Category Archives: Networking

SNMP

Simple Network Management Protocol or SNMP is a part of the Internet protocol suite. It is used in network management systems to check network-attached devices and to communicate with network elements.

SNMP consists of a set of standards for network management. This includes data objects, a database schema, and an Application Layer protocol.

In typical SNMP practice, there are a number of systems to be run, and one or more systems running them. An agent, which is a software component, handles each managed system and delivers information through SNMP to the managing systems.

SNMP Basic Components

SNMP is composed of three components: a managed device, an agent, and a network-management system (NMS).

A managed device is a network node existing on a managed network. It includes an SNMP agent. Through SNMP, management information is collected and stored, making it available to network management systems. Managed devices can be any type of device, including but are not limited to access servers, printers, computer hosts, routers, IP telephones, bridges, switches, and hubs.

An agent is a network-management software module existing in a managed device. It contains restricted knowledge of management information. It has the capacity to translate this information into a form well-matched with SNMP.

A network-management system (NMS) performs applications to monitor and control managed devices. These systems offer the memory resources and a bulk of processes required for network management.

SNMP Messages

SNMP Messages are initiated by either the network element (NE) or by the NMS.

When SNMP management programs send a request to a network device, the agent software receives the requests and retrieves information from MIBs (Management Information Bases). These MIBs manage the devices in a communications network.

The agent software then delivers the information being requested back to the SNMP management program. To carry out such tasks, it utilizes the following message types:

  1. SNMP GET is the basic SNMP request message initiated by the network management system when it wants to retrieve bits of data from a network element.
  2. SNMP GETNEXT is an extended type of request message. It is used to browse the entire ranking of management objects. It is useful for dynamic tables, such as an internal IP route table.
  3. SNMP GETBULK is a type of request message that allows the retrieval of large messages. It reduces the number of protocol exchanges required to retrieve a large amount of management information. The maximum message size allowed should not be larger than the path maximum transmission unit (MTU), the largest frame size allowed for fragmentation to occur in a single frame.
  4. SNMP TRAP is initiated by a network element and is sent to the network management system. It is an unsolicited message sent to an SNMP management system by an SNMP agent when it detects that a certain type of event has taken place locally on the managed host. The agent will deliver data without being asked using TRAP or INFORM protocol operations. For example, a printer could send an SNMP TRAP when it is out of paper.
  5. SNMP SET is initiated by the network management system when it wants to change data on a network element. It can send controlling requests or configuration updates via the SET protocol operation to run a system.

SNMP Versions

Simple Network Management Protocol has the following versions:

  • SNMPv1 – implements community-based security;
  • SNMPv2 – SNMPv2 with party-based security;
  • SNMPv2c – SNMPv2 with community-based security;
  • SNMPv2u – SNMPv2 with user-based security; and
  • SNMPv3 – it implements user-based security.

Public DNS

Public Domain Name System is a public service provided by numerous companies. This service assigns Uniform Resource Locators for websites. Each system or server connected to the Internet is provided with an IP address. An IP address is made up of a series of numbers with periods in between them. The format for an IP address is: 000.000.0.0.

A user can publish a website on the Internet with just an IP address. Users can type in an IP address on a Web browsers’ address bar and it will direct them to the home page of the server. The numbers may be a bit hard to remember if the user wants to generate large traffic for their website.

DNS is used to assign websites to IP addresses. When the user types a URL on the address bar, the system will refer to the DNS to check which IP address it corresponds to. The Web browser will then be directed to the IP address of the website.

How Does Public DNS Work?

If you’re talking about a published primary DNS, there are five steps to perform. However, if you have a registered domain, there are only three steps. Moreover, if you only want to have an MX record, you can skip the last step.

You will first have to find an unused domain name. This is because you won’t be able to register it if someone else is using it. When you are able to register it, you can create a primary DNS account. To create a DNS account, make sure that you choose the right service provider. Delegate the domain and re-delegate the in-addr domain.

The DNS service will usually provide service for anyone that requests it, as long as they have the administrative authority over the area. The service provider depends on the zone you are in. However, if you are in a company capable of providing its own DNS service, you should do so instead of relying on outside or public DNS. This way, you are assured of controlled efficiency.

How to Delegate the Domain

To delegate the domain, you have to pick the service provider that suits your needs. The company will supply you with instructions as to how to create and delegate your domain after you have created an account with them. There are always providers that offer free services.

What are the Restrictions?

Service providers often have restrictions on the usage of the service. These restrictions vary from one company to another. Usually, registrants are required to claim ownership of the zones they want to register. Also, they should be using resources they are given authority to use. These restrictions are always bound by legal issues.

Secondary DNS

To start with secondary DNS, authorize your service provider to perform zone transfers from your primary name server.

After that, create a secondary domain account and have it registered. Now, you can delegate the domain and wait for confirmation before using it.

VLAN

Virtual Local Area Networks, or VLANs, allow a network manager to segment a LAN (Local Access Network) into different domains. The segmentation is a logical setup and not a physical one. It removes the proximity requirement of LANs. VLANs remove the need for routers to define broadcast domains. All you need is a bridging software program to define workstations to be included in the broadcast domain. A router is only needed when communicating with another VLAN.

Setting Up the VLAN

Assignment to a VLAN is done at the switch level. The switch is the backbone of all available VLANs in a network. The switch has two configurations: trunk mode, and normal mode. These modes are designed to deliver maximum functionality to the network.

Decide on the environment. It is up to you if you want your VLAN to span a lot of switches or if you want to segment a single switch. If you have just one switch, this means you can configure other VLANs without other considerations. On the other hand, if you have multiple switches, you will have to decide which VLANs will be assigned under which switch. You will also have to set up the trunking and the VLAN trunking protocol.

Configuring

You will need these codes to properly set up the VLAN.

‘SwitchA# vlan database’

‘SwitchA(vlan)# vlan 2 name vlan2’

‘SwitchA(vlan)# exit’

‘SwitchA# configure terminal’

‘SwitchA(config)# interface fastethernet 0/1’

‘SwitchA(config-if)# switchport mode access’

‘SwitchA(config-if)# switchport access vlan 2’

‘SwitchA(config-if)# end’

Use these commands from a privileged mode to create VLAN Number 2. VLAN Number 1 is already there for the management of VLAN so always number created VLANs from 2-1000.

Trunking must be configured at this point because it will allow VLAN information to pass between switches. Set up the trunk mode and the trunk encapsulation mode so they will match. Otherwise, the manner that frames are identified in the data transfer process may not match your VLAN and therefore will not be effective. Remember to configure the rest of the setup according to the way you want your VLAN to work.

Additional Reading on VLAN

DNS

The Domain Name System is maintained by a distributed database system. This system uses a client-server model and has nodes called name servers. The domains and sub-domains have one authoritative DNS server showing information about that particular domain and the name servers of any of its subordinate domains.

How Do DNS Servers Work?

DNS servers involve anything that you do on the Internet. Even the mere act of sending e-mail or browsing through the Web involves DNS servers.

A DNS server can be any computer registered to join the DNS. This computer is then run with special networking software featuring a public IP address and a database of other network addresses and names for other hosts.

DNS servers convert human-readable addresses or domain names to computer-friendly addresses or IP addresses. But with so many domain names and counterpart IP addresses, this becomes a very difficult job for DNS servers. Each server is assigned with a unique address for it to execute this function properly.

This means each of these servers needs to communicate with each other. Private network protocols are used by each of the servers. There are also root servers holding the complete database of the Internet domain names and their IP addresses. As of today, there are 13 famous root servers employed by the Internet. Ten of these reside in the United States, one is found in Japan, another in London, England. The last is in Stockholm, Sweden.

Server Hierarchy

DNS servers function as parts of a hierarchy. This means the whole system is distributed in order to reduce and manage the stress on the servers and to make things easier.

The top of the hierarchy is composed of the root servers. The 13 root servers distribute the database to the lower levels of the hierarchy. Hence, all other servers maintain only a piece of the database and are only able to function with that set of data. However, it makes things work a lot faster as the machines don’t have to go through too much information to find a domain name.

This kind of networking functions on a client/server architecture. The browser you use in your computer is a DNS client. If the server linked to the client receives a request that is not in its database (if it is too far from the area of operation or if it is a low-traffic website), it changes to a temporary client and issues the request to another server. The cycle goes on until the request is found.

DNS Lookups

Every computer is assigned its own IP address in the Internet. The IP address is like an ID code or a bank account number. It follows this format: 12.3.456.789. Every time a user visits a certain website, the DNS (Domain Name System) acts as the directory of all the corresponding IP addresses of domain names. When users enter a link to a website (e.g. www.ilovedebating.com), they usually type in the domain names because it’s easier to recall them than the IP addresses. The DNS server returns the IP address corresponding to the domain name.

Since thhe Internet is a huge and indefinite arena, a single DNS server cannot be expected to record all domain names and addresses accurately. Moreover, domains are sometimes moved to other machines resulting to a change of IP addresses. To address this problem, the DNS comes up with a hierarchy of machines or units, giving a higher ranking those that don’t change IP addresses often.

To resolve a domain problem, the following process should be done:

1. Type a website link in the address bar and press enter/return.

2. Right after pressing return, the browser will send a request to the DNS server in the network settings and ask for the corresponding IP address for the website link. The settings for these are usually configured automatically.

3. The ISP DNS server will now tap its look-ups cache and check how it can respond to the request. If it knows the answer to the question, the DNS is finished with the look-up. If it doesn’t, it carries on to Step 4.

4. If the ISP DNS server is unable to find a corresponding web address in its look-ups cache, it will re-check the domains it is responsible for and attempt to find matches. If it is able to do so, it sends the answer back. If it still cannot find a result, it moves on to Step 5.

5. A query will now be sent to the root of the DNS servers. These “roots” are found at the topmost part of the hierarchy. These roots contain the top-level domains such as .com, .edu, .net, and .gov. The root server will check the zone and will run a search for the website. After this, it delivers the NS record back to the DNS server. The IP addresses usually contain the NS record, so the browser can now return with the result of the request.

For country-specific domains such as .ph (for Philippines) or .uk (for United Kingdom), the root servers at the country level are the ones to coordinate with the ISP DNS. The result is acquired only through an extra look-up in the ISP DNS. It is only when the IP addresses are not found within the hierarchical system that the country-level root servers are tapped.

A DNS server should not be confused with a caching DNS server. The latter performs the look-ups by itself while the former only forwards the requests.

192.168.0.1

192.168.0.1 is among a number of IPv4 addresses designated for use only within a private network. The following are the private IP address ranges defined for IPv4:

10.0.0.0 – 10.255.255.255
172.16.0.0 – 172.31.255.255
192.168.0.0 – 192.168.255.255

Using NAT (Network Address Translation), routers intelligently route incoming packets from the Internet to the right device on the private network. The network as a whole is identified by its public IP address.

192.168.0.1 as a Default IP address for Network Devices

Often, you’ll find that 192.168.0.1 is the default IP address for network devices, including routers manufactured by Netgear and D-Link. Visit http://192.168.0.1 in your Web browser to set up your connection preferences, such as PPPoE, firewall, and port forwarding.

After typing in http://192.168.0.1 in your browser, you may be prompted for a username and password. Look up your manual for the default username and password. Otherwise try these common ones:

  1. admin, (blank) [default for D-Link routers];
  2. admin, password [default for Netgear routers];
  3. (blank), admin;
  4. and admin, admin.

Note that you can always change the default IP address and also the username and password.

Router Page not Opening?

Try the following suggestions if you cannot connect to your router.

  1. Make sure that the IP address of your computer is 192.168.0.x (where x is between 2 to 255). To do this in Windows, right click My Network Places and choose Properties. Now, right click the LAN connection and choose Properties again. Click “Internet Protocol (TCP/IP)” and then click the Properties button. You can choose to obtain an IP address automatically from the router, or you can assign an appropriate unique IP address. For example, you can choose 192.168.0.2 as the IP address if it has not been already assigned on the network. Choose 255.255.255.0 for the Subnet mask and 192.168.0.1 for the Default gateway.
  2. If you think the IP address of the router has been changed, try one of the following:
    1. Find out the address of the default gateway. In Windows, open the command line by going to Start->Run. Type in “ipconfig” and press Enter. Visit the address listed for “Default Gateway” using your browser to get to your router’s Web interface.
    2. Reset your router to its factory defaults. Press and hold the reset button for several seconds until the router restarts. For some models, you’ll need to turn the power off first, press and hold the reset button, and then turn on power with the reset button still pressed. Release when the router lights begin to blink slowly.
  3. The router IP default address could be different from 192.168.0.1, such as 192.168.1.1. Check the router’s manual.

Additional Reading on 192.168.0.1

192.168.2.1

Like 192.168.1.1, 192.168.2.1 belongs to the range of private IPv4 addresses with the first two octets as 192.168. Private means these appear only internally within a network and cannot appear on the Internet publicly.

