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This article mainly introduces "what are the knowledge points of the EIGRP system". In the daily operation, I believe that many people have doubts about the knowledge points of the EIGRP system. The editor consulted all kinds of materials and sorted out simple and easy-to-use methods of operation. I hope it will be helpful to answer the questions of "what are the knowledge points of the EIGRP system?" Next, please follow the editor to study!

EIGRP theory

EIGRP is a Cisco private protocol, which is a mixture of distance vector and link-state routing protocols. That is, like the distance vector protocol, EIGRP gets updated information from its neighboring routers; like the link-state protocol, it keeps a topology table and then chooses an optimal loop-free path through its own DUAL algorithm. Unlike traditional distance vector protocols, EIGRP has fast convergence time and does not need to send periodic routing updates; unlike link-state protocols, EIGRP does not know what the whole network is like, it can only rely on the information published by its neighbors. EIGRP uses the same routing algorithm DUAL (Diffusion Update algorithm) as IGRP. DUAL mechanism is the core of EIGRP, which is used to realize loop-free path. The internal EIGRP administrative distance is 90 and the external EIGRP administrative distance is 170, which supports equal-cost and non-equal-cost load balancing. In the IP packet, the protocol field for EIGRP is 88.

The noun explains:

Metrics: EIGRP usage bandwidth (bandwidth), delay (delay), reliability (reliability), load (loading), maximum transmission unit

(MTU) these five values are used to calculate metrics, and only bandwidth and latency work by default. The calculation formula is-- EIGRP metric = [(10 ^ 7 / path)

The lower bandwidth on) + (sum of all delays)] × 256 th EIGRP metric = IGRP metric x 256.

Feasible distance (Feasible Distance): the minimum measure to reach a destination.

Advertised distance (Advertise Distance): the minimum metric advertised by a neighboring router to reach a destination on its own.

Feasible condition (Feasible Condition): the condition that the advertised distance (AD) is less than the feasible distance is AD.

The metric of the ground must be smaller than that of the local router arriving at the destination. This condition ensures that a path is loop-free.

EIGRP successor (Successor): a directly connected neighbor router that satisfies the FC through which it has the path with the minimum metric to the destination

By the instrument. The successor is used as the next hop to forward the message to the destination.

Feasible successor (Feasible Successor): a neighbor router that satisfies FC and has the second lowest metric to the destination. Be the master

When route S is not available, FS is used to replace the primary route and is saved in the topology table as a backup route.

Active status / active routing (active state): a state that is searching for FS when the router loses S and there is no FS available

The route is active and is an unavailable route. When a route is active, the router sends a query to all neighbors to find it

Find another route to that destination.

Passive state / passive routing (passive state): a state in which there is currently a correct route to the destination, when the router loses S and has a

FS, or when another S is found, the route goes into a passive state and is an available route.

Neighbor relationship: EIGRP establishes neighbor relationship through hello packets. The sending interval of hello packets is 60 seconds on low-speed links and 5 seconds on high-speed links.

Reset the neighbor relationship for a period of time if the hello packet is not received. This time is the hold time (hold time), which is the default hold time.

Three times as long as hello. Both times can be changed manually, and when establishing a neighbor relationship, the K value and the homemade system number must be the same. Sure

View neighbor relationships through show ip eigrp neighbor.

DUAL (diffusion update algorithm):

(not yet)

Advantages of EIGRP:

100% loop-free: if the entire network is included in a homemade system, EIGRP uses DUAL to guarantee a 100% loop-free routing forwarding table

Fast convergence: EIGRP uses DUAL to achieve fast convergence by backing up routes. When S is not available, quickly switch to FS to achieve fast convergence

Use multicast, unicast: use multicast (224.0.0.10) or unicast for routing updates to save link bandwidth

Increased the size of the network: RIP can only support a maximum of 15 hops, while EIGRP can support up to 255hops, IGRP is 224hops, and both of them default to 100hops

Three network layer protocols are supported: EIGRP supports IP, IPX and Apple Talk, which increases the scope of use of EIGRP.

