp server test
!
ipv6 local pool test 2001:1::/48 64
R1
R1#sho ipv6 interface e1/2
Ethernet1/2 is up, line protocol is up
IPv6 is enabled, link-local address is FE80::C800:5AFF:FE3F:1E
Global unicast address(es):
2001::C800:5AFF:FE3F:1E, subnet is 2001::/64 [PRE]
valid lifetime 2591870 preferred lifetime 604670
Joined group address(es):
FF02::1
FF02::2
FF02::1:FF3F:1E
MTU is 1500 bytes
ICMP error messages limited to one every 100 milliseconds
ICMP redirects are enabled
ND DAD is enabled, number of DAD attempts: 1
ND reachable time is 30000 milliseconds
ND advertised reachable time is 0 milliseconds
ND advertised retransmit interval is 0 milliseconds
ND router advertisements are sent every 200 seconds
ND router advertisements live for 1800 seconds
Hosts use stateless autoconfig for addresses.
R1#
R1#sho ipv6 dhcp interface e1/2
Ethernet1/2 is in client mode
State is OPEN
Renew will be sent in 3d08h
List of known servers:
Reachable via address: 2001::C800:5AFF:FE40:1D
DUID: 00030001CA005A400000
Preference: 0
Configuration parameters:
IA PD: IA ID 0x00060001, T1 302400, T2 483840
Prefix: 2001:1::/64
preferred lifetime 604800, valid lifetime 2592000
expires at Nov 24 2006 08:23 PM (2580964 seconds)
Prefix name: test
Rapid-Commit: disabled
R1#
R1#sho ipv6 route
IPv6 Routing Table - 7 entries
Codes: C - Connected, L - Local, S - Static, R - RIP, B - BGP
U - Per-user Static route
I1 - ISIS L1, I2 - ISIS L2, IA - ISIS interarea, IS - ISIS summary
O - OSPF intra, OI - OSPF inter, OE1 - OSPF ext 1, OE2 - OSPF ext 2
ON1 - OSPF NSSA ext 1, ON2 - OSPF NSSA ext 2
S ::/0 [1/0]
via FE80::C800:5AFF:FE40:1D, Ethernet1/2
C 2001::/64 [0/0]
via ::, Ethernet1/2
L 2001::C800:5AFF:FE3F:1E/128 [0/0]
via ::, Ethernet1/2
C 2001:1::/64 [0/0]
via ::, Ethernet1/1
L 2001:1::C800:5AFF:FE3F:1D/128 [0/0]
