Wednesday, September 16, 2015
Dynamic Routing protocol
A routing protocol specifies how routers communicate with each other, disseminating information that enables them to select routes between any two nodes on a computer network. Routing algorithms determine the specific choice of route.
Classifying Routing Protocols
IGP and EGP Routing Protocols.
An autonomous system (AS) is a collection of routers under a common administration such as a company or an organization. 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.
The Internet is based on the AS concept; therefore, two types of routing protocols are required:
A. 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.
1. Distance Vector Routing Protocols
Distance vector means that routes are advertised by providing two characteristics:
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.
Vector: Specifies the direction of the next-hop router or exit interface to reach the destination.
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.
There are four distance vector IPv4 IGPs:
2. Link-State Routing Protocols.
In contrast to distance vector routing protocol operation, a router configured with a link-state routing protocol can create a complete view or topology of the network by gathering information from all of the other routers.
Link-state protocols work best in situations where:
The network design is hierarchical, usually occurring in large networks
Fast convergence of the network is crucial
The administrators have good knowledge of the implemented link-state routing protocol
There are two link-state IPv4 IGPs:
OSPF: Popular standards-based routing protocol
IS-IS: Popular in provider networks
3. BGP.
The Border Gateway Protocol (BGP) routes traffic between autonomous systems. An autonomous system is a network or group of networks under common administration and with common routing policies. BGP exchanges routing information for the Internet and is the protocol used between ISPs. Customer networks, such as universities and corporations, usually employ an Interior Gateway Protocol (IGP), such as RIP or OSPF, to exchange 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, the protocol is referred to as external BGP (eBGP). If a service provider is using BGP to exchange routes within an autonomous system, the protocol is referred to as interior BGP (iBGP).
- RIPv1 (legacy): IGP, distance vector, classful protocol.
- IGRP (legacy): IGP, distance vector, classful protocol developed by Cisco.
- RIPv2: IGP, distance vector, classless protocol.
- EIGRP: IGP, distance vector, classless protocol developed by Cisco.
- OSPF: IGP, link-state, classless protocol.
- IS-IS: IGP, link-state, classless protocol.
- BGP: EGP, path-vector, classless protocol.
IGP and EGP Routing Protocols.
An autonomous system (AS) is a collection of routers under a common administration such as a company or an organization. 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.
The Internet is based on the AS concept; therefore, two types of routing protocols are required:
A. 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.
B. 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.
1. Distance Vector Routing Protocols
Distance vector means that routes are advertised by providing two characteristics:
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.
Vector: Specifies the direction of the next-hop router or exit interface to reach the destination.
There are four distance vector IPv4 IGPs:
RIPv1: First generation legacy protocol
RIPv2: Simple distance vector routing protocol
IGRP: First generation Cisco proprietary protocol (obsolete and replaced by EIGRP)
EIGRP: Advanced version of distance vector routing
RIPv2: Simple distance vector routing protocol
IGRP: First generation Cisco proprietary protocol (obsolete and replaced by EIGRP)
EIGRP: Advanced version of distance vector routing
2. Link-State Routing Protocols.
In contrast to distance vector routing protocol operation, a router configured with a link-state routing protocol can create a complete view or topology of the network by gathering information from all of the other routers.
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
The network design is hierarchical, usually occurring in large networks
Fast convergence of the network is crucial
The administrators have good knowledge of the implemented link-state routing protocol
There are two link-state IPv4 IGPs:
OSPF: Popular standards-based routing protocol
IS-IS: Popular in provider networks
3. BGP.
The Border Gateway Protocol (BGP) routes traffic between autonomous systems. An autonomous system is a network or group of networks under common administration and with common routing policies. BGP exchanges routing information for the Internet and is the protocol used between ISPs. Customer networks, such as universities and corporations, usually employ an Interior Gateway Protocol (IGP), such as RIP or OSPF, to exchange 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, the protocol is referred to as external BGP (eBGP). If a service provider is using BGP to exchange routes within an autonomous system, the protocol is referred to as interior BGP (iBGP).
BGP is a very robust and scalable routing protocol, as evidenced by the fact that it is the routing protocol employed on the Internet. To achieve scalability at this level, BGP uses many route parameters, called attributes, to define routing policies and maintain a stable routing environment. BGP neighbors exchange full routing information when the TCP connection between neighbors is first established. When changes to the routing table are detected, the BGP routers send to their neighbors only those routes that have changed. BGP routers do not send periodic routing updates, and BGP routing updates advertise only the optimal path to a destination network.
SHARE BY GK
Subscribe to:
Post Comments (Atom)
No comments:
Post a Comment