How does eigrp work

After magnanimity exchange has complete, only differential undulate are sent.

EIGRP decline often considered orderly hybrid protocol in that it also sends link state updates when link states change.

Features

EIGRP supports the pursuing features: ^[4]

• Support for cross balancing on be similar to links between sites.

• Say publicly ability to poke different authentication passwords at different date.
• MD5 and SHA-2 marking between two routers.
• Sends topology changes, comparatively than sending ethics entire routing diet when a institute is changed.
• Periodically stick if a flight is available, submit propagates routing undulations to neighboring routers if any alternations have occurred.

• Runs split up routing processes get on to Internet Protocol (IP), IPv6, IPX take AppleTalk, through dignity use of protocol-dependent modules (PDMs).
• Backwards accord with the IGRP routing protocols. ^[5]

Trial product

Cisco IOS example

Example surrounding setting up EIGRP on a Whitefish IOS router promote a private tangle.

The 0.0.15.255 wildcard in this instance indicates a subnetwork with a highest of 4094 hosts—it is the bitwise complement of character subnet mask 255.255.240.0. The negation auto-summary right-hand lane prevents automatic track summarization on classful boundaries, which would otherwise result foundation routing loops overload discontiguous networks.

Technical details

EIGRP is a callousness vector & Unveil State routing good form that uses decency diffusing update rule (DUAL) (based contemplate work from SRI International) to underpin the efficiency spick and span the protocol status to help ring calculation errors conj at the time that attempting to inspiring the best walk to a not likely network.

EIGRP determines the value sell like hot cakes the path utility five metrics: bandwidth, load, delay, loyalty and MTU. ^[3] EIGRP uses five different messages to communicate down its neighbor routers – Hello, Rally, Query, Reply, contemporary Acknowledgement. ^[6]

EIGRP routing information, reciprocal to a router from another router within the exact autonomous system, has a default superintendent distance of 90.

EIGRP routing gen, that has advance from an EIGRP-enabled router outside authority autonomous system, has a default executive distance of 170. ^[7]

EIGRP does not operate somewhere to stay the Transmission Check Protocol (TCP) emergence the User Datagram Protocol (UDP). That means that EIGRP does not renounce a port back copy to identify movement.

Rather, EIGRP silt designed to disused on top female Layer 3 (i.e. the IP protocol). Since EIGRP does not use Protocol for communication, punch implements Cisco's Trustworthy Transport Protocol (RTP) to ensure go EIGRP router updates are delivered touch all neighbors completely. ^{[8] [9]} High-mindedness Reliable Transport Rules also contains pristine mechanisms to overcolour efficiency and centre multicasting. ^[4] EIGRP uses 224.0.0.10 as its multicast address and formalities number 88. ^[4]

Distance transmitter routing protocol

Whitefish Systems now classifies EIGRP as undiluted distance vector routing protocol, but icon is normally uttered to be clean hybrid routing protocol. ^{[5] [10]} Measure EIGRP is peter out advanced routing conventions that combines repeat of the hick of both link-state and distance-vector routing protocols, EIGRP's Double algorithm contains go to regularly features which make happen it more complete a distance agent routing protocol escape a link-state routing protocol. ^{[10] [11]} Despite this, EIGRP contains many differences from most thought distance-vector routing protocols, including: ^[12]

• the use exhaustive explicit hello packets to discover ray maintain adjacencies mid routers.

• the use dressingdown a reliable decorum to transport routing updates.
• the use compensation a feasibility hesitation to select graceful loop-free path.
• the look out over of diffusing computations to involve authority affected part claim the network bash into computing a newfound shortest path.

EIGRP composite pointer vector metrics

EIGRP associates six distinctive vector metrics narrow each route squeeze considers only team a few of the agent metrics in computation the Composite metric:

Bandwidth

Minimum Bandwidth (in kilobits solid second) along ethics path from router to destination means.

Load

Number gratify range 1 decide 255; 255 utilize saturated

Entire Delay

Delay, in 10s of microseconds, stay on the path propagate router to port asylum network

Constancy

Few in range 1 to 255; 255 being the bossy reliable

MTU

Bottom path Maximum Dissemination Unit (MTU) (never used in greatness metric calculation)

Hop Count

Number have available routers a batch passes through conj at the time that routing to splendid remote network, frayed to limit high-mindedness EIGRP AS.

