EIGRP

1. EIGRP Routing Protocols and Concepts – Chapter 9 Modified by Mike Haines 04/01/2010

2. Introduction

3. EIGRP • Roots of EIGRP: IGRP -Developed in 1985 to overcome RIPv1’s limited hop count -Distance vector routing protocol -Metrics used by IGRP • bandwidth (used by default) • Delay (used by default) • Reliability (not used by default) • Load (not used by default) -Discontinued support starting with IOS 12.2(13)T & 12.2(R1s4)S

4. EIGRP • EIGRP is a distance vector, classless routing protocol that was released in 1992 with IOS 9.21. • As its name suggests, EIGRP is an enhancement of Cisco IGRP (Interior Gateway Routing Protocol). • Both are Cisco proprietary protocols and only operate on Cisco routers. • The main purpose in Cisco's development of EIGRP was to create a classless version of IGRP. EIGRP includes several features that are not commonly found in other distance vector routing protocols like RIP (RIPv1 and RIPv2) and IGRP. These features include: • Reliable Transport Protocol (RTP) • Bounded Updates • Diffusing Update Algorithm (DUAL) • Establishing Adjacencies • Neighbor and Topology Tables • Although EIGRP may act like a link-state routing protocol, it is still a distance vector routing protocol. • Note: The term hybrid routing protocol is sometimes used to define EIGRP. However, this term is misleading because EIGRP is not a hybrid between distance vector and link-state routing protocols - it is solely a distance vector routing protocol. Therefore, Cisco is no longer using this term to refer to EIGRP.

5. EIGRP • The Algorithm • EIGRP uses the Diffusing Update Algorithm (DUAL). • EIGRP does not send periodic updates and route entries do not age out. • Only changes in the routing information, such as a new link or a link becoming unavailable cause a routing update to occur. • EIGRP routing updates are still vectors of distances transmitted to directly connected neighbors.

6. EIGRP • Path Determination • EIGRP's DUAL maintains a topology table separate from the routing table, which includes both the best path to a destination network and any backup paths that DUAL has determined to be loop-free. • If a route becomes unavailable, DUAL will search its topology table for a valid backup path. • If one exists, that route is immediately entered into the routing table. • If one does not exist, DUAL performs a network discovery process to see if there happens to be a backup path that did not meet the requirement of the feasibility condition.

7. EIGRP • Convergence • EIGRP does not use holddown timers. • Instead, loop-free paths are achieved through a system of route calculations (diffusing computations) that are performed in a coordinated fashion among the routers. • The detail of how this is done is beyond the scope of this course, but the result is faster convergence than traditional distance vector routing protocols.

8. EIGRP EIGRP Message Format • EIGRP Header • Data link frame header - contains source and destination MAC address • IP packet header - contains source & destination IP address • EIGRP packet header - contains AS number • Type/Length/Field - data portion of EIGRP message • In the IP packet header, • the protocol field is set to 88 to indicate EIGRP • the destination address is set to the multicast 224.0.0.10. • If the EIGRP packet is encapsulated in an Ethernet frame, • the destination MAC address is also a multicast address: 01-00-5E-00-00-0A.

9. EIGRP • All fields are shown to provide an accurate picture of the EIGRP message format. However, only the fields relevant to the CCNA candidate are discussed. • EIGRP packet header contains • Opcode field • Update • Query • Reply • Hello • Autonomous System number • The AS number is used to track multiple instances of EIGRP. • EIGRP Parameters contains • Weights • EIGRP uses for its composite metric. • By default, only bandwidth and delay are weighted. Both are set to 1. • The other K values are set to zero. • Hold time • The amount of time the EIGRP neighbor receiving this message should wait before considering the advertising router to be down.

10. EIGRP • TLV: IP internal contains (EIGRP routes within an autonomous system) • Metric field (Delay and Bandwidth) • Delay is calculated as the sum of delays from source to destination in units of 10 microseconds. • Bandwidth is the lowest configured bandwidth of any interface along the route. • Subnet mask field • The subnet mask is specified as the prefix length or the number of network bits in the subnet mask. • 255.255.255.0 is 24 • Destination field • the address of the destination network. • Although only 24 bits are shown in this figure. • If a network address is longer than 24 bits, then the Destination field is extended for another 32 bits • TLV: IP external contains • Fields used when external routes are imported into EIGRP routing process • import or redistribute a route into EIGRP.

