I would make a stab at answering your questions, but Sean and Adam have already responded, and they're better qualified, anyway. :-)<div><br></div><div>If you have time, however, take a look at the on-line Cisco materials, such as</div>
<div><a href="http://www.cisco.com/web/learning/le31/le20/ssat/cim/tac_basic_ipr.html">http://www.cisco.com/web/learning/le31/le20/ssat/cim/tac_basic_ipr.html</a> </div><div>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.</div>
<div><br></div><div>Kevin</div><div><br></div><div><div class="clearfix" id="mb-title-nav-bar" style="margin-top:15px;margin-right:0px;margin-bottom:0px;margin-left:0px;padding-top:0px;padding-right:0px;padding-bottom:0px;padding-left:0px;clear:both;font-family:arial,helvetica,sans-serif;font-size:12px">
<div id="framework-content-titles" style="padding-top:0px;padding-right:10px;padding-bottom:0px;padding-left:0px"><h2 class="title-page" style="margin-right:0px;margin-bottom:0px;margin-left:0px;padding-top:4px;padding-right:0px;padding-bottom:11px;padding-left:9px;font-family:Arial,Helvetica,sans-serif;font-size:26px;line-height:1em;color:rgb(68,68,68);border-bottom-width:1px;border-bottom-style:solid;border-bottom-color:rgb(204,204,204);font-weight:normal">
CTT-TAC: Basic IP Routing Concepts</h2></div></div><table id="framework-base-main" cellspacing="0" cellpadding="0" border="0" summary="" style="margin-top:15px;margin-right:0px;margin-bottom:20px;margin-left:0px;padding-top:0px;padding-right:0px;padding-bottom:0px;padding-left:0px;width:960px;border-top-width:0px;border-right-width:0px;border-bottom-width:0px;border-left-width:0px;border-style:initial;border-color:initial;empty-cells:hide;vertical-align:top;background-image:initial;background-color:initial;color:rgb(0,0,0);font-family:arial,helvetica,sans-serif;font-size:12px">
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<tbody><tr><td id="framework-column-main" style="vertical-align:top;padding-top:0px;padding-right:0px;padding-bottom:0px;padding-left:0px;margin-top:0px;margin-right:0px;margin-bottom:0px;margin-left:0px;width:959px"><div id="framework-content-main" style="margin-top:0px;margin-right:5px;margin-bottom:0px;margin-left:5px">
<a name="content"></a><table width="645"><tbody><tr><td scope="col" width="637"><h1 class="style8" align="right" style="font-family:Arial,Helvetica,sans-serif"><span style="background-color:initial;font-size:12px">Detailed Information</span></h1>
<p class="style6" align="left" style="font-size:12px;font-family:Arial,Helvetica,sans-serif">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.</p>
<h1 class="style8" align="left" style="font-family:Arial,Helvetica,sans-serif">Objectives:</h1><p align="left" class="style6" style="font-size:12px;font-family:Arial,Helvetica,sans-serif">At the end of this tutorial, you will be able to:</p>
<ul><li>Understand local-area networks and data-link addressing.</li><li>Describe the difference between a bridge and a router.</li><li>Discuss the basic functionality of a routing table and how routers work.</li><li>Understand network addressing.</li>
<li>Identify IP addresses by class and calculate subnetting and subnet masks according to addressing needs.</li><li>Discuss IP routing fundamentals.</li><li>Understand other Internet protocols such as Address Resolution Protocol (ARP) and Internet Control Message Protocol (ICMP).</li>
<li>Identify the differences between a routed and a routing protocol.</li><li>Describe the two fundamental functions of a routing protocol: path determination and path switching.</li><li>Define the term <em>routing metrics </em>and describe how routing metrics work.</li>
<li>Define the term <em>routing algorithms </em>, describe how they work, and understand types of algorithms.</li><li>Define routing loops and understand methods to use to avoid them.</li><li>Configure, troubleshoot, and maintain IP routing, using the appropriate Cisco IOS commands.</li>
<li>Configure a default gateway.</li><li>Configure a static default route.</li><li>Configure IP unnumbered.</li><li>Configure secondary IP addressing.</li></ul></td></tr></tbody></table></div></td></tr></tbody></table></td>
</tr></tbody></table></div><div><br><div class="gmail_quote">On Sat, Jan 21, 2012 at 7:22 PM, Dan Martin <span dir="ltr"><<a href="mailto:ummar143@shaw.ca">ummar143@shaw.ca</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
Thanks for the reply, Sean.<br>
<div class="im"><br>
On 2012-01-21, at 6:21 PM, Sean Cody wrote:<br>
<br>
> 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.<br>
<br>
</div>... but you don't need a MAC address to route a frame to someone else?<br>
<div class="im"><br>
> 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.<br>
><br>
> An access point like the airport express is almost exactly the same as your Linux gateway.<br>
<br>
</div>The Linux gateway shows in routing tables etc. Default traffic is directed to it via the NIC which is visible on the LAN side.<br>
<br>
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).<br>
<br>
Does this have something to do with selecting Bridge mode?<br>
<div class="im"><br>
> 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.<br>
><br>
> 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.<br>
<br>
</div>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?<br>
<div class="HOEnZb"><div class="h5">><br>
> 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.<br>
><br>
> Anyways, hope that helps.<br>
><br>
> --<br>
> Sean (mobile)<br>
><br>
> On 2012-01-21, at 4:19 PM, Dan Martin <<a href="mailto:ummar143@shaw.ca">ummar143@shaw.ca</a>> wrote:<br>
><br>
>> 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?<br>
>><br>
>> 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.<br>
>><br>
>> 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.<br>
>><br>
>> 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.<br>
>><br>
>> 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.<br>
>><br>
>> 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.<br>
>><br>
>> 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?<br>
>><br>
>><br>
>> Dan Martin<br>
>> GP Hospital Practitioner<br>
>> Computer Scientist<br>
>> <a href="mailto:ummar143@shaw.ca">ummar143@shaw.ca</a><br>
>> <a href="tel:%28204%29%20831-1746" value="+12048311746">(204) 831-1746</a><br>
>> answering machine always on<br>
>><br>
>><br>
>> _______________________________________________<br>
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><br>
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<br>
Dan Martin<br>
GP Hospital Practitioner<br>
Computer Scientist<br>
<a href="mailto:ummar143@shaw.ca">ummar143@shaw.ca</a><br>
<a href="tel:%28204%29%20831-1746" value="+12048311746">(204) 831-1746</a><br>
answering machine always on<br>
<br>
<br>
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</div></div></blockquote></div><br></div>