How to analyze the EIGRP protocol

1. Brief description of EIGRP protocol

EIGRP (Enhanced Inerior Gateway Routing Protocol, enhanced interior gateway routing protocol) is a balanced hybrid routing protocol that combines distance vector and The advantages of the two routing protocols, link state, are also CISCO's proprietary protocols.

EIGRP is an efficient routing protocol. Its characteristics are:

• Establish and maintain neighbor relationships and exchange routing information by sending and receiving Hello packets;

• Use multicast (224.0.0.10) or unicast for routing updates;

• The administrative distance of EIGRP is 90 and 170;

• Use triggered updates to reduce bandwidth usage;

• Support variable length subnet mask (VLSM), and the automatic summary function is enabled by default;

• Supports multiple network layer protocols such as IP, IPX, and Apple Talk;

• For each network protocol, EIGRP maintains an independent neighbor table. , topology table and routing table;

• EIGRP uses the Diffusing Upadte algorithm (DUAL) to achieve fast convergence and ensure there are no routing loops;

• Stores information about the entire network topology while quickly adapting to network changes;

• Supports equal and non-equivalent load balancing;

• Use The Reliable Transport Protocol (RTP) ensures the reliability of routing information transmission;

• seamlessly connects the data link layer protocol and topology. EIGRP does not require the implementation of the layer 2 protocols of the OSI reference model. Configuration;

2. Experiment purpose

Simply understand the following two basic knowledge points of EIGRP.

• Understand the neighbor table, topology table and routing table;

• How to calculate the EIGRP metric;

3. Topology diagram

Two adjacent routers need to meet two conditions to establish an adjacency relationship, which is the same AS number. and matching K value. Taking R2 as an example, you can use the "Show ip protocols" command to view

R2#show ip protocols

Routing Protocol is "eigrp 200 "

Outgoing update filter list for all interfaces is not set

Incoming update filter list for all interfaces is not set

Default networks flagged in outgoing updates

Default networks accepted from incoming updates

EIGRP metric weight K1=1, K2=0, K3=1, K4=0, K5=0

EIGRP maximum hopcount 100

EIGRP maximum metric variance 1

Redistributing: eigrp 200

Automatic network summarization is not in effect

Maximum path: 4

Routing for Networks:

192.168.10.0

192.168.20.0

192.168.40.0

192.168.50.0

0.0.0.0

Routing Information Sources:          

Gateway Distance Last Update

192.168.10.2 90 330051

192.168.2 0.2 90 356798

192.168.40.2 90 382527

192.168.50.2 90 418109

Distance: Internet 90 External 170

Since the current maximum allowed 4 lines of load balancing, if the router allows to continue to increase the line, Maximum-Paths *can be modified ( *represents number unit). In addition, you can notice "eigrp 200" marked in red font, which indicates that the currently used EIGRP autonomous system number is 200

EIGRP metric weight K1=1, K2=0, K3=1, K4= 0, K5=0 is the K value, its meaning is as follows:

K1 represents bandwidth

K2 represents load

K3 represents delay

K4 and K5 stands for reliability

By default, EIGRP only uses bandwidth and load as metric calculation parameters. To modify the K value, you can use the metric weights tos k1 k2 k3 k4 k5 command, where tos is used as the quality of service to distinguish service levels, 0 means not enabled, and 1 means enabled.

(1), neighbor table

#R2#show ip eigrp neighbors

IP-EIGRP neighbors for process 100

H Address Interface Hold Uptime SRTT RTO Q Seq

(sec) (ms) Cnt Num

0 192.168.10.2 Se1/1 12 00 :11:47 40 1000 0 78

1 192.168.20.2 Se1/0 12 00:11:20 40 1000 0 80

2 192.168.40.2 Se1/2 11 00:10:54 40 1000 0 91

3 192.168. 50.2 Se1/3 14 00:10:19 40 1000 0 94

"H" indicates the order in which neighbors are learned, 0 is the neighbor learned first;

"Address" It is the neighbor routing interface IP;

"Interface" is the interface where the local route is connected to this neighbor;

"Hold" is the current hold time, the default is 15 seconds, which is a decreasing value;

"Uptime" is how long it has been since the neighbor entered the neighbor table;

