Type text to search here...Home > EIGRP TutorialEIGRP TutorialDecember 3rd, 2010 Go to commentsFeasible Distance (FD) and Advertised Distance (AD)In the next part, we will define these terms and take an example to make them clear.Advertised distance (AD): the cost from the neighbor to the destination.Feasible distance (FD): The sum of the AD plus the cost between the local router and the next'hop routerSuccessor: The primary route used to reach a destination. The successor route is kept in the routing table.Notice that successor is the best route to that destination. Feasible successor: The backup route. To be a feasible successor, the route must have an AD less than theFD of the current successor routeMaybe its a bit confused with these terms so below is an example to make it clear.Suppose you are in NEVADA and want to go to IOWA. From NEVADA you need to specify the best path(smallest cost) to IOWA.In this topology, suppose router A & B are exchanging their routing tables for the first time. Router B saysHey, the best metric (cost) from me to IOWA is 50 and the metric from you to IOWA is 90 and advertisesit to router A. Router A considers the first metric (50) as the Advertised distance. The second metric (90),which is from NEVADA to IOWA (through IDAHO), is called the Feasible distance.NEVADA also receives the cost path from NEVADA '> OKLAHOMA '> IOWA advertised by router Cwith the Advertised distance of 70 and Feasible distance of 130.All of these routes are placed in the topology table of router A:Route Advertised distanceFeasible distanceNEVADA '> IDAHO '> IOWA 50 90NEVADA '> OKLAHOMA '> IOWA 70 1301f8f2013 CCNA Training E!GRP Tutorial9tut.comf.f2 1f11Router A will select the route to IOWA via IDAHO as it has the lowest Feasible distance and put it into therouting table.The last thing we need to consider is if the route NEVADA '> OKLAHOMA '> IOWA will be consideredas a feasible successor. To achieve this, it must satisfy the feasibility condition:To qualify as a feasible successor, a router must have an AD less than the FD of the currentsuccessor routeMaybe you will ask why do we need this feasibility condition? Well, the answer is because it guarantees aloop'free path to the destination; in other words, it must not loop back to the current successor.If the route via the successor becomes invalid (because of a topology change) or if a neighbor changes themetric, DUAL checks for feasible successors to the destination route. If one is found, DUAL uses it, avoidingthe need to recompute the route as the re'computation can be processor'intensive. If no suitable feasiblesuccessor exists, a re'computation must occur to determine the new successor.EIGRP calls these alternative, immediately usable, loop'free routes feasible successor routes, because theycan feasibly be used as a new successor route when the current successor route fails. The next'hop router ofsuch a route is called the feasible successor.In this case, the route NEVADA '> OKLAHOMA '> IOWA has an AD (70) less than the FD of thesuccessor route (90) so it becomes the feasible successor route.Of course in some cases the feasibility condition will wrongly drop loop'free paths. For example, if the metricbetween OKLAHOMA and IOWA is greater than 90 then the route NEVADA '> OKLAHOMA '>IOWA will not be considered as a feasible successor route although it is loop'free. But this condition isnecessary because it can guarantee the feasible successor routes are loop'free.Notice that the feasible successors are placed in the topology table, not in the routing table.Now router A has 3 complete tables as follows (we only consider route to IOWA network)1f8f2013 CCNA Training E!GRP Tutorial9tut.comf.f2 2f11Now you have a basic concept of EIGRP, in the next part we will dig into the 3 tables of EIGRP theneighbor, topology & routing tables as understanding them is a requirement for a CCNA'taker and learn howto calculate the metric of EIGRP.Pages: 1 2 3Comments (138) CommentsComment pages Previous 1 2 3 3801.9tutMay 29th, 2012@Rose: The AD is one hop less than the FD so it has only 1 outgoing interface (Fa0/1 of Router1)and the delay of this interface is 10.2.AnonymousJune 14th, 2012Very amusing and educational. Good job.Thanks,Hansen Kannie CCNA, CCDA, CCNP, CCDP, CCIE R&S written.3.AnkJune 19th, 2012In Routing table Is it true, for outbound interface the value would be 50 or the interface name E0(intead of 50) ?4.nawel algeriaJuly 3rd, 2012thank you for the tuto its cool5.AnonymousJuly 9th, 2012What a great Summary of EIGRP.6.JasonJuly 11th, 2012This page should be updated to note that if K5 = 0, the formula reduces to Metric = [k1 * bandwidth+ (k2 * bandwidth)/(256 ' load) + k3 * delay].Otherwise, the metric formula solves to zero when K5 is zero.7.ShemieJuly 16th, 2012(CD'ROM) This product is ok. I got a while back for my CCNA with the CCNA kit. It has a dcenetsupporting lineup of router and switches. It seriously lacks commands especially in routers. just a few I1f8f2013 CCNA Training E!GRP Tutorial9tut.comf.f2 3f11supporting lineup of router and switches. It seriously lacks commands especially in routers. just a few Inoticed when creating my virtual network: any logging command and any exec command (which meansyou always have a logout timer) these are just a few that I can think of off the top of my head. Thereare many more but i can only remember the conf t ones right now and I have since uninstalled. Iexpected more from Sybex. Their CCNA study guide (Lammle) is amazing. All'in'all not good. To getmy CCNA I used CCNA study guide (Lammle),CCNA IOS Commands Survival Guide (Lammle),CCNA Fast Pass (Lammle) for the book/lab exercises. I used Cisco Packet Tracer 5.3 for my virtuallab.Also, the Study guide would have been enough to pass the exam, but I wanted the extra commandinfo and labs in the Fast Pass and Survival Guide.Packet Tracer is available through Cisco Academyand a few other places. I dont really know all the ways to get it unless you are DOD. If your DODyou can get it for free.8.GeetJuly 18th, 2012Thanks for the comment. To know that 1 pesron has benefited from the information that I post is goodenough for me. I completely agree with your statement that keeping a blog on going is a challenge. Thebiggest challenge is having content to post that is beneficial.When it comes to linux finding somethingthat your looking for is sometimes not very easy, and for me, its never easy. It usually takes me a fairamount of time to locate what I need for whatever im working on. I always find myself saying why cantsomeone just post the things in a easy step by step format in one place instead of having to search allover for the answer. So thats what I attempt to do.Thanks again for the comment. Its awesome. Pleasekeep coming back and feel free to post your things you have found or run into9.Please ExplainJuly 19th, 2012EIGRP Load Balancing@9tut + Load balancing: EIGRP supports UNEQUAL metric load balancing, which allowsadministrators to better distribute traffic flow in their networks.@Todd Lammle Book Load Balance up to four EQUAL cost linkPlease confirm. thanks10.learnerJuly 22nd, 2012@please Explain, EIGRP can load balance upto 4 equal cost path links by default, you can usevariance command, set it to one, it will load balance equal cost paths, but it can provide load balancingupto 16 paths(variable cost path links)11.learnerJuly 22nd, 2012@9tut and @Xallax Hii, i found these tutorials extremely good, i would like to know what you guysare doing these days and in terms of certifications by Cisco , really i would love to help u guys in thesetutorials someday .. I appreciate your efforts !!12.learner1f8f2013 