Thursday, September 4, 2008
OSI Model(7 Layers)
Answer:
OSI model is a way of describing how different applications and protocols interact on network-aware devices.
Functions of each Layer:
Physical Layer(Layer 1):This layer defines the physical and electrical characteristics of the network. Helps to pass strings(data) of ones and zeros down the wire.
Device:Hub, NIC, Repeater.. etc
Data Link Layer:
It defines the acess strategy for sharing the physical medium. Helps convert the bits into frame.
Devices: Bridge, Switch
Network Layer:
Layer 3 is the Network Layer, providing a means for communicating open systems to establish, maintain and terminate network connections.
Device:Router
Transport Layer:
The main function of Session Layer is to ensure data reliability and integrity.
Session Layer:
It provides two communicating presentation entities to exchange data with eachother.
Presentation Layer:
Application data is either unpacked or packed only in this layer. Protocol conversions, encryption/decryption and graphics expansion all takes place here.
Application Layer:
This is where you find your end-user and end-application protocols, such as telnet, ftp, and mail(pop3 and smtp).
Thanks,
Friends you have anything to update. You can do it.
OSI model is a way of describing how different applications and protocols interact on network-aware devices.
Functions of each Layer:
Physical Layer(Layer 1):This layer defines the physical and electrical characteristics of the network. Helps to pass strings(data) of ones and zeros down the wire.
Device:Hub, NIC, Repeater.. etc
Data Link Layer:
It defines the acess strategy for sharing the physical medium. Helps convert the bits into frame.
Devices: Bridge, Switch
Network Layer:
Layer 3 is the Network Layer, providing a means for communicating open systems to establish, maintain and terminate network connections.
Device:Router
Transport Layer:
The main function of Session Layer is to ensure data reliability and integrity.
Session Layer:
It provides two communicating presentation entities to exchange data with eachother.
Presentation Layer:
Application data is either unpacked or packed only in this layer. Protocol conversions, encryption/decryption and graphics expansion all takes place here.
Application Layer:
This is where you find your end-user and end-application protocols, such as telnet, ftp, and mail(pop3 and smtp).
Thanks,
Friends you have anything to update. You can do it.
VLAN and its use.
Definition of VLAN:
VLANs are used to segment the network into smaller broadcast domain or segments. In otherword VLAN is a logical grouping of network users and resources connected administratively to defined ports on a switch.The primary reason to segment your network is to relieve network congestion and increase bandwidth.By creating VLANs, you are able to create smaller broadcast domains within a switch by assigning different ports on the switch to different subnetworks. Ports assigned to the VLAN to which the node sending the broadcast is assigned will receive that broadcast.
Why use VLAN:
VLAN is like placing a router to stop broadcasts between each individual VLAN. Routers are like bug poison-they kill broadcasts dead. Broadcast can't escape through routers and they can't escape a VLAN, eigher. Each VLAN becomes its own invididual broadcast domain. When a network node or workstation sends out an advertisement or broadcast to the other nodes on a segment, only the nodes assigned to the VLAN to which the node sending the broadcast is assinged will receive that broadcast.
Using Virtual LANs, you're no longer confined to physical locations. VLANs can be organized by location, function, department, or even the application or protocol used, regardless of where the resources or users are located. In a flat network topology, your broadcast domain consists of all the interfaces in your segment or subnet. If no devices-such as switches or routers-divide your network, you have only one broadcast domain. On some switches, an almost limitless number of broadcast domains or VLANs can be configured.
VLAN Basics
Inter-Switch Link (ISL) protocol was designed to allow VLAN traffic to flow from one Cisco device to another. The protocols adds a header that uniquely identifies the source and destinations of the data as well as the VLAN the data is a member of. If data from one VLAN needs to be forwarded to another VLAN, it requires some type of Layer 3 routing.
Spanning Tree Protocol(STP), which can be applied to each individual VLAN, keeps the network from forming bridging loops when a packet can reach a given destination multiple ways. This means you can provide multiple ways to get data from Point A in your network to Point B, thereby providing redundancy in case one link fails. STP blocks the redundant ports so only one path exists for data in the network.
