Re-Post -----Original Message----- From: Kaminski, Shawn G Sent: Wednesday, December 12, 2001 10:17 AM To: 'Sergio' Cc: 'Groupstudy' Subject: RE: CCNP Switching - Mapping MAC address to IP Multicast [7:10]
Don't worry about MAC-to-IP Multicast Address conversion, only IP Multicast Address-to-MAC conversion. What you're doing is converting the decimal Multicast IP address to hexadecimal. Here's what you need to remember: 1.All Multicast IP addresses range from 224 through 239 in the first octet. 2.All Multicast MAC addresses begin with "01.00.5e" 3.When converting from decimal to hexadecimal, the second octet of the Multicast IP address must fall between 0 and 127. If it is more than 127, you must subtract 128 from it to get between 0 and 127. 4.Cisco doesn't expect you to memorize the decimal-to-hexadecimal conversions. They will give you a chart on the exam. Here's a few examples: 1.Given the address 223.128.37.255, map this to its equivalent Multicast MAC address. Answer: You can't because the first octet 223 doesn't fall between the Multicast range of 224 through 239. 2.Given the address 225.128.37.255, map this to its equivalent Multicast MAC address. Answer: A.Remember, all Multicast MAC addresses begin with "01.00.5e". So, the 225 portion (first octet) of the Multicast IP address becomes 01.00.5e. B.The second octet does not fall between 0 and 127, so subtract 128 from it. 128-128=0. 0 converted to hexadecimal is 00. C.The third octet just gets converted to hexadecimal. It doesn't have to fall between 0 and 127. So, 37 converted to hexadecimal is 25. D.The fourth octet just gets converted to hexadecimal. It doesn't have to fall between 0 and 127. So, 255 converted to hexadecimal is e1. So, the Multicast IP address 225.128.37.255 converted, or mapped, to its equivalent Multicast MAC address is 01.00.5e.00.25.e1 Shawn -----Original Message----- From: Sergio [mailto:[EMAIL PROTECTED]] Sent: Tuesday, December 11, 2001 3:33 PM To: [EMAIL PROTECTED] Subject: CCNP Switching - Mapping MAC address to IP Multicast [7:10] Hi all. This is my first message here. Greetings from Spain ;) Now, i have a question for you. I'm preparing my CCNP Switching exam, and now im reading about IP Multicast. The book says that IANA reserved some MAC address for using with IP Multicast. The book also says that MAC addresses must be mapped to IP Multicast address, and it explains how to map them. But i cant understand it. I dont understand how to map MAC address to IP Multicast addresses. Can u help me? Thanks in advice. Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=29084&t=10 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