CCNA Training E!GRP Tutorial9tut.comf.f2 +f11July 22nd, 2012@9tut.. Superb explanation of AD , FD n successor route , even Todd Lammle didnt explained it insuch a nice way..!!13.thuti_2000July 25th, 2012This was the best description of AD FD that I ever read.well done and thank you.14.LageAugust 3rd, 2012Hi guys,Thank you for the wonderful work you people are doing for everyone who is trying to learn all of thisstuff. Thanks @9tut youre great.By the way can you please tell me where i can get the Packetracer you are using please let me know.You may contact me at linking@gmail.com.Thank you and bless yall.15.LageAugust 3rd, 2012Sorry actually my email is linkony@gmail.com16.LageAugust 3rd, 2012@9tut my email is linkony@gmail.com please pass on the Packetracer tool.17.AnonymousAugust 4th, 2012This is good tutorial.For those want to understand further the strengths of EIGRP for your network, you may want to readthese articles:http://www.netxplane.com/2012/07/the'strength'of'eigrp'part'i.html (EIGRP Feasible Successor)http://www.netxplane.com/2012/07/the'strength'of'eigrp'part'ii.html (EIGRP Unequal Load Sharing)18.amilaAugust 9th, 2012loop'free path = valid path ??????????? help meeee19.nithaliaAugust 10th, 20121f8f2013 CCNA Training E!GRP Tutorial9tut.comf.f2 5f11good job....20.LucasAugust 22nd, 2012I love this, its so great ! and easy to understand21.Good jobAugust 31st, 2012This tutorial was written very good I didnt expect it to be on this site, better than some books.22.RJSeptember 4th, 2012When EIGRP comes up for the first time.(the router will try to establish a neighboring relationships bysending Hello packets to others running EIGRP)'its fine butit exchanges its TOPOLOGY tablewith its neighbors and not ROUTING tablein this above diagram R2 will also send its TOPOLOGYtable to R1 by Update packets. Remember that R2 will send its complete TOPOLOGY table for thefirst time and not ROUTING table.R1 confirms it has received the Update packet by an ACKmessage.R1 will also send to R2 all of its TOPOLOGY table for the first time.R2 sends a messagesaying it has received R1s TOPOLOGY table.23.PLEASE CORRECT THIS POINT 9TUTSeptember 4th, 2012When EIGRP comes up for the first time.(the router will try to establish a neighboring relationships bysending Hello packets to others running EIGRP)'its fine butit exchanges its TOPOLOGY tablewith its neighbors and not ROUTING tablein this above diagram R2 will also send its TOPOLOGYtable to R1 by Update packets. Remember that R2 will send its complete TOPOLOGY table for thefirst time and not ROUTING table.R1 confirms it has received the Update packet by an ACKmessage.R1 will also send to R2 all of its TOPOLOGY table for the first time.R2 sends a messagesaying it has received R1s TOPOLOGY table.24.MagnetaSeptember 9th, 2012This is very easy tutorial.25.Asok MohanSeptember 14th, 2012hats off 9tut worth 9$26.RameshSeptember 18th, 2012this tutorial is very good, i understand so much things. So please post this type of notes & improve ourknowledge.Regards & Thanks1f8f2013 CCNA Training E!GRP Tutorial9tut.comf.f2 6f11Ramesh27.RajSeptember 20th, 2012Shemie,can yo uplseaes let meknow when can i download Packet Tracer 5.3.. as i am just able to find only thebroken links and that disappoints me :(28.sotir1984September 24th, 2012One question? Do i have a brain freeze or if K5 is 0 then all is zero?29.AnonymousSeptember 27th, 2012The literature is amazing , some times we find things to be difficult because we do not have right peopleto expalin it !!!, wel doneGaid30.AnkushKSeptember 27th, 2012@anyonehow to change the AS number of eigrp without using no command?plz help me my xm is on 29th..tnx in advance31.kushal aroraSeptember 29th, 2012widout no command we cant chnge it ..we hav to putno router eigrp AS thn agn new as no as above32.C3COctober 