It is beyond discussion that the full implementation of IPv6 in all Internet services and infrastructures will take place sooner or later. However, a harsh reality has knocked our door a few months ago. The Number Resource Organization (NRO) has warned that the available free IPV4 address space has fallen below 10%, which is considered a critical level.

From this information, the organization has considered the implementation of IPv6 vital if we need to continue with the development of the Internet.

IPv4 addresses, with a length of 32 bits, helped to define the Internet address space that we have been using so far, and have 4,294,967,297 possible IP addresses. In January 2010 the barrier of less than 430 million IP addresses not yet allocated is what has caused this warning.

If we run out of IPv4 addresses this means a halt to the spread of the Internet which has grown in a steady pace since 1989, and that is the main business infrastructure in today’s technology. The key to overcoming this limitation: the global adoption of IPv6.

However, many experts argue that implementing NAT may extend the life of IPv4 a few more years. Personally, I believe that further delaying the full migration to IPv6 simply postpones the implementation of a technology that has long been awaiting implementation, which will enable significant improvements in the operation of the Internet while offering new services. The implementation of NAT at the ISP level will only result in limiting the services available, and also hinder the seamless operation of the Internet when IP addresses are translated.

Moreover, major Internet sectors are already operating with IPv6 (China, Japan, parts of Europe and USA), and Internet infrastructure design is ready to support the migration: there is an international backbone running in IPv6, DNS services have updated their record structure etc… in fact, there is already a fully operational IPv6 www. The full migration will simply allow further evolution of the Internet.

Of course, more important than the hardware requirements that the implementation of IPv6 will impose, are the training requirements for networking professionals. IPv6 will bring another opportunity for professionals to train and grow. There are many resources available to start learning about IPV6, some of them are listed below.

http://www.ipv6forum.com/
Number Resource Organization
http://www.ipv6actnow.org/

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There are different techniques and methods for maintaining accurate routing information, thus different types of routing protocols were invented over the years.

The following post is intended to offer you an overview of the different types of routing protocols currently available.

Distance Vector / Link State

The above terms refer to the algorithms that govern the exchange of routing information and the way the optimal path is identified.

Distance vector protocols exchange information previously incorporated in the device’s routing table. The routers know only their immediate neighbor (one hop away). The link-state algorithms on the other hand, exchange information regarding the status of the links in the whole network topology (they have a bigger picture of the network).

Distance vector protocols require less hardware resources, but are sensitive to the formation of routing loops. Link state protocols require more hardware resources but are more efficient and converge better.

The following are distance vector protocols: RIPv1, RIPv2, IGRP, EIGRP.
The following are link-state protocols: OSPF, IS-IS.

Classless / classful.

Classful protocols publish only the address information of the destination network, not the subnet mask, which forces the device receiving the update to assume that the subnet mask is the same as that on its interface, or the default mask that corresponds to the class.

Classless routing protocols however, advertise the subnet mask together with the network address, so the receiving router has full routing information. This allows the implementation of VLSM and CIDR.

Classful protocols: RIPv1, IGRP.
Classless Protocols: RIPv2, EIGRP, OSPF, IS-IS.

Internal Routing Protocols / External Routing Protocols.
The interior routing protocols (or IGP – Interior Gateway Protocols) are designed to operate within the same administrative domain, which means that each device is “confident” about the information received from others.

Exterior routing protocols (or EGP such as BGP), however, are used to manage routing between different administrative domains. In EGP, each administrative domain is independent. It has implemented its own routing policy.

Interior routing protocols: RIPv1, RIPv2, EIGRP, OSPF, IS-IS.
Exterior Routing Protocol: BGPv4.

This is a post for people new to networking that have just started learning IP addressing and the basis of routing and subnetting.

Every host or device on a TCP/IP network MUST have an IP address assigned in order to communicate with other devices. An IP address consists of a network part and a host part. Think about the Network part as a multi dueling Building Address number, and the Host part as your apartment number inside this building. For example, building address “Building XYZ” is the network IP address part, and “Apartment number 2” is the host address part.    

For example IP address 10.0.0.2 which identifies a single host, contains the network part 10.0.0 and the host part 2. Now, how do devices on the network know which portion is the network part and which is the host part of their assigned IP address? They know this information using the “Subnet Mask”. Every host on a TCP/IP network is configured with an IP address AND a subnet mask. The subnet mask is the one which identifies the Network Part portion of the IP address assigned to the host. For our example above, the host with IP 10.0.0.2 is assigned also a subnet mask 255.255.255.0. If you do a logical AND operation between the IP address and the subnet mask, you will find the Network potion of the address:

10.0.0.2 AND 255.255.255.0 = 10.0.0.0  (The network part is 10.0.0 and the remaining part is the host part. i.e 2 ).

Let’s see a diagram below:

From the picture above, Host A and Host B belong to the same local subnetwork (10.0.0.0/24) and are connected to the same switch together with a router interface. The router interface has also an IP address 10.0.0.254 with the same subnet mask 255.255.255.0 as the two Hosts.

Also, two other hosts (Host C, Host D) belong to another subnetwork (10.1.1.0/24) together with the second interface of the router which has address 10.1.1.254.

Each host has also a default gateway assigned (in addition to IP address and Subnet Mask). Hosts A and B must be configured with a default gateway address of the router interface which is 10.0.0.254. Similarly, Hosts C and D must be configured with a default gateway address of their router which is 10.1.1.254.

How Hosts use the Subnet Mask

When a host wants to communicate with another host, it uses its subnet mask to compare the network portion of its local network IP address with the destination network address of the packet to be sent. Before an end system can send a packet to its destination, it must first determine whether the destination address is on the local network. This is done by comparing the bits in the destination address with the network bits of its own IP address. For example, if Host A wants to send a packet to Host B, it will take the destination address 10.0.0.2 (Host B) and perform an AND operation with its subnet mask. The result will be 10.0.0.0 which will tell Host A that the destination address belongs to the same subnetwork as itself. Therefore it will NOT send the packet to the default gateway (router). Rather, Host A will perform an ARP request (Address Resolution Protocol) to find out the destination MAC address of Host B (ARP protocol maps an IP address with a MAC address). Therefore, Host A will send the packet directly to Host B through the switch without going through the router.

Now, if Host A wants to send a packet to Host C, it will take the destination address 10.1.1.1 of Host C and perform an AND operation with its subnet mask. The result will be
10.1.1.1 AND 255.255.255.0 = 10.1.1.0
which will tell Host A that the destination address has a different network portion than itself (10.1.1). Therefore Host A will have to send the packet to its default gateway (router address 10.0.0.254) in order to reach Host C on the other side of the router.

Extending the central office enterprise environment to remote branch office locations gives employees greater flexibility while enhancing productivity and reducing costs. Cisco Virtual Office solution is an umbrella of technologies and products that delivers secure data, voice, and video communication to remote teleworkers and branch offices, providing to remote employees a seamless office-caliber experience to wherever they may be located.

A high level network topology of two remote branch offices with the enterprise central site is shown in the figure below:

The components that constitute the Cisco Virtual Office solution include the following products and technologies:

 REMOTE BRANCH LOCATION:

 In the remote user premises, the equipment includes Cisco 800 series ISR (Integrated Services Routers) to provide secure IPSEC VPN connectivity towards the central site, together with unified 7900 series IP Phones that offer voice and video communication with the central call manager system.

 CENTRAL SITE LOCATION:

 The equipment and technologies here include a VPN termination device (which can be either a VPN router or a Cisco ASA Firewall), central call manager system for voice and video control, and central management software for policy enforcement, authentication services, identity management etc.