测试设备是一台Catalyst3750，从思科官网查看Catalyst3750对IPv6的支持情况：
Table 7 Catalyst 3750, 3560, 3560-C, 2960, 2960-S and 2960-C Switches and Cisco EtherSwitch Service Module Features and the Minimum Cisco IOS Release Required
当前版本是Version 15.0(2)SE11，显然也是支持ipv6的。但是无法配置。
Cisco IOS Software, C3750 Software (C3750-IPSERVICESK9-M), Version 15.0(2)SE11, RELEASE SOFTWARE (fc3)
Technical Support: http://www.cisco.com/techsupport
Copyright (c) 1986-2017 by Cisco Systems, Inc.
Compiled Sat 19-Aug-17 09:28 by prod_rel_team
HULC:Collect Entropy thread starting on box...
Initializing flashfs...
<snip>
配置尝试：没有找到ipv6的配置命令。
Switch(config)#ip? ip ipc Switch(config)#ipv6 uni Switch(config)#ip ro Switch(config)#ip routi Switch(config)#ip routing Switch(config)#ipv Switch(config)#? Configure commands: aaa Authentication, Authorization and Accounting. access-list Add an access list entry access-session Access Session Global Configuration Commands alias Create command alias archive Archive the configuration arp Set a static ARP entry authentication Auth Manager Global Configuration Commands auto Configure Automation banner Define a login banner beep Configure BEEP (Blocks Extensible Exchange Protocol) boot Modify system boot parameters bridge Bridge Group. buffers Adjust system buffer pool parameters call-home Enter call-home configuration mode cdp Global CDP configuration subcommands cef Cisco Express Forwarding cisp Set CISP parameters class-map Configure CPL Class Map clns Global CLNS configuration subcommands clock Configure time-of-day clock
解决方法：修改sdm template，然后重启设备。
Switch(config)# Switch(config)#sdm prefer dual-ipv4-and-ipv6 routing Changes to the running SDM preferences have been stored, but cannot take effect until the next reload. Use 'show sdm prefer' to see what SDM preference is currently active Switch(config)#end Switch#sho sdm prefer The current template is "desktop default" template. The selected template optimizes the resources in the switch to support this level of features for 8 routed interfaces and 1024 VLANs. number of unicast mac addresses: 6K number of IPv4 IGMP groups + multicast routes: 1K number of IPv4 unicast routes: 8K number of directly-connected IPv4 hosts: 6K number of indirect IPv4 routes: 2K number of IPv6 multicast groups: 0 number of IPv6 unicast routes: 0 number of directly-connected IPv6 addresses: 0 number of indirect IPv6 unicast routes: 0 number of IPv4 policy based routing aces: 0 number of IPv4/MAC qos aces: 0.5K number of IPv4/MAC security aces: 1K number of IPv6 policy based routing aces: 0 number of IPv6 qos aces: 20 number of IPv6 security aces: 25 On next reload, template will be "desktop IPv4 and IPv6 routing" template. Switch#wr Building configuration... [OK] Switch#reload Proceed with reload? [confirm] *Mar 1 00:17:37.996: %SYS-5-RELOAD: Reload requested by console. Reload Reason: Reload command. Boot Sector Filesystem (bs) installed, fsid: 2 <snip>
设备重启完毕之后，发现可以配置ipv6：
Switch#conf t Enter configuration commands, one per line. End with CNTL/Z. Switch(config)#ipv6 unicast-routing Switch(config)# Switch#conf t Enter configuration commands, one per line. End with CNTL/Z. Switch(config)#int vlan10 Switch(config-if)#ipv6 add Switch(config-if)#ipv6 address ? WORD General prefix name X:X:X:X::X IPv6 link-local address X:X:X:X::X/<0-128> IPv6 prefix autoconfig Obtain address using autoconfiguration dhcp Obtain a ipv6 address using dhcp