networking basics

ethermanage.com

2010-09-03T01:29:00.000-07:00

TTL values of commonly used Operating systems

2010-07-30T05:36:00.000-07:00

OSI - 7 layer model

2010-03-17T21:26:00.000-07:00

intranet & extranet

2010-02-17T05:08:00.000-08:00

crossover cable from scratch

2009-10-10T13:02:00.000-07:00

ROUTER PASSWORDS

2009-09-19T09:09:00.000-07:00

How to Reset a Router Back to the Factory Default Settings

2009-09-18T23:16:00.001-07:00

fixing loopy networks using low tech methods

2009-09-18T08:35:00.001-07:00

data communications news groups

2009-07-23T19:19:00.000-07:00

general discusssion about LANS

comp.dcom.lans
comp.dcom.lans.misc

ethernet, IEEE 802.3 , CSMA/CD standards

comp.dcom.lans.ethernet

discussion about wireless network including wireless LANS

comp.std.wireless

computer security & encryption

comp.security.misc

ATM & ATM Lans

comp.dcom.cell-relay

frame relay network

comp.dcom.fram-relay

discusssion about n/w management application, protocols and standards

comp.protocols.tcp-ip

internet-connections

2009-07-14T09:50:00.000-07:00

Fiber Distributed Data Interface (FDDI)

2009-06-25T10:51:00.000-07:00

The Fiber Distributed Data Interface (FDDI) topology is sometimes referred to as a fast, redundant Token Ring network. FDDI is similar to a Token Ring network in the sense that it uses token passing as the access method, but there are two rings instead of the one found in Token Ring. FDDI uses fiber-optic cable operating at 100 Mbps

Two rings are used in the FDDI architecture—the primary ring and the secondary ring. The primary ring is used at all times, and the secondary ring is used only if the primary ring fails. The token is passed on each ring in opposite directions.

FDDI is specifically for WAN use, not for LAN use. FDDI is used to connect multiple sites. Even if the individual LANs are using non–Token Ring topologies, they can still be connected by FDDI

Secure Sockets Layer

2009-06-25T10:49:00.000-07:00

Secure Sockets Layer (SSL) is a session-layer protocol that encrypts data sent from any higher-layer program such as FTP, HTTP, SMTP, and so on. SSL has become the standard method of encrypting traffic between a web client and a web server, ensuring that malicious users cannot capture such traffic and read it. SSL can work only with guaranteed transports—or basically anything using the TCP protocol—and is made up of the two protocols: SSL Handshake and SSL
Record.

n SSL Handshake is used to create a secure session between the two systems that are communicating. This includes all methods and parameters used for the encryption.

n SSL Record is used to encrypt all data packets, including the SSL Handshake data packets.
SSL is mainly used on e-commerce web sites during the exchange of personal information such as credit card numbers, because SSL can encrypt the traffic between the client and the server.

DMZ

2009-06-25T10:28:00.000-07:00

Tx/Ex-Carriers

2009-06-25T03:55:00.000-07:00

The T-carrier and E-carrier are both dedicated digital lines used to transmit voice, data, or images. The T-carrier is used in the United States, Japan, and Australia, whereas the E-carrier is used in Europe, Mexico, and South America. There are different categories of each carrier that indicate the speed of the line. T1 is composed of twenty-four channels that are made up of 64 Kbps bandwidth each, for a total of 1.544 Mbps. Each 64 Kbps channel is referred to as digital signal level 0 (DS0), with the twenty-four DS0 channels making a digital signal level 1 (DS1).
These lines can be multiplexed into faster links

Most companies cannot afford a T-carrier line, so it is best for some companies to look into other means of connecting to the Internet or creating a WAN. If necessary, a company can lease a partial T1 line, which is called a Fractional T1, at a lower price. A Fractional T1 will also provide only a fraction of the bandwidth.

committed information rate

2009-06-25T03:52:00.000-07:00

Multiple companies can share a Frame Relay backbone to the Internet or between office buildings. Each company pays for a specific amount of the bandwidth on the Frame Relay medium. If the bandwidth
is available, a company can use more bandwidth than that for which they have paid. Once other companies start using their bandwidth, all the companies will be limited to the bandwidth that has been committed to them. The bandwidth that each company pays for is noted by its Committed Information Rate (CIR).

Frame Relay

2009-06-25T03:44:00.000-07:00

Frame Relay is the digital version of X.25 and is much faster than X.25. Frame Relay runs at layers 1 and 2 of the OSI model and supports transfer rates as high as 50 Mbps along with features such as Quality of Service (QoS).

It is a choice for WAN networking along with ATM, Broadcast ISDN (BISDN), and Cell Relay.
Frame Relay transmission speeds are not always constant.

The data packets, or frames, are sent through a packet-switching network with higher-level protocols managing error checking, such as IPX/SPX or TCP/IP

The nodes,which are used to route the frames in the packet-switching network, each use
a routing algorithm that can help determine the efficiency of the Frame Relay
network. Frame Relay does send frames as variable-length packets that are not all
set at the same size before transmission.

