DYNAMIC ROUTING3.1 # DYNAMIC ROUTING EXPAINED WITH PRACTICAL LAB
The data networks that we use in our everyday lives to learn, play, and work range from small, local networks to large, global internetworks. At home, a user may have a router and two or more computers. At work, an organization may have multiple routers and switches servicing the data communication needs of hundreds or even thousands of PCs.
Routers forward packets by using information in the routing table. Routes to remote networks can be learned by the router in two ways: static routes and dynamic routes. In dynamic routing, when protocols are used to find networks and update routing tables on routers. True, this is easier than use Static/Default routing. A routing protocol defines the set of rules used by a router when it communicates routing information between neighbor routers. In fact, a protocol on one router communicates with the same protocol routing on other router. Admin configures the routing protocols. i.e. RIP, IGRP, EIGRP, OSPF, etc.
Dynamic routing uses algorithms to compute multiple possible routes and determine the best path for traffic to travel through the network. It uses two types of complex algorithms: distance vector protocols and link state protocols.
Main functions : Discovery of remote networks. Maintaining up-to-date routing information. Choosing the best path to destination networks. Ability to find a new best path if the current path is no longer available.
Routing protocols can be classified into different groups according to their characteristics. Specifically, routing protocols can be classified by their: -
o Purpose: Interior Gateway Protocol (IGP) or Exterior Gateway Protocol (EGP)
o Operation: Distance vector protocol, link-state protocol, or path-vector protocol
o Behavior: Classful (legacy) or classless protocol
# Difference between Static routing V/s Dynamic routing:
| Feature | Static routing | Dynamic routing |
|---|---|---|
| Routing update | Manual | Automatic |
| Network infrastructure | Small | Large |
| Flexible | No | Yes |
| Admin-Overhead | High | Low |
| Control | More | Less |
# Distance Vector routing protocol
A distance-vector routing protocol in data networks determines the best route for data packets based on distance. Distance-vector routing protocols measure the distance by the number of routers a packet has to pass, one router counts as one hop. Distance is representing to cover a distance from its destination and Vector is representing to direction in which interface to forward the packet. In otherword, Distance vector means that routes are advertised by providing two characteristics:
o Distance: Identifies how far it is to the destination network and is based on a metric such as the hop count, cost, bandwidth, delay, and more
o Vector: Specifies the direction of the next-hop router or exit interface to reach the destination
o RIP uses the hop count of the destination.
o IGRP takes into account other information such as node delay and available bandwidth.
R1 knows that the distance to reach network 172.16.3.0/24 is one hop and that the direction is out of the interface Serial 0/0/0 toward R2.
A router using a distance vector routing protocol does not have the knowledge of the entire path to a destination network. Distance vector protocols use routers as sign posts along the path to the final destination. The only information a router knows about a remote network is the distance or metric to reach that network and which path or interface to use to get there. Distance vector routing protocols do not have an actual map of the network topology.
# Link State routing protocol
Link-state routing protocols are one of the two main classes of routing protocols used in packet switching networks for computer communications, the other being distance-vector routing protocols. Some factors can be set by the network administrator.
o It know very well that which link is fast or slow and calculates a cost to ‘get there’
o It will take a path which has more hops but use a faster medium over a path using a slower medium with fewer hops.
o Use a shortest Path first algorithm to choose the best path to a destination network.
To continue our analogy of sign posts, using a link-state routing protocol is like having a complete map of the network topology. The sign posts along the way from source to destination are not necessary, because all link-state routers are using an identical map of the network. A link-state router uses the link-state information to create a topology map and to select the best path to all destination networks in the topology.
RIP-enabled routers send periodic updates of their routing information to their neighbors. Link-state routing protocols do not use periodic updates. After the network has converged, a link-state update is only sent when there is a change in the topology. For example, in diagram, the link-state update is sent when the 172.16.3.0 network goes down.
