拓扑图：
错误：对于整个拓扑来说，PC1无法ping通PC2
具体排错方法：PC1用ping命令测试，从最远程的网络开始到PC1的网关，一层一层地检查，找到对应的哪些能通，再通过测试结果分析可能存在的原因。
其中，错误原因可能有：路由器子接口上对应的VLAN封装错误、路由表不完整、交换机和路由器的链路上未启用trunk模式、交换机上端口所属VLAN划分错误、PC上的IP地址及网关配置错误
以本题为例，常见排错命令以及对应的信息显示：
1、S1#show interfaces gigabitEthernet 0/1 switchport
Name: Gig0/1
Switchport: Enabled
Administrative Mode: static access //得出该接口没有启用trunk模式，使用的是access模式
Operational Mode: static access
Administrative Trunking Encapsulation: dot1q
Operational Trunking Encapsulation: native
Negotiation of Trunking: Off
Access Mode VLAN: 1 (default)
Trunking Native Mode VLAN: 1 (default)
Voice VLAN: none
Administrative private-vlan host-association: none
Administrative private-vlan mapping: none
Administrative private-vlan trunk native VLAN: none
Administrative private-vlan trunk encapsulation: dot1q
Administrative private-vlan trunk normal VLANs: none
Administrative private-vlan trunk private VLANs: none
Operational private-vlan: none
Trunking VLANs Enabled: ALL
Pruning VLANs Enabled: 2-1001
Capture Mode Disabled
Capture VLANs Allowed: ALL
Protected: false
2、S1#show vlan brief
VLAN Name Status Ports
---- -------------------------------- --------- -------------------------------
1 default active Fa0/1, Fa0/2, Fa0/3, Fa0/4
Fa0/5, Fa0/7, Fa0/8, Fa0/9
Fa0/10, Fa0/12, Fa0/13, Fa0/14
Fa0/15, Fa0/16, Fa0/17, Fa0/18
Fa0/19, Fa0/20, Fa0/21, Fa0/22
Fa0/23, Fa0/24, Gig0/2
10 Faculty/Staff active Fa0/11
30 Guest(Default) active Fa0/6
//得出VLAN划分是正确的
1002 fddi-default active
1003 token-ring-default active
1004 fddinet-default active
1005 trnet-default active
3、R1#show interfaces gigabitEthernet 0/1.10
GigabitEthernet0/1.10 is up, line protocol is up (connected)
Hardware is PQUICC_FEC, address is 000d.bde7.0c02 (bia 000d.bde7.0c02)
Internet address is 172.17.10.1/24
MTU 1500 bytes, BW 100000 Kbit, DLY 100 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation 802.1Q Virtual LAN, Vlan ID 30 //从此处得出VLAN ID的封装错误
ARP type: ARPA, ARP Timeout 04:00:00,
Last clearing of "show interface" counters never
R1#show interfaces gigabitEthernet 0/1.30
GigabitEthernet0/1.30 is up, line protocol is up (connected)
Hardware is PQUICC_FEC, address is 000d.bde7.0c02 (bia 000d.bde7.0c02)
Internet address is 172.17.30.1/24
MTU 1500 bytes, BW 100000 Kbit, DLY 100 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation 802.1Q Virtual LAN, Vlan ID 10 //从此处得出VLAN ID的封装错误
ARP type: ARPA, ARP Timeout 04:00:00,
Last clearing of "show interface" counters never
4、R1(config)#do show ip route或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, E - EGP
i - IS-IS, 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
172.17.0.0/16 is variably subnetted, 2 subnets, 2 masks
C 172.17.10.0/24 is directly connected, GigabitEthernet0/1.10
L 172.17.10.1/32 is directly connected, GigabitEthernet0/1.10
//从路由表得出，此路由表还缺少一条172.17.30.0/24的路