[RndTbl] wireless basics

Kevin McGregor kevin.a.mcgregor at gmail.com
Sat Jan 21 20:50:05 CST 2012

I would make a stab at answering your questions, but Sean and Adam have
already responded, and they're better qualified, anyway. :-)

If you have time, however, take a look at the on-line Cisco materials, such
I just found that now, spurred by seeing your questions. I'll try to find
time to go through it myself; I'm sure I would benefit.


CTT-TAC: Basic IP Routing Concepts
Detailed Information

In this module, you will gain a fundamental understanding of IP routing.
You will also do hands-on Interface and Configuration Labs. In addition,
you will also learn basic Cisco IOS IP routing commands.

At the end of this tutorial, you will be able to:

   - Understand local-area networks and data-link addressing.
   - Describe the difference between a bridge and a router.
   - Discuss the basic functionality of a routing table and how routers
   - Understand network addressing.
   - Identify IP addresses by class and calculate subnetting and subnet
   masks according to addressing needs.
   - Discuss IP routing fundamentals.
   - Understand other Internet protocols such as Address Resolution
   Protocol (ARP) and Internet Control Message Protocol (ICMP).
   - Identify the differences between a routed and a routing protocol.
   - Describe the two fundamental functions of a routing protocol: path
   determination and path switching.
   - Define the term *routing metrics *and describe how routing metrics
   - Define the term *routing algorithms *, describe how they work, and
   understand types of algorithms.
   - Define routing loops and understand methods to use to avoid them.
   - Configure, troubleshoot, and maintain IP routing, using the
   appropriate Cisco IOS commands.
   - Configure a default gateway.
   - Configure a static default route.
   - Configure IP unnumbered.
   - Configure secondary IP addressing.

On Sat, Jan 21, 2012 at 7:22 PM, Dan Martin <ummar143 at shaw.ca> wrote:

> Thanks for the reply, Sean.
> On 2012-01-21, at 6:21 PM, Sean Cody wrote:
> > 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.
> ... but you don't need a MAC address to route a frame to someone else?
> >   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.
> The Linux gateway shows in routing tables etc.  Default traffic is
> directed to it via the NIC which is visible on the LAN side.
> The airport extreme is completely invisible.  If I didn't see the utility
> showing 2 MAC addresses and an IP address (does it map to one of the MAC
> addresses?)  I wouldn't even know it was there.  But the entire network is
> connected to the gateway via the router (some wired, some wireless).
> Does this have something to do with selecting Bridge mode?
> > 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.
> Is the WAN port different, then?  Here the WAN port is connected to the
> gateway machine (private IP address).  Even though it is not 'WAN'
> connected, I make a point to put it 'upstream', closer to the internet.
>  Does it matter?
> >
> > 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 at 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 at shaw.ca
> >> (204) 831-1746
> >> answering machine always on
> >>
> >>
> >> _______________________________________________
> >> Roundtable mailing list
> >> Roundtable at muug.mb.ca
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> >
> > _______________________________________________
> > Roundtable mailing list
> > Roundtable at muug.mb.ca
> > http://www.muug.mb.ca/mailman/listinfo/roundtable
> Dan Martin
> GP Hospital Practitioner
> Computer Scientist
> ummar143 at shaw.ca
> (204) 831-1746
> answering machine always on
> _______________________________________________
> Roundtable mailing list
> Roundtable at muug.mb.ca
> http://www.muug.mb.ca/mailman/listinfo/roundtable
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