# Difference between Distance Vector V/s Link State routing protocols:
| Distance Vector | Link State |
|---|---|
| Entire routing table is sent as an update | Updates are incremental & Entire routing table is no sent as update. |
| Send periodic update (Every fixed Interval of time) at every 30 or 90 second. | Updates are triggered (Up/Down) not periodic. |
| Update is broadcasted (not in RIP v2) | Updates are multicast. |
| Updates are sent to directly connected neighbor only. | Updates are sent to entire network. |
| Routers don’t have end to end visibility of entire network. | Routers have visibility of entire network of that area only. |
| Prone to routing loops. | No routing loops. |
# Path Vector routing protocol
In a path vector protocol, a router does not just receive the distance vector for a particular destination from its neighbor; instead, a node receives the distance as well as path information (aka BGP path attributes), that the node can use to calculate (via the BGP path selection process) how traffic is routed to the path. A path-vector routing protocol is a network routing protocol which maintains the path information that gets updated dynamically. Updates that have looped through the network and returned to the same node are easily detected and discarded.
# Autonomous system Within the Internet, an autonomous system is a collection of router (connected internet protocol routing prefixes) under the control of one or more network operators on behalf of a single administrative entity or domain that presents a common, clearly defined routing policy to the Internet The ASN uniquely identifies each network on the Internet. An AS is also known as a routing domain. Typical examples of an AS are a company’s internal network and an ISP’s network.
 ASN were defined as 16-bit integers which allowed for a maximum of 65536 assignments.
o The ASNs 0 and 65536 are register.
o 64496-64511 are reserved for use in documentation and sample code.
o The IANA has designed AS number 64512 through 65534 to be used for private purposes.
o ASN O may be used to identify non-routed networks.
o Now days RFC 4893 introduced 32-bit ASN which IANA has begun to allocate.
o These number are written either
o As simple integers or in the form x.y
o Where x and y are 16-bit numbers.
 0.x for old ASN and 1.y for new ASN.
The Internet is based on the AS concept; therefore, two types of routing protocols are required: -
o Interior Gateway Protocols (IGP): Used for routing within an AS. It is also referred to as intra-AS routing. Companies, organizations, and even service providers use an IGP on their internal networks. IGPs include RIP, EIGRP, OSPF, and IS-IS.
o Exterior Gateway Protocols (EGP): Used for routing between autonomous systems. It is also referred to as inter-AS routing. Service providers and large companies may interconnect using an EGP. The Border Gateway Protocol (BGP) is the only currently viable EGP and is the official routing protocol used by the Internet.
# Classfull and classless routing protocols
Routing protocols consider the class A, B or C network number and can automatically use default subnet performing some of its task is known as Classfull routing protocols and Routing protocols ignores the class A,B or C network number and can’t automatically use default subnet performing its tasks.
The biggest distinction between classful and classless routing protocols is that classful routing protocols do not send subnet mask information in their routing updates. Classless routing protocols include subnet mask information in the routing updates.
The two original IPv4 routing protocols developed were RIPv1 and IGRP. They were created when network addresses were allocated based on classes (i.e., class A, B, or C). At that time, a routing protocol did not need to include the subnet mask in the routing update, because the network mask could be determined based on the first octet of the network address.
# Difference between Classfull routing protocol V/s Classless routing protocol:
| Feature | Classless | Classfull |
|---|---|---|
| Support VLSM | Yes | No |
| Sends subnet mask in routing updates | Yes | No |
| Supports manual route summarization | Yes | No |
# Convergence
Once all the routers in a network know all routes to all destinations, the routing protocol has said to have ‘convergence’.
Why?
Convergence occurs as a result of a change in network topology
For example –
A link becomes available or unavailable.
3.2 # TYPES AND EXPLAINATION OF DYNAMIC ROUTING
1. Routing Information Protocol (RIP)
2. Enhanced Interior Gateway Routing Protocol (EIGRP)
3. Open Shortest Path First (OSPF)
4. Border Gateway Protocol (BGP)
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