switch mac address

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Feb 11th, 2010
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Hi guys,


Ok , I am studying little bit of switching technology for my day to day job requirement. May be following are very basic questions for you guys but really difficult to understand for me.


  • How one can fine the MAC address of a cisco switch. For example, when I run "sh ver" I get the MAC address. & when I run "sh mac addre-table"

       I also get the MAC address. So what MAC address is announced in BPDU's to decide the root of the network ?


  • How to fine the port priority of a cisco switch ?


Thanks


Tahir.

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normanjeter Thu, 02/11/2010 - 20:06
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BPDU's are used Spanning-tree, and while there is more to be explained than that, the easiest way is to point you to the section of cisco's site that covers the configuration, explanation of and adminitration of spanning-tree, and its uses.

http://www.cisco.com/en/US/docs/switches/lan/catalyst2950/software/release/12.1_9_ea1/configuration/guide/swstp.html#wp1106153

I hope this helps, if you need anything else just post any additional questions.

tahir1234 Fri, 02/12/2010 - 04:57
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Thanks Norman for your reply.


The document you refered is much technicial. I only need the answer of one question.


  1. How to find the MAC address of a cisco switch ?
  2. "sh mac address-table" shows mac addresses. "sh ver" show mac address. What is the actual MAC address of a cisco switch, Please.


Thanks

Kevin Dorrell Fri, 02/12/2010 - 05:26
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Your switch is likely to have many MAC addresses.


If you do a show interface for each of the interfaces, you will probably find that each one has a different MAC address.


There is one "master" MAC address for the switch, known as the Bridge ID.  You can see that be doing a show spanning-tree and looking for the "Bridge ID" (not necessarily the Root ID).


If you do a show mac-address-table, those are not the MAC addresses of your switch, but the MAC addresses of the things attached to your switch, together with the ports they are attached to.


Does that help?


Kevin Dorrell

Luxembourg

tahir1234 Fri, 02/12/2010 - 05:41
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Yes Kevin , it is good explaination but when we run "show version" we see the MAC address. So is this MAC address the Bridge ID that is used in spanning-tree for the selection of root bridge ?


Thanks.

Kevin Dorrell Fri, 02/12/2010 - 05:51
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Not all switches will tell you the base MAC address for a show version. For example, my 4500s do not, but my 3560s do so.  And in my 3560s, yes, the MAC address shown in show version is the same as the Bridge ID shown in show spanning-tree.


But the really reliable way to find out the Bridge ID used in spanning-tree is to do a show spanning-tree.


Kevin Dorrell

Luxembourg

AJAZ NAWAZ Tue, 10/15/2013 - 08:20
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[Kevin Dorrell] If you do a

show mac-address-table

, those are not the MAC addresses of your switch, but the MAC addresses of the things attached to your switch, together with the ports they are attached to.


i agree though if you type show mac-address-table | i No  then I think you'll find what you're after.


thank you

muralimohananan... Thu, 05/29/2014 - 12:20
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The mac address of a switch is usually the preceding number of the MAC-Address on the first port .

 

Eg: The mac-address on the first port gi0/1 is  0019.e728.8101. The mac address of  the switch would be 0019.e728.8100.

 

 

 

 


 

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