[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
as
http://www.cisco.com/web/learning/le31/le20/ssat/cim/tac_basic_ipr.html
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.
Kevin
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.
Objectives:
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
work.
- 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
work.
- 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
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> >
> > _______________________________________________
> > Roundtable mailing list
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>
> 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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