VLANs allow you to use these links to load balance data. By assigning different VLANs to each link, data from one VLAN can use one link and another VLAN can use the second, redundant link. A VLAN would use the other link only during a link failure in the network, in this case the VLANs assigned to the lost link would converge and use the link that was still available.
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http://hubpages.com/_cfghjb7oiy1d/hub/Wipro-hires-people-with-experience-in-networking
VLANs are used to segment the network into smaller broadcast domain or segments. In otherword VLAN is a logical grouping of network users and resources connected administratively to defined ports on a switch.The primary reason to segment your network is to relieve network congestion and increase bandwidth.By creating VLANs, you are able to create smaller broadcast domains within a switch by assigning different ports on the switch to different subnetworks. Ports assigned to the VLAN to which the node sending the broadcast is assigned will receive that broadcast.
Why use VLAN:
VLAN is like placing a router to stop broadcasts between each individual VLAN. Routers are like bug poison-they kill broadcasts dead. Broadcast can't escape through routers and they can't escape a VLAN, eigher. Each VLAN becomes its own invididual broadcast domain. When a network node or workstation sends out an advertisement or broadcast to the other nodes on a segment, only the nodes assigned to the VLAN to which the node sending the broadcast is assinged will receive that broadcast.
Using Virtual LANs, you're no longer confined to physical locations. VLANs can be organized by location, function, department, or even the application or protocol used, regardless of where the resources or users are located. In a flat network topology, your broadcast domain consists of all the interfaces in your segment or subnet. If no devices-such as switches or routers-divide your network, you have only one broadcast domain. On some switches, an almost limitless number of broadcast domains or VLANs can be configured.
VLAN Basics
Inter-Switch Link (ISL) protocol was designed to allow VLAN traffic to flow from one Cisco device to another. The protocols adds a header that uniquely identifies the source and destinations of the data as well as the VLAN the data is a member of. If data from one VLAN needs to be forwarded to another VLAN, it requires some type of Layer 3 routing.
Spanning Tree Protocol(STP), which can be applied to each individual VLAN, keeps the network from forming bridging loops when a packet can reach a given destination multiple ways. This means you can provide multiple ways to get data from Point A in your network to Point B, thereby providing redundancy in case one link fails. STP blocks the redundant ports so only one path exists for data in the network.
VLANs allow you to use these links to load balance data. By assigning different VLANs to each link, data from one VLAN can use one link and another VLAN can use the second, redundant link. A VLAN would use the other link only during a link failure in the network, in this case the VLANs assigned to the lost link would converge and use the link that was still available.
If you are a Networking Professional and want a job in Wipro. Visit my hub
http://hubpages.com/_cfghjb7oiy1d/hub/Wipro-hires-people-with-experience-in-networking
Spanning Tree
Spanning Tree:
1)Spanning trees are a standard technique used in local area connection. Spanning tree algorithms were developed to prevent redundant transmission of data along intermediate hops between a source and destination host on a mesh network topology. Without spanning trees, a mesh network can be flooded and rendered unusable by messages circulating in an infinite loop between hosts.
2)An algorithm used in transparent bridges that dynamically determines the best path from source to destination. It avoids bridge loops (two or more paths linking one segment to another), which can cause the bridges to misinterpret results.
The algorithm creates a hierarchical "tree" that "spans" the entire network including all switches. It determines all redundant paths and makes only one of them active at any given time. The spanning tree protocol (STP) is part of the IEEE 802.1 standard.
How STP Works:
When STP initially comes online in a network, one of its first actions is to use the STA(Spanning Tree Algorithm) to select a root bridge and a root port. The root bridge is the bridge with the lowest-value bridge identifier. Switches or bridges using STP exchange multicast frames called Bridge Protocol Data Units. All the switches on the network use these BPDUs to broadcast their bridge IDs to the other switches in the network. After the root bridge is selected, the root ports on all other bridges are determined.
In the figure below, Switch A is acting as the root bridge, calculating the least-cost path to switch D. Notice the numbers associated with the root bridge's path to each invididual destination; the path with the lowest number hs the highest priority. The higher the number between invidiual segments, the higher the coast of transmitting a frame between those two segments. The port through which the root bridge can be reached with the least amount of hops or cost determines a bridge's root port; this is referred to as the least path cost.
