CCIE Pursuit Blog

May 26, 2008

Question Of The Day: 26 May, 2008

Filed under: Cisco — cciepursuit @ 9:45 am
Tags: , , , , ,

Topic: Multicast

r1 is a multicast router.  It receives a packet with the destination address of 224.255.1.10.  What will it do with this packet?


Yesterday’s Question

Question Of The Day: 23 May, 2008 

Topic: Multicast

What is the MAC Address of 242.9.169.28?

Answer: 01:00:5e:09:a9:1c

Let’s start by converting the multicast IP address to binary:

242     11110010
9         00001001
169     10101001
28       00011100

So we have:

11110010 00001001 10101001 00011100

Multicast addresses use a base MAC Address of 01:00:5e:xx:xx:xx with the 25th bit always set to 0:

00000001 00000000 01011110 000000000 00000000 00000000

To form the Multicast MAC Address we just need to take the 23 lower order bits of the multicast IP address and replace the 23 lower order bits in the base multicast MAC address:

11110010 00001001 10101001 00011100

00000001 00000000 01011110 00000000 00000000 00000000

00000001 00000000 01011110 00001001 10101001 00011100

Converting that back to hexadecimal, we get our answer:

01:00:5e:09:a9:1c

Advertisements

2 Comments »

  1. […] by Question Of The Day: 26 May, 2008 « CCIE Pursuit — May 26, 2008 @ 9:45 […]

    Pingback by Question Of The Day: 23 May, 2008 « CCIE Pursuit — May 26, 2008 @ 9:49 am | Reply

  2. 242.9.169.28 is out of scope os multicast addresses. Is there any sense to make MAC multicast address from non-mulsticast IP address? (Mcast scope 224.0.0.0-239.255.255.255, starts with 1110 binary if I am not wrong)

    If this is a question on CCIE Lab Exam Open Ended Question, what is the answer? (there is no mcast mac address for this IP address?)

    Comment by Igor — August 20, 2009 @ 4:24 am | Reply


RSS feed for comments on this post. TrackBack URI

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

Create a free website or blog at WordPress.com.

%d bloggers like this: