Autonomous Systems can be grouped into three classs. They are categorized harmonizing to their connectivity and operating policy.
A Multihomed Autonomous System is an Autonomous System that is connected to more than one AS. The advantage of a multihomed Autonomous System is that it allows an AS to stay affiliated to the Internet in the event of a failure of one of the connexions. In a Multihomed Autonomous System traffic from one AS is non allowed to go through through to another AS.
A Stub Autonomous System is an Autonomous System that is connected to merely one AS.
A Transit Autonomous System is an Autonomous System that provides connexions through itself to other webs.
Interior Routing Protocols
An interior gateway protocol ( IGP ) is a routing protocol used within an Autonomous System ( AS ) . The interior gateway protocols can be divided into two classs ;
Link-state routing protocol
In Link-state routing protocols, each node has information about the web topology and hence each node is able to cipher the following best hop for every possible finish in the web utilizing the information of the topology. This aggregation of the following best hops forms the routing tabular array for the peculiar node. The following are illustrations of Link-state routing protocols ;
Open Shortest Path First
Open Shortest Path First ( OSPF ) is a link-state routing protocol that operates within a individual independent system. OSPF routes Internet Protocol packages within a individual routing sphere ( within a individual independent system ) . It gathers link province information from available routers and constructs a topology map of the web. The routing tabular array is presented to the Internet Layer which makes the routing determinations based on the finish IP reference that is found in IP datagrams. OSPF besides supports variable-length subnet cover ( VLSM ) or Classless Inter-Domain Routing ( CIDR ) turn toing theoretical accounts. Open Shortest Path First uses Dijkstra ‘s algorithm, a shortest way foremost algorithm to find the shortest way tree for each path.
Routers at each terminal of a point-to-point telecommunication nexus signifier contiguities when they detect each other. This sensing occurs when a router identifies itself in a hullo Open Shortest Path First protocol package. This is called the bipartisan province. The routers in a web select a designated router ( DR ) and a backup designated router ( BDR ) which acts as a hub to cut down traffic between routers. Open Shortest Path First uses both unicast and multicast to direct hello packages.
The followers are the countries that an Open Shortest Path First sphere is divided into ;
The anchor country is besides known as country 0 or country 0.0.0.0 and it forms the nucleus of an Open Shortest Path First web. It is the logical and physical construction for the Open Shortest Path First sphere. The anchor country is responsible for administering routing information between the non-backbone countries.
A stub country is the country which does non have path advertizements that are external to the independent system. Routing within the stub country is along a default path.
A not-so-stubby country ( NSSA ) is a type of stub country that can import independent system external paths and direct them to the other countries, but it can non have them.
A theodolite country is the country with two or more Open Shortest Path First boundary line routers. It is used to go through web traffic from one country to another.
Open Shortest Path First defines the undermentioned router types:
Area boundary line router
An country boundary line router ( ABR ) connects one or more countries to the chief anchor web.
Autonomous system boundary router
An independent system boundary router ( ASBR ) is connected to more than one independent system. The independent system boundary router exchanges routing information with routers in other independent systems.
An internal router is a router that has Open Shortest Path First neighbor relationships with interfaces that are in the same country.
Anchor routers are all the routers that are connected to the Open Shortest Path First anchor.
Intermediate system to intercede system
Intermediate system to intercede system ( IS-IS ) is a protocol used by routers to find the best path to send on datagrams through a packet-switched web. This procedure is called routing. Intermediate system to intercede system is used within an administrative sphere. Intermediate system to intercede system operates by deluging the topology information throughout a web of routers. Each router builds its ain image of the web topology. The Dijkstra ‘s algorithm is used to calculate the best way through the web.
Distance-vector routing protocol
Distance-vector routing protocol use the Bellman-Ford algorithm. Since each router does non hold information refering the full web topology, it advertises its distances to other routers and receives similar advertizements from other routers. Using these received routing advertizements each router populates its routing tabular array. In the following advertizement rhythm, the router advertises the updated information from its routing tabular array. This advertisement rhythm procedure continues until the routing tabular arraies of each router have stable values. The chief disadvantage of these protocols is slow convergence. The following are illustrations of Distance vector routing protocol ;
Routing Information Protocol
Routing Information Protocol ( RIP ) is a dynamic routing protocol used in local and broad country webs and uses the distance-vector routing algorithm. The distance-vector routing algorithm used in RIP is the Bellman-Ford algorithm, which was foremost used in 1967 in a computing machine web, as the initial routing algorithm of the ARPANET.
Routing Information Protocol is a distance-vector routing protocol which uses the hop count as a routing metric. Routing Information Protocol prevents routing cringles because it implements a bound on the figure of hops that are allowed in a way from the beginning to the finish. The maximal figure of hops allowed is 15. Routing Information Protocol prevents the extension of wrong routing information by implementing the split skyline, path toxic condition and hold-down mechanisms. Routing Information Protocol is implemented on top of User Datagram Protocol. The reserved port figure is 520.
