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Home» Routing & Switching » IGP QuickNotes

IGP QuickNotes

Posted on January 30, 2010 by Kerry Cordero in Routing & Switching

RIP – Distance-Vector
OSPF – Link-State (Only Intra Area Router is a pure Link-State)
EIGRP – Hybrid

Distance Vector (RIP):
Performs a distributed path calculation for a given pre-fix. As a pre-fix is advertised through an IGP distance vector routing domain, its path calculation is performed per hop by hop basis with each router increasing the metric of the prefix.

Link State (OSPF):
Performs a local path calculation for a given prefix. Each link state router advertises its links and the connections it maintains to other routers on each link. This info is flooded until all routers receive an exact copy of this link state advertising. Once they have received it, all routers then have an identical link state database. Once this happens, they all calculate the best path.

Hybrid (EIGRP):
Performs a distributed path calculation (Distance Vector)

It possesses a neighbor relationship formation requirement in order to exchange routes (Link State)

It maintains a topology table that is often compared to a link-state database (Link State)

KEY DIFFERENCE between EIGRP and Link-State Routing Protocols:
While EIGRP possesses a topology table, its topology table does not contain complete and identical information in it like a Link-State database

As mentioned earlier, EIGRP performs a distributed path calculation and not a local path calculation like a link-state database

ALL use an Additive Metrics for Path Calculation:
Ripv2: Hop Count
OSPF: Link Costs
EIGRP: Composite Metrics

Alternative path seletion method for ALL three: Policy Routing

RIPv2:
Exchanges routes on periodic basis, by default every 30 seconds

Performs path selection by comparing a metric based upon a simple hop count

Dynamically adapts to changes in network conditions such as link-failures or router-failures. However it possesses ineffeciencies that prevent it from performing this operation as rapidly as EIGRP and OSPF

RIPV2 does NOT require any explicit neighbor relationship to be formed (advertised or received from another RIPv2 speaker). In fact one RIPv2 speaker can be configured as a passive router and still learn routes from another RIPv2 speaker. This can NOT be performed by EIGRP or OSPF.

RIP only allows you to configure a classful pre-fix with the network command

Primary Benefit of EIGRP over RIP:
It does not advertise all of its routes periodically. It advertise only a hello to maintain a neighbor relationship.

It reconverges much more rapidly than RIPv2.

Primary Benefit of EIGRP over OSPF:
It is less complex

Although it uses a different convergence algorithm, EIGRP performs rapid reconvergence like OSPF

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(c) 2012 Kerry Cordero