11. EIGRP Protocol Dependent Modules (PDM) • EIGRP uses PDM to route several different protocols i.e. IP, IPX & AppleTalk • PDMs are responsible for the specific routing task for each network layer protocol • As you can see in the figure, EIGRP uses different EIGRP packets and maintains separate neighbor, topology, and routing tables for each Network layer protocol. • The IP-EIGRP module is responsible for sending and receiving EIGRP packets that are encapsulated in IP and for using DUAL to build and maintain the IP routing table. • The IPX EIGRP module is responsible for exchanging routing information about IPX networks with other IPX EIGRP routers. • Apple-Talk EIGRP is for Apple-talk How do people route IPX or Appletalk today if they still get either IPX or Appletalk?

12. EIGRP Reliable Transport Protocol (RTP) • Purpose of RTP • Used by EIGRP to transmit and receive EIGRP packets • EIGRP was designed as a Network layer independent routing protocol; therefore, it cannot use the services of UDP or TCP because IPX and Appletalk do not use protocols from the TCP/IP protocol suite. • Characteristics of RTP • Involves both reliable & unreliable delivery of EIGRP packet • Reliable delivery requires acknowledgment from destination • Unreliable delivery does not require an acknowledgement from destination • Packets can be sent • Unicast • Multicast • Using address 224.0.0.10

13. EIGRP • Hello • Update • ACK • Query • Reply EIGRP’s 5 Packet Types • Hello packets • Used to discover & form adjacencies with neighbors • EIGRP hello packets are multicasts and use unreliable delivery.

14. EIGRP • Hello • Update • ACK • Query • Reply • Update packets • Update packets are used to propagate routing information • Update packets are sent only when necessary. • EIGRP updates are sent only to those routers that require it. • When a new neighbor is discovered, unicast update packets are sent so that the neighbor can build up its topology table. • In other cases, such as a link-cost change, updates are multicast. • Updates always are transmitted reliably • Acknowledgement packets • Used to acknowledge receipt of update, query & reply packets • An acknowledgment packet is a hello packet that has no data. • EIGRP acknowledgement packets are always sent as an unreliable unicast • R2 has lost connectivity to the LAN attached to its FastEthernet interface. • R2 immediately sends an unicast Update to R1 and R3 noting the downed route. • R1 and R3 respond with an unicast acknowledgement.

15. EIGRP • Hello • Update • ACK • Query • Reply • Query & Reply packets • Used by DUAL for searching for networks • Queries and replies use reliable delivery. • Query packets can use • Multicast • Reply packet use only • unicast • R2 has lost connectivity to the LAN and it sends out queries to all EIGRP neighbors. • All neighbors must send a reply regardless of whether or not they have a route to the downed network.

16. EIGRP

17. EIGRP • Purpose of Hello Protocol • To discover neighbors & establishadjacencies with neighbor routers • Characteristics of hello protocol • Time interval for sending hello packet • 5 seconds - high bandwidth (greater than T1) • 60 seconds - multipoint circuits T1 bandwidth or slower -Holdtime • This is the maximum time router should wait before declaring a neighbor down • Default holdtime • 3 times hello interval • 15 seconds • 180 seconds

18. EIGRP EIGRP Bounded Updates • EIGRP only sends update when there is a change in route status • Partial update • A partial update includes only the route information that has changed • the whole routing table is NOT sent • Bounded update • When a route changes, only those devices that are impacted will be notified of the change • EIGRP’s use of partial bounded updates minimizes use of bandwidth

19. EIGRP Diffusing Update Algorithm (DUAL) • Purpose • EIGRP’s primary method for preventing routing loops • And also hold-down timers and split horizon, too. • Advantage of using DUAL • Provides for fast convergence time by keeping a list of loop-free backup routes • DUAL maintains a list of backup routes it has already determined to be loop-free. If the primary route in the routing table fails, the best backup route is immediately added to the routing table.

20. EIGRP • Administrative Distance (AD) • Defined as the trustworthiness of the source route • EIGRP default administrative distances • Summary routes = 5 • Internal routes = 90 • Imported routes = 170

21. EIGRP Authentication • EIGRP can • Encrypt routing information • Authenticate routing information • It is good practice to authenticate transmitted routing information. • This practice ensures that routers will only accept routing information from other routers that have been configured with the same password or authentication information. • Note: Authentication does not encrypt the router's routing table. http://www.ciscopress.com/articles/article.asp?p=1171169&seqNum=3

22. EIGRP Network Topology • Topology used is the same as previous chapters with the addition of an ISP router • ISP router does not physically exist • EIGRP will automatically summarizes at classful boundaries, similar to RIP.

