9 Replies Latest reply: Nov 21, 2011 2:15 PM by FentonRSFezLearn

Hey guys, just a short quesiton about MAC addresses in relation to calculations and indirectly STP RP elections.

Wendells ICND2 guide gave MAC addresses such as 2222.2222.2222 and 3333.3333.3333. I basically took these and said well 2+2+2+2+2+2+2+2+2+2+2+2  is less than 3+3+3+3+3+3+3+3+3+3+3+3 (24 vs 36) so the latter one is the lowest and therefore in the context of the question was the root switch.

This worked well for me and in examples later in the book this method that I assumed was correct. There is an example later in the book that gives you two slightly more realistic addresses (0019.e859.5380 and 0019.e86a.6f80) and I assumed the same for these addresses. (62 vs 77).

Is this the correct way to deal with MAC addresses?

Also just an off topic question for those with experience sitting Cisco exams.

I have failed my ICND2 exams twice now, both times by about a question each time... I have a horrible fear of failing exams so while I can answer practice exams etc almost perfectly in most cases, I freeze up horribly in exams. That and the testing facility I go to has horriblly small desks that you have to shift the keyboard around to actually have the room to write something down (on paper etc)....v frustrating in testing conditions.

If anyone has any tips to deal with these tests better they would be much appreciated.

Thanks

• ###### 1. Re: MAC Address calculation

fortuntaly we do not have to do this calculation;

STP selects  Root by comparing HEX digits one by one;

0019.e859.5380 and

0019.e86a.6f80

5 is lower than 6, so 0019.e859.5380 Wins!

• ###### 2. Re: MAC Address calculation

Hmmm what about the numbers after the 5? I thought it was the sum of the entire Mac address? Or is it only the "leading" numbers?

Thanks

• ###### 3. Re: MAC Address calculation

no, one by one starting at left, until one HEX is lower then the other one.

• ###### 4. Re: MAC Address calculation

Thanks Martin, wish that was explained in the book.

• ###### 5. Re: MAC Address calculation

Do you have any insight into leaving feedback? The options are not appearing for me in multiple browsers even after restarting.

• ###### 6. Re: MAC Address calculation

feedback ? or points ?

you just this; thanks is enough;  although if u mark your topic as question when u create it, you will have option to give people points.

• ###### 7. Re: MAC Address calculation

Hi FentonRSFezLearn,

I am sorry to hear of your failed ICND2 exam.

We enocurage you to try the practice/review questions for the ICND2 exam before your next attempt. In addition, you may also want to try a few of the learning games available in the Games Arcade section.

Good luck!

Regards,

Rigo

Cisco Learning Network Moderator

• ###### 8. Re: MAC Address calculation

Ahhhh yes thats why I am not seeing the option for points, thanks for reminding me.

• ###### 9. Re: MAC Address calculation

Thanks for this I will be sure to give both of these a look.