11th, 2012Since I cant afford to enroll into any online or onsite classes I have had to use whatever help I can findon the Internet. The Sybex test engine is very limited so I turned to GNS3. Since it is a Cisco cert Irequire i have found that using the Cisco learning forum a big help. I just now found 9tut and it alsohelps. I feel that it is possible to pass any Cisco test without buying into any online or onsite training.Again thanks to 9tut for your help.33.S ShresthaOctober 13th, 2012Much gratitude to 9tut.com. Your work is like a Gem for those who wants to learn about Cisco1f8f2013 CCNA Training E!GRP Tutorial9tut.comf.f2 7f11system and face the CCNA exam. Although, I have once gone through Todd Lamelles book, theconcise presentation of your materials helps to quickly review the concepts and retain in the brain. Ihave already taken the membership to support your effort. Keep going 9tut.com, you are the hope forall of us!!!Cheers!!34.tinasoftNovember 2nd, 2012thank so much.35.avish malrotraNovember 9th, 2012plz i want a full summary of eigrp36.TelcoGuyDecember 2nd, 2012When calculating the metric you say 1024 is the speed of T1, are you talking about a T1 carrier? T1sare 1.544Mbps37.ShriDecember 4th, 2012Didnt get the use of no auto summary command plz explain38.PijushJanuary 2nd, 2013@9tutYou guys are Rockstar! Even Todd lamle have not explained this way, about AD and FD. I have usedReachard Deals(easy and vast) book to understand AD and FD. Its is truly great@ Shirauto summary is the term used to refer summarized boundary of a class full network. so 10.0.5.0would be treated as 10.0.0.0, where subnet bit of an address is situated to that class(known as defaultmask(means no subnet)). whether it is under class A,B or C.192.168.1.1 = 192.168.1.0 (for class c)172.16.25.0 = 172.16.0.0 (for class b)21.25.35.74 = 21.0.0.0 (for class a)Comment pages Previous 1 2 3 380Add a Comment Name1f8f2013 CCNA Training E!GRP Tutorial9tut.comf.f2 8f11Submit CommentSubscribe to comments feedCCNA Operations 3 OSPF TutorialPremium MembershipBecome a member to interact with all questions and read all tutorials, labs!Find out more or Sign InCCNA 640-802CCNA Lab SimCCNA Basic QuestionsCCNA Basic Questions 2CCNA Cisco IOS QuestionsCCNA Cisco IOS Questions 2CCNA Cisco IOS Questions 3CCNA OSI Model QuestionsCCNA TCP/IP Model & OperationCCNA Show Command QuestionsCCNA Protocols & ServicesCCNA Access List QuestionsCCNA Access List Questions 2CCNA WANCCNA WAN 2CCNA IP Address QuestionsCCNA IP Routing QuestionsCCNA IP Routing Questions 2CCNA RIP QuestionsCCNA OSPF QuestionsCCNA OSPF Questions 2CCNA EIGRP Questions1f8f2013 CCNA Training E!GRP Tutorial9tut.comf.f2 9f11CCNA EIGRP Questions 2CCNA Security QuestionsCCNA DHCP QuestionsDHCP Group of Four QuestionsCCNA NAT & PAT QuestionsCCNA Drag and Drop 1CCNA Drag and Drop 2CCNA Drag and Drop 3CCNA Drag and Drop 4CCNA Drag and Drop 5CCNA Switch QuestionsCCNA Switch Questions 2CCNA Switch Questions 3CCNA VLAN QuestionsCCNA VLAN Questions 2CCNA VTP QuestionsCCNA HotspotCCNA STP QuestionsCCNA STP Questions 2CCNA IPv6 QuestionsCCNA SubnettingCCNA Subnetting Questions 2CCNA Subnetting Questions 3CCNA Subnetting Questions 4CCNA Operations 1CCNA Operations 2CCNA Operations 3CCNA Troubleshooting 1CCNA Troubleshooting 2CCNA WirelessCCNA FAQs & TipsShare your CCNA ExperienceCCNA Self-StudyPractice CCNA GNS3 LabsCCNA KnowledgeNetwork ResourcesFree Router SimulatorsICND1/ICND2 Website1f8f2013 CCNA Training E!GRP Tutorial9tut.comf.f2 10f11CCNP ' ROUTE WebsiteCCNP ' SWITCH WebsiteCCNP ' TSHOOT WebsiteCCNA Voice WebsiteCCNA Wireless WebsiteCCNA Security WebsiteCCDA WebsiteCCIP WebsiteCCIE Written WebsiteSupport 9tutYour contribution will help keep this site updated!TopCopyright 2010'2012 CCNA TrainingPrivacy Policy. 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