Routing
Router
A network device that forwards traffic depending on the destination address of that traffic
Basic Routing
A router
- Receives data packet
- Looks up IP destination network in routing table
- Forwards traffic to destination
Routing Table
Destination Network
definition of remote network
network ID & Subnet Mask or CIDR
Routing Table generally has "Catch All Entry" that matches any IP address that doesn't have explicit network listing for
Next Hop
IP address of the next router that should receive data intended for the destination network in question
Total Hops
for each next hop and each destination network, the router have to keep track of how far away the destination currently is. That way, when it receives updated information from neighbouring routers, it will know if it currently knows the best path or if it knew better path is available.
Interface
the router should also know which of its interface it should forward traffic, matching the destination network out of.
Interior Gateway Protocols
Routing Protocols
*Interior gateway protocols are further split into two categories: Link state routing protocols and distance-vector protocols.*
Interior gateway protocols
Used by routers to share information within a single autonomous system
Autonomous System
A collection of networks that all fall under the control of a single network operator
The two main types of interior gateway protocols are link state routing protocols and distance-vector protocols.
Distance-Vector Protocols
Old one. Very slow and inefficient.
A router send whole list, or vector in other words, of routing table to other routers that are directly connected. A router only know the state of nearby routers, not the whole autonomous system. If the whole system is large enough, it will be slow for all routers in that system using distance-vector protocols to react to the changes, updating its routing tables.
Link State Protocols
Sophisticated way of determining best path to a network
Each router advertises the state of the link of the each of its interfaces. These interfaces can be connected to other routers or there could be direct connection to the networks. The information about each router is propagated to every other routers on the autonomous system. Every router on the system knows every details about every other router on the system.
Requires both more memory in order to hold all this data and also much more processing power.
Link state protocols > Distance-vector protocols
Exterior Gateway Protocols
Used to communicate data between routers representing edges of an Autonomous System. Since routers sharing data using interior gateway protocols are all under control of the same organization, routers use exterior gateway protocols when they need to share information across different organizations.
Getting data to the edge router of Autonomous System is the number 1 goal of core internet routers.
Internet Assigend Numbers Authority (IANA)
A non-profit organization that helps manage things like IP adress allocation
Along with managing IP address allocation, the IANA is also responsible for ASN, or Autonomous System Number allocation.
Autonomous System Number (ASN)
Numbers assigned to individual autonomous systems
32 bit numbers, but single decimal number
ASN and how core internet routers route traffic between them is important to understand some of the basic building blocks of the internet.
Non-Routable Address Space
32 bit number = 4,294,967,295 unique numbers
The IPv4 standards doesn't even have enough IP addresses available for every person on the planet.
1996 RFC 1918 was published
It outlined number of networks would be defined as non-routable address space.
Non-routable address space allows for nodes on such a network to communicate each other but no gateway router will attempt to forward traffic to this type of network.
The primary three ranges of non-routable address spaces
- 10.0.0.0/8
- 172.16.0.0/12
- 192.168.0.0/16
