eigrp的基本原理及实例

?EIGRP is an advanced distance vector routing protocol
–Automatically establishes neighbor relationships with peer devices
–Relies on IP packets for delivery of routing information



1.EIGRP 特征
 








2.DUAL 算法
*选择最小代价，无环路的路径到每个目的网络
*AD=下一跳路由器到达目的网络的cost值
*FD=AD+本路由器到下一跳路由器的cost值
*Lowest-cost = lowest FD
*(Current) successor = 拥有Lowest-cost的路径及下一跳路由
*Feasible successor =无环路的备份路由器 (该路径的AD必须比当前的successor的FD小)
*邻居之间相互通告路由
*选择successor放入数据库中，同时把feasible successors也放入数据库中
*如果successor丢失了，使用feasible successor
*如果没有feasible successor，则向邻居查询并重新计算新的successor
3.三张表格：
EIGRP IP路由表






4.报文格式：

*Hello: 维持邻居关系.
*Update: 发送路由更新.
*Query: 向邻居查询路由信息.
*Reply: 相应路由器的查询.
*ACK: 对EIGRP可靠包的确认.
5.初始路由发现


 
6.默认路由方法：
*重分布静态
*R(config)#ip route 0.0.0.0 0.0.0.0 s0
*R(config-router)#redistribute static
*宣告0.0.0.0
*R(config)#ip route 0.0.0.0 0.0.0.0 s0
*R(config-router)#network 0.0.0.0
*配置默认网络
*R(config)#ip default-network 10.0.0.0
*R(config-router)#network 10.0.0.0
*R(config)#ip route 10.0.0.0 255.0.0.0 null0
 
7.等代价负载均衡




?Router E chooses router C to get to network Z, because it has lowest FD of 20.
?With a variance of 2, router E chooses router B to get to network Z (20 + 10 = 30) < [2 * (FD) = 40].
?Router D is never considered to get to network Z (because 25 > 20).
8.支持的网络 vlsm



?EIGRP supports
–Multiaccess (LANs)
–Point-to-point (HDLC)
–NBMA (Frame Relay)




9.组播地址 224.0.0.10  hello包每5秒发送一次（在高速链路上）
?Two routers become neighbors when they see each other’s hello packet
–Hello address = 224.0.0.10
?Hellos sent once every 5 seconds on the following links:
–Broadcast media: Ethernet, Token Ring, FDDI
–Point-to-point serial links: PPP, HDLC,
point-to-point Frame Relay/ATM subinterfaces
–Multipoint circuits with bandwidth greater than T1: ISDN PRI, SMDS, Frame Relay
 
?Hellos sent once every 60 seconds on the following links:
–Multipoint circuits with bandwidth less than T1: ISDN BRI, Frame Relay, SMDS, and so on
?Neighbor declared dead when no EIGRP packets are received within hold interval
–Not only hello can reset the hold timer
?Hold time by default is three times the hello time  保持时间 是3倍的HELLO时间