The lowest calculated path is not always the most ideal path. For example, if mutliple high-speed links to a destination exist, the links may total more than the cost of a very slow link, such as a modem. Even though the straight path has the fewest hops, it is much slower than using a high-spped, longer path. To over this problem, you as the administrator can manually change a slower-speed link to have a higher port cost, which STP will use to calculate a higher path cost. The goal is to make changes to the network so that the fastest, most efficient route to the root port is designated for the switch to user. The fastest links should always have the lower port costs.
A designated bridge is the bridge, or switch on each LAN that provides the shortest route with the least path cost. The designated bridge is the onley bridge that is allowed to forward frames to and from the other bridges.A designated prot on the switch is the port that connects the switch to the physical interface of the designated bridge.
Types of frames:(These are the frames that will cause strom)
Broadcast frames
Multicast frames
Unknown unicasts
Various States of STP
1)Blocking
2)Listening
3)Learning
4)Forwarding
5)Disabled.
Thanks
Karthick M
1)Spanning trees are a standard technique used in local area connection. Spanning tree algorithms were developed to prevent redundant transmission of data along intermediate hops between a source and destination host on a mesh network topology. Without spanning trees, a mesh network can be flooded and rendered unusable by messages circulating in an infinite loop between hosts.
2)An algorithm used in transparent bridges that dynamically determines the best path from source to destination. It avoids bridge loops (two or more paths linking one segment to another), which can cause the bridges to misinterpret results.
The algorithm creates a hierarchical "tree" that "spans" the entire network including all switches. It determines all redundant paths and makes only one of them active at any given time. The spanning tree protocol (STP) is part of the IEEE 802.1 standard.
How STP Works:
When STP initially comes online in a network, one of its first actions is to use the STA(Spanning Tree Algorithm) to select a root bridge and a root port. The root bridge is the bridge with the lowest-value bridge identifier. Switches or bridges using STP exchange multicast frames called Bridge Protocol Data Units. All the switches on the network use these BPDUs to broadcast their bridge IDs to the other switches in the network. After the root bridge is selected, the root ports on all other bridges are determined.
In the figure below, Switch A is acting as the root bridge, calculating the least-cost path to switch D. Notice the numbers associated with the root bridge's path to each invididual destination; the path with the lowest number hs the highest priority. The higher the number between invidiual segments, the higher the coast of transmitting a frame between those two segments. The port through which the root bridge can be reached with the least amount of hops or cost determines a bridge's root port; this is referred to as the least path cost.
The lowest calculated path is not always the most ideal path. For example, if mutliple high-speed links to a destination exist, the links may total more than the cost of a very slow link, such as a modem. Even though the straight path has the fewest hops, it is much slower than using a high-spped, longer path. To over this problem, you as the administrator can manually change a slower-speed link to have a higher port cost, which STP will use to calculate a higher path cost. The goal is to make changes to the network so that the fastest, most efficient route to the root port is designated for the switch to user. The fastest links should always have the lower port costs.
A designated bridge is the bridge, or switch on each LAN that provides the shortest route with the least path cost. The designated bridge is the onley bridge that is allowed to forward frames to and from the other bridges.A designated prot on the switch is the port that connects the switch to the physical interface of the designated bridge.
Types of frames:(These are the frames that will cause strom)
Broadcast frames
Multicast frames
Unknown unicasts
Various States of STP
1)Blocking
2)Listening
3)Learning
4)Forwarding
5)Disabled.
Thanks
Karthick M
Routing Protocols
Types of Routing Protocol:
There are several routing protocol that are popular in this world. Please find the list of the protocols below.
There are several routing protocol that are popular in this world. Please find the list of the protocols below.
RIP V1
RIP V2
IGRP
EIGRP
OSPF
BGP
IS-IS
FRAME RELAy.
