Cisco private dynamic routing protocol: EIGRP

Hello , This is the network technology alliance station .

Today we bring you another dynamic routing protocol ：EIGRP.

If you haven't studied Cisco , It must be the first time I have heard that there is another dynamic routing protocol called EIGRP Of .

EIGRP It is a private agreement of Cisco , Today, Rego will take you to study hard EIGRP, Let's go straight to ！

What is? EIGRP？

• English full name ：
  Enhanced Interior Gateway Routing Protocol

• Chinese name ：
  Enhanced internal gateway routing protocol

• Cisco private
  Hybrid routing protocol

• Belong to  
  IGP
  （ Internal gateway protocol ）

• Use  
  DUAL
    Diffusion update algorithm

• It has both distance vector and link state routing protocol attributes

• Agreement No  
  88

• Support classless routing 、VLSM、 Route summary 、 Load balancing and many other useful functions

• Use multicast addresses  
  224.0.0.10
    Dynamically discover neighbors

EIGRP characteristic

• Fast convergence
  ： Use  DUAL  Algorithm to support fast convergence .

• Less bandwidth usage
  ： Unlike other distance vector routing protocols, which send periodic updates

• Support all  LAN  and  WAN  Data link protocol and topology .

• Support automatic summary
  ： Auto summary is enabled by default .

• Support variable length subnet mask  (VLSM).

• Support  IPv4  and  IPv6

EIGRP The term

• DUAL
  ： Diffusion update algorithm

• Neighborhood watch
  ： function  EIGRP  List of adjacent routers of , For reliable messaging

• Topology table
  ： adopt  EIGRP  All routes learned are saved in the topology table

• Routing table
  ： Contains the best  EIGRP  route

• Internal routing
  ：EIGRP AS  Internal routing .

• External routing
  ： Another routing protocol or   the other one AS  Get route

EIGRP Sample topology

EIGRP Three tables

EIGRP Use different tables for its routing operations , stay EIGRP There are three main types of  EIGRP surface ：

• Neighborhood watch

• Topology table

• Routing table

Let's introduce ：

Neighborhood watch

The neighbor table holds all the created EIGRP Neighbor router ,EIGRP  The neighbor list is composed of  Hello  Message establishment .

Each router is based on its neighbors  EIGRP  Received by the router  Hello  Packets build neighbor tables .

see  EIGRP  Neighbor table command ：

show ip eigrp neighbors


Topology table

The topology table saves all routes to all destinations , Is a control plane or  EIGRP  database .

see EIGRP  Topology table command ：

show ip eigrp topology


Routing table

The routing table is saved to any destination

The best

Routing table .

see  EIGRP  Routing table command ：

show ip route eigrp


EIGRP Package type

To deliver messages and facilitate session management ,EIGRP  Five package types are used ：

HELLO

EIGRP Send regularly HELLO Packets to facilitate neighbor discovery .

Ack

ACK  Packets are used to update 、 Query or reply to the feedback of the data package , As a feedback mechanism .

UPDATE

Update packets are used to send routing updates .

QUERY

QUERY Packets are used to request any route updates , Request an update .

REPLY

After receiving the whole  QUERY  Send after packet , To confirm the receipt of the packet .

EIGRP Manage distance

• Aggregate routing ：
  5

• Internal routing ：
  90

• External routing ：
  170

The smaller the management distance value , The more reliable the agreement .

for example , If the router comes from OSPF)（ Default management distance ：

110

） and  EIGRP（ Default management distance ：

90

） Receive a route from a network , Then the router selects  EIGRP, because  EIGRP  More reliable .

EIGRP How it works

EIGRP The operation process can be simply classified as 3 Step ：

First step ： The neighbors found out

function EIGRP  Of routers through switching  Hello  News to find each other , And compare the parameters （ for example , Autonomous system number 、K  Value and network address ） To determine if they can form neighbors .

The second step ： Topology switching

If adjacent  EIGRP  The router decides to form a neighbor , They exchange their complete topology tables with each other . however , After building a neighborhood , Only changes to the existing topology will communicate between routers . This method makes  EIGRP  Such as  RIP  Such routing protocols are more effective , The latter periodically informs them of their entire list of known Networks .

The third step ： Choose a route

fill  EIGRP  After the topology table of the router ,EIGRP  The process checks all learned network routes and selects the route to each network

The best route

,EIGRP  It is considered that the network route with the lowest metric is the best route to the network .

Explain neighbor discovery and topology exchange in detail

Neighbor discovery and topology switching are important , Here we use a diagram to illustrate the steps , Now that we talk about , Then we must speak to the point .

Combined with the above EIGRP Package type

The first  1  Step ：R1 -> R2  The neighbors found out

R1 take  EIGRP Hello  news   Broadcast to  EIGRP  Multicast address  

224.0.0.10

, Require any use of  EIGRP  Your router identifies itself .

The first  2  Step ：R2 -> R1  Full routing information

R2 After receiving the router  R1  Of  Hello  After the news , Send a unicast update message back to  R1  Of  IP  Address  192.168.1.1, This update message contains R2  Integrity  EIGRP  Topology table , That is, full routing information .

The first  3  Step ：R1 -> R2  confirm

R1  receive  R2  Update , And send to the road  R2  Of  IP  Address  192.168.1.2  The confirmation of  (ACK)  Unicast messages in response .

The first  4  Step ：R2 -> R1  The neighbors found out

Then the roles change ,R2  towards  EIGRP  Multicast address  224.0.0.10  send out  Hello  news .

The first  5  Step ：R1 -> R2  Full routing information

R1  Use contains  R1  Integrity  EIGRP  Unicast update of topology table in response to router  R2  Of  Hello  news , The destination of this update message is the router  R2  Of  IP  Address  192.168.1.2.

The first  6  Step ：R2 -> R1  confirm

R2  Received  R1  Routing information for , And send to R1  Of  IP  Address  192.168.1.1  Of  ACK  Unicast messages in response .

here , Router  R1  and  R2  Between has been established  

EIGRP  Neighborhood

, Routers will switch periodically  Hello  news , To confirm that the neighbors of each router still exist . However , This is the last time routers exchange their complete routing information , Subsequent topology changes are made through

Partial update

Make an announcement , Instead of the full update used during neighbor establishment .

EIGRP measurements

EIGRP The measurement calculation is a bit complicated , Use bandwidth 、 Delay 、 load 、 reliability   and  MTU  Value to calculate , Let's look at the formula ：

In order to keep everyone's brain cells , I used color to distinguish , among ：

• K1 =  bandwidth

• K2 =  load

• K3 =  Delay

• K4  and  K5 =  reliability

these K Values have default values ：

• K1（ bandwidth ）= 1

• K2（ load ）= 0

• K3（ Delay ）= 1

• K4（ reliability ）= 0

• K5（MTU）= 0

Usually we don't use  K2、K4  and  K5  value , Because load and reliability are dynamic values , They change over time .

EIGRP Measurement calculation is very tedious , But it is also more important , After reading this article, you can find a few more examples to practice .

summary

EIGRP It is a routing protocol based on internal gateway  (IGRP)  Principle of advanced distance vector routing protocol , It has the unique characteristics of improving operation ability and fast convergence speed .

In this article, Ruige gives you a list of EIGRP Important technical points , I hope it will help you ！