Interior Gateway Routing Protocol (IGRP) is a kind of IGP which is a distance-vector routing protocol invented by Cisco, used by routers to exchange routing data within an autonomous system.
IGRP is a proprietary protocol. IGRP was created in part to overcome the limitations of RIP (maximum hop count of only 15, and a single routing metric) when used within large networks. IGRP supports multiple metrics for each route, including bandwidth, delay, load, MTU, and reliability; to compare two routes these metrics are combined together into a single metric, using a formula which can be adjusted through the use of pre-set constants. The maximum hop count of IGRP-routed packets is 255 (default 100), and routing updates are broadcast every 90 seconds (by default).
IGRP is considered a classful routing protocol. Because the protocol has no field for a subnet mask, the router assumes that all interface addresses within the same Class A, Class B, or Class C network have the same subnet mask as the subnet mask configured for the interfaces in question. This contrasts with classless routing protocols that can use variable length subnet masks. Classful protocols have become less popular as they are wasteful of IP address space.
Friday, April 10, 2009
OSPF Definition and advantage and disadvantages
OSPF Definition:
Open Shortest Path First (OSPF), is a routing protocol used to determine the correct route for packets within IP networks. It was designed by the Internet Engineering Task Force to serve as an Interior Gateway Protocol replacing RIP.
Advantages of OSPF:
Changes in an OSPF network are propagated quickly.
OSPF is heirarchical, using area 0 as the top as the heirarchy.
OSPF is a Link State Algorithm.
OSPF supports Variable Length Subnet Masks (VLSM).
OSPF uses multicasting within areas.
After initialization, OSPF only sends updates on routing table sections which have changed, it does not send the entire routing table.
Using areas, OSPF networks can be logically segmented to decrease the size of routing tables. Table size can be further reduced by using route summarization.
OSPF is an open standard, not related to any particular vendor. Disadvantages of OSPF:
OSPF is very processor intensive.
OSPF maintains multiple copies of routing information, increasing the amount of memory needed.
Using areas, OSPF can be logically segmented (this can be a good thing and a bad thing).
OSPF is not as easy to learn as some other protocols.
In the case where an entire network is running OSPF, and one link within it is "bouncing" every few seconds, OSPF updates would dominate the network by informing every other router every time the link changed state (I've done this). OSPF routers check the status of other routers on the network by sending a small hello packet at regular intervals. If a router does not respond to the hello packet, it is assumed dead, and routing updates are sent to every other router by using a multicast address.
In the case where there are no network changes, OSPF will use very little bandwidth (only sending hello packets). As soon as there is an outage, however, OSPF will flood the network as the change is sent to every router (and then every router notifies every other router about the change). This system of near silence when possible and flooding when necessary ensures that routing information gets propagated throughout the network as quickly as possible.
Open Shortest Path First (OSPF), is a routing protocol used to determine the correct route for packets within IP networks. It was designed by the Internet Engineering Task Force to serve as an Interior Gateway Protocol replacing RIP.
Advantages of OSPF:
Changes in an OSPF network are propagated quickly.
OSPF is heirarchical, using area 0 as the top as the heirarchy.
OSPF is a Link State Algorithm.
OSPF supports Variable Length Subnet Masks (VLSM).
OSPF uses multicasting within areas.
After initialization, OSPF only sends updates on routing table sections which have changed, it does not send the entire routing table.
Using areas, OSPF networks can be logically segmented to decrease the size of routing tables. Table size can be further reduced by using route summarization.
OSPF is an open standard, not related to any particular vendor. Disadvantages of OSPF:
OSPF is very processor intensive.
OSPF maintains multiple copies of routing information, increasing the amount of memory needed.
Using areas, OSPF can be logically segmented (this can be a good thing and a bad thing).
OSPF is not as easy to learn as some other protocols.
In the case where an entire network is running OSPF, and one link within it is "bouncing" every few seconds, OSPF updates would dominate the network by informing every other router every time the link changed state (I've done this). OSPF routers check the status of other routers on the network by sending a small hello packet at regular intervals. If a router does not respond to the hello packet, it is assumed dead, and routing updates are sent to every other router by using a multicast address.
In the case where there are no network changes, OSPF will use very little bandwidth (only sending hello packets). As soon as there is an outage, however, OSPF will flood the network as the change is sent to every router (and then every router notifies every other router about the change). This system of near silence when possible and flooding when necessary ensures that routing information gets propagated throughout the network as quickly as possible.
Border Gateway Protocol
The Border Gateway Protocol (BGP) is the core routing protocol of the Internet It maintains a table of IP networks or 'prefixes' which designate network reachability among autonomous systems(AS). It is described as a path vector protocol BGP does not use traditional IGP metrics, but makes routing decisions based on path, network policies and/or rulesets.
