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Is there mask for class D ip address? As it is for multicast, I am not sure about it. I read somewhere that D ip addressas are 32-bit network addresses and they dont have hostID, but in the following link I read that the number of bits for network and host is undefined in the class D. I am a little confuse a bout it, would you please guide me?

http://en.wikipedia.org/wiki/Classful_network

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It looks like you read right. "I read somewhere that D ip addressas are 32-bit network addresses and they dont have hostID," ok you're wrong that it's a 32-bit network address. Network address is something else, network address is an IP ending in .0 But on the other aspect it seems you're right that Class D doesn't have a network and host portion. Maybe was a good source you read. Where did you read that? – barlop May 27 '11 at 9:14
you are righ, I made a mistake. I got the site material wrong. paessler.com/support/kb/questions/34 – Roshio May 27 '11 at 10:10
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3 Answers

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First classful addressing isn't used anymore, it's classless now.

Class D like any other Classes, all IPv4 addresses , are 32-bit.

Now, Judging by this link.. http://www.tcpipguide.com/free/t_IPMulticastAddressing.htm

it doesn't have network and host bits. If it's a multi-cast address then one IP would go to multiple machines anyway 'cos they'd all have that IP.

That tcpipguide link about Class D addresses has a table with more than the table on the wikipedia page on classful addressing. enter image description here

I suppose in this case not defined means no network fields and host bit fields which is what you say you read, which makes sense and I think that's what the wikipedia page really meant when it said undefined. There are also going to be some addresses that IANA never assigned..but no doubt some multi-cast addresses were given out.

I don't know if you'd call the whole thing a network address. Network address is normally an address ending in .0 representing the subnet. I don't think a multi-cast address is referred to as a network address.

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So,As we know there are mask for classes A: 8 bits, class B: 16 bits and class C : 24 bits, can we say that the number of bits for class D is undefined? – Roshio May 27 '11 at 9:06
they're all 32-bit. Class A has an 8 bit network portion , Class B a 16-bit network portion. Class D doesn't have a network and host portion. – barlop May 27 '11 at 9:13
thanks, I understand it – Roshio May 27 '11 at 9:19
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up vote 3 down vote

A netmask is used to divide an IP address into a network part and a host part. Multicast addresses don't have network parts and host parts, so it is meaningless to talk about a netmask.

A multicast address is just a 32-bit address within a well-known range that hosts subscribe to using a protocol such as IGMP.

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up vote 0 down vote

Class D IP addresses have the first four bits set to 1110, the rest of the bits are available. So the range for class D addresses is from 224.0.0.0 to 239.255.255.255.

And the netmask will be 11110000.00000000.00000000.00000000 in binary and 240.0.0.0 in decimal.

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The first 4 bits are that..the class ID. I think the class ID only makes part of the network id. Also 15.255.255.255 is Class A. Class D covers a higher range than that. I'm not sure what routers/where would zero out just the class ID.. where did read that? – barlop May 27 '11 at 8:27
@barlop 15.255.255.255 is not a IP address but the netmask of the range for class D addresses. Source Wikipedia. – Quentin May 27 '11 at 8:35
@Quentin Can you be more specific when you make a reference? 15.255.255.255 is not mentioned on that page, neither even is the word netmask. – barlop May 27 '11 at 8:37
I can see you're zeroing out the first 4 bits.. but i'm not sure what routers do that. I suppose some might, if one router did a mask of 11110000.0.0.0 and sent Class A to one router Class B to another e.t.c. then one of those routers dealing with just one Class, could do that. Though classes aren't used anymore doing so may be useful but anyhow also, I don't see how mentioning the netmask(assuming that's the right term) is relevant to the question though. – barlop May 27 '11 at 8:43
So,As we know there are mask for classes A: 8 bits, class B: 16 bits and class C : 24 bits. So, what is the number of bits for a D class? – Roshio May 27 '11 at 8:45
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