23. Basic EIGRP Configuration • Autonomous System (AS) & Process IDs • This is a collection of networks under the control of a single authority (reference RFC 1930) • AS Numbers are assigned by IANA  ARIN not IANA • Entities needing AS numbers • ISP • Internet Backbone prodiers • Institutions connecting to other institutions using AS numbers • These ISPs and large institutions use the exterior gateway routing protocol or BGP, to propagate routing information. 16-bit and 32-bit AS Numbers Commencing 1 January 2007, "16-bit only AS Numbers" refers to AS numbers in the range 0 - 65535"32-bit only AS Numbers" refers to AS Numbers in the range 65,536 - 4,294,967,295"32-bit AS Numbers" refers to AS Numbers in the range 0 - 4,294,967,295

24. Basic EIGRP Configuration • EIGRP autonomous system number actually functions as a process ID • The vast majority of companies and institutions with IP networks do not need an AS number • The ISP is responsible for the routing of packets within its autonomous system and between other autonomous systems. • Process ID represents an instance of the routing protocol running on a router • Example Router(config)#router eigrp autonomous-system

25. Basic EIGRP Configuration The router eigrp command • The global command that enables eigrp is router eigrp autonomous-system -All routers in the EIGRP routing domain must use the same process ID number (autonomous-system number)

26. Basic EIGRP Configuration The Network Command • Functions of the network command • Enables interfaces to transmit & receive EIGRP updates • Includes network or subnet in EIGRP updates • Example • Router(config-router)#network network-address The network-address is the classful network address for this interface. a single classful network statement is used on R1 to include both 172.16.1.0/24 and 172.16.3.0/30 subnets: When EIGRP is configured on R2, DUAL sends a notification message to the console stating that a neighbor relationship with another EIGRP router has been established.

27. Basic EIGRP Configuration • The network Command with a Wildcard Mask -This option is used when you want to configure EIGRP to advertise specific subnets -Example Router(config-router)#network network-address [wildcard-mask] 192.168.10.8 – 192.168.10.11

28. Basic EIGRP Configuration • Think of a wildcard mask as the inverse of a subnet mask. • The inverse of subnet mask 255.255.255.252 is 0.0.0.3. • To calculate the inverse of the subnet mask, subtract the subnet mask from 255.255.255.255: 255.255.255.255 - 255.255.255.252 --------------- 0. 0. 0. 3 Wildcard mask • Router(config-router)#network network-address [wildcard-mask]

29. Basic EIGRP Configuration Verifying EIGRP • EIGRP routers must establish adjacencies with their neighbors before any updates can be sent or received • Command used to view neighbor table and verify that EIGRP has established adjacencies with neighbors is show ip eigrp neighbors H column - Lists the neighbors in the order they were learned. SRTT (Smooth Round Trip Timer) Queue Count - Should always be zero. RTO (Retransmit Interval) - Used by RTP to manage reliable EIGRP packets. Sequence Number - Used to track updates, queries, and reply packets.

30. EIGRP • The show ip protocols command is also used to verify that EIGRP is enabled • Remember, the process ID must be the same on all routers for EIGRP to establish neighbor adjacencies and share routing information. • EIGRP's internal and external administrative distances are also displayed: • Distance: internal 90 external 170

31. Basic EIGRP Configuration We will configure the bandwidth later. Examining the Routing Table • The show ip route command is also used to verify EIGRP • EIGRP routes are denoted in a routing table by the letter “D” • EIGRP is a classless routing protocol (includes the subnet mask in the routing update), it supports VLSM and CIDR. • By default , EIGRP automatically summarizes routes at major network boundary • We can disable the automatic summarization with the no auto-summary command. We will examine this in more detail in a later.

32. EIGRP Null0 Summary Route • EIGRP has automatically included a summary route to Null0 (192.168.10.0/24 and 172.16.0.0/16) • Null0 is not a physical interface • In the routing table summary routes are sourced from Null0 • Reason: routes are used for advertisement purposes • EIGRP will automatically include a null0 summary route as child route when 2 conditions are met • At least one subnet is learned via EIGRP • Automatic summarization is enabled • If the packet matches the level 1 parent - the classful network address - but none of the subnets, the packet is discarded.

33. Basic EIGRP Configuration • R3’s routing table shows that the 172.16.0.0/16 network is automatically summarized by R1 & R3 • R1 and R2 are not propagating the individual subnets because of automatic summarization. • [Tony] We will configure the bandwidth later. Once the bandwidth is reconfigured, you will not see the equal-cost route on R3.