Support for VLSM and discontiguous networks: not for RIP and IGRP

Reduce bandwidth consumption and make better use of bandwidth: unlike RIP and IGRP, which exchange routing information at regular intervals, EIGRP uses

Triggered and incremental updates that send routes to neighbors only when the routing state of a destination network changes or the metric of the route changes.

Update, so the bandwidth required to update the route is much smaller than that of RIP and EIGRP. EIGRP gets bandwidth from the interface that the EIGRP packet is about to send out

Parameter, which is specified based on the interface. For example, all serial interfaces have the bandwidth of 1544kb/s by default, but this

Bandwidth values are configurable, and EIGRP can use up to 50% of the interface bandwidth to host EIGRP packets (you can use ip bandwidth-

Percent eigrp to modify), which ensures that EIGRP packets will not "starve" conventional data packets during the main network convergence process.

RIP and IGRP do not have this feature, so a large number of RIP and IGRP update packets may prevent regular packets from passing through.

The multicast MAC address is 01-00-5E-00-00-0A.

Note: EIGRP is a proprietary protocol for Cisco. When Cisco devices are interconnected with devices from other manufacturers, EIGRP protocol cannot be used.

Conditions for EIGRP to form a neighbor:

1.AS number is the same

two。 The value of K calculated by the metric is the same.

3. The authentication is the same (EIGRP only supports ciphertext authentication)

4. The Neighbor ID advertised by the peer must exist in the directly connected network segment of the local side.

Note: routing protocols transmit data streams through the port's Primary IP and form a Neighbor ID (representing an interface). After receiving the Hello, the EIGRP router will use the subnet mask of its own Primary IP to do the and operation with the Neighbor ID in the Hello, get the network address and match the directly connected network segment in its own routing table, and some will think that the other party is a neighbor and put it into the neighbor table. If not, it will refuse to form a neighbor on the ground that it is not in the same subnet.

Description: IGRP and EIGRP can automatically republish routing information in the same homemade system, but you can also turn off automatic republishing of routing information.

EIGRP detailed explanation

Three tables of EIGRP: Neighbor Table, Topology Table, Routing Table

The routers that initially run EIGRP have to go through the process of discovering neighbors, understanding the network and choosing routes. In this process, three independent tables are established at the same time: Neighbor Table, Topology Table, Routing Table. Neighbor Table stores the directly connected routers that have established a neighbor relationship with the router; Topology Table contains all the routing entries that the router has learned to reach the destination; and Routing Table is the routing table of the best path.

Take router R4 as an example to introduce Neighbor Table, Topology Table and Routing Table

1. Each neighbor in the Neighbor Table of R4 forwards a backup of the IP routing table to R4.

2. R4 stores the routing table received from its neighbors in its own Topology Table. As shown in the figure, R4 receives R2 and R3 to the network 172.16.1.0, respectively.

Advertised, the advertised distances are 110 and 160, respectively. R4 received it and added its own metrics to R2 and R3 to get the calculated distances 210 and 260.

3. R4 checks the Topology Table, then selects the best route to the destination, determines that the best Successor routers is R2, and then

Put it in Routing Table.

Routing Table of EIGRP:

D: routing learned in this homemade system.

D EX: routes published from the outside.

Neighbor Table of EIGRP:

Address: the address of the neighbor router.

Interface: local to neighbor interface.

Hold time: the maximum time to wait for Miyou to receive any data message from the neighbor, and the Hold time resets when a new message is received.

SRTT (Smooth round-trip time) smooth round-trip time: an EIGRP message is sent to the neighbor and then received by the local router from the neighbor

The time it takes to confirm the message, in ms.

RTO (Retransmission timeout) retransmission timeout: the time in ms to wait for an acknowledgement before retransmitting the message.

Q Cnt (Queue count) queue count: the number of EIGRP packets waiting to be sent. If this value continues to be higher than 0, the network is congested.

Topology Table of EIGRP:

P:passive, indicating that the network is in a stable state.

