EIGRP-High Level Overview

1. ·      Cisco Proprietary
2. ·      Hybrid or Advanced distance vector Routing Protocol
3. ·      Max hop Count: 255
4. ·      Route sharing through Autonomous System
5. ·      Classless Routing Protocol
6. ·      Supports VLSM
7. ·      Support for IP,IPX & Apple Talk
8. ·      Communication via Reliable Transport Protocol
9. ·      Best Path Selection via DUAL
10. ·      Split horizon and DUAL(Diffusing Update Algorithm) form the basis of loop prevention for EIGRP.
11. ·      Automatic summarization is on by default, but summarization and filtering can be accomplished anywhere inside the network.
12. ·      It supports trigger updates.
13. ·      Multicast & Unicast instead of broadcast address.
14. ·      Load Balancing across equal and un-equal cost paths.
15. ·      Multicast address used for EIGRP is 224.0.0.10
16. ·      AD Value : 90 – EIGRP Internal;170-EIGRP Exterior

DUAL : diffusing update algorithm:

o   Its used to create a loop free routing table.

o   It also used to find a alternate paths without waiting  on updates from other router.

o   Ref: http://cirotammaro.blogspot.in/2013/05/cisco-networking-diffusing-update.html

RTP:

It simply provides sequencing and acknowledgment for EIGRP packets between neighbours. Sequence and acknowledgment numbers are used to provide ordering similar to TCP, but without any fancy windowing or congestion control (only one packet can be sent at a time).

EIGRP uses metric to select the best route from all available routes for destination.

• ·      Bandwidth
• ·      Load
• ·      Delay
• ·      Reliability
• ·      MTU

From these only bandwidth and delay are by default enabled.

Setting bandwidth or delay on an interface does not change any physical properties of the interface at all; you are just changing the values that the interface reports for EIGRP metric purposes.

Simplified Metric calculation:

Metric = [10⁷/Lowest BW in kbps+(1/10 of Sum of Delay in micro Seconds)]*256