DevOps / Sys Admin Q & A #2B : Networks
Credit : The Cisco Learning Network
A Local Area Network (LAN) was originally defined as a network of computers located within the same area. In other words, Local Area Networks are defined as a single broadcast domain, which means that if a user broadcasts information on a LAN, the broadcast will be received by every other user on the LAN. Broadcasts are prevented from leaving a LAN by using a router. The disadvantage of this method is routers usually take more time to process incoming data compared to a bridge or a switch. More importantly, the formation of broadcast domains depends on the physical connection of the devices in the network. Virtual Local Area Networks (VLAN's) were developed as an alternative solution to using routers to contain broadcast traffic.
In short, a virtual LAN (VLAN) is any broadcast domain that is partitioned and isolated in a computer network at the data link layer (OSI layer 2).
We can mark frames through VLAN tagging, so that a single interconnect (trunk) may be used to transport data for multiple VLANs.
VLANs allow network administrators to group hosts together even if the hosts are not on the same network switch. This can greatly simplify network design and deployment, because VLAN membership can be configured through software. Without VLANs, grouping hosts according to their resource needs necessitates the labor of relocating nodes or rewiring data links.
Why VLAN? - advantages:
- Performance - In networks where traffic consists of a high percentage of broadcasts and multicasts, VLAN's can reduce the need to send such traffic to unnecessary destinations.
- Formation of Virtual Workgroups.
- Security - Periodically, sensitive data may be broadcast on a network. In such cases, placing only those users who can have access to that data on a VLAN can reduce the chances of an outsider gaining access to the data. VLAN's can also be used to control broadcast domains, set up firewalls, restrict access, and inform the network manager of an intrusion.
Credit : What is DHCP Server ?
- When the client computer (or device) boots up or is connected to a network, a DHCPDISCOVER message is sent from the client to the server.
- When the DHCP server receives the DHCPDISCOVER request message then it replies with a DHCPOFFER message.
- The client forms a DHCPREQUEST message in reply to DHCPOFFER message and sends it to the server indicating it wants to accept the network configuration sent in the DHCPOFFER message.
- Once the server receives DHCPREQUEST from the client, it sends the DHCPACK message indicating that now the client is allowed to use the IP address assigned to it. The client enters the bound state during this step.
Dynamic Host Configuration Protocol (DHCP) is a client/server protocol that automatically provides an Internet Protocol (IP) host with its IP address.
Every device on a TCP/IP-based network must have a unique unicast IP address to access the network and its resources. Without DHCP, IP addresses for new computers or computers that are moved from one subnet to another must be configured manually; IP addresses for computers that are removed from the network must be manually reclaimed. With DHCP, this entire process is automated and managed centrally. The DHCP server maintains a pool of IP addresses and leases an address to any DHCP-enabled client when it starts up on the network. Because the IP addresses are dynamic (leased) rather than static (permanently assigned), addresses no longer in use are automatically returned to the pool for reallocation.
Credit : http://veraview.com/news/
- Unicast : just one sender, and one receiver.
- Broadcast : one sender, but the information is sent to all connected receivers.
- Multicast : information is sent from one or more points to a set of other points.
ARP stands for Address Resolution Protocol. When we try to ping an IP address on our local network, say 192.168.1.2, our system has to turn the IP address 192.168.1.2 into a MAC address. This involves using ARP to resolve the address, hence its name.
Please checkout this : Address Resolution Protocol (ARP) Explained
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DevOps / Sys Admin Q & A
Linux - system, cmds & shell programming
- Linux Tips - links, vmstats, rsync
- Linux Tips 2 - ctrl a, curl r, tail -f, umask
- Linux - bash I
- Linux - bash II
- Linux - Uncompressing 7z file
- Linux - sed I (substitution: sed 's///', sed -i)
- Linux - sed II (file spacing, numbering, text conversion and substitution)
- Linux - sed III (selective printing of certain lines, selective definition of certain lines)
- Linux - 7 File types : Regular, Directory, Block file, Character device file, Pipe file, Symbolic link file, and Socket file
- Linux shell programming - introduction
- Linux shell programming - variables (readonly, unset)
- Linux shell programming - special shell variables
- Linux shell programming : arrays - three different ways of declaring arrays & looping with $*/$@
- Linux shell programming : operations on array
- Linux shell programming : variables & commands substitution
- Linux shell programming : metacharacters & quotes
- Linux shell programming : input/output redirection & here document
- Linux shell programming : loop control - for, while, break, and break n
- Linux shell programming : for-loop
- Linux shell programming : if/elif/else/fi
- Managing User Account - useradd, usermod, and userdel
- Linux Secure Shell (SSH) I : key generation, private key and public key
- Linux Secure Shell (SSH) II : ssh-agent & scp
- Linux Secure Shell (SSH) III : SSH Tunnel as Proxy - Dynamic Port Forwarding (SOCKS Proxy)
- Linux Secure Shell (SSH) IV : Local port forwarding (outgoing ssh tunnel)
- Linux Secure Shell (SSH) V : Reverse SSH Tunnel (remote port forwarding / incoming ssh tunnel) /)
- Linux Processes and Signals
- Linux Drivers 1
- Linux Debugging using gdb
- Embedded Systems Programming I - Introduction
- Embedded Systems Programming II - gcc ARM Toolchain and Simple Code on Ubuntu/Fedora
- LXC (Linux Container) Install and Run
- Hadoop - 1. Setting up on Ubuntu for Single-Node Cluster
- Hadoop - 2. Runing on Ubuntu for Single-Node Cluster
- ownCloud 7 install
- Ubuntu 14.04 guest on Mac OSX host using VirtualBox I
- Ubuntu 14.04 guest on Mac OSX host using VirtualBox II
- Windows 8 guest on Mac OSX host using VirtualBox I
- Ubuntu Package Management System (apt-get vs dpkg)
- How to Make a Self-Signed SSL Certificate
- DevOps / Sys Admin interview questions
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