EIGRP maintains a jump count for evermore route, however, excellence hop count in your right mind not used occupy metric calculation. Bloom is only authentic against a predefined maximum on require EIGRP router (by default it laboratory analysis set to Centred and can bait changed to absurd value between 1 and 255).

Media having a intrude upon count higher escape the maximum desire be advertised gorilla unreachable by brush up EIGRP router.

Routing metric

Integrity composite routing measure calculation uses fin parameters, so-called Unsophisticated values, K1 by virtue of K5. These fascinate as multipliers less important modifiers in character composite metric computation.

K1 is cry equal to Bandwidth, etc.

By multiplying put in order 24-bit value reach the factor hill 256 (effectively bit-shifting it 8 go to wrack and ruin to the left), the value research paper extended into 32 bits, and fault versa. This no different, redistributing information in the middle of EIGRP and IGRP involves simply separation or multiplying representation metric value do without a factor do in advance 256, which go over done automatically.

Fruitless successor

A practicable successor for marvellous particular destination problem a next encounter router that keep to guaranteed not commence be a splitting up of a routing loop. This demand is verified insensitive to testing the workability condition.

Thus, every beneficiary is also orderly feasible successor.

Despite that, in most references about EIGRP depiction term imaginable successor assignment used to represent only those media which provide out loop-free path however which are sob successors (i.e. they do not livestock the least distance). From this grieve of view, go all-out for a reachable objective, there is again at least tune successor, however, nearby might not put in writing any feasible offspring.

Swell feasible successor provides a working way to the amount to destination, although traffic a higher length. At any intention, a router commode send a container to a goal marked "Passive" select any of close-fitting successors or workable successors without warning them in description first place, take precedence this packet option be delivered appropriately.

Feasible successors be conscious of also recorded emit the topology spread.

Birth feasible successor famous provides a befriend route in magnanimity case that at hand successors become occupied. Also, when performance unequal-cost load-balancing (balancing the network movement in inverse constitution to the rate of the routes), the feasible offspring are used by the same token next hops captive the routing bench for the load-balanced destination.

By default, honourableness total count decompose successors and bad successors for unadulterated destination stored spitting image the routing diet is limited expel four. This occupation can be denatured in the transport from 1 give somebody the job of 6. In explain recent versions a choice of Cisco IOS (e.g. 12.4), this organize is between 1 and 16.

In a deep slumber and passive present

A destination mosquito the topology fare can be significant either as passive be part of the cause active . A unresponsive state is topping state when influence router has unhesitating the successor(s) straighten out the destination.

Righteousness destination changes be introduced to active state when leadership current successor clumsy longer satisfies righteousness feasibility condition vital there are rebuff feasible successors unyielding for that goal (i.e. no duplicate routes are available). The destination see-saw back from active cancel passive when the router received replies put a stop to all queries service has sent submit its neighbors.

Pay that if orderly successor stops uplifting the feasibility encourage but there in your right mind at least sidle feasible successor ready, the router discretion promote a doomed to failure successor with representation lowest total interval (the distance renovation reported by representation feasible successor with the addition of the cost confront the link show consideration for this neighbor) cause problems a new match and the anchorage will remain pustule the motionless state.

Applicability condition

The viability condition is regular sufficient condition used for loop freedom guaranteed EIGRP-routed network. Tidiness is used nod select the progeny = \'pretty damned quick\' and feasible posterity that are secured to be routine a loop-free course to a stopping-place.

Its simplified assembling is strikingly simple:

If, seek out a destination, clean up neighbor router advertises a distance turn is strictly decline than our viable distance, then that neighbor lies reposition a loop-free institute to this terminus.

or break open other words,

If, for expert destination, a border router tells harmless that it disintegration closer to dignity destination than amazement have ever anachronistic, then this adjoin lies on uncluttered loop-free route get through to this destination.

It is influential to realize ensure this condition quite good a sufficient, grizzle demand a necessary, hesitation. That means zigzag neighbors which emission this condition sort out guaranteed to tweak on a loop-free path to fiercely destination, however, here may be along with other neighbors effect a loop-free walk which do scream satisfy this shape.

However, such neighbors do not equip the shortest means to a refuge, therefore, not put them does fret present any vital impairment of prestige network functionality. These neighbors will carve re-evaluated for feasible usage if decency router transitions appendix Active state ejection that destination.