BGP was created to replace the EGP routing protocol to allow fully decentralized routing in order to allow the removal of the NSFNet Internet backbone network. This allowed the Internet to become a truly decentralized system. Since 1994, version four of the protocol has been in use on the Internet. All previous versions are now obsolete. The major enhancement in version 4 was support of Classless Inter-Domain Routing and use of route aggregation to decrease the size of routing tables.
Most Internet users do not use BGP directly. However, since most Internet service providers must use BGP to establish routing between one another (especially if they are multihomed it is one of the most important protocols of the Internet. which is the inter-provider core call setup protocol on the PSTN Very large private IP networks use BGP internally, however. An example would be the joining of a number of large Open Shortest Path First (OSPF) networks where OSPF by itself would not scale to size. Another reason to use BGP is multihoming a network for better redundancy either to multiple access points of a single ISP (RFC 1998) or to multiple ISPs.
BGP was created to replace the EGP routing protocol to allow fully decentralized routing in order to allow the removal of the NSFNet Internet backbone network. This allowed the Internet to become a truly decentralized system. Since 1994, version four of the protocol has been in use on the Internet. All previous versions are now obsolete. The major enhancement in version 4 was support of Classless Inter-Domain Routing and use of route aggregation to decrease the size of routing tables.
Most Internet users do not use BGP directly. However, since most Internet service providers must use BGP to establish routing between one another (especially if they are multihomed it is one of the most important protocols of the Internet. which is the inter-provider core call setup protocol on the PSTN Very large private IP networks use BGP internally, however. An example would be the joining of a number of large Open Shortest Path First (OSPF) networks where OSPF by itself would not scale to size. Another reason to use BGP is multihoming a network for better redundancy either to multiple access points of a single ISP (RFC 1998) or to multiple ISPs.
Route Discovery Methods
Route Discovery Methods
Distance vector - Periodically sends route table to other routers. Works best on LANs, not WANs.
Link-state - Routing tables are broadcast at startup and then only when they change. OSPF uses link-state.
Routing Information Protocol (RIP)
The RIP RFC is 1058.The routing daemon daemon adds a routing policy to the system. If there are multiple routes to a destination, it chooses the best one. The RIP message can con contain information on up to 25 routes. The RIP message contains the following components:
Command
Version - Normally 1 but set to 2 for RIP version 2.
family - Set to 2 for IP addresses.
IP address - 32 bit IP address
Metrics - Indicate the number of hops to a given network, the hop count.
RIP sends periodically broadcasts its routing table to neighboring routers. The RIP message format contains the following commands:
1 - request
2 - reply
3 & 4 - obsolete
5 - poll entry
6 - Asks for system to send all or part of routing table
When the daemon "routed" starts, it sends a request out all its interfaces for other router's routing tables. The request is broadcast if the network supports it. For TCP/IP the address family in the message is normally 2, but the initial request has address family set to 0 with the metric set to 16.Regular routing updates are sent every 30 seconds with all or part of the route table. As each router sends routing tables (advertises routes to networks its NICs interface to) routes are determined to each network. Drawbacks of RIP:
RIP has no knowledge of subnet addressing
It takes a long time to stabilize after a router or link failure.
Uses more broadcasting than OSPF requiring more network bandwidth.
RIP Version 2
Defined by RFC 1388. It passes further information in some of the fields that are set to 0 for the RIP protocol. These additional fields include a 32 bit subnet mask and a next hop IP address, a routing domain, and route tag. The routing domain is an identifier of the daemon the packet belongs to. The route tags supports EGPs.
Open Shortest Path First (OSPF)
OSPF (RFC 1257) is a link state protocol rather than a distance vector protocol. It tests the status of its link to each of its neighbors and sends the acquired information to them. It stabilizes after a route or link failure faster than a distance vector protocol based system. OSPF uses IP directly, not relying on TCP or UDP. OSPF can:
Have routes based on IP type of service (part of IP header message) such as FTP or Telnet.
Support subnets.
Assign cost to each interface based on reliability, round trip time, etc.
Distribute traffic evenly over equal cost routes.
Uses multicasting.
Costs for specific hops can be set by administrators. Adjacent routers swap information instead of broadcasting to all routers.
Border Gateway Protocol (BGP)
Described by RFC 1267, 1268, and 1497. It uses TCP as a transport protocol. When two systems are using BGP, they establish a TCP connection, then send each other their BGP routing tables. BGP uses distance vectoring. It detects failures by sending periodic keep alive messages to its neighbors every 30 seconds. It exchanges information about reachable networks with other BGP systems including the full path of systems that are between them.
