Community Routing Protocols – IGRP, EIGRP, OSPF, ISIS, BGP



The aim of routing protocols is to be taught of accessible routes that exist on the enterprise community, construct routing tables and make routing choices. Among the most typical routing protocols embrace RIP, IGRP, EIGRP, OSPF, IS-IS and BGP. There are two major routing protocol sorts though many alternative routing protocols outlined with these two sorts. Hyperlink state and distance vector protocols comprise the first sorts. Distance vector protocols promote their routing desk to all instantly related neighbors at common frequent intervals utilizing plenty of bandwidth and are gradual to converge. When a route turns into unavailable, all router tables should be up to date with that new data. The issue is with every router having to promote that new data to its neighbors, it takes a very long time for all routers to have a present correct view of the community. Distance vector protocols use mounted size subnet masks which are not scalable. Hyperlink state protocols promote routing updates solely once they happen which makes use of bandwidth extra successfully. Routers do not promote the routing desk which makes convergence sooner. The routing protocol will flood the community with hyperlink state ads to all neighbor routers per space in an try and converge the community with new route data. The incremental change is all that’s marketed to all routers as a multicast LSA replace. They use variable size subnet masks, that are scalable and use addressing extra effectively.

Inside Gateway Routing Protocol (IGRP)

Inside Gateway Routing Protocol is a distance vector routing protocol developed by Cisco programs for routing a number of protocols throughout small and medium sized Cisco networks. It’s proprietary which requires that you just use Cisco routers. This contrasts with IP RIP and IPX RIP, that are designed for multi-vendor networks. IGRP will route IP, IPX, Decnet and AppleTalk which makes it very versatile for purchasers operating many alternative protocols. It’s considerably extra scalable than RIP because it helps a hop rely of 100, solely advertises each 90 seconds and makes use of a composite of 5 completely different metrics to pick a greatest path vacation spot. Word that since IGRP advertises much less steadily, it makes use of much less bandwidth than RIP however converges a lot slower since it’s 90 seconds earlier than IGRP routers are conscious of community topology adjustments. IGRP does acknowledge task of various autonomous programs and routinely summarizes at community class boundaries. As effectively there may be the choice to load stability visitors throughout equal or unequal metric price paths.


• Distance Vector

• Routes IP, IPX, Decnet, Appletalk

• Routing Desk Ads Each 90 Seconds

• Metric: Bandwidth, Delay, Reliability, Load, MTU Measurement

• Hop Rely: 100

• Mounted Size Subnet Masks

• Summarization on Community Class Deal with

• Load Balancing Throughout 6 Equal or Unequal Price Paths ( IOS )

• Replace Timer: 90 seconds

• Invalid Timer: 270 seconds

• Holddown Timer: 280 seconds

• Metric Calculation = vacation spot path minimal bandwidth x delay (usec)

• Break up Horizon

Enhanced Inside Gateway Routing Protocol (EIGRP)

Enhanced Inside Gateway Routing Protocol is a hybrid routing protocol developed by Cisco programs for routing many protocols throughout an enterprise Cisco community. It has traits of each distance vector routing protocols and hyperlink state routing protocols. It’s proprietary which requires that you just use Cisco routers. EIGRP will route the identical protocols that IGRP routes (IP, IPX, Decnet and Appletalk) and use the identical composite metrics as IGRP to pick a greatest path vacation spot. As effectively there may be the choice to load stability visitors throughout equal or unequal metric price paths. Summarization is computerized at a community class handle nevertheless it may be configured to summarize at subnet boundaries as effectively. Redistribution between IGRP and EIGRP is computerized as effectively. There’s help for a hop rely of 255 and variable size subnet masks.


Convergence with EIGRP is quicker because it makes use of an algorithm referred to as twin replace algorithm or DUAL, which is run when a router detects specific route is unavailable. The router queries its neighbors on the lookout for a possible successor. That’s outlined as a neighbor with a least price path to a selected vacation spot that does not trigger any routing loops. EIGRP will replace its routing desk with the brand new route and the related metric. Route adjustments are marketed solely to affected routers when adjustments happen. That makes use of bandwidth extra effectively than distance vector routing protocols.

Autonomous Programs

EIGRP does acknowledge task of various autonomous programs that are processes operating beneath the identical administrative routing area. Assigning completely different autonomous system numbers is not for outlining a spine reminiscent of with OSPF. With IGRP and EIGRP it’s used to vary route redistribution, filtering and summarization factors.


