e-计算机网络基础3-IP路由

192.100.0.0
192.100.192.0 192.201.0.0 192.202.0.0
255.255.0.0
255.255.224.0 255.255.0.0 255.255.0.0
192.201.0.1
192.202.0.1 C C
I00
I01 I00 I01
1
1 0 0
Example#5: Multi-routes / route backup
I00 .2 R0 I02 170.10.0.0/16 .2 I01
192.201.0.0/16
192.100.128.0/19 R1 .1
192.202.0.0/16
.1 R3 192.200.0.0/19 .1
192.100.64.0/19 192.100.0.0/19 Targ. SubnetID Mask Next Hop Outbound Intf. RIP Dist.
Example#1:Write the correct forwarding table for each router( including the default route)
I00 .2 170.10.0.0/16(public internet)
B.G.
I02
.2 I01
192.100.0.0/19
Principles for Multi-routes Scheduling
• For Reliability: Master/Slave Backup • For Traffic Balance: Scheduling packets according (say) bandwidth or traffic load over different candidate routes( between two hosts)
192.100.128.0
192.100.0.0 192.100.64.0
255.255.224.0
255.255.224.0 255.255.224.0
192.201.0.1
192.201.0.1 192.201.0.1
I00
I00 I00
1
1 1
Example#4(Route Aggregation): Order really matters!
Example#1: When an IP packet of dest. Addr. 202.39.2.79 arrives at R2, 1) R2 checks its forwarding table line after line until discovering a line such that
} else { /* d表示目标网络就是接口I连接的邻接网段, 例如, d表示网络距离且d=0.*/
将队列项[A, P]放入接口I的离出队列; /* 涵义同上 */ } found = TRUE; break;
} /* if…*/
} /* for…*/ if( ! found ) { /* 假设默认路由项是(0.0.0.0, 0.0.0.0, N*, I*, -) */ 将队列项[N*, P]放入接口I*的离出队列; /*涵义同上*/ }
192.100.128.0/19
I21 I22 .2 R2 .2
R1’s table( incomplete ) Tagt. SubnetID 192.100.32.0 192.100.128.0 Mask 255.255.224.0 255.255.224.0 Next Hop 192.100.0.2(M) 192.100.64.2(S) 192.100.64.2(M) 192.100.0.2(S) Outbound Intf. I11 I12 I12 I11 RIP Dist. 1 2 1 2
Vlan2
Vlan2 Vlan2 Vlan160
3
4 0 1
202.124.254.0 255.255.255.0 176.20ectly Connected”
Example#3(Route Aggregation): How few(!) route items are needed to correctly represent the topology?
I00 .2 170.10.0.0/16(public internet) .2 I01
B.G. I02
192.100.0.0/19
192.100.96.0/19 .1 R1 I10 .1 I12 192.100.64.0/19 .1 I11
192.100.32.0/19 .1 I31 .2 192.100.192.0/19 .1 R3 I30 I32
Targeted Subnet ID Mask
I20 .1 192.100.160.0/19 Next Hop Outbound Intef. RIP Dist.
Example#2： Determine the neighbor topology via forwarding table.
Targeted SubnetID Mask Next Hop Outbound Intf. RIP Dist.
Router
IP Addr. = 192.108.0.9
Routing on Internet(3)：Router
Routing on Internet(4-1)：Forwarding Table
Routing on Internet(4-2) How an IP Packet is forwarded by a Router？
RIP algorithm（no fault detections）
172.200.0.0
255.255.255.0 0.0.0.0
172.200.0.0
172.200.1.1 172.200.1.1
172.200.0.0
I21 I21
172.200.0.0
1
Routing on Internet(4-3): Default Route
Example#2: An IP packet of dst. Addr. 110.240.10.89 arrives at R2: 1)R2 does the same as in example#1, however, no matching route is found ! Tageted SubnetID= 110.240.10.89 &Mask 2)R2 forwards this packet according to “next hop” indicated by default route.
