eigrp的基本原理及实例
?EIGRP is an advanced distance vector routing protocol
�CAutomatically establishes neighbor relationships with peer devices
�CRelies 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
�CMultiaccess (LANs)
�CPoint-to-point (HDLC)
�CNBMA (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
�CHello address = 224.0.0.10
?Hellos sent once every 5 seconds on the following links:
�CBroadcast media: Ethernet, Token Ring, FDDI
�CPoint-to-point serial links: PPP, HDLC,
point-to-point Frame Relay/ATM subinterfaces
�CMultipoint circuits with bandwidth greater than T1: ISDN PRI, SMDS, Frame Relay
?Hellos sent once every 60 seconds on the following links:
�CMultipoint 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
�CNot 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