配置GRE

1、配置GRE
1. 配置基础网络环境
1) 配置R1：
R1(config)#int e0/0
R1(config-if)#ip add 10.1.1.1 255.255.255.0
R1(config-if)#no sh
R1(config-if)#int e0/1
R1(config-if)#ip add 100.1.1.1 255.255.255.0
R1(config-if)#no sh
R1(config-if)#exit
R1(config)#ip route 0.0.0.0 0.0.0.0 100.1.1.5
说明：配置R1的接口地址，并写默认路由指向Internet（路由器R5），地址100.1.1.5。

2) 配置R2：
R2(config)#int e0/0
R2(config-if)#ip add 10.1.1.2 255.255.255.0
R2(config-if)#no sh
R2(config-if)#exit
R2(config)#ip route 0.0.0.0 0.0.0.0 10.1.1.1
说明：配置R2的接口地址，并写默认路由指向R1。

3) 配置R3：
R3(config)#int e0/0
R3(config-if)#ip add 200.1.1.1 255.255.255.0
R3(config-if)#no sh
R3(config-if)#int e0/1
R3(config-if)#ip add 192.168.1.3 255.255.255.0
R3(config-if)#no sh
R3(config-if)#exit
R3(config)#ip route 0.0.0.0 0.0.0.0 200.1.1.5
说明：配置R3的接口地址，并写默认路由指向Internet（路由器
R5），地址200.1.1.5。

4) 配置R4：
R4(config)#int e0/1
R4(config-if)#ip add 192.168.1.4 255.255.255.0
R4(config-if)#no sh
R4(config-if)#exit
R4(config)#ip route 0.0.0.0 0.0.0.0 192.168.1.3
说明：配置R4的接口地址，并写默认路由指向R3。

5) 配置R5：
R5(config)#int e0/1
R5(config-if)#ip add 100.1.1.5 255.255.255.0
R5(config-if)#no sh
R5(config-if)#int e0/0
R5(config-if)#ip add 200.1.1.5 255.255.255.0
R5(config-if)#no sh
说明：配置R5的接口地址，因为R5模拟Internet，R5只需要有公网路由100.1.1.0和200.1.1.0即可，所以R5不需要写任何路由，也不允许写任何路由。

2. 测试基础网络环境
1) 查看R5的路由表：
R5#show ip route
Codes: L - local, 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, H - NHRP, l - LISP + - replicated route, % - next hop override
Gateway of last resort is not set
100.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C 100.1.1.0/24 is directly connected, Ethernet0/1
L 100.1.1.5/32 is directly connected, Ethernet0/1
200.1.1.0/24 is variably subnetted, 2 subnets, 2 masks
C 200.1.1.0/24 is directly connected, Ethernet0/0
L 200.1.1.5/32 is directly connected, Ethernet0/0
说明：因为R5为Internet路由器，所以R5只有公网路由，没有用
户的私网路由，也不应该有用户的私网路由。

2) 测试上海分公司路由器R1到北京分公司路由器R3的连通
性：
R1#ping 200.1.1.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 200.1.1.1, timeout is 2 seconds:
.!!!!
Success rate is 80 percent (4/5), round-trip min/avg/max = 1/1/1 ms
说明：因为双方路由器都接入Internet，所以使用公网地址
100.1.1.1和200.1.1.1是可以正常通信的。

3) 测试上海分公司R2直接使用私有地址192.168.1.4到北京分公
司R4的连通性：
R2#ping 192.168.1.4
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.168.1.4, timeout is 2 seconds:
.....
Success rate is 0 percent (0/5)
说明：因为Internet中的路由器只有公网路由，没有用户的私有
网段，所以上海分公司R2直接使用私有地址192.168.1.4与北京分
公司R4无法通信。

4) 跟踪上海分公司R2到北京分公司的路径信息：
R2#traceroute 192.168.1.4
Type escape sequence to abort.
Tracing the route to 192.168.1.4
VRF info: (vrf in name/id, vrf out name/id)
1 10.1.1.1 0 msec 0 msec 0 msec
2 * * *
3 * * *
4 * * *
5 * * *
6 * * *
说明：从结果中可以看出，由于Internet没有用户的私有网段，
所以数据包出了公司路由器后，到达Internet就被丢弃了。

3. 在上海分公司与北京分公司之间配置GRE隧道
1) 在上海分公司路由器R1上配置连接到北京分公司路由器R3
的GRE隧道：
R1(config)#int tunnel 1
R1(config-if)#ip add 1.1.1.1 255.255.255.0
R1(config-if)#tunnel source 100.1.1.1
R1(config-if)#tunnel destination 200.1.1.1
说明：在R1上创建GRE虚拟链路（隧道）接口，号码为1，两端
号码可不相同；隧道接口地址为1.1.1.1/24，隧道的起源为
100.1.1.1，隧道的终点为200.1.1.1。

2) 查看R1当前的隧道接口状态：
R1#show interfaces tunnel 1
Tunnel1 is up, line protocol is up
Hardware is Tunnel
Internet address is 1.1.1.1/24
MTU 17916 bytes, BW 100 Kbit/sec, DLY 50000 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation TUNNEL, loopback not set
Keepalive not set
Tunnel source 100.1.1.1, destination 200.1.1.1
Tunnel protocol/transport GRE/IP
Key disabled, sequencing disabled
Checksumming of packets disabled
Tunnel TTL 255, Fast tunneling enabled
Tunnel transport MTU 1476 bytes
Tunnel transmit bandwidth 8000 (kbps)
Tunnel receive bandwidth 8000 (kbps)
Last input never, output never, output hang never
Last clearing of "show interface" counters 00:02:31
Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
Queueing strategy: fifo
Output queue: 0/0 (size/max)
5 minute input rate 0 bits/sec, 0 packets/sec
5 minute output rate 0 bits/sec, 0 packets/sec
0 packets input, 0 bytes, 0 no buffer
Received 0 broadcasts (0 IP multicasts)
0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
0 packets output, 0 bytes, 0 underruns
0 output errors, 0 collisions, 0 interface resets
0 unknown protocol drops
0 output buffer failures, 0 output buffers swapped out
说明：可以看出，在R1创建GRE隧道之后，隧道接口状态便已
经up，这是因为默认情况下，GRE隧道接口没有OSI一层协议做检测，只要本端源地址有效，并且隧道终点地址有路由可达，那么GRE隧道接口就会up，而无论隧道对端是否已经配置隧道接口。

3) 在北京分公司路由器R3上配置连接到上海分公司路由器R1
的GRE隧道：
R3(config)#int tunnel 3
R3(config-if)#ip add 1.1.1.2 255.255.255.0
R3(config-if)#tunnel source 200.1.1.1
R3(config-if)#tunnel destination 100.1.1.1
说明：在R3上创建GRE虚拟链路（隧道）接口，号码为3，两端
号码可不相同；隧道接口地址为1.1.1.2/24，隧道的起源为
200.1.1.1，隧道的终点为100.1.1.1。

4) 查看R3当前的隧道接口状态：
R3#show interfaces tunnel 3
Tunnel3 is up, line protocol is up
Hardware is Tunnel
Internet address is 1.1.1.2/24
MTU 17916 bytes, BW 100 Kbit/sec, DLY 50000 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation TUNNEL, loopback not set
Keepalive not set
Tunnel source 200.1.1.1, destination 100.1.1.1
Tunnel protocol/transport GRE/IP
Key disabled, sequencing disabled
Checksumming of packets disabled
Tunnel TTL 255, Fast tunneling enabled
Tunnel transport MTU 1476 bytes
Tunnel transmit bandwidth 8000 (kbps)
Tunnel receive bandwidth 8000 (kbps)
Last input never, output never, output hang never
Last clearing of "show interface" counters 00:00:57
Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
Queueing strategy: fifo
Output queue: 0/0 (size/max)
5 minute input rate 0 bits/sec, 0 packets/sec
5 minute output rate 0 bits/sec, 0 packets/sec
0 packets input, 0 bytes, 0 no buffer
Received 0 broadcasts (0 IP multicasts)
0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
0 packets output, 0 bytes, 0 underruns
0 output errors, 0 collisions, 0 interface resets
0 unknown protocol drops
0 output buffer failures, 0 output buffers swapped out
说明：R3上GRE隧道状态也已经up。

4. 测试GRE隧道
1) 测试R1与R3之间的GRE隧道连通性：
R1#ping 1.1.1.2
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 1.1.1.2, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 1/1/1 ms
说明：因为R1与R3双方GRE隧道已经成功建立，并且状态都为up，所以隧道连通性正常。

