Thursday, November 21, 2013

Routing Protocol & Dynamic Routing (part I)

Today our subject is Routing Protocol and Dynamic Routing
First let us discuss about Routing Protocol.
Routing Protocol is protocol which had function to change routing information between each router automatic by sending update to neighbor router.
There are 2 type of Routing protocol that you need to know, that is Classful and Classless.
Classful routing protocols do not send subnet mask information with their routing updates. A router running a classful routing protocol will react in one of two ways when receiving a route:
• If the router has a directly connected interface belonging to the same major network, it will apply the same subnet mask as that interface.
• If the router does not have any interfaces belonging to the same major network, it will apply the classful subnet mask to the route.
Belonging to same “major network” simply indicates that they belong to the
same “classful” network. For example:
• and belong to the same major network (
• and do not belong to the same major network
• and belong to the same major network (
• and do not belong to the same major network.
Take the following example (assume the routing protocol is classful):

If Router B sends a routing update to Router A, it will not include the subnetmask for the network. Thus, Router A must make a decision.
If Router A has a directly connected interface that belongs to the same major network (, it will use the subnet mask of that interface for the route.
For example, if Router A has an interface on the network, it will apply a subnet mask of /16 to the network.
If Router A does not have a directly connected interfacing belonging to the same major network, it will apply the classful subnet mask of /8. This can obviously cause routing difficulties.
When using classful routing protocols, the subnet mask must remain consistent throughout your entire network.
example of Classful routing protocols is RIPv1 and IGRP.
Now let us go to Classless Routing protocol.
Classless routing protocols do send the subnet mask with their updates. Thus, Variable Length Subnet Masks (VLSMs) are allowed when using classless routing protocols.
example of Classless routing Protocol is RIPv2, EIGRP, OSPF and IS-IS.
There are a few term that you need to know.
Below is the term:
Interior Gateway Protocols (IGP)-> Routing protocol that working to connect router inside same “Autonomous System”
Exterior Gateway Protocols (EGP)-> Routing Protocol that connect between each “Autonomous System”
Border Gateway Protocol (BGP)-> Routing protocol that developed from EGP which connect between “Autonomous System”
Autonomous System -> is a set of router/network device which locate inside same scope administrative
Distance Vector Routing Protocol -> Routing protocol that know about direction and distance to network destination
Distance-vector routing protocols use the Bellman-Ford algorithm, Ford–Fulkerson algorithm, or DUAL FSM (in the case of Cisco Systems’s protocols) to calculate paths.
Distance Vector is implemented in a simple network. Distance Vector had character slow convergence and send periodic update in router’s routing table which directly connected
Link state Routing Protocol -> Routing Protocol that know all topology in a network
Link state is implemented in a large network and need more knowledge. Link state had character Fast convergence.
Link state track status and type connection each link and generate counted metric based on another factor.
Link state protocol know what is the uplink or downlink, how many cost and time to reach destination/
Link state protocol will take a way that have a lot of hop and fast than a slow way that have a little hop.
Now let us go to Dynamic Routing.
Before we describe more about Dynamic Routing. I want to flashback a little about Static Routing.
For further information, u can see in my last blog with subject Route protocol.
Benefit using static Routing
- More secure
- less CPU resource
- More easy to known and configured
Weakness using Static Routing
- susceptible with any misconfiguration
- any changes in topology will make all router need to be configured
- not scalable
Benefit using Dynamic routing
- more scalable
- any change in topology just need to configure in new router or changed router.
- infrequently happen misconfiguration
Weakness using Dynamic Routing
- less secure
- More CPU resources
- need more knowledge
Metric -> unit of measure for the distance of a route ( the smaller is better)
RIP using Hop Count (Max 15)
IS-IS & OSPF using cost (Open Standart)
IGRP & EIGRP using bandwith, delay (by default), Reliability, load (Cisco Proprietary)


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