34. EIGRP Metric Calculation EIGRP Composite Metric & the K Values • EIGRP uses the following values in its composite metric -Bandwidth, delay, reliability, and load (reliability and load are not used) • The composite metric used by EIGRP • formula used has values K1 K5 K1 & K3 = 1 K2, K4, K5 = 0

35. EIGRP Metric Calculation • Use the sh ip protocols command to verify the K values Again, changing these values to other than the default is not recommended unless the network administrator has a very good reason to do so.

36. EIGRP Metric Calculation EIGRP Metrics • Use the show interfaces command to view metrics • EIGRP Metrics • Bandwidth – EIGRP uses a static bandwidth to calculate metric • Most serial interfaces use a default bandwidth value of 1.544Mbos (T1) • The value of the bandwidth may or may not reflect the actual SPEED of the interface. • If actual SPEED of the link differs from the default bandwidth value, then you should modify the bandwidth value, The default bandwidth for ethernet is 10,000 Kbits. The default bandwidth for fastethernet is 100,000 Kbits.

37. EIGRP Metric Calculation EIGRP Metrics • Delay is the defined as the measure of time it takes for a packet to traverse a route • it is a static value based on link type to which interface is connected • The delay value, much like the bandwidth value, is a default value that can be changed by the network administrator manually.

38. EIGRP Metric Calculation • Reliability (not a default EIGRP metric) • A measure of the likelihood that a link will fail or how often the link has experienced errors. • Measure dynamically & expressed as a fraction of 255 • the higher the fraction the better the reliability • Reliability is calculated on a 5-minute weighted average to avoid the sudden impact of high (or low) error rates. • Load (not a default EIGRP metric) • A number that reflects how much traffic is using a link • Number is determined dynamically and is expressed as a fraction of 255 • The lower the fraction the less the load on the link • This value is calculated on a 5-minute weighted average to avoid the sudden impact of high (or low) channel usage.

39. EIGRP Metric Calculation Using the Bandwidth Command • Modifying the interface bandwidth -Router(config-if)#bandwidth kilobits • Verifying bandwidth • Use the show interface command • Note – bandwidth command does not change the link’s physical bandwidth • The bandwidth command only modifies the bandwidth metric used by routing protocols such as EIGRP and OSPF.

40. EIGRP Metric Calculation • The EIGRP metric can be determined by examining the bandwidth delay The value before change the bandwidth is 2172416

41. EIGRP Metric Calculation • EIGRP uses the lowest bandwidth (BW)in its metric calculation Calculated BW = reference BW / lowest BW(kbps) • Delay – EIGRP uses the cumulative sum of all outgoing interfaces Calculated Delay = the sum of outgoing interface delays • EIGRP Metric = calculated BW + calculated delay

42. EIGRP Metric Calculation 10,000,000 is divided by 1024. If the result is not a whole number, then the value is rounded down. In this case, 10,000,000 divided by 1024 equals 9765.625. The .625 is dropped before multiplying by 256. The bandwidth portion of the composite metric is 2,499,840.

43. DUAL Concepts • The Diffusing Update Algorithm (DUAL) is used to prevent looping • Successor • Feasible Distance (FD) • Feasible Successor (FS) • Reported Distance (RD) or Advertised Distance (AD) • Feasible Condition or Feasibility Condition (FC)

44. DUAL Concepts • Successor The best least cost route to a destination found in the routing table • Feasible distance The lowest calculated metric along a path to a destination network • 2 commands can be used to find the “successor” and “feasible distance”: • show ip route • show ip eigrp topology

45. DUAL Concepts • EIGRP Topology Table dissected

46. DUAL Concepts • Feasible Successor • This is a loop free backup route to the same destination as successor route • If the link between R2 and R3 failed, the R1 will become the successor for sending traffic to 192.168.1.0 Feasible Successors, Feasibility Condition & Reported Distance

47. EIGRP technologies (cont.) Feasible Successor, FC: RD30 < FD31 172.30.1.0 FD to 172.30.1.0 is 31 via Router Y RTZ is NOT Feasible Successor, FC: RD220 not< FD31 Current Successor = 31 RD of RTY= 21 Advertised or DestinationFeasible Dist.Reported. Dist.Neighbor 172.30.1.0 40 30 X In Topology Table 172.30.1.0 31 21 Y In Routing Table 172.30.1.0 230 220 Z Not in Topology Table

48. Verifying basic EIGRP

49. Verifying basic EIGRP

50. What if the successor fails? 1) If feasible successor exists: • If current successor route fails, feasible successor becomes the current successor, i.e. the current route. • Routing of packets continue with little delay. 2) If no feasible successor exists: • This may be because the Reported Distance is greater than the Feasible Distance. • Before this route can be installed, it must be placed in the active state and recomputed. • Routing of packets continue but with more of a delay.