If the bandwidth becomes too congested, Frame Relay will drop any frames that it cannot handle. This can include corrupted frames, as well as those that are unable to be delivered because the destination cannot be reached. Any dropped frames must be requested for retransmission by the protocols being used.

X.25

2009-06-25T03:38:00.000-07:00

X.25 is a packet-switched network that uses a device called a Packet Assembler/Dissembler (PAD) to connect a system to the X.25 network. The PAD is a device that connects to serial ports of a device and is therefore considered RS-232 compliant.

X.25 runs at layers 1, 2, and 3 of the OSI model and has transfer rates of 2 Mbps. Overall
this technology is fairly old and slow compared with some of today’s standards. Most X.25
implementations communicate over analog lines.

SONET / SDH

2009-06-25T03:32:00.000-07:00

The Synchronous Optical Network (SONET) is a North American standard that allows the uniting of unlike transmissions into one single data stream. The Synchronous Digital Hierarchy (SDH) is the European standard designed for the same purpose as SONET. Basically, SONET allows multiple companies to transmit the packets on their networks onto a SONET backbone to be transmitted to a
remote location using fiber-optic cabling. Because many companies might be using different network topologies and protocols, the data streams from each company would most likely differ. These companies can transmit their information over SONET without having to conform to a network standard

For example, one company might have a 10 Mbps category-5 Ethernet network using IPX/SPX,

while another is using fiber-optic cable with TCP/IP. These can be combined into a single data stream (this is called multiplexing) for transmission over one cable. More companies can be added for transmission over the SONET medium without making any changes to any of the company networks.

typical cable modem set up

2009-06-25T03:28:00.001-07:00

Asynchronous transfer mode

2009-06-25T03:21:00.000-07:00

Asynchronous Transfer Mode (ATM) is a circuit-switching technology that uses a consistent packet size of 53 bytes, called a cell. A 53-byte cell is broken into a 48-byte payload and a 5-byte header. The lack of overhead in the ATM packet (it is always 53 bytes) helps promote the performance of this very fast LAN/WAN technology.

ATM will provide for high bandwidth as needed if enough users are requesting the bandwidth. ATM bandwidth ranges from slow speeds (around 12.96–25 Mbps using copper media such as category-3 UTP
cable), to high speeds (around 622 Mbps using fiber-optic cable). With advances in technology,
ATM speeds can reach 2.488 Gbps.

ATM can allow for parallel transmissions between nodes. This means that if data is being passed to and from PC A and PC B, the data packets can be passed between two routers (nodes) simultaneously. Remember that with ATM, data packets are referred to as cells, and each cell has a fixed length of 53 bytes. There are no variable-length cells as with some transmission standards.

ATM can be used in LAN environments, but its use is uncommon due to the high price of ATM networking equipment such as ATM network cards and ATM hubs or switches. ATM also supports Quality of Service (QOS), which allows bandwidth to be allocated to different types of traffic.

vpn

2009-06-24T21:05:00.000-07:00

Link State protocol

2009-06-24T10:14:00.000-07:00

Link state routing protocols are a little more advanced than distance vector routing protocols in the sense that a link state routing protocol knows about the entire network topology. A link state protocol is responsible for monitoring the state of the link between the routers. This link state information is then used to determine the optimal route to a destination network. Although protocols such as RIP have knowledge of neighboring routers, link state protocols have knowledge of the entire network topology and multicast the routing table information to the entire network.
One of the benefits of the link state routing protocols is that if a link is down, that information is stored in the routing table and that pathway will not be used. Because a distance vector routing protocol does not store link state information, it is possible that it will not know of a link that is unavailable for some time and it could still send traffic through that pathway.

Ex:- OSPF

MTR

2009-06-24T10:04:00.001-07:00

MTR is a network diagnostics program available in Linux that combines features of Tracert and Ping. It is a glorified traceroute tool that sends multiple ping messages to each router between the source and the destination. To use MTR, you simply type mtr and then specify your destination

tracert/traceroute

2009-06-24T09:57:00.000-07:00

Tracert is a command-line utility that was designed to perform a very basic task: to determine the path taken by a data packet to reach its destination.

Tracert will send you a response with each router that is hit on the way. This will help you understand the number of networks, or hops, between you and the destination.

Although a Tracert might look rather confusing at first, it is fairly easy to understand.Each row gathers information about that hop three times. The first column shows the number of hops away that router is. The next three columns show the time it took for the router to respond for each attempt. The last column lists the fully qualified domain name of that router, which typically gives you an indication of where the router is.

WINS ?