2) 再次测试上海分公司R2直接使用私有地址192.168.1.4到北京
分公司R4的连通性：
R2#ping 192.168.1.4
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.168.1.4, timeout is 2 seconds:
.....
Success rate is 0 percent (0/5)
说明：上海分公司的路由器R1在收到去往192.168.1.4后，因为
默认路由从真实接口E0/1出去，结果数据包被发到Internet中的路
由器R5，由于Internet路由器R5只有公网路由，没有用户的私有网段，所以上海分公司R2直接使用私有地址192.168.1.4与北京分公
司R4无法通信，如下是R1路由表：
R1#show ip route
Codes: L - local, 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, H - NHRP, l - LISP
+ - replicated route, % - next hop override
Gateway of last resort is 100.1.1.5 to network 0.0.0.0
S* 0.0.0.0/0 [1/0] via 100.1.1.5
1.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C 1.1.1.0/24 is directly connected, Tunnel1
L 1.1.1.1/32 is directly connected, Tunnel1
10.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C 10.1.1.0/24 is directly connected, Ethernet0/0
L 10.1.1.1/32 is directly connected, Ethernet0/0
100.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C 100.1.1.0/24 is directly connected, Ethernet0/1
L 100.1.1.1/32 is directly connected, Ethernet0/1
要解决此问题，必须让流量从GRE隧道中传输。

3) 在创建GRE隧道的路由器双方将去往对方私有网段的数据包
引入GRE隧道中传输：
R1：
R1(config)#ip route 192.168.1.0 255.255.255.0 tunnel 1
R3：
R3(config)#ip route 10.1.1.0 255.255.255.0 tunnel 3
4) 再次测试上海分公司R2直接使用私有地址192.168.1.4到北京
分公司R4的连通性：
R2#ping 192.168.1.4
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.168.1.4, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 1/1/1 ms
说明：上海分公司的路由器R1在收到去往192.168.1.4后，因为
路由192.168.1.0已经指向GRE隧道，对方同样也已经回指向GRE隧道，所以上海分公司R2直接使用私有地址192.168.1.4与北京分公
司R4通信正常。

5) 再次跟踪上海分公司R2到北京分公司的路径信息：
R2#traceroute 192.168.1.4
Type escape sequence to abort.
Tracing the route to 192.168.1.4
VRF info: (vrf in name/id, vrf out name/id)
1 10.1.1.1 0 msec 0 msec 0 msec
2 1.1.1.2 0 msec 0 msec 0 msec
3 192.168.1.
4 0 msec 0 msec *
说明：可以看见，上海与北京分公司私有网段之间的流量已经在隧道中传输，所以通信正常。

2、配置GRE keepalive
说明：延续上一小节的实验环境，继续测试GRE keepalive。

1. 检测当前GRE隧道状态
1) 查看R1当前的隧道接口状态：
r1#show interfaces tunnel 1
Tunnel1 is up, line protocol is up
Hardware is Tunnel
Internet address is 1.1.1.1/24
MTU 1514 bytes, BW 9 Kbit, DLY 500000 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation TUNNEL, loopback not set
Keepalive not set
Tunnel source 100.1.1.1, destination 200.1.1.1
Tunnel protocol/transport GRE/IP
Key disabled, sequencing disabled
Checksumming of packets disabled
Tunnel TTL 255
Fast tunneling enabled
Tunnel transmit bandwidth 8000 (kbps)
Tunnel receive bandwidth 8000 (kbps)
Last input 01:16:00, output 01:12:27, output hang never
Last clearing of "show interface" counters never
Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 1
Queueing strategy: fifo
Output queue: 0/0 (size/max)
5 minute input rate 0 bits/sec, 0 packets/sec
5 minute output rate 0 bits/sec, 0 packets/sec
54 packets input, 6476 bytes, 0 no buffer
Received 0 broadcasts, 0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
70 packets output, 8248 bytes, 0 underruns
0 output errors, 0 collisions, 0 interface resets
0 output buffer failures, 0 output buffers swapped out
r1#
说明：隧道接口地址为1.1.1.1/24，隧道的起源为100.1.1.1，隧道的终点为200.1.1.1，因为源地址100.1.1.1所在的接口为正常状态，并且也有去往隧道终点200.1.1.1的路由，所以隧道状态为up。

