I thought I had subnetting sorted...
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Member Posts: 309
in CCNA & CCENT
Until an ICND1 class...I just seem to be more confused now with the examples we are going through. Might have to sit down and go through them again in my own time.
Before I start, this is not homework (my homework days finished over 15years ago).
I took an ICND1 class and we were going through subnetting. Once of the examples we went through is below.
I.P address - 2.2.2.0 /25
Require 32 subnets.
Can someone go through this (not at a hundred miles per hour like it was done here).
Thanks
Before I start, this is not homework (my homework days finished over 15years ago).
I took an ICND1 class and we were going through subnetting. Once of the examples we went through is below.
I.P address - 2.2.2.0 /25
Require 32 subnets.
Can someone go through this (not at a hundred miles per hour like it was done here).
Thanks
Comments
I am not sure I know what the question is.
With a Class A address, you only would need a /13 mask to have 32 subnets.
31 = 11111
It looks like you will need 5 bits to use as subnet bits. Now convert your given mask into binary.
/25 => 255.255.255.128 => 11111111.11111111.11111111.10000000
To make this a little easier on the eyes I like to identify each bit with a letter to show it's role: N=Network, S=Subnet and H=Host
Original Mask: NNNNNNNN.NNNNNNNN.NHHHHHHH
You need to allow for 32 subnets, so you need to convert some host bits to subnet bits. You will start at the rightmost network bit and go right.
New Mask: NNNNNNNN.NNNNNNNN.NSSSSSHH
Now that you have reserved bits for your subnets, you can convert the mask back. N's and S's will be 1's and H's will be 0's.
11111111.11111111.11111111.11111100 => 255.255.255.252 => /30
So you will be using /30 to get 32 subnets out of your /25 you had to start:
Subnet 1 = 2.2.2.0/30
Subnet 2 = 2.2.2.4/30
Subnet 3 = 2.2.2.8/30
Subnet 4 = 2.2.2.12/30
Subnet 5 = 2.2.2.16/30
Subnet 6 = 2.2.2.20/30
Subnet 7 = 2.2.2.24/30
Subnet 8 = 2.2.2.28/30
Subnet 9 = 2.2.2.32/30
Subnet 10 = 2.2.2.36/30
Subnet 11 = 2.2.2.40/30
Subnet 12 = 2.2.2.44/30
Subnet 13 = 2.2.2.48/30
Subnet 14 = 2.2.2.52/30
Subnet 15 = 2.2.2.56/30
Subnet 16 = 2.2.2.60/30
Subnet 17 = 2.2.2.64/30
Subnet 18 = 2.2.2.68/30
Subnet 19 = 2.2.2.72/30
Subnet 20 = 2.2.2.76/30
Subnet 21 = 2.2.2.80/30
Subnet 22 = 2.2.2.84/30
Subnet 23 = 2.2.2.88/30
Subnet 24 = 2.2.2.92/30
Subnet 25 = 2.2.2.96/30
Subnet 26 = 2.2.2.100/30
Subnet 27 = 2.2.2.104/30
Subnet 28 = 2.2.2.108/30
Subnet 29 = 2.2.2.112/30
Subnet 30 = 2.2.2.116/30
Subnet 31 = 2.2.2.120/30
Subnet 32 = 2.2.2.124/30
Yes, this is exactly what they were looking for.
I had almost forgotten about these kinds of questions.
Great job Monkerz!
To anyone working in the networking field, do you actually do all this in your head, or always use a calculator when the need arises?
I always do it in my head. Keeps it fresh.
I'd rather keep my specialty skills fresh, not sub-netting. However, because I have experiance in the work place, I now have most of the sub-netting variations memorized. The likly hood of you walking into a real-world network and have someone hand you 'we have 31 people in 6 floors of this building, 5 people per floor and 6 on the last one. Tell me what VLSM scheme we should use to meet these requirements.' is never.
In my experience.
I don't want to keep going
4
8
12
16
20 and so forth to work out address ranges for subnets in the 200's
Hopefully that makes sense..
You can also subtract from 256.
in my head. my actual "way" of thinking for your initial task would have been:
/25 subnet needs to be divided to get 32 out of it
hmmmmmmmmmmmmmmm
/24 = 256 hosts, so /25 is 128, 128/32=4
4 equals a point to point /30 subnet - 2 hosts usable
answer is /30
DOC
Subnetting actually came to me slowly and from different sources. The subnetting made easy thread in this forum was where I started, but then pieced together techniques from different CCIE's whom have published training materials. It is really just a matter of how your brain comprehends subnetting. Some get it quick, others it takes longer.
All in all, I think it took me around 6 months of studying off and on, as well as labbing. I think labs which included VLSM really helped me with subnetting on the fly.
Yep. The key is to know your powers of 2. To find an address in the 220 range, go up by a higher increment of say 64 until you get close to your answer. You know that going up by 64 will give you the following...
.0
.64
.128
.192
Then go up by smaller increments until you find your answer.
Going up by 32 takes you to 224 (192 + 32)
Going up by 16 takes you to 208 (192 + 16)
Going up by 8 takes you to .200, .208, .216, .224 etc
Key is to really know your powers of two...4, 8, 16, 32, 64, 128
128 + 16 = 144...144 + 16 = 160
128 + 32 = 160...160 + 32 = 192
128 + 64 = 192 etc...192 + 32 = 224
192 + 64 = 256 etc
After you subnet for a while you will know these numbers like the back of your hand and you can just skip/jump up by a higher increment of 64 or 32 until you get close to your answer. Then just go up by smaller increments until you find the answer.
What is the first valid host on the subnetwork that the node 172.24.166.240/26 belongs to ?
First thing to do is to find the increment. /26 = 255.255.255.192...256 -192 = 64
Or a quicker way to find the increment is to use the last bit position where the value is a 1.
For example.../26 in binary is...11111111.11111111.11111111.1100000
You know each octet has the values 128 64 32 16 8 4 2 1
See where the last 1 is...it is 64...so your increment is 64 and in the last octet.
So the networks would be...
172.24.166.0
172.24.166.64
172.24.166.128
172.24.166.192 (valid hosts are .193 - .254)
But you could jump straight to the .192 network because you know that 192 is an increment of 64...
So then the first valid host is 192.24.166.193
I'm relearning in my head now but; as most have said you can Google it faster and seem like an genius to novices and upper-management. I want to be able to know subnetting again in my head just as I know the OSI model and network/security ports with ease or even the PDU i.e. bit, frames, packets, segments, data etc... (just my thoughts)
CCNP R/S
its not only with subnetting... some weeks ago preparing für the ROUTE exam i was fighting ipv6 and ospf LSA types like that. but once get it you wonder why you had so much "respect" from it all the time...