How does Internet routing work?
I have dabbled with networking protocols and TCP/IP suite for over 27 years.
Let us examine how Internet routing and packet forwarding works behind the scenes.
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I have dabbled with networking protocols and TCP/IP suite for over 27 years.
Let us examine how Internet routing and packet forwarding works behind the scenes.
๐งต
Simple packet forwarding
The web is connected by networks and routing devices.
Once a map of the connected networks is available then the job of the forwarding devices is quite easy.
Simply send to the right place.
The web is connected by networks and routing devices.
Once a map of the connected networks is available then the job of the forwarding devices is quite easy.
Simply send to the right place.
But how to get there in first place?
Most of the complexity we find is in making this network map.
To understand network maps we must know addressing and subnets.
IP addressing uses subnets and masks.
Most of the complexity we find is in making this network map.
To understand network maps we must know addressing and subnets.
IP addressing uses subnets and masks.
An IP address always has a host part and a network part.
All IP addresses in a given network always have identical network part or octets.
And the network part comes first.
The routing table in each edge device in the network ferries packets between networks.
All IP addresses in a given network always have identical network part or octets.
And the network part comes first.
The routing table in each edge device in the network ferries packets between networks.
The routing protocols on Internet
There are two types:
- exterior gateway protocol
- interior gateway protocol
OSPF is very complex, it is interior gateway protocol.
BGP is the routing engine of the Internet used by core routers.
They work using AS == autonomous systems.
There are two types:
- exterior gateway protocol
- interior gateway protocol
OSPF is very complex, it is interior gateway protocol.
BGP is the routing engine of the Internet used by core routers.
They work using AS == autonomous systems.
Since today's Internet works in a classless way the CIDR prefix determines the network to route to.
Once the routing topology of the connected devices is known a simple map or tree or graph is created by routers to keep track of changing topologies.
Once the routing topology of the connected devices is known a simple map or tree or graph is created by routers to keep track of changing topologies.
The routing protocols have timers that determine the liveness or caching of information.
It goes out and explores the Internet to fetch topology changes and updates the database in memory.
It is similar to DNS but much more complex.
It goes out and explores the Internet to fetch topology changes and updates the database in memory.
It is similar to DNS but much more complex.
All sorts of combinations
In today's world you have IoT devices, phone devices, laptops , servers and other endpoints.
In terms of networks you have Wifi, Ethernet, Fiber optic cables, mobile wireless, satellite, mircrowave towers.
In today's world you have IoT devices, phone devices, laptops , servers and other endpoints.
In terms of networks you have Wifi, Ethernet, Fiber optic cables, mobile wireless, satellite, mircrowave towers.
But routing does not care
Although the Internet is so diverse in which much of the traffic traverses oceans through undersea fiber cables, the routing does not care about physical or link layer differences.
Routing is layer III of the OSI model.
Although the Internet is so diverse in which much of the traffic traverses oceans through undersea fiber cables, the routing does not care about physical or link layer differences.
Routing is layer III of the OSI model.
Resilience and fault tolerance
Due to the inherent character of packet switched networks in which forward and reverse path could be different, the path taken by each packet could change, Internet is basically tolerant to failures.
Due to the inherent character of packet switched networks in which forward and reverse path could be different, the path taken by each packet could change, Internet is basically tolerant to failures.
Routing changes are minimal
Due to the BGP timers and discovery process and due to the hierarchy of routing protocols and delegation of responsibilities packet switching is quite robust and durable.
Due to the BGP timers and discovery process and due to the hierarchy of routing protocols and delegation of responsibilities packet switching is quite robust and durable.
How it all works together?
Once the map is created, every packet is inspected for header fields like IP address and other IP layer bits and flags and forwarding is a simple process of identifying the physical interface to send to.
Once the map is created, every packet is inspected for header fields like IP address and other IP layer bits and flags and forwarding is a simple process of identifying the physical interface to send to.
That is a wrap.
TL;DR
- routing, addressing, forwarding
- BGP is core router protocol
- Internet runs on BGP
- OSPF is within AS
- Topology changes are detected with timers
- It is entirely packet switched
- Physical/Link layers are diverse
Follow @girish1729 for such topics.
TL;DR
- routing, addressing, forwarding
- BGP is core router protocol
- Internet runs on BGP
- OSPF is within AS
- Topology changes are detected with timers
- It is entirely packet switched
- Physical/Link layers are diverse
Follow @girish1729 for such topics.
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girish1729.gumroad.com
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