Some pretty pictures, and definitions and thoughs.

So I thought I'd do some pictures of some of the common and possible configurations that people might have out there.

First a few thoughts and definitions:

What defines a router?
Any node that is running a BGP daemon and advertising an AS number and routes.
eg. a Linux box, A Cisco router, A Windows NT/2K/XP box, and embeded system.

Who gets a /24 IP range?
Anyone the needs a range bigger then the AP they connect to can allocate. Eg The AP you connect to is allocating smaller ranges then you need for all your nodes.

What is an Autonomous System?
And Autonomous System (AS) is a network or group of networks with have a consistant exteriour routing policy. In practice, a network controlled by one person / organisation is a good enough definition for now.

What is multihoming?
Multihoming is a term given to the idea of having more then one link to a wider network, and router connected to more then one other AS could be considered multihomed.

Who gets an Autonomous System Number (ASN) to advertise routes?
Any router that is multihomed, that is the router connects to more then one existing AS. Eg A router that connects to two AP's that are allready running BGP and have different ASN's.


That's all I could think off that may help clear some things up. As promised, a pretty picture:


Short Description of each AS.

AS123
This node connets to multiple other AP's and has it's own IP range. It has clients directly connecting to it.

AS124
A large network with a router conencted to multiple AP's and has a large number of users connected via a LAN. Due to the number of users, NAT is not effecient so all users have IP's allocated from the AP's range.

AS125
Kinda of a AP hub, One router feeding other AP's via Point-Point or Point-Multipoint. The AP's just act as relays and do no more than provide connections. IP's are allocated by the DHCP server on the router, not the AP the user connects to.
A cheap way to put in another AP is use a directional antenna on an AP, in client mode, a cross over ethernet cable into another AP, in AP mode, and put and omni on it.

Non-multihomed systems
Any of these setups could be done with only one connection to another AP. These systems would not be allocated, or need an ASN. They could advertise the ASN of the router they connect, if they wanted to use dynamic routing (for one route it's a bit pointless though).

Multi-router systems
An AS may have more then one router, these would all advertise the same ASN.

In reality
In reality most setups will be a combination of these, some will be more complex than others, some will have other internal routers, local internet connections etc that will not be visible from the outside.


Well that ends some random thoughts from Mike, if anyone has any comments, questions, thoughts on anything I have presented here. Feel free to post a reply here. My email is broken so this is the best place to get me.

- Mike :-)

it seems your picture link is also broken, I get timeouts

Thanks, fixed now :-)