The Functions of Routing

Within routing there are three main topics that cover a variety of areas on how routing takes place within systems. A few of the basic things to know about routing include addressing technologies and addressing schemes such as NAT, PAT, and SNAT. Another would be to know the common IPv4 and IPv6 networking protocols, and most importantly knowing how routers work giving the tools used today. Routing enables everyone to interconnect individual LANs into WANs. Within the three topics are sub topics that must be explained along with the three over all topics of routing those include various terms and properties.

Addressing technologies and addressing schemes such as NAT, PAT, and SNAT are important to know for security and other reasons when creating a network. NAT is defined as the process of mapping addresses on one network to addresses on another network. The first thing to understand about routing over a network using NAT is that it works by replacing the source IP address of a computer with the source IP address from the router on outgoing packets. “When private addresses are used for hosts and mapped to public addresses through NAT, external hosts cannot initiate connections directly to the internal hosts because private addresses are not routable across the internet. Thus, all attacks against the network must be focused at the NAT router itself. Like firewalls, this provides security because only one point of access must be protected, and the router will generally be far more secure than a PC directly connected to the internet. The abstraction of the LAN from the internet through a NAT also simplifies network management.” (http://en.wikipedia.org/wiki/Network_address_translation) A Static NAT (SNAT) is another form that maps a single routable IP address to a machine so there is accessibility from outside the network. This also keeps track of the IP addresses and applies them permanently on a one to one basis with computers on the network. It’s defined as “a type of NAT in which a private IP is mapped to a public IP address, where the public address is always the same IP address (i.e., it has a static address). This allows an internal host, such as a web server, to have an unregistered (private) IP address and still be reachable over the internet.” (http://www.webopedia.com/TERM/S/static_NAT.html) A PAT is a network address translation and goes through a process where each computer on LAN is translated to the same IP address, that have a different port number.

IPv4 and IPv6 common routing protocols cover a wide range of concepts. One of the things to understand when dealing with routing is the link state routing protocol which has information passed down between routers that are related to the current connectivity. This is basically strait forward stating that if the signal is up it will connect if it’s not you won’t. The link state is very scalable and because of that it’s used most often in large networks. OPSF stands for open shortest path first and it works by choosing the shortest path first. OPSF routers are grouped logically into areas; each area has its own database and links with 0 being the default area. Each link has a cost such as throughput, reliability and round trip time. The lowest cost is the first choice, while identical costs are load balance. OPSF detects changes in the network link state and modifies the routing structure very quickly usually within seconds. The IS-IS is seen most often in large provider networks, there are two different levels the first routs within an area the second routs between areas. IS-IS stands for intermediate system to intermediate system and because there is less chatty many service providers like it over OSPF. An important routing protocol of RIP is the distance vector which has information passed between routers containing routing tables. This means that it determines how many hops away is another network which is basically the distance. With this there is very little configuration and is usually automatic. However, this is good for small networks because it doesn’t scale well in large networks. RIP 1 and RIP2 meaning the routing information protocol was updated and version two includes authentication to verify the source. This deals with network address, number of hops and destination, the maximum number of hops is 15. Boarder gateway protocol is the core routing protocol of the internet that is fully decentralized and is used by ISP’s. This allows multhoming which is multiple links to the same network. Hybrid is the last thing that includes aside from a little link state and distance vector an EIGRP which makes is reliable and use minimum bandwidth.

Routing enables everyone to interconnect individual LANs into WANs. The properties of routing include things such as Dynamic and static routing, dynamic routing is automatic all routing is handled by the protocol. Static Routing is a manual process; if you’re going on network 1 to network 2 then the tables set will that if to a link to get to the second network. When understanding routing, the next hop is another key for input and output of information across the network. A router isn’t generally concerned with the rest of the network, when a packet comes in a packet goes out. The next hop is a crucial piece of information which is why a router exists. The router determines where should a packet go and if it should go to the next hop.