Routers use NAT (Network Address Translation) to intelligently route incoming packets from the Internet to the right machine. The router itself has a public IP address leased by the Internet Service Provider. This public IP address is also the address by which computers within the network are identified when accessing the Internet.

192.168.2.1 as a Router’s Default IP Address

192.168.2.1 is the default IP address for many routers and other network devices, including those manufactured by Belkin. For these routers, you can use http://192.168.2.1 to set up functions such as PPPoE (to connect to your ISP automatically), firewall settings, and port forwarding on the router’s firmware.
After typing in http://192.168.2.1 in your browser, you’ll be asked for a username and password. Here are some common ones to try if you’ve lost your manual:

  1. Administrator, (blank) [default for Belkin routers];
  2. admin, admin;
  3. admin, (blank);
  4. admin, password; and
  5. (blank), admin.

Cannot Connect to 192.168.2.1?

If you are facing problems connecting to 192.168.2.1, try the following suggestions. Note that these apply similarly for routers with different IP addresses, such as 192.168.1.1 or 192.168.0.1.

  1. Make sure that the IP address of your computer is 192.168.2.x, with x in the range of 2-255. To do this in Windows, right click My Network Places and choose Properties. Now, right click the LAN connection and choose Properties again. Click “Internet Protocol (TCP/IP)” and then click the Properties button. You can choose to obtain an IP address automatically, or you could assign an appropriate, unique IP address. For example, you can choose 192.168.2.2 as the IP address, if it has not been already assigned on the network. Choose 255.255.255.0 for the Subnet mask and 192.168.2.1 for the Default gateway.
  2. Someone might have changed the router’s IP address. Try one of the following:
    1. Find out the address of the default gateway. In Windows, open the command line by going to Start->Run. Type in “ipconfig” and press Enter. Visit the address listed for “Default Gateway” using your browser to get to your router.
    2. Reset your router using the reset button. For Belkin routers, press and hold the button for exactly 7 seconds. This will cause your router to restore all settings to the factory defaults.
  3. The router IP address could be different from 192.168.2.1, such as 192.168.1.1. Check the router’s manual.

Additional Reading on 192.168.2.1

192.168.1.1

Like any IP address of the form 192.168.x.y, 192.168.1.1 is a private IPv4 address. Devices on different networks can have this same IP address, but only one device on an internal network can have it.

Typically, this is the address of routers manufactured for home use by companies such as Linksys. Note that a router actually has at least two IP addresses visible to other devices: one for devices within the network and the other for the Internet.

Configuring your Router through 192.168.1.1

You can visit http://192.168.1.1 to access your router’s configuration software through your computer’s browser. Your connection to the router could be wired or wireless, although it is recommendable to be wired if you’re a novice.

You may now be prompted for a username and password. For Linksys, the default username and password are “admin.” In some firmware versions, the username is blank. For other models, try using “admin”-<blank> or “admin”-“password”.

Note that you can always change the router’s IP address from its default.

Cannot Connect to 192.168.1.1?

If you cannot connect to 192.168.1.1, try looking up the following suggested solutions.

  1. Make sure that the IP address of your computer is 192.168.1.x (where x is between 2 to 255). To do this in Windows, right click on Network (in the Start menu) and choose Properties. Now, choose “View Status” of your LAN connection. Go to “Properties” and then click “Internet Protocol (TCP/IPv4)” and click the Properties button. You can choose to obtain an IP address automatically (i.e. through DHCP), or you can assign an appropriate, unique IP address. For example, you can choose 192.168.1.2 as the IP address, if it has not been already assigned on the network. Leave the Subnet mask at 255.255.255.0 and type in 192.168.1.1 for the Default gateway.
  2. If you think the IP address of the router has been changed, try one of the following:
    1. Find out the address of the default gateway. In Windows, open the command line by going to Start->Run. Type in “ipconfig” and press Enter. Try visiting the address listed for “Default Gateway” using your browser to get to your router’s Web interface.
    2. Reset your router using the reset button. You should keep the button pressed for about 30 seconds (while powered on) until it restarts. Now, switch off the power supply and switch it on again. This will cause your router to reset the IP address as well as all other settings.
  3. The router’s default IP address could be something other than 192.168.1.1, such as 192.168.2.1. Check the router’s manual or website.

Additional Reading on 192.168.1.1