Distance vector - Periodically sends route table to other routers. Works best on LANs, not WANs.
Link-state - Routing tables are broadcast at startup and then only when they change. OSPF uses link-state.
Routing Information Protocol (RIP)
The RIP RFC is 1058.The routing daemon daemon adds a routing policy to the system. If there are multiple routes to a destination, it chooses the best one. The RIP message can con contain information on up to 25 routes. The RIP message contains the following components:
Command
Version - Normally 1 but set to 2 for RIP version 2.
family - Set to 2 for IP addresses.
IP address - 32 bit IP address
Metrics - Indicate the number of hops to a given network, the hop count.
RIP sends periodically broadcasts its routing table to neighboring routers. The RIP message format contains the following commands:
1 - request
2 - reply
3 & 4 - obsolete
5 - poll entry
6 - Asks for system to send all or part of routing table
When the daemon "routed" starts, it sends a request out all its interfaces for other router's routing tables. The request is broadcast if the network supports it. For TCP/IP the address family in the message is normally 2, but the initial request has address family set to 0 with the metric set to 16.Regular routing updates are sent every 30 seconds with all or part of the route table. As each router sends routing tables (advertises routes to networks its NICs interface to) routes are determined to each network. Drawbacks of RIP:
RIP has no knowledge of subnet addressing
It takes a long time to stabilize after a router or link failure.
Uses more broadcasting than OSPF requiring more network bandwidth.
RIP Version 2
Defined by RFC 1388. It passes further information in some of the fields that are set to 0 for the RIP protocol. These additional fields include a 32 bit subnet mask and a next hop IP address, a routing domain, and route tag. The routing domain is an identifier of the daemon the packet belongs to. The route tags supports EGPs.
Open Shortest Path First (OSPF)
OSPF (RFC 1257) is a link state protocol rather than a distance vector protocol. It tests the status of its link to each of its neighbors and sends the acquired information to them. It stabilizes after a route or link failure faster than a distance vector protocol based system. OSPF uses IP directly, not relying on TCP or UDP. OSPF can:
Have routes based on IP type of service (part of IP header message) such as FTP or Telnet.
Support subnets.
Assign cost to each interface based on reliability, round trip time, etc.
Distribute traffic evenly over equal cost routes.
Uses multicasting.
Costs for specific hops can be set by administrators. Adjacent routers swap information instead of broadcasting to all routers.
Border Gateway Protocol (BGP)
Described by RFC 1267, 1268, and 1497. It uses TCP as a transport protocol. When two systems are using BGP, they establish a TCP connection, then send each other their BGP routing tables. BGP uses distance vectoring. It detects failures by sending periodic keep alive messages to its neighbors every 30 seconds. It exchanges information about reachable networks with other BGP systems including the full path of systems that are between them.
Dynamic routing
Dynamic routing performs the same function as static routing except it is more robust. Static routing allows routing tables in specific routers to be set up in a static manner so network routes for packets are set. If a router on the route goes down the destination may become unreachable. Dynamic routing allows routing tables in routers to change as the possible routes change. There are several protocols used to support dynamic routing including RIP and OSPF.
Routing cost
Counting route cost is based on one of the following calculations:
Hop count - How many routers the message must go through to reach the recipient.
Tic count - The time to route in 1/18 seconds (ticks).
Dynamic routing protocols do not change how routing is done. They just allow for dynamic altering of routing tables.There are two classifications of protocols:
IGP - Interior Gateway Protocol. The name used to describe the fact that each system on the internet can choose its own routing protocol. RIP and OSPF are interior gateway protocols.
EGP - Exterior Gateway Protocol. Used between routers of different systems. There are two of these, the first having the same name as this protocol description:
EGP - Exterior Gateway Protocol
BGP - Border Gateway Protocol.
The daemen "routed" uses RIP. The daemon "gated" supports IGP's and EGP's.
Routing cost
Counting route cost is based on one of the following calculations:
Hop count - How many routers the message must go through to reach the recipient.
Tic count - The time to route in 1/18 seconds (ticks).
Dynamic routing protocols do not change how routing is done. They just allow for dynamic altering of routing tables.There are two classifications of protocols:
IGP - Interior Gateway Protocol. The name used to describe the fact that each system on the internet can choose its own routing protocol. RIP and OSPF are interior gateway protocols.
EGP - Exterior Gateway Protocol. Used between routers of different systems. There are two of these, the first having the same name as this protocol description:
EGP - Exterior Gateway Protocol
BGP - Border Gateway Protocol.
The daemen "routed" uses RIP. The daemon "gated" supports IGP's and EGP's.