（2）清除去往隧道终点200.1.1.1的路由：
r1(config)#no ip route 0.0.0.0 0.0.0.0 100.1.1.5
r1#sh 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 not set
100.0.0.0/24 is subnetted, 1 subnets
C 100.1.1.0 is directly connected, FastEthernet0/1
10.0.0.0/24 is subnetted, 1 subnets
C 10.1.1.0 is directly connected, FastEthernet0/0
r1#
说明：R1上已经没有了去往隧道终点200.1.1.1的路由。

（3）查看R1上清除去往隧道终点200.1.1.1的路由后，隧道接口的状态：
r1#show interfaces tunnel 1
Tunnel1 is up, line protocol is down
Hardware is Tunnel
Internet address is 1.1.1.1/24
MTU 1514 bytes, BW 9 Kbit, DLY 500000 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation TUNNEL, loopback not set
Keepalive not set
Tunnel source 100.1.1.1, destination 200.1.1.1
Tunnel protocol/transport GRE/IP
Key disabled, sequencing disabled
Checksumming of packets disabled
Tunnel TTL 255
Fast tunneling enabled
Tunnel transmit bandwidth 8000 (kbps)
Tunnel receive bandwidth 8000 (kbps)
Last input 01:19:18, output 01:15:45, output hang never
Last clearing of "show interface" counters never
Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 1
Queueing strategy: fifo
Output queue: 0/0 (size/max)
5 minute input rate 0 bits/sec, 0 packets/sec
5 minute output rate 0 bits/sec, 0 packets/sec
54 packets input, 6476 bytes, 0 no buffer
Received 0 broadcasts, 0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
70 packets output, 8248 bytes, 0 underruns
0 output errors, 0 collisions, 0 interface resets
0 output buffer failures, 0 output buffers swapped out
r1#
说明：R1上没有了去往隧道终点200.1.1.1的路由后，隧道接口状态变为down。

2．配置GRE keepalive
（1）恢复R1上去往隧道终点200.1.1.1的路由后，再查看隧道接口状态：
r1(config)#ip route 0.0.0.0 0.0.0.0 100.1.1.5
r1#show interfaces tunnel 1
Tunnel1 is up, line protocol is up
Hardware is Tunnel
Internet address is 1.1.1.1/24
MTU 1514 bytes, BW 9 Kbit, DLY 500000 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation TUNNEL, loopback not set
Keepalive not set
Tunnel source 100.1.1.1, destination 200.1.1.1
Tunnel protocol/transport GRE/IP
Key disabled, sequencing disabled
Checksumming of packets disabled
Tunnel TTL 255
Fast tunneling enabled
Tunnel transmit bandwidth 8000 (kbps)
Tunnel receive bandwidth 8000 (kbps)
Last input 01:19:57, output 01:16:23, output hang never
Last clearing of "show interface" counters never
Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 1
Queueing strategy: fifo
Output queue: 0/0 (size/max)
5 minute input rate 0 bits/sec, 0 packets/sec
5 minute output rate 0 bits/sec, 0 packets/sec
54 packets input, 6476 bytes, 0 no buffer
Received 0 broadcasts, 0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
70 packets output, 8248 bytes, 0 underruns
0 output errors, 0 collisions, 0 interface resets
0 output buffer failures, 0 output buffers swapped out
r1#
说明：恢复R1上去往隧道终点200.1.1.1的路由后，隧道接口状态变成up。

（2）在R1的隧道接口上配置GRE keepalive：
r1(config)#int tunnel 1
r1(config-if)#keepalive 5 3
说明：配置了keepalive的发送间隔为5秒，连续3个包，即15秒没有收到回应但认为对端失效，默认配置参数为10秒，连续3个包，即30秒没有收到回应但认为对端失效。