Interior Gateway Routing Protocol
Interior Gateway Routing Protocol ( IGRP ) was invented by Cisco and is used by routers to interchange routing informations within an independent system. Interior Gateway Routing Protocol was chiefly created to get the better of the restrictions of Routing Information Protocol. Interior Gateway Routing Protocol supports multiple line prosodies for each path. The maximal hop count of Interior Gateway Routing Protocol-routed packages is 255 and the default is 100. The routing updates are broadcast every 90 seconds.
Enhanced Interior Gateway Routing Protocol
Enhanced Interior Gateway Routing Protocol ( EIGRP ) was invented by Cisco. Enhanced Interior Gateway Routing Protocol minimizes the routing instability that occurs after topology alterations and the usage of bandwidth and treating power in the router.
Datas collected by the Enhanced Interior Gateway Routing Protocol is stored in three tabular arraies ;
Neighbor Table shops the informations about the adjacent routers.
Topology Table contains the collection of the routing tabular arraies gathered from all straight connected neighbours.
Routing tabular array shops the existent paths to all finishs.
Exterior Routing Protocols
Exterior Gateway Protocol ( EGP ) is a simple reachability protocol. Border Gateway Protocol ( BGP ) is the recognized criterion for Internet routing.
Border Gateway Protocol
Border Gateway Protocol ( BGP ) is a nucleus routing protocol of the Internet. Border Gateway Protocol maintains a tabular array of IP webs which designate web reachability among independent. It is besides called a way vector protocol. Border Gateway Protocol was chiefly created to replace Exterior Gateway Protocol to let a complete decentralized routing for the remotion of the NSFNet Internet anchor web.
When a category reference is divided into a figure of smaller webs each with a figure of hosts, The smaller webs are called subnets. The procedure in which the host field is split into a subnet is called subnetting. The boundary between the subnet and host Fieldss can be between two spots and this is decided utilizing a subnet mask. The IP reference now has a three-level hierarch ; the NetID which is the chief web site, the SubNetID which is the physical subnet and the HostID which points the connexion of a host to a subnetwork. Purposes of subnetting include organisation, control web traffic, different physical media use, saving of address infinite, and security.
A simple manner to subnet is to take the eight in the subnet mask that covers the first unassigned eight in the IP reference block and do all its spots high ( a high spot is a 1 ) .
The followers are the seven chief stairss needed to cipher a subnet ;
Determining Number of Subnets Needed
Determining Number of Bits You Can Borrow
Determining Number of Bits You Must Borrow to Get Needed Number of Subnets
Turning On Borrowed Bits and Determining Decimal Value
Determining New Subnet Mask
Finding Host/Subnet Variable
Determining Range of Addresses
Determine the web category ( A, B or C ) based on IP reference ;
If an IP reference begins with 1 to 126 so it is Class A.
If an IP reference begins with 128 to 191 so it is Class B.
If an IP reference begins with 192 to 223 so it is Class C.
For illustration, For the IP reference 188.8.131.52 the web is category C since the IP address start with 192.
Determine figure of spots needed to specify subnets.
Using the undermentioned expression the figure of spots are calculated.
Number of subnets = ( 2^Number of spots ) – 2.
Number of spots = Log2 ( Number of subnets + 2 ) .
For illustration, if there are six subnets:
Number of spots = Log2 ( 6 + 2 ) = Log2 ( 8 ) = 3.
Therefore three spots in the IP reference are used for the subnet.
Compose the subnet mask in binary signifier by widening the default subnet mask with subnet spots. Default subnet mask for the different categories are as follows ;
11111111.00000000.00000000.00000000 ( Class A, web portion is 8 spots )
11111111.11111111.00000000.00000000 ( Class B, web portion is 16 spots )
11111111.11111111.11111111.00000000 ( Class C, web portion is 24 spots )
For illustration, the extension of the default category C subnet mask with 3 spots consequences in the subnet mask
Using the undermentioned set of regulations convert the binary subnet mask to the decimal-dot signifier. The binary signifier contains four eights ( 8 spots in each ) .
For 1111111 eight, the decimal is 255 and for 00000000 eight, the decimal is 0.
If the eight contains both 1 and 0 the expression is used ;
Integer figure = ( 128 x N ) + ( 64 x N ) + ( 32 x N ) + ( 16 x N ) + ( 8 x N ) + ( 4 x N ) + ( 2 x N ) + ( 1 x N )
For the above illustration 11111111.11111111.11111111.11100000
11111111 — – & A ; gt ; 255
11111111 — – & A ; gt ; 255
11111111 — – & A ; gt ; 255
11100000 — – & A ; gt ; ( 128 x 1 ) + ( 64 x 1 ) + ( 32 x 1 ) + ( 16 x 0 ) + ( 8 x 0 ) + ( 4 x 0 ) + ( 2 x 0 ) + ( 1 x 0 ) = 224
Subnet mask is 255.255.255.224.