2009-06-23T20:45:00.001-07:00

Windows Internet Naming Service

The Windows Internet Naming Service (WINS) provides name resolution for NetBIOS names to matching IP addresses and is popular on large Microsoft networks. WINS is very similar to DNS but contains a database of different-style names—NetBIOS names instead of fully qualified domain names.When a WINS client boots up, it registers its names within the WINS database and then queries that server any time it needs to have a computer name resolved to a matching IP address. When the WINS client shuts down, it also de-registers its names from the WINS database so that another system can register the names while it is offline.

Before WINS, the LMHOSTS file was used to assist with remote NetBIOS name resolution. The LMHOSTS file is a static file that maps NetBIOS names to IP addresses. This file is similar to the hosts file in functionality; the only difference is that the hosts file is used for mapping hostnames to IP addresses.

ICS ?

2009-06-23T20:41:00.000-07:00

Internet Connection Sharing (ICS) is a service built into Windows operating systems that allows you to share your Internet connection with other users on the network. ICS acts as a NAT server and a DHCP server at the same time. When you enable ICS in Windows, it automatically starts assigning IP addresses out on the network so that the DHCP clients use the ICS computer as their default gateway.
When clients send information to the ICS machine to be sent on the Internet, the ICS machine translates the source address (the NAT feature) to use the external interface of the system

2009-06-23T20:38:00.000-07:00

APIPA

2009-06-23T20:37:00.000-07:00

Windows clients support a feature known as automatic private IP addressing (APIPA), which is a feature that provides that, when a Windows client boots up and cannot contact a DHCP server, it will configure itself automatically with a 169.254.x.y address. If there is something wrong with the DHCP server and all the systems on the network cannot obtain an address from the DHCP server, the clients will all assign themselves an address within the 169.254 address range and then be
able to communicate with one another.

APIPA does not assign a default gateway, so you will be unable to access resources on a remote network and the Internet—but you can still communicate with systems on your network. When troubleshooting to find out why a machine cannot communicate on the network, watch for systems that have the 169.254.x.y address range because it means they could not find a DHCP server.

IS-IS

2009-06-23T20:33:00.001-07:00

The intermediate system–to–intermediate system (IS-IS) routing protocol competes with OSPF by being a link state routing protocol for inside the network (interior gateway). IS-IS was developed by Digital Equipment Corporation (DEC) and has become an industry-standard protocol, although
not as popular as OSPF.

Like OSPF, IS-IS uses a link state algorithm to maintain status information on all the links
and routes on the network so that each router running the IS-IS protocol will have knowledge
of the entire network topology.

CSU/DSU

2009-06-23T20:29:00.000-07:00

A channel service unit/data service unit (CSU/DSU) is either one device or a pair of devices that allows an organization to get a very-high-speed WAN connection from the telephone company, such as a T1 or T3 link. The CSU is used at the business end to get the connection to the WAN, and the DSU may be used at the provider’s end to allow the CSU to connect.

zeroconfig

2009-06-23T20:27:00.000-07:00

Zero Configuration Networking (ZeroConfig) is a network service designed to minimize the configuration of the network clients by broadcasting configured services on the network to network clients who automatically discover these network services. After the service has been discovered, the client is automatically configured to use this service with no interaction from the network administrator.

what is Supernetting ?

2009-06-23T20:25:00.000-07:00

Supernetting, like subnetting, is part of the CIDR concept where we are altering the default way the IP address scheme works. Supernetting works the opposite way: you take bits away from the network ID to combine networks. The goal of supernetting is to combine multiple smaller networks into one big network ID.

what is convergence in routing ?

2009-06-23T20:23:00.001-07:00

Convergence in routing is when the routes on each router are shared with all other routers and merged into each router’s routing table.

what is a socket ?

2009-06-23T20:18:00.000-07:00

A socket is the end point of communication and is made up of three components: the IP address of the system, the port number of the application, and the protocol that is being used—either TCP
or UDP. The socket is the end point of communication for a TCP/IP application and is how data is sent from one system to another, or more accurately, from one application to another. The following formula defines what a socket is:

Socket = IP address + Port number + Protocol (TCP or UDP)

content switch

2009-06-23T10:01:00.000-07:00

Content Switch A content switch is a special switch that is designed for optimizing data delivery to clients by incorporating features to improve performance such as data caching or load balancing features on the switch. Here is an example of how the switch can load-balance traffic: if you connect two servers into the switch, the switch creates a virtual server using a virtual IP, and when a request comes in to the virtual IP, the switch then forwards the request to one of the servers connected to the switch. The result is that the load is balanced across both servers and performance is increased.

port authentication

2009-06-23T09:57:00.001-07:00

Port Authentication Port authentication is another important feature of the switch that allows the administrator to associate the MAC address of the system that will connect to the port. The administrator can also specify that if a system with a different MAC address connects to the port, the port is to be automatically disabled. Port authentication will help increase the security of the network by allowing only authorized systems to connect to the network—a critical feature of any switch

5-4-3 rule

2009-06-23T09:43:00.000-07:00

port mirroring

2009-06-23T09:36:00.000-07:00

Port Mirroring Port mirroring, also known as port monitoring, is a feature that allows the switch to send a copy of data that reaches certain ports to the mirrored, or monitored, port. Port monitoring allows an administrator to plug his/her workstation into the port that the copy of the data is being sent to, and monitor the network traffic.

