Hello Everyone , From today onwards i m sharing my skills regarding Hardware networking.
Lets start From the course of cisco , cisco certified network professional ( CCNP )
In Todays lesson i m going to talk about EIGRP
- Introduction to EIGRP
The first routing protocol we will look at is called EIGRP (Enhanced Interior Gateway Routing Protocol). EIGRP was created by Cisco which means you can only run it on Cisco hardware. If you want routing with devices from different vendors (like Juniper) you will have to look for another routing protocol.
In this chapter I’m going to give you an introduction to EIGRP, we’ll see how it works and how EIGRP is different compared to OSPF. Most of the information in this chapter is a review of EIGRP on CCNA level so if you have everything still fresh in mind you might want to skim through the chapter. Let me start by giving you an overview:
• Advanced distance vector or Hybrid routing protocol. • Multicast or unicast is used for exchange of information. • Multiple network layer protocols are supported. • 100% loop-free.
Why do we call EIGRP an advanced distance vector or hybrid routing protocol? If you studied CCNA you have seen RIP. RIP is a true distance vector routing protocol and very simple:
• No neighbor discovery.
• Periodic updates.
• Vulnerable to loops.
• Simple metric (hop count).
Cisco added some of the features from link-state routing protocols to EIGRP which makes it far more advanced than a true distance vector routing protocol like RIP. This is why (probably the marketing department) calls EIGRP an advanced distance vector or hybrid routing protocol.
EIGRP does not use broadcast packets to send information to other neighbors but will use multicast or unicast. Besides IPv4 you can also use EIGRP to route IPv6 or even some older network layer protocols like IPX or AppleTalk. Last but not least…EIGRP is 100% loop-free and I’m going to show you why this is true.
EIGRP runs directly on top of the IP header. If you look at the picture above you see we have a frame header (for example an Ethernet Frame), an IP Header (we are using IPv4) and inside the IP packet you’ll find EIGRP. EIGRP has its own protocol number which is 88. Other protocol numbers you are familiar with are TCP (6) and UDP (17).
EIGRP routers will start sending hello packets to other routers just like OSPF does, if you send hello packets and you receive them you will become neighbors. EIGRP neighbors will exchange routing information which will be saved in the topology table. The best path from the topology table will be copied in the routing table.
Selecting the best path with EIGRP works a bit different than other routing protocols so let’s see it in action:
We have three routers named KingKong, Ann and Carl. We are going to calculate the best path to the destination which is behind router Carl.
EIGRP uses a rich set of metrics namely bandwidth, delay, load and reliability which we will cover later. These values will be put into a formula and each link will be assigned a metric. The lower these metrics the better
In the picture above I have assigned some values on the interfaces, if you would look on a real EIGRP router you’ll see the numbers are very high and a bit annoying to work with
Router Carl will advertise to router Ann its metric towards the destination. Basically router Carl is saying to router Ann: “It costs me 5 to get there”. This is called the advertised distance.
Router Ann has a topology table and in this topology table it will save this metric, the advertised distance to reach this destination is 5.
We are not done yet since there is something else that router Ann will save in its topology table. We know the advertised distance is 5 since this is what router Carl told us. We also know the metric of the link between router Ann and router Carl since this is directly connected. Router Ann now knows the metric for the total path to the destination, this total path is called the feasible distance and it will be saved in the topology table. ..
we will discuss more on next post ...