BGP:
The Border Gateway Protocol (BGP) is an interautonomous system routing protocol. An autonomous system is a network or group of networks under a common administration and with common routing policies. BGP is used to exchange routing information for the Internet and is the protocol used between Internet service providers (ISP). Customer networks, such as universities and corporations, usually employ an Interior Gateway Protocol (IGP) such as RIP or OSPF for the exchange of 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 (AS), the protocol is referred to as External BGP (EBGP). If a service provider is using BGP to exchange routes within an AS, then the protocol is referred to as Interior BGP (IBGP)
BGP Path Selection
BGP could possibly receive multiple advertisements for the same route from multiple sources. BGP selects only one path as the best path. When the path is selected, BGP puts the selected path in the IP routing table and propagates the path to its neighbors. BGP uses the following criteria, in the order presented, to select a path for a destination:
1)If the path specifies a next hop that is inaccessible, drop the update.
2)Prefer the path with the largest weight.
3)If the weights are the same, prefer the path with the largest local preference.
4)If the local preferences are the same, prefer the path that was originated by BGP running on this router.
5)If no route was originated, prefer the route that has the shortest AS_path.
6)If all paths have the same AS_path length, prefer the path with the lowest origin type (where IGP is lower than EGP, and EGP is lower than incomplete).
7)If the origin codes are the same, prefer the path with the lowest MED attribute.
8)If the paths have the same MED, prefer the external path over the internal path.
9)If the paths are still the same, prefer the path through the closest IGP neighbor.
10)Prefer the path with the lowest IP address, as specified by the BGP router ID.
Intermediate System-to-Intermediate System
(IS-IS) is an OSI link-state hierarchical routing protocol that floods the network with link-state information to build a complete, consistent picture of network topology. To simplify router design and operation, IS-IS distinguishes between Level 1 and Level 2 ISs. Level 1 ISs communicate with other Level 1 ISs in the same area. Level 2 ISs route between Level 1 areas and form an intradomain routing backbone. Hierarchical routing simplifies backbone design because Level 1 ISs need to know only how to get to the nearest Level 2 IS. The backbone routing protocol also can change without impacting the intra-area routing protocol.
RIP V1: It is a simple distance vector protocol. It has been enhance with various techniques, including Split Horizon and Poison Reverse in order to enable it to perform better in complicated network
The longest path cannot exceed 15 hops.
RIP uses static metrics to compare routes.
ADMINISTRATIVE DISTANCE:120
METRIC:HOB COUNT
What you mean by RIP v2?
RIP V2: It added several new features.
External route tags.
Subnet masks
Next hop router addresses.
Authentication.
Multicast support.
METRIC:SAME AS RIP V1
Explain about OSPF?
OSPF: Open Shortest Path First is a dynamic routing protocol for use in Internt Protocol(IP networks).It is a link state routing protocols. It falls into the group of interior gateway protocols, operating within an autonomous system(AS). Link-State routing protocol that calls for the sending of link-state advertisements (LSAs) to all other routers within the same hierarchial area. Information on attached interfaces, metrics used, and other variables is included in OSPF LSAs. As OSPF routers accumulate link-state information, they use the SPF algorithm to calculate the shortest path to each node.
METRIC: COST=bandwidth/interface bandwidth
AD:110
Explain about EIGRP?
EIGRP: EIGRP is a Cisco proprietary routing protocol derived from IGRP. EIGRP can be called as hybrid protocol or an advanced distance-vector routing protocol, with optimizations to minimize both the routing instability incurred after topology changes, as well as the use of bandwidth and procession power in the router. Routers that support EIGRP will automatically redistribute route information to IGRP neighbors by converting the 32 bit EIGRP metric to the 24 bit IGRP metric. Most of the routing optimizations are based on the Diffusing update Algorithm(DUAL).
MERIC: Load, delay,bandwidth, reliability and MTU
Explain about IGRP?
IGRP:IGRP is a distance vector Interior Gateway Protocol(IGP). Distance vector routing protocols mathematically compare routes using some measurement of distance. This measurement is know as distance vector. Routers using a distance vector protocol must send all or a portion of their routing table in a routing-update message at regular intervals to each of their neighboring routers. As routing information proliferates through the network, routers can identify new destinations as they are added to the network, learn of failures in the network, and, most improtanly, calculate distances to all know destinations. IGRP uses a composite metric that is calculated by factoring weighted mathematical values for internetwork delay, bandwidth, reliability, and load. Network administrators can set the weighting factors for each of these metrics. Default metrics are Reliability and load.
Administrative Distance:100
MERIC: Load, delay,bandwidth, reliability and MTU
Thanks
Karthick M
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