Port mirroring is an important feature of a switch because by default the switch filters traffic by only sending the data to the port that the destination system resides on. The switch’s filtering feature will prevent the monitoring of traffic, and as a result the administrator will have to enable port mirroring (monitoring) and specify the port that receives the copy of data.

brouter

2009-06-23T09:30:00.000-07:00

A brouter is the combination of a bridge and a router, and it makes the decision whether it needs
to bridge the data or route the data according to the protocol being used. If the protocol is a nonroutable protocol such as NetBEUI, the data will be bridged. If the protocol is TCP/IP or IPX/SPX, the routing features of the brouter will be used

Trunking

2009-06-23T09:22:00.001-07:00

Trunking Trunking is a feature on Cisco switches that allows you to connect the switches together and then assign one of the ports as a trunk port. The trunk port is the port that is used to carry VLAN traffic to the other switch. VLANs are allowed to contain ports as members that are from multiple switches. If data is destined for all systems in the VLAN, the VLAN identification information is added to the data packet and then the switch sends the packet out the trunk port. When another switch receives the packet, it checks the VLAN identification information and then
sends the data to all of its ports that are a member of that particular VLAN.

spanning tree protocol

2009-06-23T09:19:00.000-07:00

Spanning Tree Protocol (STP) The Spanning Tree Protocol (STP) runs at layer 2 and is designed to prevent loops on a network that could occur if you connect a number of switches together. For example, a loop is created if you connect Switch1 to Switch2 and then turn around and connect Switch2 back to Switch1 using a different cable and ports on the switches.

Having a loop on the network could cause the network to go down and creates instability in the switches. To prevent this, STP was designed. STP is a protocol that looks at all of the ports used to create a loop and then places one of those ports in a blocking state so that no data traffic can pass through the port. Once the port is in a blocking state, the loop is broken and the network becomes more stable.

The fact that the port is in a blocking state instead of being disabled means that if one of the other links go down, then the port is transitioned into a forwarding state automatically. When a port is in a forwarding state, it is allowed to send and receive data on the port.

multistation access units (MAUS)

2009-06-23T09:13:00.000-07:00

ethernet name jargon

2009-06-23T09:10:00.001-07:00

bridge

2009-06-23T09:08:00.001-07:00

A bridge is a network connectivity device that is used to break the network down into multiple network segments. A bridge runs at layer 2, the data link layer, and is used to filter traffic by only forwarding traffic to the destination network segment.

peer to peer n/w

2009-06-21T23:56:00.000-07:00

A peer-to-peer network has no dedicated servers; instead, a number of workstations are connected together for the purpose of sharing information or devices. When there is no dedicated server, all workstations are considered equal; any one of them can participate as the client or the server. Peer-to-peer networks are designed to satisfy the networking needs of home networks or of small companies that do not want to spend a lot of money on a dedicated server but still want to have the capability to share information or devices

The Microsoft term for a peer-to-peer network is a workgroup. Be aware that peer-to-peer networks typically consist of fewer than 10 systems.

Most of the modern operating systems such as Windows XP and Windows Vista already have built-in peer-to-peer networking capabilities, which is why building a peer-to-peer network would be a “cheap” network solution. The disadvantage of a peer-to-peer network is the lack of centralized administration—with peer-to-peer networks, you need to build user accounts and configure security on each system.

server based n/w

2009-06-21T23:46:00.000-07:00

pin-out diagrams for straight through & cross over cables

2009-06-21T23:36:00.000-07:00

voltage levels & ethernet

2009-06-21T09:50:00.000-07:00

A LAN analyzer has to know about the voltage levels of signal in an ethernet cable isn't it ?

so what are the industry standards for these voltage levels(for different ethernet types) ?, where can i find information about it ?

i didn't find the answer here:- http://www.faqs.org/qa/qa-27732.html

mark hobley

I saw the answers to this on Wikipedia, but I don't know whether the article
contains the detail or the accuracy that you require.

http://en.wikipedia.org/wiki/100BASE-T

You will need to verify the article against appropriate industry standards.(Hopefully these will be cross referenced in the article). I haven't looked at this in any great depth, because I am not manufacturing ethernet cards.

