ITIS 107 - Chapter 8 - Routing

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Routers

A router is any piece of hardware or software that forwards packets based on their destination IP address. Routers work, therefore, at the Network layer of the OSI model and at the Internet layer of the TCP/IP model.

Every router will come with a routing table. 0.0.0.0 on the routing table means send to any router.

These routers have interfaces which are the physical ports available on the device.

Metric : A relative value that defines the "cost" of using this route. The power of routing is that a packet can take more than one route to get to the same place. If a route were suddenly cut off, then you would have an alternative.

NAT (Network Address Translation)

NAT hides the IP addresses of computers on the LAN but still enable those computers to communicate with the broader Internet. NAT extended the useful life of IPv4 addressing on the Internet for many years. NAT is extremely common and heavily in use, so learning how it works is important.

NAT is used to hide the LAN IP addresses to the public keeping the private internal addresses hidden.

PAT (Port Address Translation)

PAT uses port numbers to map traffic from specific machines in the network.

SNAT (Static NAT)

SNAT maps a single routable (that is, not private) IP address to a single machine, enabling you to access that machine from outside the network. The NAT keeps track of the IP address or addresses and applies them permanently on a one-to-one basis with computers on the network.

Distance

RIP v1

Every 30 seconds it advertised the routing tables.

Hops are the amount of routers it can travel to before the packet dying.

15 maximum hops

Type : Distance Vector

IGP or BGP : IGP

RIP v2

15 Maximum hops

30 second advertisement of routing table.

Little bit faster than RIP v1.

Type : Distance Vector

IGP or BGP : IGP

BGP (Border Gateway Protocol)

AS (Autonomous System)

Two 16-bit numbers separated by a dot making 32 bits.

BGP v4

Type : Distance Vector

IGP or BGP : BGP

Link State Protocol

Sends incremental routing tables.

OSPF (Open Shortest Path First)

This protocol will use the least amount of hops to reach it's destination. Once all of the routers are in convergence they send each other LSA Hellos to every router on the network.

Type : Link State

IGP or BGP : IGP

IS-IS (Intermediate System)

IS-IS is the de facto standard for ISPs. IS-IS is a link state dynamic routing protocol.

Type : Link State

IGP or BGP : IGP

EIGRP (Enhanced Interior Gateway Routing Protocol)

Type : Hybrid Protocol

IGP or BGP : IGP