在实际网络运用中我们时常跑GRE+IPSEC来实现我们中心到分支的远程访问回话，这样以来容易配置，而来可用性高，我们知道L2L无论是链路备份还是设备备份，都不是状态备份，当一个点断掉后，用经过几十秒甚至1分多种的时间收敛，才能切换到另一条线路上，重新构建ipsec回话。我们用GRE+IPSEC则可以用更少的时间来切换线路。
要求：
1.实现ipsec高可用性切换
2.在中心站点部署两台***网管，跑gre
R1:
crypto isakmp policy 10
authentication pre-share
group 2
crypto isakmp key cisco address 69.1.10.5 no-xauth
crypto isakmp key cisco address 88.88.8.4 no-xauth
crypto ipsec transform-set liang esp-des esp-md5-hmac
mode transport
crypto map mymap local-address Ethernet0/0
crypto map mymap 10 ipsec-isakmp
set peer 69.1.10.5
set transform-set liang
match address 101
crypto map mymap 20 ipsec-isakmp
set peer 88.88.8.4
set transform-set liang
match address 102
!interface Loopback0
ip address 192.168.1.1 255.255.255.0
interface Loopback1
ip address 1.1.1.1 255.255.255.255
interface Tunnel0
bandwidth 1000
ip address 10.1.15.1 255.255.255.0
ip mtu 1438
keepalive 10 3
tunnel source Ethernet0/0
tunnel destination 69.1.10.5
interface Tunnel1
ip address 10.1.14.1 255.255.255.0
ip mtu 1438
keepalive 10 3
tunnel source Ethernet0/0
tunnel destination 88.88.8.4
interface Ethernet0/0
ip address 191.1.1.1 255.255.255.0
half-duplex
crypto map mymap
router ospf 10
router-id 1.1.1.1
log-adjacency-changes
network 1.1.1.1 0.0.0.0 area 0
network 10.1.15.0 0.0.0.255 area 1
network 10.1.14.0 0.0.0.255 area 1
network 192.168.1.0 0.0.0.255 area 0
ip route 0.0.0.0 0.0.0.0 191.1.1.3
access-list 101 permit gre host 191.1.1.1 host 69.1.10.5
access-list 102 permit gre host 191.1.1.1 host 88.88.8.4
R2:
crypto isakmp policy 10
authentication pre-share
group 2
crypto isakmp key cisco address 88.88.8.4 no-xauth
crypto isakmp key cisco address 69.1.10.5 no-xauth
crypto ipsec transform-set liang esp-des esp-md5-hmac
mode transport
crypto map mymap local-address Ethernet0/1
crypto map mymap 10 ipsec-isakmp
set peer 88.88.8.4
set transform-set liang
match address 101
crypto map mymap 20 ipsec-isakmp
set peer 69.1.10.5
set transform-set liang
match address 102
interface Loopback0
ip address 192.168.2.2 255.255.255.0
interface Loopback1
ip address 2.2.2.2 255.255.255.255
interface Tunnel0
bandwidth 1000
ip address 10.1.24.2 255.255.255.0
ip mtu 1483
keepalive 10 3
tunnel source Ethernet0/1
tunnel destination 88.88.8.4
interface Tunnel1
ip address 10.1.25.2 255.255.255.0
ip mtu 1438
keepalive 10 3
tunnel source Ethernet0/1
tunnel destination 69.1.10.5
interface Ethernet0/1
ip address 192.1.1.2 255.255.255.0
router ospf 10
log-adjacency-changes
network 10.1.24.0 0.0.0.255 area 1
network 10.1.25.0 0.0.0.255 area 1
ip route 0.0.0.0 0.0.0.0 192.1.1.3
access-list 101 permit gre host 192.1.1.2 host 88.88.8.4
access-list 102 permit gre host 192.1.1.2 host 69.1.10.5
R4
crypto isakmp policy 10
authentication pre-share
group 2
crypto isakmp key cisco address 192.1.1.2 no-xauth
crypto isakmp key cisco address 191.1.1.1 no-xauth
crypto ipsec transform-set liang esp-des esp-md5-hmac
mode transport
crypto map mymap local-address Ethernet0/2
crypto map mymap 10 ipsec-isakmp
set peer 192.1.1.2
set transform-set liang
match address 101
crypto map mymap 20 ipsec-isakmp
set peer 191.1.1.1
set transform-set liang
match address 102
interface Loopback0
ip address 4.4.4.4 255.255.255.255
iterface Tunnel0
bandwidth 1000
ip address 10.1.24.4 255.255.255.0
ip mtu 1483
keepalive 10 3
tunnel source Ethernet0/2
tunnel destination 192.1.1.2
