eigrp iccneig001
DESCRIPTION
ICAOTRANSCRIPT
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1EIGRP
EIGRP
MODULE ID: ICCNEIG001
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2EIGRP
Topics Covered
1. Features & Operations2. Various tables maintained by EIGRP3. EIGRP Terminologies4. Algorithm used5. EIGRP Metric6. EIGRP Packet types7. Configuring & Verifying8. Authentication
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3EIGRP
EIGRP Features and Operation
Referred to as a hybrid routing protocol as it has characteristics of both distance-vector and link-state protocols.
Sends traditional distance-vector updates containing information about networks plus the cost of reaching them
Link-state characteristics it synchronizes routing tables between neighbors at startup, and then sends specific updates only when topology changes occur.
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EIGRP Features and Operation Suitable for very large networks. Maximum hop count of 255. powerful features of EIGRP
Support for IP, IPX, and AppleTalk via protocol-dependent modules
Classless Support for VLSM/CIDR Support for summaries and discontiguous
networks Efficient neighbor discovery Communication via Reliable Transport Protocol
(RTP) Best path selection via Diffusing Update Algorithm
(DUAL)
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Protocol-Dependent Modules
EIGRP supports different Network layer
protocols through the use of protocol-
dependent modules (PDMs)
Each EIGRP PDM maintains a separate
series of tables containing the routing
information that applies to a specific protocol.
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Neighbor Discovery
EIGRP routers must become neighbors before exchanging routes with each other. Three conditions for neighborship establishment:
Hello or ACK received AS numbers match Identical metrics (K values)
To maintain the neighborship relationship, EIGRP routers must continue receiving Hellos from their neighbors.
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Neighbor Discovery
EIGRP routers belonging to different autonomous systems (AS) do not automatically share routing information and they dont become neighbors.
EIGRP advertises its entire routing table only when it discovers a new neighbor and forms an adjacency with it through the exchange of Hello packets.
When this happens, both neighbors advertise their entire routing tables to one another.
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Neighbor Table
The neighbor table is maintained by means of Hello packets.
Hello packets are multicast announcements that the router is alive.
Hello packets place the router into adjacent routers neighbor tables.
Reciprocal hellos build the local neighbor table. Once neighbor tables are built, hellos continue periodically to maintain neighborship
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Neighbor Table
The Layer 3 address of the neighbor The interface through which the neighbors Hello was
heard. The holdtime, which is three times the value of the Hello timer by default. The uptime, or period since the router first heard from the neighbor. The sequence number. Retransmission timeout (RTO) Smooth Round Trip Time (SRTT) which calculates the
RTO. SRTT is the time (in milliseconds) that it takes a packet to be sent to a neighbor and a reply to be received.
The number of packets in a queue
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Topology TableThe topology table has a record not only of feasiblesuccessors and successors but also of all received routes with the following information Whether the route is passive or active. Whether an update has been sent to the neighbor. Whether a query packet has been sent to the neighbor. If
this field is positive, at least one route will be marked as active.
Whether a query packet has been sent; if so, another field will track whether any replies have been received from the neighbor.
That a reply packet has been sent in response to a query packet received from a neighbor.
Prefixes, masks, interface, next-hop, and feasible and advertised distances for remote networks.
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Routing Table
The routing table is built from the topology table using
DUAL
Successor paths are transferred to the routing table
and used as the basis for routing decisions
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Definitions of related terms
Feasible distance This is the best metric along all paths to a
remote network, including the metric to the neighbor that is advertising that remote network.
This is the route in the routing table, because it is considered the best path.
Reported distance This is the metric of a remote network, as
reported by a neighbor.
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Definitions of related terms
Feasible successor A feasible successor is a path whose reported
distance is less than the feasible distance, and it is considered a backup route.
EIGRP will keep up to six feasible successors in the topology table.
Only the successor with the best metric is placed in the routing table.
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Definitions of related terms
Successor A successor route is the best route to a remote
network. A successor route is used by EIGRP to
forward traffic to a destination and is stored in the routing table.
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Feasible Distance/Advertised Distance
PUNE MUMBAI DELHI SRINAGAR
BHOPAL
200 1100 500
1500 500
Eg:- Mumbai to Srinagar Path Selection
AD
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Unequal Cost Load Balancing
All IP routing protocols on Cisco routers support equal-cost load sharing. EIGRP is unique in its support for unequal-cost load sharing.
EIGRP does proportional unequal-cost load sharing EIGRP will pass a relative portion of the traffic to each interface.
Eg:-A 384 kbps link would get 60 percent and the 256 kbps link would handle 40 percent of the traffic.
This allows all links to a destination to be used to carry data without saturating the slower links or limiting the faster links
Unequal-cost load balancing takes the best FD and multiplies it by variance. Any other path with an FD less than this product is used for load sharing
Maximum 6 feasible successors can do load balancing Default is 4
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Reliable Transport Protocol (RTP)
EIGRP uses a proprietary protocol, called Reliable Transport Protocol (RTP) , to manage the communication of messages between EIGRP-speaking routers.
Cisco has designed a mechanism that uses multicasts and unicasts to deliver updates quickly, and to track the receipt of the data.
When EIGRP sends multicast traffic, it uses the Class D address 224.0.0.10.
