CCNA Cisco network EIGRP protocol

EIGRP summary

EIGRP: (Enhanced Interior Gateway Routing Protocol) Enhance internal Gateway Routing Protocol . Also translated as Enhanced internal gateway routing protocol . EIGRP Combined with the Link state and distance vector routing protocol Of Cisco Special agreement , use Dispersion correction algorithm （DUAL） To achieve rapid convergence , You can not send regular route update information to reduce the occupation of bandwidth , Support Appletalk、IP、Novell and NetWare And other network layer protocols . EIGRP yes Cisco The company's private agreement （2013 It has been publicly owned in ）.

EIGRP At the same time, it has the advantages of link state and distance vector routing protocol . Send only changed messages ( This is similar to link state protocol ), At the same time, only these information will be sent to the adjacent router ( This is similar to the distance vector protocol ).
The routing learning of distance vector routing protocol is “ What I hear ”, The router does not know the topology of the whole network , Therefore, a loop may be generated ;
The link state is that each router learns the topology of the entire network , Then calculate the path from itself to other routers , Therefore, it is impossible to generate a loop .

EIGRP Protocol related modules

EIGRP It can provide routing support for a variety of network layer protocols , for example IPv4、IPX、AppleTalk and IPv6.EIGRP By using PDM(Protocol-Dependent Module, Protocol related modules ） To support different network layer protocols , Every EIGRP PDM Multiple independent tables will be maintained for the specified protocol , It stores the routing information of a specific protocol .

EIGRP It's enhanced IGRP , Because it converges fast , And it can ensure that there is no loop in the topology at any time .

EIGRP Characteristics of

(1). By sending and receiving Hello Package to build and maintain neighborhoods , And exchange routing information ;

(2). Adopt multicast (224.0.0.10) Or unicast for route update ;

(3). Manage distance values AD by 90 ( Inside EIGRP) or 170 ( external EIGRP);

(4). Use trigger update , Reduce bandwidth usage ;

(5). Support variable length subnet mask (VLSM), The automatic summary function is enabled by default ;

(6). Support IP ,IPX and AppleTalk And other network layer protocols ;

(7). For every network protocol ,EIGRP All remain independent 3 A watch :

	⦁      Neighborhood watch (show ip eigrp neighbor)
	
	⦁      Topology table (show ip eigrp topology)
	
	⦁      Routing table (show ip route eigrp)

(8). EIGRP Use Diffusing Update Algorithm (DUAL), To achieve fast convergence and ensure that there is no routing loop ;

(9). Store the entire network topology information , In order to quickly adapt to network changes ;

(10). Support equivalent and non equivalent load balancing ;

(11). be based on IP Process number 88.

DUAL Algorithm

EIGRP Use the diffusion update algorithm (DUAL) Determine the best route , The algorithm can realize route backup preparation at any time 、 Support VLSM And dynamic route recovery , If no feasible successor route is found, query the replacement route .
EIGRP The router maintains the topology table , Calculate the cost of reaching the remote network through the topology table , If the best path is not available , Just test the contents of the topology table and select the new and best alternative route . When there is no alternative route in the local topology table ,EIGRP The router will quickly ask the neighbor for help , Namely DUAL Of “ Dispersion ” characteristic .EIGRP Send query packets to neighbors to query routing information , Neighbors use reply packets to mechanically respond .

EIGRP The term

EIGRP The term :

Feasible distance （FD）： The minimum measure of reaching a destination network ; FD: The distance from my neighbor +AD

advertise distance （AD）： The destination that the router advertises to its own network is the smallest ; AD: How far is it for my neighbor to reach the target network

Feasibility conditions （FC）： yes EIGRP The basis for the router to update the routing table and topology table . Feasibility conditions can effectively prevent routing loops , Realize the fast convergence of routing . The formula of feasibility condition is ：AD<FD.

Follow up station (successor): The router with the lowest cost to reach the destination network –FD The minimum

Feasible successor station ( FS ): In addition to the lowest cost path , It also stores alternate paths , To become a viable successor , Next hop router AD Must be smaller than the current router FD

EIGRP Three tables of

For every network protocol ,EIGRP All remain independent 3 A watch :

⦁ Neighborhood watch (show ip eigrp neighbor)

⦁ Topology table (show ip eigrp topology)

⦁ Routing table (show ip route eigrp)

Table name	function
Neighborhood watch	Record the relevant information of the router that has established a good neighbor relationship
Topology table	Save route announcements from each neighbor about each route description in the Internet
Routing table	Save the route currently in use for route determination

