subnets

In this series we'll set up a Samba server that serves two subnets, which is is a common scenario even on home networks: one wired and one wireless.

LXer Linux News 2008

Many large organizations find it convenient to divide their network number into "subnets".

The KA9Q Internet Software Package by Bdale Garbee 1989

Each gadget will need its local port map, specifying what each port is to do - for ports connecting to computers, which subnets to provide; for ports used as trunks between gadgets, perhaps a shared secret so that the traffic can be encrypted, as somebody tapping into that link could let themselves onto subnets they're not allowed to.

Snell-Pym » Why are networks so hard to build? 2009

Now, you can organise your uptime requirements by putting in multiple routers between given pairs of subnets, easily enough; then any one router or the cables connecting it, or the switches its subnets go through can fail and there'll be another path.

Snell-Pym » Why are networks so hard to build? 2009

Since routers tend to have low numbers of actual ports to plug cables into, it's normal to either have a bunch of routers, each talking to a number of subnets or connections to external networks, and then all connected to a special "backbone" subnet set up purely for the routers to communicate with each other.

Snell-Pym » Why are networks so hard to build? 2009

But sometimes you are limited to a single subnet over the inter-site cable, and sometimes not even that; sometimes you are restricted to a leased line over which you can only carry a tiny subnet with two IPs, to join two routers, and you cannot have any proper inter-site subnets, and need to have routers joining the inter-site link to backbone subnets in each site.

Snell-Pym » Why are networks so hard to build? 2009

All subnets can be trunked onto the links between gadgets, along with a special internal VLAN for gadgets to communicate with each other directly.

Snell-Pym » Why are networks so hard to build? 2009

Each switch can carry multiple subnets, using VLANs, and if a subnet exists on multiple switches, we need a 'trunk' cable joining the two switches which can carry multiple VLANs using tagging.

Snell-Pym » Why are networks so hard to build? 2009

SIXXS provides both tunnels(/64) and subnets(/48).

IPv6 to the people! magnio 2009

This means that, while the backbone subnets can have lots of routers on them quite happily, all talking OSPF and BGP to share their routes between each other and so route traffic to the right router to forward it on, edge subnets prefer to have just a single router.

Snell-Pym » Why are networks so hard to build? 2009