• Superior Distance Vector

• Routes IP, IPX, Decnet, Appletalk

• Routing Ads: Partial When Route Modifications Happen

• Metrics: Bandwidth, Delay, Reliability, Load, MTU Measurement

• Hop Rely: 255

• Variable Size Subnet Masks

• Summarization on Community Class Deal with or Subnet Boundary

• Load Balancing Throughout 6 Equal or Unequal Price Paths (IOS

• Howdy Timer: 5 seconds on Ethernet / 60 seconds on Non-Broadcast

• Holddown Timer: 15 seconds on Ethernet / 180 seconds on Non-Broadcast

• Metric Calculation = vacation spot path minimal bandwidth x delay (msec) x 256

• Break up Horizon

• LSA Multicast Deal with:

Open Shortest Path First (OSPF)

Open Shortest Path First is a real hyperlink state protocol developed as an open normal for routing IP throughout giant multi-vendor networks. A hyperlink state protocol will ship hyperlink state ads to all related neighbors of the identical space to speak route data. Every OSPF enabled router, when began, will ship whats up packets to all instantly related OSPF routers. The whats up packets include data reminiscent of router timers, router ID and subnet masks. If the routers agree on the data they turn out to be OSPF neighbors. As soon as routers turn out to be neighbors they set up adjacencies by exchanging hyperlink state databases. Routers on point-to-point and point-to-multipoint hyperlinks (as specified with the OSPF interface kind setting) routinely set up adjacencies. Routers with OSPF interfaces configured as broadcast (Ethernet) and NBMA (Body Relay) will use a delegated router that establishes these adjacencies.


OSPF makes use of a hierarchy with assigned areas that connect with a core spine of routers. Every space is outlined by a number of routers which have established adjacencies. OSPF has outlined spine space zero, stub areas, not-so-stubby areas and completely stubby areas. Space zero is constructed with a gaggle of routers related at a delegated workplace or by WAN hyperlinks throughout a number of workplaces. It’s preferable to have all space zero routers related with a full mesh utilizing an Ethernet section at a core workplace. This gives for top efficiency and prevents partitioning of the realm ought to a router connection fail. Space zero is a transit space for all visitors from hooked up areas. Any inter-area visitors should route via space zero first. Stub areas use a default route injected from the ABR to ahead visitors destined for any exterior routes (LSA 5,7) to the realm border router. Inter-area (LSA three,four) and intra-area (LSA 1,2) routing is as traditional. Completely stubby areas are a Cisco specification that makes use of a default route injected from the ABR for all inter-area and exterior routes. The completely stubby space does not ship or obtain exterior or inter-area LSA’s. The not-so-stubby space ABR will promote exterior routes with kind 7 LSA. Exterior routes aren’t acquired at that space kind. Inter-area and intra-area routing is as traditional. OSPF defines inner routers, spine routers, space border routers (ABR) and autonomous system boundary routers (ASBR). Inner routers are particular to at least one space. Space border routers have interfaces which can be assigned to multiple space reminiscent of space zero and space 10. An autonomous system boundary router has interfaces assigned to OSPF and a special routing protocol reminiscent of EIGRP or BGP. A digital hyperlink is utilized when an space does not have a direct connection to space zero. A digital hyperlink is established between an space border router for an space that is not related to space zero, and an space border router for an space that’s related to space zero. Space design includes contemplating geographical location of workplaces and visitors flows throughout the enterprise. It is very important have the ability to summarize addresses for a lot of workplaces per space and reduce broadcast visitors.


Quick convergence is achieved with the SPF (Dijkstra) algorithm which determines a shortest path from supply to vacation spot. The routing desk is constructed from operating SPF which determines all routes from neighbor routers. Since every OSPF router has a replica of the topology database and routing desk for its specific space, any route adjustments are detected sooner than with distance vector protocols and alternate routes are decided.

Designated Router

Broadcast networks reminiscent of Ethernet and Non-Broadcast Multi Entry networks reminiscent of Body Relay have a delegated router (DR) and a backup designated router (BDR) which can be elected. Designated routers set up adjacencies with all routers on that community section. That is to scale back broadcasts from all routers sending common whats up packets to its neighbors. The DR sends multicast packets to all routers that it has established adjacencies with. If the DR fails, it’s the BDR that sends multicasts to particular routers. Every router is assigned a router ID, which is the best assigned IP handle on a working interface. OSPF makes use of the Router ID (RID) for all routing processes.


• Hyperlink State

• Routes IP

• Routing Ads: Partial When Route Modifications Happen

• Metric: Composite Price of every Router to Vacation spot (100,000,000/interface velocity)

• Hop Rely: None (Restricted by Community)

• Variable Size Subnet Masks

• Summarization on Community Class Deal with or Subnet Boundary

• Load Balancing Throughout four Equal Price Paths

• Router Sorts: Inner, Spine, ABR, ASBR

• Space Sorts: Spine, Stubby, Not-So-Stubby, Completely Stubby

• LSA Sorts: Intra-Space (1,2) Inter-Space (three,four), Exterior (5,7)

• Howdy Timer Interval: 10 seconds for Ethernet / 30 seconds for Non-Broadcast

• Lifeless Timer Interval: 40 seconds for Ethernet / 120 seconds for Non-Broadcast

• LSA Multicast Deal with: and (DR/BDR) Do not Filter!

