Anyone understand this? [Archive]

robust59

08-05-2008, 01:02 PM

Hi I am preparing for my CCNA exam and while studying IP addressing came across this question that I am unable to answer.On How stuff works.com and Cisco website the article on IP addressing says:

Class B addresses also include the second octet as part of the Net identifier. The other two octets are used to identify each host. This means that there are 16,384 (214) Class B networks each with 65,534 (216 -2) possible hosts for a total of 1,073,741,824 (230) unique IP addresses.

I understand the part where it is 2^16 because two octets are for network add and two octets are for host id, but how have they done the math of 2^16 -2.Can anyone help me understand this?

Thanks,

Taimur

Solostryker

08-05-2008, 08:56 PM

Hi I am preparing for my CCNA exam and while studying IP addressing came across this question that I am unable to answer.On How stuff works.com and Cisco website the article on IP addressing says:

Class B addresses also include the second octet as part of the Net identifier. The other two octets are used to identify each host. This means that there are 16,384 (214) Class B networks each with 65,534 (216 -2) possible hosts for a total of 1,073,741,824 (230) unique IP addresses.

I understand the part where it is 2^16 because two octets are for network add and two octets are for host id, but how have they done the math of 2^16 -2.Can anyone help me understand this?

Thanks,

Taimur

Yes,
The range of host ip addresses for a Class B are from x.x.0.0 to x.x.255.255, however x.x.0.0 is the domain ip address and x.x.255.255 is the broadcast ip address, so these two are not valid IP addresses. so they are removed hence 216-2. understand?:)

Hiro

09-28-2008, 05:04 AM

怎么没有中文页面啊啊啊啊啊啊

Mirza Nevjestic

10-11-2008, 02:23 AM

I agree with Solostryker (http://www.lammle.com/discussion/member.php?u=1594)

qasimkhanpk1

12-03-2008, 10:35 AM

ya i agree in 2 one is the network id and the other is broadcast id.

pm123

01-16-2009, 04:44 AM

On the page 95 (todd lammle ccna guide), it is written that:-

Yes, I know 0 and 127 are not valid in a Class A network.

Could anyone let me know that why 127 entire network (Class A) is not valid, as only 127.0.0.1 address is the loopback address used and all the other host of 127 network would not be valid? Means {(255*255*255)-1} should be valid hosts with the network 127. But its written that the entire 127 network is not used. So why so?

Fuzz

01-16-2009, 06:23 AM

The whole network is used as loopback, so that any packet that begins with a destination address of binary 01111111 will be sent to the loopback.

It's not the only time a whole block of addresses have been reserved for a purpose. Check out this RFC http://tools.ietf.org/html/rfc3330

pm123

01-23-2009, 04:23 AM

please clearly let know where exactly is this on the book of todd lammle for networking. give the page numbers of the book or the complete website address where have you read this. so that is could be elaborated with a better explanation.

Fuzz

01-23-2009, 05:55 AM

...I gave you the link to the IETF website where they explain reserved IP address blocks. Please read this as it is the basis of all reserved IP addresses.

darklord

04-21-2009, 01:41 PM

Hi I am preparing for my CCNA exam and while studying IP addressing came across this question that I am unable to answer.On How stuff works.com and Cisco website the article on IP addressing says:

Class B addresses also include the second octet as part of the Net identifier. The other two octets are used to identify each host. This means that there are 16,384 (214) Class B networks each with 65,534 (216 -2) possible hosts for a total of 1,073,741,824 (230) unique IP addresses.

I understand the part where it is 2^16 because two octets are for network add and two octets are for host id, but how have they done the math of 2^16 -2.Can anyone help me understand this?

Thanks,

Taimur

well the "16" is the total number of bits in the first 2 octets eg . For 132.24.x.x ...
here 134 - 1st octet
24 - 2nd octet and so on...
BUT the first 2 bits for class B address is FIXED i.e 10 ,
hence the "2 bits " is subtracted from the "16 bits " as those 2 bits wont ever take any other value besides "1 0" respectively !!

d15k

04-22-2009, 11:10 AM

darklord,
you really should change your mind on why two is subtracted from host count. Network address pattern has nothing to do with it. Better read earlier replies

d15k

04-22-2009, 11:13 AM

Yes,
The range of host ip addresses for a Class B are from x.x.0.0 to x.x.255.255, however x.x.0.0 is the domain ip address and x.x.255.255 is the broadcast ip address, so these two are not valid IP addresses. so they are removed hence 216-2. understand?:)

It's called network address, not domain ip address.

They're not "not valid", they just cannot be used for individual host addressing.

mrworldwarrior

01-13-2010, 10:24 PM

Just repeat your IP Addressing and Subneting studies, until you nail in your mind, Bucause most of the Topic also cover IP and subnet too

pradap

11-11-2010, 12:07 AM

Yes,
The range of host ip addresses for a Class B are from x.x.0.0 to x.x.255.255, however x.x.0.0 is the domain ip address and x.x.255.255 is the broadcast ip address, so these two are not valid IP addresses. so they are removed hence 216-2. understand?:)
ya i argee with this:):D
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