A:active, which indicates that the current network is not available and is in the state of sending a query.

U:update, indicating that the network is in a state of waiting for confirmation of update packets.

Q:query, indicating that the network is in a state of waiting for confirmation of query packets.

SIA:stuck-in-active, indicating that the network is in a continuous active state, indicating that there is a problem with the convergence of the EIGRP network.

Traffic Table (receive and send information table) for EIGRP routes:

Message type of EIGRP:

EIGRP uses reliable transport protocol RTP (Reliable Transport Protocl). RTP ensures that every EIGRP packet must be acknowledged, and the next packet will be sent only after the previous packet has been acknowledged. RTP's retransmission mechanism allows the RTP to retransmit the packet (retransmission to unicast in order not to affect the routes that have been properly acknowledged) if the reliable message sent to the neighbor has not been acknowledged after the RTO (Retransmit Time Out) is exceeded. Retransmit up to 16 times, and if it is not confirmed after 16 times, the neighbor relationship is reset until the neighbor relationship duration (hold time) expires and the neighbor is declared unreachable. Receivers need to acknowledge messages with serial numbers such as update, reply and query, while messages that do not require reliability (such as Hello and ACK) do not need to be acknowledged.

Hello: sent as a multicast to discover neighboring routers and maintain neighbor relationships.

Update: when a router receives the first Hello message from a neighboring router, it sends back a message containing what it knows as a single point of delivery

Update message for routing information. When the routing information changes, an update message containing only the change information is sent in the way of multicast. Note

Meaning, the contents of the two update messages are different.

Query (query): when a link fails, the router recalculates the route. However, when there is no feasible successor route in the topology table, the router uses the

Multicast sends a query message to its neighbors to ask them if they have a feasible successor route to the destination.

Reply (reply): a single point is sent back to the querying party to reply to the query data message.

ACK: transmitted in a single point, used to confirm update, query, and reply data messages to ensure the reliability of transmission.

Note: OSPF requires that neighbors must have the same decision interval between Hello and Down in order to communicate, but EIGRP does not have this restriction. In practical application, the hold time of EIGRP is set to 3 times that of Hello interval, while in OSPF, the hold time is set to 4 times of Hello interval.

EIGRP route maintenance process:

1. Establish adjacency: since the start of operation, routers running EIGRP have been using the multicast address 224.0.0.10 from the interfaces participating in EIGRP

Send Hello messages out. When the routers receive Hello messages to each other, the two sides establish a neighbor relationship.

two。 Discover the network topology and choose the shortest route: when the router dynamically discovers a new neighbor through the Hello message, it also gets the information from the new

Routing information advertised by neighbor update. The routing update information obtained by the router is first compared with the information recorded in the topology table, and the FD is the smallest

For S, if there is the same FD, there can be more than one S in the routing table, and 4 by default. FC-compliant routes are placed in the topology table as FS

Alternate router, if S is invalid for some reason and a valid FS exists, FS will replace S without recalculating. Topology of EIGRP

Table can have more than one valid FS at a time.

3. Routing query, update: when the routing information does not change, EIGRP neighbors only send Hello messages to maintain the neighbor relationship, so as to reduce the

The use of network bandwidth. When a neighbor is lost and a link is unavailable, EIGRP immediately looks for FS from the topology table to enable alternative paths.

By the instrument. If there is no FS in the topology table, set the route to active and send query data messages to all neighbors except invalid neighbors. If

If a neighbor has a route to the destination, it will reply to the query and no longer spread the query. Otherwise, adjacent rout

The server will further query each of its own neighbors, and only after all queries have been answered will EIGRP recalculate the route, reset FD, and select the new

The successor to the. If the neighboring router does not have a replaceable route and does not have a neighboring router, it sends a

A reply message whose metric is infinity.

At this point, the study of "what are the knowledge points of the EIGRP system" is over. I hope to be able to solve your doubts. The collocation of theory and practice can better help you learn, go and try it! If you want to continue to learn more related knowledge, please continue to follow the website, the editor will continue to work hard to bring you more practical articles!

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