"SRTT" refers to the normal round trip time, which calculates the average round trip of packets transmitted between routers in milliseconds Time measurement;

"RTO" refers to determining the retransmission interval value;

"Q" refers to the queue count, and the column is the number of waiting messages in the sending queue. If this value is higher than 0, it means there is congestion in the link;

(2), routing table

R2#show ip route

Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP

D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area

N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2

E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP

i - IS -IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area

* - candidate default, U - per-user static route, o - ODR

P - periodic downloaded static route

Gateway of last resort is not set

10.0.0.0/16 is subnetted, 5 subnets

D            10.2. 0.0 [90/20640000] via 192.168.10.2, 00:13:00, Serial1/1

##D

##C             10.6.0.0 is directly connected, Loopback0

D             10.11.0.0 [90/20640000] via 192.168.50.2, 00:12:23, Serial1/3

D 10.12.0.0 [90/20640000] via 192.168.40.2, 00:12:35, Serial1/2

192.168.10.0/30 is subnetted, 1 subnets

C        192.168.10.0 is directly connected, Serial1/1

192.168.20.0/30 is directly connected, 1 subnets

C Subnetted, 1 subnets

# D 192.168.30.0 [90/21024000] VIA 192.168.40.2, 00:12:35, Serial1/2

# [90/21024000] VIA 192.168.50.2, 00 12:23 /30 is subnetted, 1 subnets

C 192.168.50.0 is directly connected, Serial1/3

If "D *.*.*.*/* appears in the routing table, it is a summary, 00:15:00, Null0" is an automatically summarized route. Both EIGRP and RIP automatically summarize at the main network boundary by default. The difference is that EIGRP will generate an automatically summarized route locally, with the target pointing to the null interface ( Null0) Data sent to the empty interface will be discarded. Each link will have automatic summary records to effectively avoid routing loops. It is not necessary to use the automatic summary function, which can be achieved by canceling no auto-summary.

D 192.168.30.0 [90/21024000] via 192.168.40.2, 00:12:35, Serial1/2 This is the final route learned through EIGRP. D means it was learned through EIGRP. You can see 192.168 The link .30.0/30 is summarized. The 90 in [90/21024000] is the default administrative distance of EIGRP, followed by the metric value. The link 192.168.30.0/30 can be reached through any router in R4 or R5.

（3）、Topology table

R2#show ip eigrp topology

IP-EIGRP Topology Table for AS 200

Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply,

r - Reply status

P 10.2.0.0/16, 1 successors, FD is 20640000

via 192.168.10.2 (20640000/128256), Serial1/1

P 10.5.0.0/16, 1 successors, FD is 20640000

via 192.168.20.2 (20640000/128256), Serial1 /0

P 10.6.0.0/16, 1 successors, FD is 128256

via Connected, Loopback0

P 10.11.0.0/16, 1 successors, FD is 20640000

via 192.168.50.2 (20640000/128256), Serial1/3

via 192.168.40.2 (21152000/2297856), Serial1/2

P 10.12.0.0/16 , 1 successors, FD is 20640000

via 192.168.40.2 (20640000/128256), Serial1/2

via 192.168.50.2 (21152000/2297856), Serial1/3

P 192.168.10.0/30, 1 successors, FD is 20512000

via Connected, Serial1/1

P 192.168.20.0/30, 1 successors, FD is 20512000

via Connected, Serial1/0

P 192.168.30.0/30, 2 successors, FD is 21024000

via 192.168.40.2 (21024000/2169856), Serial1/2

via 192.168.50.2 (21024000/2169856), Serial1/3

P 192.168.40.0/30, 1 successors, FD is 20512000

via Connected, Serial1/2

P 192.168.50.0/30, 1 successors, FD is 20512000

via Connected, Serial1/3

where P represents passive routing, that is, the routing is stable and available.

Successors are the primary routes to the remote network. There can be up to 4 successor routes for any particular route.

For example: 192.168.10.0/30, 1 successors, is the best path to 192.168.10.0/30, FD is the feasible distance.