(Obviously things will be different for Coaxial based networking systems. You may need to look at the Ethernet article, and follow the links for your network cabling type):

http://en.wikipedia.org/wiki/Ethernet

DHCP trivia

2009-06-21T09:46:00.001-07:00

arp attacks

2009-06-21T09:33:00.000-07:00

ARP poisoning

2009-06-21T09:29:00.000-07:00

Bus topology

2009-06-21T08:51:00.000-07:00

zone file

2009-06-21T05:25:00.000-07:00

syslogd

2009-06-21T05:18:00.000-07:00

domain name questions

2009-06-21T05:11:00.000-07:00

exercize

2009-06-21T05:05:00.001-07:00

SOA, CNAME,IN,NS,PTR,A,MX

2009-06-21T04:58:00.001-07:00

Inside a switch

2009-06-21T04:52:00.000-07:00

frame protocol

2009-06-20T11:08:00.001-07:00

cables & noises

2009-06-20T11:01:00.000-07:00

Your cables are carrying electrical signals, anything that affects the cable electrically or mechanically can create noise

ethernet & encoding schemes

2009-06-20T10:51:00.000-07:00

router trivia

2009-06-20T10:43:00.000-07:00

network tools

2009-06-20T08:22:00.000-07:00

oscilloscope

2009-06-20T08:20:00.000-07:00

potential network cable problems

2009-06-20T08:14:00.000-07:00

Behind the scenes of a patch panel

2009-06-20T07:28:00.000-07:00

toner-tracer set

2009-06-19T21:28:00.001-07:00

Cat 5 cable

2009-06-19T21:18:00.000-07:00

Internet registries and address assignment

2009-06-15T20:39:00.000-07:00

a subnetted network example

2009-06-10T03:16:00.000-07:00

TCP flags

2009-05-19T01:32:00.001-07:00

idle scan

2009-05-19T01:29:00.000-07:00

xmas scan

2009-05-19T01:28:00.001-07:00

syn scan

2009-05-19T01:27:00.001-07:00

rev ident scan

2009-05-19T01:26:00.001-07:00

null scan

2009-05-19T01:25:00.001-07:00

FIN scan

2009-05-19T01:23:00.000-07:00

Public DNS servers

2009-05-12T22:01:00.000-07:00

source:- http://www.tech-faq.com/public-dns-servers.shtml

arp poisoning

2009-05-06T05:49:00.000-07:00

T.T.L value

2009-05-04T04:38:00.000-07:00

I have heard that depending on the TTL value , we can identify from which O.S an IP packet has come from , how true is this statement ?

It is somewhat true. Different operating systems may emit a different time to live value. Of course, the values changes as the packet is routed downstream, so this is not reliable. You would need to consider other factors.

mark hobley

sample packet in a network

2009-04-30T06:19:00.000-07:00

IPV4 ARP & RARP

2009-04-27T22:08:00.000-07:00

Ethernet Crossover Adapter

2009-03-08T01:22:00.000-08:00

Ethernet LoopBack jack

2009-03-08T01:17:00.000-08:00

Understanding n/w communication, TCP, UDP

2009-03-03T19:26:00.000-08:00

3-way handshake

2009-03-02T23:26:00.000-08:00

A TCP/IP packet on an Ethernet network

2009-02-17T01:46:00.000-08:00

From networking basics

source quench message

2009-02-11T22:03:00.001-08:00

Why patch Panel ?

2009-02-10T04:22:00.000-08:00

Hi all,

the following is the definition of Patch panel ,

A panel of network ports contained together, usually within a telecommunications closet, that connects incoming and outgoing lines of a LAN or other communication, electronic or electrical system. In a LAN, the patch panel connects the network's computers to each other and to the outside lines that enable the LAN to connect to the Internet or another WAN. Connections are made with patch cords. The patch panel allows circuits to be arranged and rearranged by plugging and unplugging the patch cords.

which is given here: http://www.webopedia.com/TERM/P/patch_panel.html

does this means that the patch panel can be used to perform the same function of a switch or a router ?

can anyone explain me the exact role/function of patch panel in LAN ?

callan79

A patch panel is used to make wiring tidy in a large network.

Say you're in an office with 2 companies. Each company has 3 computers. Each company has their own Internet connection.

WITHOUT a patch panel, you'd have all the network cables from the office coming out the wall. Half would connect to one router, and half to the other one.

Imagine if one user wanted to connect to the other router - you have no way of knowing which cable is which!

So instead, you connect all 6 network cables to a patch panel. The ports on the panel are labelled 1,2,3,4,5,6.

Then you simply take a short cable from port 1, and connect it to whichever router you want. Same for all the rest.

If a user wants to change router, they just tell you the number which is written on their network socket on the wall. Say it's number 4. You just look in port 4 on your patch panel, unplug the cable from the first router, and change it to the second one.

I have made some drawings to help you.

While the concept is simple, it's proving hard to explain!

WITHOUT PATCH PANEL

WITH PATCH PANEL

camh

No, you still need to use switches/routers. A patch panel is basically just a centralized point in which you can route cabling.

