还记得大学时,老师说“童鞋们,不同网段的IP是无法互通的,要记住哦”

其实,老师没说全。。。

今天本宝宝带大家回顾一下广域网协议,PPP、HDLC、frame-relay,加上Ethernet做比较

因个人崇尚实验出真知,用实验总结理论


拓扑:(因HCL无法模拟FR-SW,又不想用LITO,加上好久没敲cisco了,所以用GNS3)

不同网段互联能通吗?


  1. PPP

R1#conf t

Enter configuration commands, one per line.  End with CNTL/Z.

R1(config)#int s0/0

R1(config-if)#encapsulation ppp

R1(config-if)#ip add 12.12.12.1 255.255.255.0

R1(config-if)#no shut

========================================

R2#conf t

Enter configuration commands, one per line.  End with CNTL/Z.

R2(config)#int s0/0

R2(config-if)#ip add 21.21.21.2 255.255.255.0

R2(config-if)#en

R2(config-if)#encapsulation ppp 

R2(config-if)#no shut

R2(config-if)#do ping 12.12.12.1 


Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 12.12.12.1, timeout is 2 seconds:

!!!!!

Success rate is 100 percent (5/5), round-trip min/avg/max = 16/25/36 ms

#不同网段通了,我们来看看为什么

R2(config-if)#do show ip rou

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


     21.0.0.0/24 is subnetted, 1 subnets

C       21.21.21.0 is directly connected, Serial0/0

     12.0.0.0/32 is subnetted, 1 subnets

C       12.12.12.1 is directly connected, Serial0/0

#现象一:

#自动生成了一条对端网络的主机路由

#为什么自动生成路由呢?  抓包

不同网段互联能通吗?

不同网段互联能通吗?

#原来是IPCP自协商对端IP

2.HDLC

R1#conf t

Enter configuration commands, one per line.  End with CNTL/Z.

R1(config)#int s0/0

R1(config-if)#en 

R1(config-if)#ip add 12.12.12.1 255.255.255.0

R1(config-if)#no shut

=============================================

R2#conf t

Enter configuration commands, one per line.  End with CNTL/Z.

R2(config)#int s0/0

R2(config-if)#ip add 21.21.21.2 255.255.255.0

R2(config-if)#no shut

R2(config-if)# do ping 12.12.12.1  


Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 12.12.12.1, timeout is 2 seconds:

.....

Success rate is 0 percent (0/5)

#不通了,我们试试如PPP一样写主机路由试试

R1(config)#ip route 21.21.21.2 255.255.255.255 s0/0 

R2(config)#ip route 12.12.12.1 255.255.255.255 s0/0

R2(config)# do ping 12.12.12.1                     


Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 12.12.12.1, timeout is 2 seconds:

!!!!!

Success rate is 100 percent (5/5), round-trip min/avg/max = 20/25/32 ms

#o了,可以总结出,PPP可以通,HDLC不可以通,因为NCP自协商路由的源故


3.frame-relay

不同网段互联能通吗?

R1#conf t

Enter configuration commands, one per line.  End with CNTL/Z.

R1(config)#int s0/0

R1(config-if)#ip add 13.13.13.1 255.255.255.0

R1(config-if)#en

R1(config-if)#encapsulation fr

R1(config-if)#encapsulation frame-relay 

R1(config-if)#no shut

===================================

R2#conf t

Enter configuration commands, one per line.  End with CNTL/Z.

R2(config)#frame-relay switching 

R2(config)#int s0/0

R2(config-if)#encapsulation frame-relay 

R2(config-if)#frame-relay intf-type dce

R2(config-if)#frame-relay route 102 interface s0/1 201

R2(config-if)#no shut

R2(config)#int s0/1

R2(config-if)#encapsulation frame-relay 

R2(config-if)#frame-relay intf-type dce

R2(config-if)#frame-relay route 201 interface s0/0 102

R2(config-if)#no shut

===================================

R3#conf t

Enter configuration commands, one per line.  End with CNTL/Z.

R3(config)#int s0/1

R3(config-if)#encapsulation frame-relay

R3(config-if)#ip add 31.31.31.3 255.255.255.0

R3(config-if)#no shut

R3(config-if)#do ping 13.13.13.1

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 13.13.13.1, timeout is 2 seconds:

!!!!!

Success rate is 100 percent (5/5), round-trip min/avg/max = 32/40/44 ms

#默认情况下是可以通的,为什么呢?

R1(config-if)#do show frame-relay map    

Serial0/0 (up): ip 31.31.31.3 dlci 102(0x66,0x1860), dynamic,

              broadcast,

              CISCO, status defined, active

#因为根据标签转发,下面让其不通

R1(config)#int s0/0

R1(config-if)#no frame-relay inverse-arp

R3(config)#int s0/1

R3(config-if)#no frame-relay inverse-arp

R3(config-if)#exit

R3(config)#exit

R3#clear frame-relay inarp

R3#ping 13.13.13.1


Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 13.13.13.1, timeout is 2 seconds:

.....

Success rate is 0 percent (0/5)

#其不通原因在于inverse-arp,我们尝试着不开启inverse-arp让其通

R1(config)#int s0/0

R1(config-if)#frame-relay intf-dlci 102

R3(config)#int s0/1

R3(config-if)#frame-relay intf-dlci 201

R3(config-if)#do ping 13.13.13.1

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 13.13.13.1, timeout is 2 seconds:

!!!!!


4.Ethernet

R1#conf t

Enter configuration commands, one per line.  End with CNTL/Z.

R1(config)#int f0/0

R1(config-if)#no shutR1(config-if)#ip add 12.12.12.1 255.255.255.0

==============================================


R2#conf t

Enter configuration commands, one per line.  End with CNTL/Z.

R2(config)#int f0/0

R2(config-if)#no shut 

R2(config-if)#ip add 21.21.21.2 255.255.255.0R2(config-if)#do ping 12.12.12.1

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 12.12.12.1, timeout is 2 seconds:

.....

Success rate is 0 percent (0/5)

#默认肯定不通的,我们尝试写路由试试
R1(config)#ip route 21.21.21.2 255.255.255.255 f0/0 

R2(config)#ip route 12.12.12.1 255.255.255.255 f0/0

R2(config)#do ping 12.12.12.1


Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 12.12.12.1, timeout is 2 seconds:

.!!!!

Success rate is 80 percent (4/5), round-trip min/avg/max = 20/29/44 ms

#写路由可以互通


5.总结

对于Ethernet,不同网段互通的前提在于ARP,写路由是让其学习MAC,如果手工写静态MAC也可互通

对于帧中继,默认根据DLCI转发,通过inverse-arp学习

对于PPP,IPCP自协商对端IP,本地自动生成对端主机路由

对于HDLC,默认不可互通,通过SLARP解析