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Diffusing Update Algorithm (DUAL)
EIGRP uses Diffusing Update Algorithm (DUAL) for selecting and maintaining the best path to each remote network.
This algorithm allows for the following: Backup route determination if one is available Support of Variable-Length Subnet Masks
(VLSMs) Dynamic route recoveries Queries for an alternate route if no route can
be found DUAL provides EIGRP the fastest route
convergence time among all protocols.
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Multiple ASes
EIGRP uses autonomous system numbers to identify the collection of routers that share route information.
Only routers that have the same autonomous system numbers share routes.
In large networks, the complicated topology and route tables, slows convergence during diffusing computation operations.
Its possible to divide the network into multiple distinct EIGRP autonomous systems, or ASes.
Each AS is populated by a contiguous series of routers, and route information can be shared among the different ASes via redistribution.
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VLSM Support and Summarization
EIGRP supports the use of Variable-Length Subnet Masks.
EIGRP also supports the use of discontiguous subnets,
A discontiguous network is one that has two or more subnetworks of a classful network connected together by different classful networks.
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A discontiguous network
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EIGRP auto summarization
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EIGRP Metrics
EIGRP can use a combination of four metrics: Bandwidth Delay Load Reliability MTU
EIGRP uses only bandwidth and delay of the line to determine the best path to a remote network by default.
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Metric calculation
By default, K1=K3=1 and K2=K4=K5=0. Those who followed the math will note that when K5=0the metric is always zero. Because this is not useful, EIGRP simply ignores everything outsidethe parentheses. Therefore, given the default K-values the equation becomesMetric= 256 (bandwidth +delay )Actually:metric = slowest bandwidth + sum of all delays
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EIGRP Packet Types
Response to a queryReply
Needing specific info from a neighbor
Query
When a router discovers a new neighbor or a topology change
Update
Indicates receipt of an EIGRP during a reliable packet
Acknowledgement (unicast)
Discovers, verifies, rediscovers neighbor routers
Hello multicast every 5 seconds
DefinitionPacket
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Configuring EIGRP
Two modes from which EIGRP commands are entered: router configuration mode and interface configuration mode
Router configuration mode enables the protocol determines which networks will run EIGRP sets global characteristics
Interface configuration mode allows customization of Summaries Metrics Timers Bandwidth
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Configuring EIGRP
Configuring involves enabling the following 3 items The EIGRP processThe routing protocol needs to be
started on the router. The EIGRP autonomous system numberRouters in
the same administrative domain should be identified and grouped by a common AS number. This 16-bit number is arbitrary. Organizations that have a BGP AS will sometimes use that number; others just make up a number or use AS 1. The significance of the AS is that a router will not become a neighbor with a router in a foreign AS.
Participating router interfacesYou can activate EIGRP on some or all interfaces. For instance, a router might run EIGRP on internal interfaces and BGP on external interfaces
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EIGRP Configuration
Router#config tRouter(config)#interface Router(config-if)#ip address
Router(config)#router eigrp 100
Router(config-router)#network 172.17.0.0
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EIGRP Authentication
EIGRP supports two forms of authentication: simple passwords and MD5 hashes
Simple passwords are not secure, because any listener can see this traffic and read the key value.
Hashed keys, sent as MD5 values, are secure because a listener cannot use the value in one transmission to compute the key.
Using MD5 Authentication, the router generates a hash value for every EIGRP transmission and checks the hash of every received EIGRP packet.
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Other optional commands
no auto-summary Turns off automatic classful summarization. ip summary-address Manually configures summarization. variance Configures unequal proportional load balancing. ip hello-interval eigrp autonomous-systemnumber seconds
Changes the hello frequency. ip hold-time eigrp autonomous-system-number seconds
Changes the length of time before a neighbor is considered dead.
bandwidth Changes the bandwidth setting on an interface, which is used to calculate the EIGRP metric and the maximum percentage of bandwidth to which EIGRP traffic will limit itself.
ip bandwidth-percent eigrp as-number Changes the maximum amount of bandwidth EIGRP traffic will use. The default is 50%
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Verification
show ip route
show ip protocols
show ip eigrp neighbors
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Summary
1. EIGRP Features2. Neighbor discovery & Neighbor Tables3. Topology Table & Routing Table4. Feasible & Reporting Distance5. Successor & Feasible Successor6. RTP & DUAL7. EIGRP Metric & EIGRP Packet Types8. Summarisation9. Configuration & Verification
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References
Books Hand book on Internetworking by CISCO Building Scalable Cisco Internetworks by
CISCO CCNA Study guide by Todd Lamle
URLs http://www.cisco.com http://en.wikipedia.org
Slide 1Slide 2EIGRP Features and OperationSlide 4Protocol-Dependent ModulesNeighbor DiscoverySlide 7Neighbor TableSlide 9Topology TableRouting TableDefinitions of related termsSlide 13Slide 14Feasible Distance/Advertised DistanceUnequal Cost Load BalancingReliable Transport Protocol (RTP)Diffusing Update Algorithm (DUAL)Multiple ASesVLSM Support and SummarizationA discontiguous networkEIGRP auto summarizationEIGRP MetricsMetric calculationEIGRP Packet TypesConfiguring EIGRPSlide 27EIGRP ConfigurationEIGRP AuthenticationOther optional commandsVerificationSummaryReferences