some routing protocol fundas

EIGRP http://en.wikipedia.org/wiki/EIGRP

Enhanced Interior Gateway Routing Protocol (EIGRP) is a Cisco proprietary routing protocol loosely based on their original IGRP. EIGRP is an advanced distance-vector routing protocol, with optimizations to minimize both the routing instability incurred after topology changes, as well as the use of bandwidth and processing power in the router. EIGRP and IGRP are compatible with each other.

The data EIGRP collects is stored in three tables:

Neighbor Table: Stores data about the neighbouring routers,

Topology Table: It effectively contains the aggregation of the routing tables gathered from all the neighbours, with their respective metric. This will be in two states "ACTIVE" during the aquiring and reshuffle process ( when a router added or went down), and "PASSIVE" during the stable topology is established.

Routing table: Stores the actual routes to all destinations; the routing table is populated from the topology table with every destination network.

STP http://en.wikipedia.org/wiki/Spanning_tree_protocol

Spanning Tree Protocol Is an OSI layer-2 protocol which ensures a loop free topology for any bridged LAN

Multiple active paths between network nodes causes a bridge loop. Bridge loops create several problems.it creates a spanning tree within a mesh network of connected layer-2 bridges (typically ethernet switches), and disables the links which are not part of that tree, leaving a single active path between any two network nodes.

It acts with following rules

Elect a root bridge
Determine the least cost paths to the root bridge
Disable all other root paths.
Modifications in case of ties

There are 3 types of STP
1. Per-VLAN Spanning Tree (PVST)
2. Rapid Spanning Tree Protocol (RSTP)
3. Multiple Spanning Tree Protocol (MSTP)

OSPF http://en.wikipedia.org/wiki/OSPF

The Open Shortest Path First (OSPF) protocol is a hierarchical interior gateway protocol (IGP) for routing in Internet Protocol, using a link-state in the individual areas that make up the hierarchy. A computation based on Dijkstra's algorithm is used to calculate the shortest path tree inside each area.

An OSPF network is divided into areas

Backbone area

The backbone area (also known as area zero or area 0.0.0.0)is responsible for distributing routing information between nonbackbone areas. The backbone must be contiguous, but it does not need to be physically contiguous; backbone connectivity can be established and maintained through the configuration of virtual links. All OSPF areas must connect to the backbone area.

Stub area
A stub area is an area which does not receive external routes except the default route, but does receive inter-area routes. This kind of area is useful when, for example, all Internet access goes through autonomous system border routers (ASBRs) in Area 0.0.0.0, but there are multiple paths to other nonzero areas in the OSPF domain.

OSPF defines the following router types:

* Area border router (ABR)
* Autonomous system border router (ASBR)
* Internal router (IR)
* Backbone router (BR)


Designated "router"

A designated router (DR) is the router interface elected among all routers on a particular multiaccess network segment, generally assumed to be broadcast multiaccess.

A backup designated router (BDR) is a router that becomes the designated router if the current designated router has a problem or fails