In short every Ethernet device that expects to be addressable on an ethernet will have a MAC address. The device will then use the ARP protocol to turn MAC addresses into IP addresses (and vice versa for RARP). Then things will look as you expect. You need a MAC to be a node on an Ethernet that is to send an receive frames for and to yourself. Cheap switches and some 'invisible' routers do not because they do not participate in the network they just act as a bridge (which is a other type of device) between two networks. They use MAC addresses to differentiate items on the switch but don't need their own because they are not an addressable node on the network. You don't pass traffic _to_ them but _through_ them.
An access point like the airport express is almost exactly the same as your Linux gateway.
A router is the same. In a wireless access point you transceive Ethernet frames into wireless ethernet frames and vice versa. Everything operates as you expect but encapsulated in a wireless radio protocol.
This whole WAN LAN is unnecessarily confusing. A commodity router's WAN port is an uplink to your ISP. It is still a LAN port just is expected to uplink outside.
In 'bridge' mode a device is only concerned with forwarding frames so any other services the device has is turned off (like dhcp and nat). Most wireless access points are bridges and if they have dhcp/nat/firewall features they get called wireless routers. Most wireless routers can be configured 'down' to being access points and not necessarily vice versa.
Anyways, hope that helps.
--
Sean (mobile)
On 2012-01-21, at 4:19 PM, Dan Martin
ummar143@shaw.ca wrote:
> I want to do some (hopefully minor) tinkering with my wireless network, but it is clear that I don't get some basic concepts. To help me visualize my network at the NIC / MAC address level, could someone explain who has MAC addresses and why?
>
> I have a network connected (indirectly) to a cable modem. A linux box serves as a gateway. It is connected by ethernet to the WAN port of an airport extreme base station. 2 windows machines are connected to LAN ports on the base station. 1 windows machine and 2 Macs are connected by wireless. All the machines have manually assigned IP addresses, and the base station is configured in "bridge mode" since it appears the other options involve NAT or DHCP.
>
> My gateway box is acting as a router. It has 2 NICs (hence 2 MAC addresses), 1 for inet connection and 1 to the LAN.
>
> When I used a CentreCom router, on the other hand, it appeared invisible, or at least I wasn't aware of any MAC addresses for the router.
>
> The utility for the base station lists what appears to be 2 MAC addresses: an "AirPort ID" and an "Ethernet ID". I have assigned the base station an IP address.
>
> The Mac computer I'm using, attached by wireless, does not show the base station in the routing tables [except the "Ethernet ID" does show in the IPv6 tables]. traceroute shows only a single hop to the gateway.
>
> Am I to assume that dedicated routers - unlike my Linux gateway - appear invisible in the network and just magically connect nodes to each other? If so, what are the MAC addresses on the base station for? Just to access the box itself for configuration? To access something connected to its USB port?
>
>
> Dan Martin
> GP Hospital Practitioner
> Computer Scientist
> ummar143@shaw.ca
> (204) 831-1746
> answering machine always on
>
>
> _______________________________________________
> Roundtable mailing list
> Roundtable@muug.mb.ca
>
http://www.muug.mb.ca/mailman/listinfo/roundtable
