About EIGRP

EIGRP is a hybrid protocol.
Hybrid Routing is a combination of the both distance-vector and link-state routing.
Hybrid routing protocols use distance-vectors for more accurate metrics to determine the best paths to destination networks, and report routing information only when there is a change in the topology of the network.
They have the nature of hybrid routing allows for rapid convergence (as with the link state protocols), but compare with link-state protocol it requires much less processing power and memory.

EIGRP stands for Enhanced Interior Gateway Routing Protocol, EIGRP is a hybrid routing protocol developed by Cisco. EIGRP uses "Distributed update algorithm" or "DUAL", it combines the Link-state and Distance-Vector algorithms. EIGRP is considered balanced hybrid protocol. Unlike IGRP that only understands major network numbers, EIGRP can be configured to use subnet masks and supernet masks. The format of the EIGRP routing table is different from IGRP routing table.
Advantages of EIGRP are:

Fast convergence, Support for multiple protocols, requires less bandwidth than Distance-vector protocols because only partial updates are broadcasted and only when changes in topology are detected. EIGRP does not use periodic broadcasts. Improved loop detection and prevention.

Here are some of EIGRP's improvements over IGRP:

• DUAL
• Incremental updates
• Reduced bandwidth usage
• Support for multiple network layer protocols (IP, IPX, AppleTalk)
• Support for variable-length subnet masks (VLSMs), discontiguous networks, and classless routing
• Advanced distance vector capabilities
• Automatic route summarization on major network boundaries

EIGRP uses bandwidth and delay by default to calculate  metric. Metric can also be configured to use reliability, load, and MTU.

Link State Vs Distance Vector

Comparison: Link State vs Distance Vector

See below diagram. If all routers were running a Distance Vector protocol, the path or 'route' chosen would be from A  B directly over the ISDN serial link, even though that link is about 10 times slower than the indirect route from A  C  D  B.

A Link State protocol would choose the A  C  D  B path because it's using a faster medium (100 Mb Ethernet). In this example, it would be better to run a Link State routing protocol, but if all the links in the network are the same speed, then a Distance Vector protocol is better.

 

LINK STATE  

Link State protocols track the status and connection type of each link and provides a calculated metric based on many factors, including some set by the network administrator. Link state protocols are aware whether a link is up or down and how fast it is and calculates a cost to 'get there'. Since routers run routing protocols to figure out how to get to a destination, you can think of the 'link states' as being the status of the interfaces on the router. Link State protocols will take a path which has more hops, but that uses a faster medium over a path using a slower medium with fewer hops.
Because of their awareness of media types and other factors, link state protocols require more CPU resources and memory. Distance vector algorithms being simple they don’t consume more CPU resources.