Typically, you'd have cabling running from each jack (wall, floor, etc.) in a building to one or more central patch panels. Since it's easier to run cable without the RJ45 connector attached, these would be punched into the back of a patch panel. Each cable would then be routed from the patch panel into the appropriate port of the switch/router using another regular patch cord.

farslayer

The cables described by camh that connect to the patch panel and the other end is a network or phone jack somewhere else in the building.. This is refered to as structured cabling

see: http://en.wikipedia.org/wiki/Structured_cabling

SIMPLIFIED STRUCTURED CABLING DIAGRAM

CABLES CONNECTING TO BACK OF PATCH PANEL

Rack full of patch panels along with cable management. This is what your rack SHOULD LOOK LIKE if you do things properly

You would then use patch cables to connect between your switches nad routers to the internal structured cabling using patch cables. Heres some pictures showing the patch cables connected to a switch then routed through cable management and attached to patch panels.

I had patch panels installed for my phone system at our new facility. So to move a phone extension I simply unplug one end of the cable from the patch panel, and plug it into a different location on the patch panel that corresponds to the new office location for that extension. MUCH easier than using a punch tool or reprogramming the phone system to move an extension.

Just for comparison this is what a poorly managed rack looks like when you cheap out on purchasing wire management.

Err NO, I do NOT want to trace any cables in that mess thank you very much.

Patch Panel

2009-02-09T16:30:00.000-08:00

multicast address

2009-02-05T22:44:00.000-08:00

The vast majority of traffic on IP internetworks is of the unicast variety: one source device sending to one destination device. IP also supports multicasting, where a source device can send to a group of devices. Multicasting is not used a great deal on the Internet
as a whole at the present time, mainly due to lack of widespread hardware support, so most of our focus in looking at IP is on unicast. Multicast is useful in certain circumstances, however, especially as a more efficient alternative to broadcasting

The “classful” IP addressing scheme sets aside a full one-sixteenth of the address space for multicast addresses: Class D. Multicast addresses are identified by the pattern “1110” in the first four bits, which corresponds to a first octet of 224 to 239. So, the full range of multicast addresses is from 224.0.0.0 to 239.255.255.255. Since multicast addresses represent a group of IP devices (sometimes called a host group) they can only be used as the destination of a datagram; never the source.

source:- tcpipguide

OUI

2009-01-26T19:37:00.000-08:00

An Organizationally Unique Identifier (OUI) is a 24-bit number that is purchased from the Institute of Electrical and Electronics Engineers, Incorporated (IEEE) Registration Authority. This identifier uniquely identifies a vendor, manufacturer, or other organization (referred to by the IEEE as the 'assignee' ) globally or worldwide and effectively reserves a block of each possible type of derivative identifier (such as MAC addresses, group addresses, Subnetwork Access Protocol protocol identifiers, etc.) for the exclusive use of the assignee. The OUI is subsequently used by the vendor, manufacturer, or organization (the assignee) to create particular instances of these identifiers for various purposes, such as the identification of a particular piece of equipment (e.g., a network interface controller (NIC)) or the identification of a network protocol, and for use in various computer hardware products, including MAC addresses for Ethernet and other NICs, World Wide Names for Fibre Channel host bus adapters, and other Fibre Channel and Serial Attached SCSI devices.[1][2].

In MAC addresses, the OUI is combined with a 24-bit number (assigned by the owner or 'assignee' of the OUI) to form the address. The first three octets of the address are the OUI.

List of OUI's
http://standards.ieee.org/regauth/oui/oui.txt

Loop back address

2009-01-26T19:25:00.000-08:00

aarklon

The following is the definition of loop back address ,i saw in the book tcp/ip guide

special range of addresses ,127.0.0.0 to 127.255.255.255 , is set aside for loop back functionality.IP datagrams sent by a host to a 127.x.x.x loop back address are not passed down to the data link layer for transmission,instead they loopback to the source device at the IP level. In essence this short circuits the normal protocol stack; data is sent by a device's layer 3 IP implementation and immediately received by it.

This loopback range is used for testing the TCP/IP protocol implementation on a host. since the lower layers are short circuited ,sending to a loopback address allows you to isolate and
test the higher layers ,IP and above without interference from lower layers. 127.0.0.1 is the address most commonly used for testing purposes

now my question is as follows

1)This loop back range is used for testing the TCP/IP protocol implementation on a host. since the lower layers are short circuited ,sending to a loopback address allows you to isolate and
test the higher layers

can any one give example(s) for this or a situation where this is used ?

Mario lztem

I'm using the loopback-IF to for e.q. to check, if my deamons (apache,snmpd, ...) are locally running and if the right ports are in listenning state (well, this can show netstat too ...).

tamoneya

If i install an apache server on my computer and I want to test it without going to another computer I can open Firefox (or any web browser) and go to 127.0.0.1 and I can see if everything is configured right.

sanjay krk

A simple answer.
If I want to check if TCP/IP works fine on my local machine, I would simply fire this command from the prompt:- $ping localhost #or ping 127.0.0.1

kari Hurtta

127.0.0.1 is used for 'localhost'

/ Kari Hurtta

hurtta@Hurtta06k:~$ head -1 /etc/hosts
127.0.0.1 localhost
hurtta@Hurtta06k:~$

hardcorelinux

Some applications work together by intersocket communication - localhost provides that address so that the elements can all work on the same PC

Enables you to run a web/ftp/ any other server on the same PC that you are working on without having to know the allocated IP address from a DHCP server.

robertwessel2

> The following is the definition of loop back address ,i saw in the
> book tcp/ip guide

> special range of addresses ,127.0.0.0 to 127.255.255.255 , is set
> aside for loop back functionality.IP datagrams sent by a host to a
> 127.x.x.x loop back address are not passed down to the data link layer
> for transmission,instead they loopback
> to the source device at the IP level. In essence this short circuits
> the normal protocol stack; data is sent by a device's layer 3 IP
> implementation and immediately received by it.

