我正在尝试设置 LAN 到 LAN IPsec 隧道，并且在一个端点我有一个运行 IOS 12.3(8)YI2 的旧 CISCO 871W。命令“隧道模式 ipsec ipv4”不起作用：
router#configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
router(config)#interface tunnel 1
router(config-if)#tunnel mode ipsec ipv4
^
% Invalid input detected at '^' marker.
router(config-if)#tunnel mode ?
aurp AURP TunnelTalk AppleTalk encapsulation
cayman Cayman TunnelTalk AppleTalk encapsulation
dvmrp DVMRP multicast tunnel
eon EON compatible CLNS tunnel
gre generic route encapsulation protocol
ipip IP over IP encapsulation
iptalk Apple IPTalk encapsulation
nos IP over IP encapsulation (KA9Q/NOS compatible)
任何想法为什么？谢谢！