642-901 BSCI Routing Protocols- (EIGRP,OSPF,IS-IS and BGP)

Passed BSCI--> Next stop BCMSN
Passed BCMSN--> Next stop TSHOOT/CCNA Voice

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EIGRP Principals:

1. Protocol "dependent" modules- Several protocol dependent modules are used, the two most important are IPV4 and IPV6
2. Reliable Transport Protocol (RTP): EIGRP sends "some" reliable packets using RTP
3. Neighbor discovery and recovery: EIGRP sends hellos to discovery neighbors, once neighbors are discovered hellos are sent between neighbors as a means of saying the links are up.
   
4. Diffusing Update Algorithm (DUAL): Is used to select the best routes, and feasible fail over routes.

Enabling EIGRP

1. To enable EIGRP as an active routing protocol use the router command and specify an autonomous system number. Eg Router EIGRP 1 Note (unlike OSPF the autonomous system number must be the same on all routers in an EIGRP domain)
   
2. At this point EIGRP is enabled but NOT active on the interface. EIGRP will NOT produce hellos or advertise networks until it is activated on the particular links.
3. Interfaces are attached to the EIGRP process with the network command eg Network 10.0.0.0, 192.168.2.0.

To enable EIGRP you must enable the following:

1. The EIGRP process: The routing protocol needs to be started on the router- router EIGRP
2. The EIGRP Autonomous System Number: This is a 16 bit number
3. Participating Router Interface: You can enable EIGRP on "some or all interfaces"

Passive interfaces: Prevents EIGRP from speaking on an interface, It does NOT send hellos or advertisements.

Neighbors and Reliable Incremental Updates

EIGRP produces reliable updates by identifying its packets using IP protocol 88. Reliable means that the receiver acknowledges that the transmission was received and understood. EIGRP only repeats itself if an advertisement is lost.

EIGRP usesfive types of packets to communicate. These packets are directly
encapsulated by the IP protocol.

• Hello—Identifies neighbors. Hellos are sent as periodic multicasts and are not acknowledged directly.
  

• Update—Advertises routes. Updates are sent as multicasts only when there is a change.

• Ack—Acknowledges receipt of an update.

• Query—Used to ask about routes for which the previous best path has been lost. If an update indicates that a path is down, multicast queries are used to ask other neighbors if they still have a path. If the quering router does not receive a reply from each of its neighbors, it repeats the query as a unicast to each unresponsive neighbor until it either gets a reply or gives up after sixteen tries.
  

• Reply—Used to answer a query. Each neighbor responds to the query with a unicast reply indicating an alternative path or the fact that it does not have a path.