Contabilidad

INTRO: From IGRP to EIGRP

Enhanced Interior Gateway Routing Protocol, or EIGRP, is the successor of Interior Gateway Routing Protocol, or IGRP, both CISCO proprietary routing protocols used to exchange routing data within an autonomous system. IGRP was a distance vector interior routing protocol designed to overcome the limitations of Routing Information Protocol (RIP) by supporting multiplemetrics, reliability, a much greater hop count and lastly by routing updates that are broadcast every 90 seconds (by default).
While IGRP was a great improvement over RIP, networks grew and technology expanded, creating new demands from users to better the exchange of routing data, broadening the amount of information shared over a network to include all users ever while maintaining thesimplicity of its implementation and calming any security concerns. EIGRP did just that, and as the name suggests, it truly is an enhancement over IGRP.
One of the big differences between IGRP and EIGRP is the fact that the former is a classful routing protocol while the later is a classless one. This means that EIGRP can route to Variable Length Subnet Masks (VLSMs) giving users freedom to betterdesignate their resources, while IGRP does not. Also, EIGRP used Reliable Transport Protocol (RTP) to reliably manage the communication of messages between EIGRP-speaking routers and Diffusing Update Algorithm (DUAL) for selecting and maintaining the best path to each remote network.

EIGRP PACKETS
EIGRP works thanks to its packets:
* Hello: This packet is used for neighbor discovery and to keepexisting neighbor relationships alive. EIGRP Hello packets are multicast to 224.0.0.10.
* Update: This packet is used to advertise routes and is only sent when there is a change to one of EIGRPs tables. If the update is concerning a change in the link cost the Update packet goes on the 224.0.0.10 multicast, if the update is about the discovery of a new neighbor, the packet is sent as aunicast.
* Acknowledgement (Ack): This packet is a Hello packet with no info. sent to acknowledge the receipt of a Hello or Update packet.
* Query: This packet is used to query routes from neighbors. A 224.0.0.10 multicast is sent first, if there is no response to the multicast, 16 unicast are attempted.
* Reply: This packet is used as an answer to a Query packet and is sent as a unicast.* Request: Request packets are used to get specific information from one or more neighbors. Request packets are used in route server applications. They can be multicast or unicast. Requests are transmitted unreliably.

Protocol-Dependent Mods.

EIGRP Supports Network layer protocols, such as IP, IPX, AppleTalk and IPv6, through the use of protocol-dependent modules (PDMs). Each EIGRP PDMwill maintain a separate series of tables containing the routing information that applies to a specific protocol.

Neighbor Discovery

3 conditions for establishing neighbors in EIGRP:
* Hellos received
* AS numbers match
* Identical metrics (K values)

To maintain neighbors in EIGRP routers must continue to receive Hellos and when a new neighbor is found, both routers share alltheir information with one another (this is the only time EIGRP advertises its complete info.) and stores the info. in a local topology table. This table contains all known routes from all known neighbors and serves, from which the best are chosen and placed in the routing table.

EIGRP Tables

Neighbor Table:
* Rec. the address and interface of new neighbors.
* There is one neighbortable for each protocol-dependent mod.
* Sequence numbers are used to match ack. with update packets.
* The last sequence number received from the neighbor is recorded so that out-of-order packets can be detected.

Topology Table:
* Populated by the protocol-dependent mod. And acted upon by DUAL.
* It contains all destinations advertised by neighboring routers.
* For each...