Learning about slightly more advanced networking with linux
Paul Warren
Mastodon: @pwarren@mastodon.thewarrens.name
email: paul at thewarrens.name
© 2021 Paul Warren
CC BY-NC-SA
! WARNING !
I am not a network engineer, there are gaps in my knowledge
The words I use might not be the correct ones
Please don't blame me if your network stops networking
Maybe don't go and try building an ISP based off this talk :)
What even is a network
Ethernet?
Token Ring?
IPX?
AX.25?
What even is a network
ipv4?
ipv6?
tcp?
Allows connections between computers
Managed network?
Controls connections between computers
Scales connections between computers
Layers!
Like an onion!
That 7 layer thing from the OSI
Ethernet -> IP -> ICMP/TCP/UDP
Administrative overlays
VPNs and Tunnels
Layers!
This means the Physical layers do not have to match the Logical connections
Networks are also a bit fractal in nature
For the purposes of this talk, we can ignore a lot of complexity
An easy one!
VLANS
Ethernet layer
Designed to limit broadcast storms
Can also separate IP networks on the same Ethernet
Tagged and Untagged or Default
VLANs in linux
Are pretty easy!
ip link add link enp0s2 name enp0s2.2501 vlan id 2501
ip -6 addr add 2001:db8:2501::10/64 dev enp0s2.2501
ip link set dev enp0s2.2501 up
VLANs in linux
Various different methods of making it go in different distributions
What even is a router?
Two or more interfaces
Some logic to determine where a packet goes
Linux Routing
net.ipv4.ip_forward = 1
net.ipv6.conf.all.forwarding = 1
net.ipv6.conf.default.forwarding = 1
And we're done!
Yeah, not really :)
Static Routes!
Manually added, or scripted routes that don't change
ip route add 172.17.0.0/24 via 172.16.0.254 dev wg0
What I'm assuming we're familiar with
Diagram showing standard leaf node of a network with a bit cloud containg "The rest of the org"
What we're familiar with
Diagram showing added storage and server network
How things evolve
Uh Oh, we've got a new Datacentre
How things evolve
which has its own lot of storage and servers
How things evolve
And now people want to work in Tasmania!
Dynamic Routing
Open Shortest Path First (OSPF)
The algorithm is pretty interesting
RFC2328
RFC5340
Dynamic Routing
Border Gateway Protocol (BGP)
RF4271
more detail on what VLANs, OSPF and BGP are for
how to do these things in linux
intro to bird
more detail on bird
building out a virtual network with LXC
ergh, NAT
Why use a 'real' router
OpenWRT
Multi Host IPs (Authoritative DNS example like in the facebook thing)
Bonus homework
Why did I use 2001::db8::/32?
Why did I use /64s?
something ansible?
DSA is relatively new, nicer way if interacting with actual switch hardware
Resources
These slides: https://gitea.pwarren.id.au/pwarren/SysAdmin2022
bird: https://bird.network.cz
KNorrie's network examples: https://github.com/knorrie/network-examples
Openwrt: https://openwrt.org/
The OpenWRT IRC channel, currently on the OFTC network
BenEater's "Why was facebook down for five hours"