• Interface Sorts: Level to Level, Broadcast, Non-Broadcast, Level to Multipoint, Loopback

Built-in IS-IS

Built-in Intermediate System – Intermediate System routing protocol is a hyperlink state protocol much like OSPF that’s used with giant enterprise and ISP prospects. An intermediate system is a router and IS-IS is the routing protocol that routes packets between intermediate programs. IS-IS makes use of a hyperlink state database and runs the SPF Dijkstra algorithm to pick shortest paths routes. Neighbor routers on level to level and level to multipoint hyperlinks set up adjacencies by sending whats up packets and exchanging hyperlink state databases. IS-IS routers on broadcast and NBMA networks choose a delegated router that establishes adjacencies with all neighbor routers on that community. The designated router and every neighbor router will set up an adjacency with all neighbor routers by multicasting hyperlink state ads to the community itself. That’s completely different from OSPF, which establishes adjacencies between the DR and every neighbor router solely. IS-IS makes use of a hierarchical space construction with degree 1 and degree 2 router sorts. Stage 1 routers are much like OSPF intra-area routers, which don’t have any direct connections outdoors of its space. Stage 2 routers comprise the spine space which connects completely different areas much like OSPF space zero. With IS-IS a router might be an L1/L2 router which is like an OSPF space border router (ABR) which has connections with its space and the spine space. The distinction with IS-IS is that the hyperlinks between routers comprise the realm borders and never the router.

Every IS-IS router will need to have an assigned handle that’s distinctive for that routing area. An handle format is used which is comprised of an space ID and a system ID. The world ID is the assigned space quantity and the system ID is a MAC handle from one of many router interfaces. There’s help for variable size subnet masks, which is normal with all hyperlink state protocols. Word that IS-IS assigns the routing course of to an interface as a substitute of a community.


• Hyperlink State

• Routes IP, CLNS

• Routing Ads: Partial When Routing Modifications Happen

• Metric: Variable Price (default price 10 assigned to every interface)

• Hop Rely: None (restricted by community)

• Variable Size Subnet Masks

• Summarization on Community Class Deal with or Subnet Boundary

• Load Balancing Throughout 6 Equal Price Paths

• Howdy Timer Interval: 10 seconds

• Lifeless Timer Interval: 30 seconds

• Space Sorts: Hierarchical Topology much like OSPF

• Router Sorts: Stage 1 and Stage 2

• LSP Sorts: Inner L1 and L2, Exterior L2

• Designated Router Election, No BDR

Border Gateway Protocol (BGP)

Border Gateway Protocol is an exterior gateway protocol, which is completely different from the inside gateway protocols mentioned thus far. The excellence is necessary because the time period autonomous system is used considerably otherwise with protocols reminiscent of EIGRP than it’s with BGP. Exterior gateway protocols reminiscent of BGP route between autonomous programs, that are assigned a selected AS quantity. AS numbers might be assigned to an workplace with one or a number of BGP routers. The BGP routing desk is comprised of vacation spot IP addresses, an related AS-Path to succeed in that vacation spot and a subsequent hop router handle. The AS-Path is a group of AS numbers that characterize every workplace concerned with routing packets. Distinction that with EIGRP, which makes use of autonomous programs as effectively. The distinction is their autonomous programs check with a logical grouping of routers inside the identical administrative system. An EIGRP community can configure many autonomous programs. They’re all managed by the corporate for outlining route summarization, redistribution and filtering. BGP is utilized quite a bit by Web Service Suppliers (ISP) and enormous enterprise firms which have twin homed web connections with single or twin routers homed to the identical or completely different Web Service Suppliers. BGP will route packets throughout an ISP community, which is a separate routing area that’s managed by them. The ISP has its personal assigned AS quantity, which is assigned by InterNIC. New prospects can both request an AS task for his or her workplace from the ISP or InterNIC. A singular AS quantity task is required for patrons once they join utilizing BGP. There are 10 outlined attributes which have a selected order or sequence, which BGP makes use of as metrics to find out one of the best path to a vacation spot. Corporations with just one circuit connection to an ISP will implement a default route at their router, which forwards any packets which can be destined for an exterior community. BGP routers will redistribute routing data (peering) with all IGP routers on the community (EIGRP, RIP, OSPF and so forth) which contain alternate of full routing tables. As soon as that’s completed, incremental updates are despatched with topology adjustments. The BGP default keepalive timer is 60 seconds whereas the maintain timer is 180 seconds. Every BGP router might be configured to filter routing broadcasts with route maps as a substitute of sending/receiving your complete web routing desk.


• Path Vector

• Routes IP

• Routing Ads: Partial When Route Modifications Happen

• Metrics: Weight, Native Choice, Native Originated, AS-Path, Origin Kind, MED

• Hop Rely: 255

• Variable Size Subnet Masks

• Summarization on Community Class Deal with or Subnet Boundary

• Load Balancing Throughout 6 Equal Price Paths

• Keepalive Timer: 60 seconds

• Holddown Timer: 180 seconds

• Designated Router: Route Reflector

BGP Routing Desk Elements

• Vacation spot IP Deal with / Subnet Masks

• AS-Path

• Subsequent Hop IP Deal with