interface Tunnel1
ip address 10.1.14.4 255.255.255.0
ip mtu 1483
keepalive 10 3
tunnel source Ethernet0/2
tunnel destination 191.1.1.1
interface Ethernet0/0
ip address 192.168.3.4 255.255.255.0
full-duplex
interface Ethernet0/2
ip address 88.88.8.4 255.255.255.0
crypto map mymap
router ospf 10
router-id 4.4.4.4
log-adjacency-changes
network 4.4.4.4 0.0.0.0 area 0
network 10.1.14.0 0.0.0.255 area 1
network 10.1.24.0 0.0.0.255 area 1
network 192.168.3.0 0.0.0.255 area 0
ip route 0.0.0.0 0.0.0.0 88.88.8.3
access-list 101 permit gre host 88.88.8.4 host 192.1.1.2
access-list 102 permit gre host 88.88.8.4 host 191.1.1.1
R5
crypto isakmp policy 10
authentication pre-share
group 2
crypto isakmp key cisco address 191.1.1.1 no-xauth 两个peer 在上为主
crypto isakmp key cisco address 192.1.1.2 no-xauth
crypto ipsec transform-set liang esp-des esp-md5-hmac
mode transport
crypto map mymap local-address Ethernet1/3
crypto map mymap 10 ipsec-isakmp
set peer 191.1.1.1
set transform-set liang
match address 101
crypto map mymap 20 ipsec-isakmp
set peer 192.1.1.2
set transform-set liang
match address 102
interface Loopback0
ip address 5.5.5.5 255.255.255.255
interface Tunnel0
bandwidth 1000 GRE默认带宽是9我们指定1000 使其优先级高成为主线路
ip address 10.1.15.5 255.255.255.0
ip mtu 1438
keepalive 10 3
tunnel source Ethernet1/3
tunnel destination 191.1.1.1
interface Tunnel1
ip address 10.1.25.5 255.255.255.0
ip mtu 1438 指定mtu
keepalive 10 3
tunnel source Ethernet1/3
tunnel destination 192.1.1.2
interface Ethernet1/3
ip address 69.1.10.5 255.255.255.0
half-duplex
crypto map mymap
interface Vlan1
no ip address
router ospf 10
log-adjacency-changes
network 5.5.5.5 0.0.0.0 area 0
network 10.1.15.0 0.0.0.255 area 1
network 10.1.25.0 0.0.0.255 area 1
network 192.168.4.0 0.0.0.255 area 0
ip route 0.0.0.0 0.0.0.0 69.1.10.3
access-list 101 permit gre host 69.1.10.5 host 191.1.1.1
access-list 102 permit gre host 69.1.10.5 host 192.1.1.2
r2#show ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route
Gateway of last resort is 192.1.1.3 to network 0.0.0.0
1.0.0.0/32 is subnetted, 1 subnets
O IA 1.1.1.1 [110/11212] via 10.1.25.5, 00:19:40, Tunnel1 通过主链路学到的路由
2.0.0.0/32 is subnetted, 1 subnets
C 2.2.2.2 is directly connected, Loopback1
4.0.0.0/32 is subnetted, 1 subnets
O IA 4.4.4.4 [110/11114] via 10.1.25.5, 00:19:40, Tunnel1
5.0.0.0/32 is subnetted, 1 subnets
O IA 5.5.5.5 [110/11112] via 10.1.25.5, 00:19:40, Tunnel1
6.0.0.0/32 is subnetted, 1 subnets
O IA 6.6.6.6 [110/11113] via 10.1.25.5, 00:19:40, Tunnel1
O IA 192.168.4.0/24 [110/11112] via 10.1.25.5, 00:19:40, Tunnel1
10.0.0.0/24 is subnetted, 4 subnets
O 10.1.15.0 [110/11211] via 10.1.25.5, 00:19:40, Tunnel1
O IA 10.1.14.0 [110/22224] via 10.1.25.5, 00:00:09, Tunnel1
C 10.1.25.0 is directly connected, Tunnel1
C 10.1.24.0 is directly connected, Tunnel0
C 192.1.1.0/24 is directly connected, Ethernet0/1
192.168.1.0/32 is subnetted, 1 subnets
O IA 192.168.1.1 [110/11212] via 10.1.25.5, 00:19:40, Tunnel1
C 192.168.2.0/24 is directly connected, Loopback0
O IA 192.168.3.0/24 [110/11113] via 10.1.25.5, 00:19:40, Tunnel1
S* 0.0.0.0/0 [1/0] via 192.1.1.3
当r4出现线路故障，自动切换到r5
此图与L2L站点到站点***优势：
1.自动切换，时间短，
2.无须匹配加密数据流，可跑动态路由协议，自己协商，方便，我们只需配置GRE其他的让她们自己去协商
3.配置简单，方便配错，特别是对于多点配置，L2L***配置起来超麻烦，站点多了要配DM×××，在这我们只需起一条 tunnel 隧道就行了!
4.还有更加简单的配置 用ipsec pro 这个有时间我补在后面
5.等等 呵呵