Routing Protocols

Types of Routing Protocol:


There are several routing protocol that are popular in this world. Please find the list of the protocols below.

RIP V1
RIP V2
IGRP
EIGRP
OSPF
BGP
IS-IS
FRAME RELAy.


BGP:
The Border Gateway Protocol (BGP) is an interautonomous system routing protocol. An autonomous system is a network or group of networks under a common administration and with common routing policies. BGP is used to exchange routing information for the Internet and is the protocol used between Internet service providers (ISP). Customer networks, such as universities and corporations, usually employ an Interior Gateway Protocol (IGP) such as RIP or OSPF for the exchange of routing information within their networks. Customers connect to ISPs, and ISPs use BGP to exchange customer and ISP routes. When BGP is used between autonomous systems (AS), the protocol is referred to as External BGP (EBGP). If a service provider is using BGP to exchange routes within an AS, then the protocol is referred to as Interior BGP (IBGP)

BGP Path Selection

BGP could possibly receive multiple advertisements for the same route from multiple sources. BGP selects only one path as the best path. When the path is selected, BGP puts the selected path in the IP routing table and propagates the path to its neighbors. BGP uses the following criteria, in the order presented, to select a path for a destination:

1)If the path specifies a next hop that is inaccessible, drop the update.

2)Prefer the path with the largest weight.

3)If the weights are the same, prefer the path with the largest local preference.

4)If the local preferences are the same, prefer the path that was originated by BGP running on this router.

5)If no route was originated, prefer the route that has the shortest AS_path.

6)If all paths have the same AS_path length, prefer the path with the lowest origin type (where IGP is lower than EGP, and EGP is lower than incomplete).

7)If the origin codes are the same, prefer the path with the lowest MED attribute.

8)If the paths have the same MED, prefer the external path over the internal path.

9)If the paths are still the same, prefer the path through the closest IGP neighbor.

10)Prefer the path with the lowest IP address, as specified by the BGP router ID.

Intermediate System-to-Intermediate System
(IS-IS) is an OSI link-state hierarchical routing protocol that floods the network with link-state information to build a complete, consistent picture of network topology. To simplify router design and operation, IS-IS distinguishes between Level 1 and Level 2 ISs. Level 1 ISs communicate with other Level 1 ISs in the same area. Level 2 ISs route between Level 1 areas and form an intradomain routing backbone. Hierarchical routing simplifies backbone design because Level 1 ISs need to know only how to get to the nearest Level 2 IS. The backbone routing protocol also can change without impacting the intra-area routing protocol.

RIP V1: It is a simple distance vector protocol. It has been enhance with various techniques, including Split Horizon and Poison Reverse in order to enable it to perform better in complicated network
The longest path cannot exceed 15 hops.
RIP uses static metrics to compare routes.
ADMINISTRATIVE DISTANCE:120
METRIC:HOB COUNT


What you mean by RIP v2?


RIP V2: It added several new features.
External route tags.
Subnet masks
Next hop router addresses.
Authentication.
Multicast support.

METRIC:SAME AS RIP V1

Explain about OSPF?
OSPF: Open Shortest Path First is a dynamic routing protocol for use in Internt Protocol(IP networks).It is a link state routing protocols. It falls into the group of interior gateway protocols, operating within an autonomous system(AS). Link-State routing protocol that calls for the sending of link-state advertisements (LSAs) to all other routers within the same hierarchial area. Information on attached interfaces, metrics used, and other variables is included in OSPF LSAs. As OSPF routers accumulate link-state information, they use the SPF algorithm to calculate the shortest path to each node.
METRIC: COST=bandwidth/interface bandwidth
AD:110


Explain about EIGRP?
EIGRP: EIGRP is a Cisco proprietary routing protocol derived from IGRP. EIGRP can be called as hybrid protocol or 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 procession power in the router. Routers that support EIGRP will automatically redistribute route information to IGRP neighbors by converting the 32 bit EIGRP metric to the 24 bit IGRP metric. Most of the routing optimizations are based on the Diffusing update Algorithm(DUAL).
MERIC: Load, delay,bandwidth, reliability and MTU

Explain about IGRP?
IGRP:IGRP is a distance vector Interior Gateway Protocol(IGP). Distance vector routing protocols mathematically compare routes using some measurement of distance. This measurement is know as distance vector. Routers using a distance vector protocol must send all or a portion of their routing table in a routing-update message at regular intervals to each of their neighboring routers. As routing information proliferates through the network, routers can identify new destinations as they are added to the network, learn of failures in the network, and, most improtanly, calculate distances to all know destinations. IGRP uses a composite metric that is calculated by factoring weighted mathematical values for internetwork delay, bandwidth, reliability, and load. Network administrators can set the weighting factors for each of these metrics. Default metrics are Reliability and load.
Administrative Distance:100
MERIC: Load, delay,bandwidth, reliability and MTU


Thanks
Karthick M