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# what is the meaning of Prefix ?

hi all

confusion happens when I read prefix on one hand

and network address on the other hand !!

so what is the difference ??

• ###### 1. Re: what is the meaning of Prefix ?

Hi Mohammed,

I hope this would help.

suppose you have a network like 10.5.10.0/24
so you will have the 10.5.10 prefix in that subnet from 1 to 255 and your network address will be 10.5.10.0

• ###### 2. Re: what is the meaning of Prefix ?

Perfix - as the name itself state, it's fix. we can't change it for that perticular subnet

• ###### 3. Re: what is the meaning of Prefix ?

I know that 10.5.10 is the network part, and the rest is for client

so which one the prefix ??

for example, 172.22.0.0 255.255.224.0

also what is he benefit of considering it ?

thanks,

• ###### 4. Re: what is the meaning of Prefix ?

Hi Mohammed,

Obiviously it's network part that would be considered peifix in above example..

Remeber that number of on bit in subnet mask represent the network and off bit represent hosts
in your classless case you have 19 bits on in the subnet so according that your 1st subnet range will be

172.22.0.0 to 172.22.31.255

now the range from 172.22.0 to 172.22.31 would be your prefix..

• ###### 5. Re: what is the meaning of Prefix ?

ok

I am trying to make in binary,

255.255.224.0

11111111.11111111.11100000.00000000

2^5 = 32 (from 0 - 31)

so that number which is in red will specify the prefix ! right ?

172.22.0.0  -   172.22.31.255

in if we take another example

10.0.0.0/8

255.0.0.0

11111111.00000000.00000000.00000000

this will be

2^0 = 1

10.0.0.0

the red color is the prefix

so my outcome is, if it is classless then the prefix will be address range not only the address ! right ?

regards

• ###### 6. Re: what is the meaning of Prefix ?

Correct ! but remember that range is in single subnet

• ###### 7. Re: what is the meaning of Prefix ?

yes   thanks for the clarification

• ###### 8. Re: what is the meaning of Prefix ?

prefix is just the number of 1's in the subnet mask

if there are 8 1's then the prefix is 8

27 1's then the prefix is 27

192.168.1.0   255.255.255.128

has a prefix of 25

10.0.0.0  255.255.0.0

has a prefix 0f 16

so prefix is really network + subnet part of an address

it depends on the context

if they are referrring to the classful network

10.2.2.0 255.255.255.0

but classful network address is 10.0.0.0

• ###### 9. Re: what is the meaning of Prefix ?

Hi jason,

So can we call it CIDR too. ?

• ###### 10. Re: what is the meaning of Prefix ?

as you said here

192.168.1.0   255.255.255.128

has a prefix of 25

25 also represent CIDR.. so can we say prefix or CIDR both same ?

• ###### 11. Re: what is the meaning of Prefix ?

CIDR as a technology is much more than the concept of a prefix that is created at any bit position, but yeah, you are right, because without that ability, there would be no CIDR.

And its usually referred to as "CIDR notation" (older terminology) in the form IP ADDRESS + PREFIX, eg 10.1.1.1/18, or simply "slash".

"Prefix" is becoming the general umbrella term these days, and it is used commonly in BGP.

• ###### 12. Re: what is the meaning of Prefix ?

no

its the prefix....25

cidr is classless inter domain routing.....and in my opinion is usually a term used for public addressing. used by isps for bgp ...and route aggregation.

where the isp breaks a network into different prefixes and distributes subnets of the network to clients and then groups these subnets ( summarizes ) them out to the internet.

for me its always better to referr to private addresses as classful and classless with a prefix of xyz

i dont mention the term cidr unless im dealing with the internet at large and public external networks..

so if you were working on an enterprise network and started discussing cidr..for internal subnetting...maybe it would seem a bit confusing

if you get me.

imo ...cidr should be reserved for speaking about BGP and the main core routing tables and isps and the like ( the big stuff )

the breakup of addresses handed down from ip distributors to isps

not for private addressing with your little rip routing protocol and your 2600 second hand router from ebay., and your homemade ethernet cable that your mum had when she bought a lap top from wall mart ( buy one get one free ).....for her birthday.

sorry im humoring myself...dont be offended.

• ###### 13. Re: what is the meaning of Prefix ?

Thanks

• ###### 14. Re: what is the meaning of Prefix ?

these late nights at the computer are sending me crazy.

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