(4), EIGRP metric calculation method

EIGRP calculates the distance to the destination address by combining the composite metric value of factors such as bandwidth, delay, reliability, and load. Best path. If K1, K2, K3, K4, K5 are not 0, the following formula can be used to calculate the composite metric value:

Metric=[K1*Bandwidth (K2*Bandwidth)/(256-Load) K3* Delay]*[K5/(Reliability K4)]

K1 affects bandwidth (Bandwidth), K2 affects load (Load), K3 affects delay (Delay), and K4 and K5 affect Reliability;

Generally, Cisco routers only use K1 and K3 to calculate the composite metric value, so the formula can also use the following formula:

After rewriting sentence: The metric is calculated as 256 times the sum of (10000M divided by the minimum link bandwidth between the source and destination, plus the sum of all link delays between the source and destination divided by 10).

where source and The minimum link bandwidth between the destination, the unit is M; the total delay of all links between the source and the destination, the unit is microseconds (usec); then why do I divide the total delay by 10, that is because of the EIGRP metric value The calculation is performed in units of 10 microseconds.

Let's take a look at the experiment. For example, if we want to calculate the composite metric value of the loopback0 interface from R2 to R1, how to calculate it?

First of all, we need to pay attention to the measurement value of the loopback0 interface from R2 to R1, and use the bandwidth and delay of the outbound interface from R2 to the loopback0 interface of R1 as parameters to calculate:

R2# show int se1/1

Serial1/1 is up, line protocol is up (connected)

Hardware is HD64570

Internet address is 192.168.10.1/30

MTU 1500 bytes, BW 128 Kbit, DLY 20000 usec,

As shown above, you can see that the Serial 1/1 interface parameters of R2 are BW bandwidth, etc. 0.128M, and the delay is 20000 microseconds.

R1#show int loopback0

Loopback0 is up, line protocol is up (connected)

Hardware is Loopback

Internet address is 10.2.0.2/ 16

MTU 1514 bytes, BW 8000000 Kbit, DLY 5000 usec,

The above are the parameters of the loopback0 interface of R1. Its bandwidth is 8000M and the delay is 5000 microseconds.

Then let me rewrite the sentence according to the formula: The metric is calculated as 256 times the sum of (10000M divided by the minimum link bandwidth between the source and destination, plus the sum of all link delays between the source and destination divided by 10).", if R2's Serial1/1 goes To the loopback0 interface of R1, the minimum link bandwidth is 0.128M. The total delay is the delay of Serial1/1. The delay of the loopback0 interface of R1 = 20000 5000. Substitute it into the formula to calculate:

[10000/ R2's serial1/1 interface bandwidth (unit M) (R2's serial1/1 interface delay R1's loopback0 interface delay)/10]*256

That is [10000/0.128 (20000 5000)/10] *256

[78125 2500]*256=20640000

Let’s verify that R2 goes to the loopback0 port of R1

R2#show ip eigrp topology

IP-EIGRP Topology Table for AS 200

Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply,

r - Reply status

P 10.2.0.0/16, 1 successors, FD is 20640000

via 192.168.10.2 (20640000/128256), Serial1/1

P 10.5.0.0/16, 1 successors, FD is 20640000

via 192.168.20.2 (20640000/128256), Serial1/0

P 10.6.0.0/16, 1 successors, FD is 128256

via Connected, Loopback0

P 10.11.0.0/16, 1 successors, FD is 20640000

via 192.168.50.2 (20640000/128256), Serial1/3

via 192.168.40.2 (21152000/2297856), Serial1/2

P 10.12.0.0/16, 1 successors, FD is 20640000

via 192.168.40.2 (20640000/128256), Serial1/2

via 192.168.50.2 (21152000/2297856), Serial1/3

P 192.168.10.0/30, 1 successors, FD is 20512000

via Connected, Serial1/1

P 192.168.20.0/30, 1 successors, FD is 20512000

via Connected, Serial1/0

P 192.168.30.0/30, 2 successors, FD is 21024000

via 192.168.40.2 (21024000/2169856), Serial1/2

via 192.168.50.2 (21024000/2169856), Serial1/3

P 192.168.40.0/30, 1 successors, FD is 20512000

via Connected, Serial1/2

P 192.168.50.0/30, 1 successors, FD is 20512000

via Connected, Serial1/3

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