Knowing EIGRP Routing Protocol on Cisco Router

     This time i will make a review about eigrp routing protocol, especially on cisco router.
First, you have to know this :

Introducing Eigrp

1. Eigrp is routing distance vector which means eigrp relying ont the diffused update algorithm to calculate the shortest path to a destination within network.The multicast address 224.0.0.10 usually broadcasting routing information to its neighbour. Its sends broadcast which have information about distance and direction. The direction define by metric while direction is its next-hop.
2. Fast Convergence, so this routing protocol is faster to gather information from all router in its topology.
3. Support VLSM means clasless
4. Manual Summarization, eigrp allows you to summarize internal and external routes on virtually any bit boundary using manual summarization.
5. Load balancing on equal & unequal cost which means eigrp can establish multiple link and make it load balancing/sharing based on each link bandwidth (cost metric).
6. Dual algorithm
7. Composite matric calculation (k5 value)
8. IP protocol number 88
9. Multicast 224.0.0.10
10. Auto-summarize by default, you have to add command "no auto-summary" on its configuration

Metric Value in EIGRP

1. By default its metric is Bw+delay
2. Delay = the amount of end to end (microseconds)*256
3. Bandwidth = [10^7/ minimum bandwidth, kbps]*256
4. Default formula K5 value [k1=1, k2=0, k3=1, k4=0, k5=0
5. Metric=[k1*BW+((k2*BW)/256-load))+k3*delay]
6. If k5 value not worth 0, then its metric value is =metric*[k5/(reliability+k4)]t

EIGRP Features

1. Only support MD5 authentication
2. Neighbour command can be used, if you want to make its update as unicast
3. Never ever use "passive-interface" on eigrp cause it will affect, the interface can't send/receive update
4. Route-filtering & Summarization is same as in RIP
5. By default its split-horizon is enable, use command "no ip split horizon eigrp xxx" to disable it

AD & FD (Administrator Distance & Feasible Distance)

1. The lowest metric value will be chose by EIGRP
2. AD = cost value between next-hop router and network destination
3. FD = cost values from local router to network destination = AD next-hop router+cost between local router and next-hop router
4. Lowest-cost = lowest FD
5. Successor = next-hop router with lowest cost value
6. Feassible Successor = Backup successor
7. the value of feasible successor is lower than its FD successor

Router Authentication

1. Support clear text authentication

• RIPv2
• OSPF
• IS-IS

1. Support MD5 Authentication

• RIPv2
• OSPF
• BGP 
• EIGRP

EIGRP MD5 Authentication

here are EIGRP MD5 configuration on cisco

• key-chain IDN
• key 1
• key-string cisco

int S0/0

• Ip authentication key-chain eigrp 100 IDN
• Ip authentication mode eigrp 100 md5

EIGRP Leak Map

Example, between network summary 10.0.0.0/8, there is one network 10.0.1.0/24 which you want to be treated specially, for instance is just like through the different path or treated differently from the other, then you can use Leak Map

• R1(config)#access-list 3 permit 10.0.1.0 0.0.0.255
• R1(config)#route-map Leak1 permit 10
• R1(config-route-map)#match ip address 3
• R1(config)#interface se0/0
• R1(config-if)#ip summary-address eigrp 1 10.0.0.0 255.0.0.0 leak-map Leak1

Advance EIGRP

1. By default, EIGRP have limit hop count 100, you can configure until 255 use command "metric maximum-hop 255"
2. Default AD to internal is 90, external 170. That value can be configured with these command "distance eigrp internal-AD-value external-AD-value"
3. Maximum default Routing protocol is just using 50% its bandwidth capacity. Meanwhile, this value can be configured with "ip bandwidth-percent eigrp AS"

 EIGRP Stub Routing

1. Stub means end, because the router is in the end eigrp, so it's not too necessary receiving routing update quite often, cause it's only have one gateway
2. With using stub, then network stbilization is more convincing
3. If it configure as only "eigrp stub", then the default is connected and summary
4. Connected means it will only shows route from the network which advertised by using network command and redistribute connected
5. The choice is :

• R1(config)#router eigrp 1
• R1(config-router)#eigrp stub [receive-only | static | summary | redistributed]

EIGRP Load Balancing

1. Each routing protocol whether it RIP, OSPF, EIGRP etc, definitely support equal cost path load balancing
2. However, IGRP & EIGRP supporting unequal cost path load balancing with these kind of configuration :

• router eigrp 1
• network x.x.x.x
• variance 2

EIGRP WAN Link

• EIGRP support WAN links below :

1. Point-to-point links
2. NBMA
3. Multipoint links

• EIGRP by default is using up to 50% bandwidth
• It can be configured with this configuration below:

1. R1(config-router)#int fa0/0
2. R1(config-subif)#ip bandwidth-percent eigrp 1 45

• If it is using bandwidth command. then EIGRP will use half of configured value

1. R1(config-router)#int fa0/0
2. R1(config-subif)#bandwidth 1024

EIGRP STUB Routing

• Receive-only : Router will not advertise its network to other router
• Connected : Router will only advertised its connected route, which come from network command
• Static : Router will advertise static route which have redistributed into EIGRP
• Summary : Router will advertised summary route
• Redistributed : Router will advertised any route which redistributed into EIGRP