There are a number of TCP/IP stacks where the loopback driver is, in fact, a driver at the same level as a normal Ethernet card device driver. It just doesn't talk to much real hardware. Whether that approach is used, or the packet flow is actually short circuited that at the IP layer is entirely implementation dependent.

The loopback address is often used when a service resides on the same machine as a client. As far as usage goes, that's far more common than for testing the TCP/IP stack.

Digital Mercenary for honor

Usually, more than one loopback address can be defined on most OS's that have a TCP/IP stack - small, embedded operating systems may not be able to do this, however.

A previous poster mentioned services on a host being attached to the loopback interface - very common and efficient use of resources on the host, especially programmatically - write once, and a client / server application can even run on a single box. A lot of the common X-Windows
software suites make extensive use of this (KDE, Gnome) in popular Linux distributions.

Another use for loopbacks that's common is security. SSH tunneling,where the SSH secure-shell software and server is used to encrypt otherwise unencrypted data, often makes use of loopback interfaces. SSH attaches a listener process to a loopback address and port the user specifies, also connecting to the remote SSH server, which will forward traffic (if the configuration permits) to the desired "real" destination. The "real" destination can also be an interface on the
remote server, providing an encrypted connection for any service. I use this to "wrap" my POP3 e-mail and some other services directly to the hosts the services reside on.

Directly addressing your post - loopbacks can be really useful for simulating a client-server connection between two pieces of an application, and taking a packet capture to debug issues - the traffic stays on your host, where you can enjoy complete control over what the application does and get packet dumps anytime you want, etc.

screened subnet

2008-12-15T20:47:00.001-08:00

see:- http://www.linuxjournal.com/article/4415

Dual homed firewall architecture

2008-12-15T20:32:00.001-08:00

source:- articles.techrepublic.com

source routing

2008-12-15T03:31:00.000-08:00

Soure routing is an IP option which allows the originator of a packet to specify what path that packet will take, and what path return packets sent back to the originator will take. Source routing is useful when the default route that a connection will take fails or is suboptimal for some
reason, or for network diagnostic purposes.

now can anyone give me examples for this diagnostic purposes or the commonly encountered situations where source routing is used ?

kenneho

Well, say you have load balance server with a public key installed, then all traffic to and from this server may use that key. That includes as many backend web servers or whatevere else as you need. By routing everything via that load balance server you need only one public key, and not one per backend server.

baldy3105

Source routing is used in MPLS networks to build traffic engineering tunnels. The internal routing protocols will calculate shortest paths as normal, but then you can use traffic engineering tunnels to direct specific traffic via another path, and this is done using source routing.

Autonomous Systems

2008-12-14T21:42:00.000-08:00

Latency vs Throughput

2008-12-11T22:04:00.000-08:00

sulekha

1) can any one give me a more precise explanation/practical example
which clarifies the concept of latency and throughput

2) how can we measure the latency in a LAN using the httping utility

the following definitions seems to be more confusing

throughput

Throughput is a specific measure of how much data flows over a channel in a given period of time. It is usually a practical measurement.

Latency

refers to the timing of data transfers on a communications channel or network. One important aspect of latency is how long it takes from the time a request for data is made until it starts to arrive. Another aspect is how much control a device has over the timing of the data that is sent, and whether the network can be arranged to allow for the consistent delivery of data over a period of time. Low latency is considered better than high latency.

salasi

These seem to be good definitions; the only thing I can add, in a practical manner is that latency is pragmatically taken as a measure of how long before something happens.

Quakeboy02

Let's say that you want to use 5 gallons of water to take a 5 minute shower. Would you rather that all 5 gallons be dumped on you at the end of 5 minutes, or that it flowed at a linear rate for the whole 5 minutes? In both cases the throughput would be the same over 5 minutes, but in one case, the latency would be 5 minutes

sulekha

After going through the book "Linux Networking Cookbook" by Carla Schroder i found the following explanation

there is often confusion between bandwidth,latency, and throughput. Broadband means fat pipe, not necessarily a fast pipe. As us folks out here in the sticks say, “Bandwidth is capacity, and latency is response time.

Bandwidth is the diameter of your irrigation line.

Latency is waiting for the water to come out.”

Throughput is the amount of data transferred per unit of time, like 100 Kbps.

So, you could say throughput is the intersection of bandwidth and latency.

doctor cisco

Bandwidth is generally understood to mean the maximum data transfer rate of a given link. A 6-meg satellite internet connection has much greater bandwidth than a 56k dial-up modem does.

Latency means delay -- in networking, it refers to how long it takes to send one packet from one host to another -- often measured with ping, and therefore the time is for the round trip. Due to the 44,000-mile trip to and from the satellite -- 88,000 for your ping to get to the other system and then back -- the latency for the satellite link is MUCH MUCH WORSE than for the dial-up modem. You cannot possibly ping anything over the satellite link in less than 500ms -- light can only go 186,000 miles/sec. You can ping the other end of your dial-up connection is something under 50ms.

The kicker comes when you want to transfer a file. The modem will be slow due to the low bandwidth. But it will also be far less than 6 megabits over the satellite link, due to the nature of TCP. (The transfer will flow, then stop while the receiving host acknowledges receiving the data, which takes 1/4 second in this example, over and over.) You can improve the behavior of the transfer over satellite by dramatically increasing the tcp window size on both hosts involved in the transfer.

httping

2008-12-11T21:46:00.000-08:00

Testing HTTP Throughput and Latency with httping

Problem

As always, your users are complaining “the web site is too slow! We’re dying here!” But it seems OK to you. Isn’t there some way you can make some objective measurements without having to master some expensive, complicated analysis tool?

Solution

While sophisticated HTTP server analysis tools are nice, and there are dozens of them, sometimes you just want something quick and easy. httping is an excellent utility for measuring HTTP server throughput and latency, and because it’s a tiny command-line tool, you can easily run it from multiple locations via SSH. Its simplest invocation is to test latency:

$ httping -c4 -g http://www.oreilly.com
PING www.oreilly.com:80 (http://www.oreilly.com):
connected to www.oreilly.com:80, seq=0 time=177.37 ms
connected to www.oreilly.com:80, seq=1 time=170.28 ms
connected to www.oreilly.com:80, seq=2 time=165.71 ms
connected to www.oreilly.com:80, seq=3 time=179.51 ms
--- http://www.oreilly.com ping statistics ---
4 connects, 4 ok, 0.00% failed
round-trip min/avg/max = 165.7/173.2/179.5 ms

That’s not too bad. This doesn’t tell you how long it takes pages to load, only how long it takes the server to respond to a HEAD request, which means fetching only the page headers without the content. So, let’s do a GET (-G) request, which fetches the whole page:

$ httping -c4 -Gg http://www.oreilly.com
PING www.oreilly.com:80 (http://www.oreilly.com):
connected to www.oreilly.com:80, seq=0 time=1553.78 ms
connected to www.oreilly.com:80, seq=1 time=2790.99 ms
connected to www.oreilly.com:80, seq=2 time=2067.32 ms
connected to www.oreilly.com:80, seq=3 time=2033.02 ms
--- http://www.oreilly.com ping statistics ---
4 connects, 4 ok, 0.00% failed
round-trip min/avg/max = 1553.8/2111.3/2791.0 ms
That slowed it down a bit!

The -r switch tells httping to resolve the hostname only once, to remove DNS latency
from its measurements: $ httping -c4 -Grg http://www.oreilly.com

You can test SSL-enabled sites with the -l switch:
$ httping -c4 -lGg https://www.fictionalsslsite.org

To specify an alternate port, append it to the URL:
$ httping -c4 -Gg http://www.fictionalsslsite.org:8080

httping will report the roundtrip time with the -b switch in kilobytes per second
(not kilobits):

$ httping -c4 -Gbg http://www.fictionalsslsite.org
PING www.fictionalsslsite.org:80 (http://www.fictionalsslsite.org):
connected to www.fictionalsslsite.org:80, seq=0 time=2553.96 ms 43KB/s

Use the -s switch to display return codes. Put it all together, and this is what you get:

$ httping -c4 -Gsbrg http://www.oreilly.com
PING www.oreilly.com:80 (http://www.oreilly.com):
75KB/sed to www.oreilly.com:80, seq=0 time=1567.91 ms 200 OK
72KB/sed to www.oreilly.com:80, seq=1 time=1618.20 ms 200 OK
18KB/sed to www.oreilly.com:80, seq=2 time=5869.12 ms 200 OK
58KB/sed to www.oreilly.com:80, seq=3 time=1979.43 ms 200 OK
--- http://www.oreilly.com ping statistics ---
4 connects, 4 ok, 0.00% failed
round-trip min/avg/max = 1567.9/2758.7/5869.1 ms
Transfer speed: min/avg/max = 18/56/75 KB

You can test a local server by specifying the hostname and port instead of the URL:
$ httping -c4 -h xena -p 80

source:- carla schroder

see:- http://www.vanheusden.com/httping/

what is my IP Address

2008-12-09T21:12:00.000-08:00

see:- http://www.whatismyip.com/

for your external IP,Internet speed test, IP info plus more