IP Pkt，Dst. Addr =170.100.2.9
170.100.0.0/16：192.101.0.1 170.200.0.0/16: 192.102.0.1
IP Addr. = 192.101.0.1
170.100.0.0/16: 192.108.0.9
170.200.0.0/16: XXXX
Routing on Internet(1) How is an IP Packet traverse over the Internet?
上海：南 北京：北
上海：东
上海：南
北京：北
北京：西
Routing on Internet(2)
How is an IP Packet is forwarded to its destination？
Targetted subnetID 172.100.0.0 172.2100.0
Mask 255.255.0.0 255.255.0.0
Next Hop 172.210.0.0 C
Outbound Intf. I22 I22
RIP Dist. 1 0
172.200.0.0
202.39.2.0 0.0.0.0
“targetted subnetID”=202.39.2.79 & “mask”
i.e., a matching route item is found; 2) R2 forwards the packet to one of its neighbor according to “next hop”.
172.200.0.0
255.255.255.0 0.0.0.0
172.200.0.0
172.200.1.1 172.200.1.1
172.200.0.0
I21 I21
172.200.0.0
1
Routing on Internet(4-4)：Forwarding Algorithm
IP_Packet_Routing(IP分组P) { int found = FALSE; A=P的目标IP地址; for( 每个非默认路由项(D, M, N, I, d) ) { /*D是目标网络的IP地址, M是子网掩码, N是下一站路由器的IP地址,I是离出接口, d是路由的性能度量 */ if(A&M==D) { /* & 是逐位逻辑与 */ if( d表示P的目标网络并非邻接) { /* 例如, d表示网络距离且d>0. */ 将队列项[N, P]放入接口I的离出队列; /*[N, P]的涵义是: 将分组P载入数据链路帧, 帧的目标MAC地址与IP地址N对应. */
Targeted subnetID 172.100.0.0 172.2100.0
Mask 255.255.0.0 255.255.0.0
Next Hop 172.210.0.0 C
Outbound Intf. I22 I22
RIP Dist. 1 0
172.200.0.0
202.39.2.0 0.0.0.0
192.100.96.0/19 .1 R1 I10 .1 I12 192.100.64.0/19 .1 I11
192.100.32.0/19 .1 I31 .2 192.100.192.0/19 .1 R3 I30 I32
192.100.128.0/19
I21 I22 .2 R2 .2
e.g., R2’s table
}
IP分组转发算法：上机作业
题目：实现IP分组高速转发算法 要求：完成路由表详细的数据结构与算法设计，路由表要能支 持路由项的高速查询（关键性能）、插入、更新和删除；必须 逻辑正确、查询速度尽可能地高；用C语言实现程序并实际运 行；给出明确的测试方案；给出明确测试结果。 本题目不要求实现IP分组的实际输入/输出功能。 结果：写出设计报告（明确说明以上每项要求是如何具体实现 的，特别是数据结构的设计思想及详细实现）。
202.204.65.0 202.204.64.0
255.255.255.0 255.255.255.0
C C
Vlan160 Valn159
0 0
202.14.71.0
202.38.70.0
255.255.255.0 202.124.254.9
255.255.255.0 202.124.254.9 C 202.204.65.1
I00 .2 R0 I02 170.10.0.0/16 .2 I01
192.201.0.0/16
192.100.128.0/19 R1 .1
192.202.0.0/16
.1 R3 192.101.192.0/19
.1
192.100.64.0/19 192.100.0.0/19 Tagt. SubnetID Mask Next Hop Outbound Intf. RIP Dist.
Dynamic Route Discovery(1): RIP
• Route Vector Principles
How does RIP work on each router: 1)Initial forwarding table is setup to (only) indicate directly connected subnets. 2)Each router periodically multicasts its current forwarding table to its neighbors; 3) Each router tries to find/extract new route information from its neighbors’ reports.