（3）中断对端路由器R3的GRE隧道接口，观察R1本端的隧道接口状态：
中断R3隧道接口：
r3(config)#int tunnel 3
r3(config-if)#shutdown
R1上弹出log:
r1#
*Mar 1 01:59:44.419: %LINEPROTO-5-UPDOWN: Line protocol on Interface
Tunnel1, changed state to down
r1#
R1当前隧道接口状态：
r1#show interfaces tunnel 1
Tunnel1 is up, line protocol is down
Hardware is Tunnel
Internet address is 1.1.1.1/24
MTU 1514 bytes, BW 9 Kbit, DLY 500000 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation TUNNEL, loopback not set
Keepalive set (5 sec), retries 3
Tunnel source 100.1.1.1, destination 200.1.1.1
Tunnel protocol/transport GRE/IP
Key disabled, sequencing disabled
Checksumming of packets disabled
Tunnel TTL 255
Fast tunneling enabled
Tunnel transmit bandwidth 8000 (kbps)
Tunnel receive bandwidth 8000 (kbps)
Last input 00:04:48, output 00:00:03, output hang never
Last clearing of "show interface" counters never
Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 2
Queueing strategy: fifo
Output queue: 0/0 (size/max)
5 minute input rate 0 bits/sec, 0 packets/sec
5 minute output rate 0 bits/sec, 0 packets/sec
67 packets input, 8088 bytes, 0 no buffer
Received 0 broadcasts, 0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
105 packets output, 10992 bytes, 0 underruns
0 output errors, 0 collisions, 0 interface resets
0 output buffer failures, 0 output buffers swapped out
r1#
说明：当对端隧道接口中断后，R1在本端弹出的log显示隧道接口已变为down，并查看当前隧道接口确定为down状态。

（4）恢复R3的隧道接口，并开启GRE keepalive：
r3(config)#int tunnel 3
r3(config-if)#no shutdown
r3(config-if)#keepalive
说明：R3隧道接口上配置了默认的GRE keepalive参数。

（5）再次查看R1的隧道接口状态：
r1#show interfaces tunnel 1
Tunnel1 is up, line protocol is up
Hardware is Tunnel
Internet address is 1.1.1.1/24
MTU 1514 bytes, BW 9 Kbit, DLY 500000 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation TUNNEL, loopback not set
Keepalive set (5 sec), retries 3
Tunnel source 100.1.1.1, destination 200.1.1.1
Tunnel protocol/transport GRE/IP
Key disabled, sequencing disabled
Checksumming of packets disabled
Tunnel TTL 255
Fast tunneling enabled
Tunnel transmit bandwidth 8000 (kbps)
Tunnel receive bandwidth 8000 (kbps)
Last input 00:06:01, output 00:00:01, output hang never
Last clearing of "show interface" counters never
Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 2
Queueing strategy: fifo
Output queue: 0/0 (size/max)
5 minute input rate 0 bits/sec, 0 packets/sec
5 minute output rate 0 bits/sec, 0 packets/sec
71 packets input, 8280 bytes, 0 no buffer
Received 0 broadcasts, 0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
120 packets output, 11712 bytes, 0 underruns
0 output errors, 0 collisions, 0 interface resets
0 output buffer failures, 0 output buffers swapped out
r1#
说明：由于对端路由器R3的隧道接口已经up，所以本端隧道接口状态也变为up；接口参数显示了Keepalive发送间隔为5秒，连续3个包，即15秒没有收到回应但认为对端失效。

（6）查看R3路由器上的GRE隧道状态：
r3#show interfaces tunnel 3
Tunnel3 is up, line protocol is up
Hardware is Tunnel
Internet address is 1.1.1.2/24
MTU 1514 bytes, BW 9 Kbit, DLY 500000 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation TUNNEL, loopback not set
Keepalive set (10 sec), retries 3
Tunnel source 200.1.1.1, destination 100.1.1.1
Tunnel protocol/transport GRE/IP
Key disabled, sequencing disabled
Checksumming of packets disabled
Tunnel TTL 255
Fast tunneling enabled
Tunnel transmit bandwidth 8000 (kbps)
Tunnel receive bandwidth 8000 (kbps)
Last input 00:06:21, output 00:00:00, output hang never
Last clearing of "show interface" counters never
Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 1
Queueing strategy: fifo
Output queue: 0/0 (size/max)
5 minute input rate 0 bits/sec, 0 packets/sec
5 minute output rate 0 bits/sec, 0 packets/sec
111 packets input, 11280 bytes, 0 no buffer
Received 0 broadcasts, 0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
74 packets output, 8424 bytes, 0 underruns
0 output errors, 0 collisions, 0 interface resets
0 output buffer failures, 0 output buffers swapped out
r3#
说明：因为接口配置了默认参数，所以发送间隔10秒，连续3个包，即30秒没有收到回应但认为对端失效，虽然双方时间间隔不一致，但不影响正常工作。