MAC codes - a real technical reason for them?

  eddieareader 06:54 30 Jul 08
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I understand the procedural role for MAC codes but is there an actual technical reason to do with the way TCP packets are routed?
If you search on these codes only the UK seems to have them. The explanations I have read, allowing a BT engineeer to identify the connection, are procedural and not technical. Furthermore, since these codes last only 30 days why are these connections so nomadic?
I have just been migrated from a Bulldog server that I had been on for years and years to a Tiscali one courtesy of Pipex. Their migration process was poor but simply involved me entering a new userid and password into my modem. I am obviously running on a different server, as if I had changed ISP, so why these MAC codes when a different login is all that is required?

  Jim_F 08:27 31 Jul 08

There are two definitions for the term.

Migration Access Code is part of the Ofcom migration process and is used when both providers use shared (BT) resources - as you point out these codes are created soley for this migration but in the right circumstances can be used to reroute traffic between ISPs with no break in service (migration rather than cease and provide). click here

Machine Access Code is no relation to the above-it is a unique code provided on the firmware of your network card-it can be changed or even spoofed by a router so its value for security purposes is limited but ISPs can use the MAC of either your modem or the first connected item of network kit to identify your connection.

  recap 09:39 31 Jul 08

In a local area network (LAN) or other network, the MAC (Media Access Control) address is your computer's unique hardware number. (On an Ethernet LAN, it's the same as your Ethernet address.) When you're connected to the Internet from your computer (or host as the Internet protocol thinks of it), a correspondence table relates your IP address to your computer's physical (MAC) address on the LAN.
The MAC address is used by the Media Access Control sublayer of the Data-Link Layer (DLC) of telecommunication protocols. There is a different MAC sublayer for each physical device type. The other sublayer level in the DLC layer is the Logical Link Control sublayer.

All network interface cards (NIC) have a MAC it is a string of alpha numeric characters like: 00-31-22-36-E5-AA

This article click here from Microsoft explains what TCP addressing is down to the binary level.

  Jim_F 15:08 01 Aug 08

Agreed - the 'Media Access' definition is the more common - AFAIK 'Media' and 'Machine' codes are used interchangeably.

I think its wrong to say MACs are unique - the last two NICs I installed had MACs set to null by default and MAC spoofing is essential to home networking.

When broadband started most ISPs only supported connection to a single computer so they would connect to it, test it and then walk away. Then you set up your own router to spoof the PC MAC and provide local addresses to each computer using address translation. Duplication of the MAC doesn't matter as the router effectively puts these in two seperate networks but is essential if your broadband ISP will only support and test to one computer identified by its MAC.

  eddieareader 16:38 03 Aug 08

Thanks for the updates. My understanding of these is that these MAC (Migration Access Codes) codes are in fact a UK only procedural barrier, or at least have nothing to add technically.
I say this because if I search on yahoo.co.uk I get loads of problems with getting codes, migrating codes, etc. If I look on Yahoo.com (i.e. US) I get a typical American situation where the authorities are promoting competition rather than acting in collusion with existing players to reduce competition. This in in marked contrast to the UK where competion, be it in the Premier League, NHS, banks, energy providers or broadband providers is very un-British.
Search as I might I find no US based information relating to this migration code, only UK ones (and I am searching the US version of Yahoo). So either Americans never change their ISPs (highly improbable) or the FCC ensures a competitive market (highly probable).
This piece of advice from a US business site regarding ISP change makes (as far as I can see) no mention of migration codes
click here
Ofcom should do better.
The Machine Access Code explanation does, however, hold water against the US experience as being the means by which an ISP may assign an IP adddress to a router. This will not change within 30 days, indeed it would seem that technical wizadry allows a consumer to switch between ISP's by the mere act of changing the userid and password - as one would expect.

  Jim_F 18:51 03 Aug 08

Hi eddyreader,

I may have not explained it very well but as the link you posted makes clear in the US you can be left high and dry while one ISP disconnects your old service and the new one provides your new service - the Ofcom MAC should make sure this does not happen.

To be fair Ofcom has to implement our regulations - which allow ISPs to provide DSL services in a number of ways including direct connection to the copper wires which enter your house or connection via a datastream from BT equipment. Changing an ISP requires your data to be directed to a different service provider. This can be done by physical means (cabling) or electronic (rerouting via a telecoms switch).
I think the migration codes currently relate to the latter but they could identify where your copper wires appear on a distribution frame for cabling purposes.

The Machine/Media code from your network card is used by the ISP to determine if they will grant you an address (some use the MAC from the modem)-the password/id won't do it if your IP traffic doesn't route to them.

The address is generally granted for 2-3 days but this is dynamic so if you power cycle your equipment you could get another address - it won't normally change unless the network is overloaded but it can.

I hope this helps explain...

(BTW I have no connection with Ofcom or any telco)

  Jim_F 18:53 03 Aug 08

In the third para from last I should have said 'the IP address' :)

  AlHill 09:23 04 Aug 08

Hi Jim,

Thanks for the above comments. Quick question though, does anyone know why Ofcom doesn't make it mandatory for service providers to provide MAC codes online, making it easier for people to switch providers?

I am just in the process of switching providers, and at the start I couldn't find any details on my current providers web site of how to obtain a MAC code, or a number to call. I had to use a 3rd party site to understand the process and get a number to call click here, and when I finally did get through to my service provider after 30 minutes, they spent a further 30 minutes trying to persuade me to stay. Not the easiest or quickest process in the world, would be nice if someone could help make it a lot simpler...

  Jim_F 22:08 07 Aug 08

Hi AlHill,

I waited to see if anyone has a better answer but I think its down to diversity of the way the systems are/can be connected.

The MAC code is actually provided to the ISP by their wholesale provider and it will change as bandwidth is reassigned (as your ISP grows it will gain larger bandwidth routes). I'm not saying it can't be done but its the wholesalers (network operators) who would need to track your connection and its routeing and update this as a MAC.

  AlHill 12:03 08 Aug 08

Thanks Jim, appreciate the feedback

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