EIGRP Five groups

EIGRP send out 5 Groups of types :

grouping	The function of grouping
Hello	Used to find and recover neighbors , Send by multicast , Use unreliable sending
Update	Propagate route update information , Irregular , Send in a reliable way ( For example, the network link changes ). When only one router needs to be updated ,update adopt unicast By sending ; When there are multiple routers that need to be updated , Send by multicast
ACK(acknowledgement)	No data (data) Of Hello package , Use unicast The way , Unreliable sending
Reply( The reply )	Respond to query message .
Query( Inquire about )	When you can't find it Feasible Successor when , Send inquiry message （Unicast） yes DUAL finite state machine Used to manage diffusion Computing , Query packets can be multicast or unicast; The reply packet is through unicast By sending , And the way is reliable

EIGRP Build a relationship diagram

(1) Router on link A After starting , Through its location EIGRP Interface send Hello grouping

(2) Received through its interfaces Hello After grouping , Router B Reply with update packet , The update packet contains all routes in the routing table

(3) The two routes are exchanged with each other Hello After grouping , Adjacency relationship establishment . Router A use ACK Packet answering router B

(4) Router A Add the information in the update group to the topology table

(5) Router A To the router B Send an update packet

(6) After receiving the update group , Router B To the router A Send a ACK grouping

EIGRP The reason why building neighbors failed

EIGRP There are three reasons why neighbors can't get up ：

1）AS The number doesn't match

AS Two different numbers EIGRP We can't afford to build neighbors , Because their process numbers are different .

2）K The value is different

EIGRP The calculation cost is 5 One factor ： bandwidth , Delay , load , reliability ,MTU. use K1,K2,K3,K4,K5 Replace these values respectively . When K When values are different , The way of calculating the cost is different , The route cannot be delivered , That is, you can't build neighbors （ By default K1 =K3=1,K2,K4,K5=0）

3）HELLO Time is different

EIGRP Of hello Package update time is 5 second , The time of death is 15 second , If there is a process hello The time is changed to be greater than 5 second , stay 5 Within seconds, the other party did not receive hello Bao will think that there are no neighbors , I can't get up at this time, neighbors , But after the changed time, they will give the other party another hello package , The other party passed 5 Seconds back hello package , At this time, the neighbors will get up again , therefore hello At different times, neighbors sometimes break up .

EIGPR Routing of

Choose a route

EIGRP The biggest difference from other routing protocols may be its routing process .EIGRP Select the primary route ( Subsequent routing ) And alternate routes ( Feasible successor route ), And add them to the topology table . then , Route the main route ( Subsequent routing ) Add to the routing table .EIGRP Support multiple types of routes , Including interior . External and aggregate routing .

⦁ Internal routing : From the EIGRP Routing within autonomous systems

⦁ External routing : Is from another routing protocol or another EIGRP The route learned by the autonomous system

⦁ Aggregate routing : It is a route for multiple subnets

EIGRP Calculation of measures

EIGRP Use metrics to determine the best path to the destination . For each subnet ,EIGRP The topology table contains one or more possible routes . Every possible route contains various metrics ： bandwidth , Delay, etc .EIGRP The router calculates an integer metric based on the metric , To choose the best route to the destination .

When the router chooses the route , Calculate the path with the lowest metric , That is to say FD, To determine the best route . When the route fails , Use RD To choose an alternative route .

Calculation EIGRP Use 5 A variable , But by default , Use only two of them ( bandwidth . Delay )

1) bandwidth : Minimum bandwidth between source and destination

2) Delay : Cumulative delay of the interface on the path

3) reliability : Minimum reliability between source and destination , Based on survival messages

4) load : The heaviest load on the link between source and destination , Configure bandwidth based on packet rate and interface

5)MTU: Maximum transmission unit , The smallest on the path MTU

EIGRP Calculation formula of measurement ={ K1 * Bandwidth + ( K2 * Bandwidth ) / ( 256-Load) + K3 * Delay }*{K5/(Reliability + K4) } * 256

By default ,K1 = K3 = 1 ,K2 = K4 = K5 = 0

• Bandwidth =10 ^ 7/ The access bandwidth in the link （ Unit is Kbps） The minimum value of

• Delay= The sum of the delays of the entries in the link （ Unit is μs）/10

That is to say, by default ,EIGRP The measurement calculation formula of is ：

 Calculation formula =[ 10 ^ 7 / Bandwidth + Delay ] * 256

• EIGRP according to AD and FD To determine the subsequent route to the destination ( The best route ) And feasible successor routes ( Alternate routing ).

• The router is responsible for all routes to a specific network in its topology table FD Compare , And will FD The smallest route is added to the routing table , This route is the best route

EIGRP Configuration command of

R1(config-router)# network 172.16.1.0 0.0.0.255
R1(config-router)# network 172.16.3.0 0.0.0.3
R1(config-router)# network 192.168.10.4 0.0.0.3

R2(config-router)# network 172.16.2.0 0.0.0.255
R2(config-router)# network 172.16.3.0 0.0.0.3
R2(config-router)# network 192.168.10.8 0.0.0.3

R3(config-router)# network 192.168.1.0 0.0.0.255
R3(config-router)# network 192.168.10.4 0.0.0.3
R3(config-router)# network 192.168.10.8 0.0.0.3