Static Ip Routing
Static routing describes a system that does not implement adaptive routing . In these systems, routes through a data network are described by fixed paths (statically). These routes are usually entered into the router by the system administrator. An entire network can be configured using static routes, but this type of configuration is not fault tolerant. When there is a change in the network or a failure occurs between two statically defined nodes, traffic will not be rerouted. This means that anything that wishes to take an affected path will either have to wait for the failure to be repaired or the static route to be updated by the administrator before restarting its journey. Most requests will time out (ultimately failing) before these repairs can be made. There are, however, times when static routes make sense and can even improve the performance of a network. Some of these include stub network and default routes.
The phenomena of adding routers manually to the routing table, is termed as static routing. This is feasible in small networks, but not in large networks.
Example
conf tip route 10.10.20.0 255.255.255.0 192.168.100.1
or the default route
(config-router)#network 192.169.16.0
The phenomena of adding routers manually to the routing table, is termed as static routing. This is feasible in small networks, but not in large networks.
Example
conf tip route 10.10.20.0 255.255.255.0 192.168.100.1
or the default route
(config-router)#network 192.169.16.0
What is Networking
Definitions of networking on the Web:
the act of working using computer network; the act of connecting computers into network; the act of meeting new people in a business or social contexten.
network - an interconnected system of things or people; "he owned a network of shops"; "retirement meant dropping out of a whole network of people who had ...
network - (broadcasting) a communication system consisting of a group of broadcasting stations that all transmit the same programs; "the networks compete to broadcast important sports events"
network - net: an open fabric of string or rope or wire woven together at regular intervals
network - a system of intersecting lines or channels; "a railroad network"; "a network of canals"
network - communicate with and within a group; "You have to network if you want to get a good job"
network - (electronics) a system of interconnected electronic components or circuits.
Network is a Canadian variety television series which aired on CTV for one season during the 1962-63 television season. ...
The Network refers to the television channel a professional wrestling program is shown on. There are occasions when an actor or a wrestler is (in storylines) a member or representative of that network. The Network series is an in-progress rewrite of the "Dragon Tamers" series by British author Emma Maree Urquhart. A sample for submission to major publishers is underway.
The Network is a six-piece New Wave band. They released their debut album Money Money 2020 on Billie Joe Armstrong's independent record label Adeline Records on September 30, 2003. A re-release of the album, with two bonus tracks, followed in 2004. ...
Network of Eternal Democracy (Red Eternal Democratico) is a political party in Aruba. At the last elections for the Estates, 23 September 2005, the party won 7 % of the popular vote and 1 out of 21 seats.
Network is a 1976 New Hollywood drama film about a fictional television network, Union Broadcasting System (UBS), and its struggle with poor ratings. Network is a real-time, two player business simulation game developed by David Mullich for the Apple II in 1980. Two players play competitively against the computer, each taking the role of the programming chief for a major television network. Network - In graph theory, a network is a digraph with weighted edges. These networks have become an especially useful concept in analysing the interaction between biology and mathematics. ...
the act of working using computer network; the act of connecting computers into network; the act of meeting new people in a business or social contexten.
network - an interconnected system of things or people; "he owned a network of shops"; "retirement meant dropping out of a whole network of people who had ...
network - (broadcasting) a communication system consisting of a group of broadcasting stations that all transmit the same programs; "the networks compete to broadcast important sports events"
network - net: an open fabric of string or rope or wire woven together at regular intervals
network - a system of intersecting lines or channels; "a railroad network"; "a network of canals"
network - communicate with and within a group; "You have to network if you want to get a good job"
network - (electronics) a system of interconnected electronic components or circuits.
Network is a Canadian variety television series which aired on CTV for one season during the 1962-63 television season. ...
The Network refers to the television channel a professional wrestling program is shown on. There are occasions when an actor or a wrestler is (in storylines) a member or representative of that network. The Network series is an in-progress rewrite of the "Dragon Tamers" series by British author Emma Maree Urquhart. A sample for submission to major publishers is underway.
The Network is a six-piece New Wave band. They released their debut album Money Money 2020 on Billie Joe Armstrong's independent record label Adeline Records on September 30, 2003. A re-release of the album, with two bonus tracks, followed in 2004. ...
Network of Eternal Democracy (Red Eternal Democratico) is a political party in Aruba. At the last elections for the Estates, 23 September 2005, the party won 7 % of the popular vote and 1 out of 21 seats.
Network is a 1976 New Hollywood drama film about a fictional television network, Union Broadcasting System (UBS), and its struggle with poor ratings. Network is a real-time, two player business simulation game developed by David Mullich for the Apple II in 1980. Two players play competitively against the computer, each taking the role of the programming chief for a major television network. Network - In graph theory, a network is a digraph with weighted edges. These networks have become an especially useful concept in analysing the interaction between biology and mathematics. ...
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