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CCENT/CCNA [H] study group

saedrin said:
That is exactly how my internal LAN is setup at my home. Network gear is on 0.x, servers on 1.x, hard wired clients on 2.x, and wireless on 3.x.
Click to expand...

mine to, that way viruses from other units can infect the server, and guest wireless can't see servers and home network stuff.
 
Approximately how many Simulations should you expect to do on the CCENT? and the rest of them will be multiple choice?

Not sure if this is under the NDA but any info would be appreciated. I am starting to prepare for my exam that will be next week!:eek:
 
Interesting. My Gateway is 192.168.1.1 and I have my two computers in different subnets. (One is 192.168.1.7 and the other 192.168.1.10 both in the 255.255.255.248 subnet.) They can both ping the gateway and get internet access via the 192.168.1.1 even though it's in the first subnet range. Is this only because I added it as the gateway therefore making a static route? Could I make a static route to the other computer in the other subnet and they would then be able to communicate?
 
/usr/home said:
Interesting. My Gateway is 192.168.1.1 and I have my two computers in different subnets. (One is 192.168.1.7 and the other 192.168.1.10 both in the 255.255.255.248 subnet.) They can both ping the gateway and get internet access via the 192.168.1.1 even though it's in the first subnet range. Is this only because I added it as the gateway therefore making a static route? Could I make a static route to the other computer in the other subnet and they would then be able to communicate?
Click to expand...

umm, i think you just typed the same 2 subnets,

if you had 2 wouldn't it be

192.168.2.x
192.168.1.x

Correct ?
 
dashpuppy said:
umm, i think you just typed the same 2 subnets,

if you had 2 wouldn't it be

192.168.2.x
192.168.1.x

Correct ?
Click to expand...

No he is subnetting the last octet with .248 which gives you a block size of 8.

I told you before man you need to get a CCENT/CCNA book and do some reading.
 
AMD_Gamer said:
No he is subnetting the last octet with .248 which gives you a block size of 8.

I told you before man you need to get a CCENT/CCNA book and do some reading.
Click to expand...

It's on my to get list here. I'm leaving in a few days for a 2.5 week vacation (getting married :D) so when I get back I'll order one. I did my network+ last year and never had to get real deep into subnetting, but I find it really interesting. If I gave my computer an IP of 192.168.1.11, it would be in the range of the subnet the other computer is on, but I left it at 255.255.255.0. It should still be able to access that subnet then, correct? If it can, like I'm seeing in my testing here, where's the security in subnetting if I can just set my mask differently and be able to access the other subnets? Or can I access that subnet because my IP is in that subnet range? I know I'm really confusing....
 
AMD_Gamer said:
No he is subnetting the last octet with .248 which gives you a block size of 8.

I told you before man you need to get a CCENT/CCNA book and do some reading.
Click to expand...

Yah, when i get some time, when you have a full time baby that wants to play and keep you up all night, plus work all day 10 hour days, then come home to lexmark / dell / hp training i dont have to much time for reading a book that has nothing to do with work LOL

In a hotel as we all type.
 
/usr/home said:
They can both ping the gateway and get internet access via the 192.168.1.1 even though it's in the first subnet range. Is this only because I added it as the gateway therefore making a static route?
Click to expand...
Yup, it'll do arp lookup for static routes on interface/without default gw.

/usr/home said:
Could I make a static route to the other computer in the other subnet and they would then be able to communicate?
Click to expand...
Not really. While 7 could reach 10, 10 couldn't reach 7 unless you set up static routes there as well. Another downside to not setting stuff up with correct netmasks.
 
/usr/home said:
If I gave my computer an IP of 192.168.1.11, it would be in the range of the subnet the other computer is on, but I left it at 255.255.255.0. It should still be able to access that subnet then, correct? If it can, like I'm seeing in my testing here, where's the security in subnetting if I can just set my mask differently and be able to access the other subnets? Or can I access that subnet because my IP is in that subnet range? I know I'm really confusing....
Click to expand...
While your comp. can access the whole /24 subnet, the other way around won't necessarily work (just like previous case). It really depends on default gw setup etc., since there also exists arp redirect mechanism. Also, ip broadcasts won't work.

Different subnets on their own are mostly useless and you should really avoid them because they only complicate matters. For security you put them in different vlans, so you can filter traffic on router connecting them.

Basically all subnet mask does is tell your computer for what addresses to use arp (and defines broadcast ip address).

Edit: clarified first part.
 
Last edited:
/usr/home said:
It's on my to get list here. I'm leaving in a few days for a 2.5 week vacation (getting married :D) so when I get back I'll order one. I did my network+ last year and never had to get real deep into subnetting, but I find it really interesting. If I gave my computer an IP of 192.168.1.11, it would be in the range of the subnet the other computer is on, but I left it at 255.255.255.0. It should still be able to access that subnet then, correct? If it can, like I'm seeing in my testing here, where's the security in subnetting if I can just set my mask differently and be able to access the other subnets? Or can I access that subnet because my IP is in that subnet range? I know I'm really confusing....
Click to expand...

To use an example to explain this:

Let's take a /24 block and call it a transit station, it goes from 192.168.1.0 to 192.168.1.255 (minus network(first) and broadcast(last) addresses if you're counting usable IP addresses). With that, you have a subnet mask of 255.255.255.0, meaning you have wildcard bits in the entire last octet.

Let's say we only have two trains that use the transit station, so you split the tracks to allow for space for two trains. For an IP address range that would be splitting the 255 space in half which would give you:

Code: 
Address Space #1: 192.168.1.0 to 192.168.1.127
Address Space #2: 192.168.1.128 to 192.168.1.255
Given this, the subnet mask of this is /25 (255.255.255.128) because if you look at the generalization of the bits between the two address spaces, only the left-most bit in the last octet is different, meaning 25 bits are for the network address, and the last 7 bits are used for host addresses.
Code: 
Address Space #1 First IP = 192.168.1.0   192.168.1.[COLOR=Red]0[/COLOR]0000000
Address Space #1 Last  IP = 192.168.1.127 192.168.1.[COLOR=Red]0[/COLOR]1111111

Address Space #2 First IP = 192.168.1.128 192.168.1.[COLOR=Red]1[/COLOR]0000000
Address Space #2 Last  IP = 192.168.1.255 192.168.1.[COLOR=Red]1[/COLOR]1111111
When you're inside one of the trains, your view is limited to what you can see from within the train. Similar to being inside the subnet mask, if your subnet mask limits you to a particular range that is all you can see, but if you have a subnet mask that encompasses the entire subnet then you'll see everything.

The security comes in when you do stuff like port-security and ACLs on switch ports, that prevent a user from changing their IP and subnet to whatever they want.
 
ShadowStriker said:
To use an example to explain this:

Let's take a /24 block and call it a transit station, it goes from 192.168.1.0 to 192.168.1.255 (minus network(first) and broadcast(last) addresses if you're counting usable IP addresses). With that, you have a subnet mask of 255.255.255.0, meaning you have wildcard bits in the entire last octet.

Let's say we only have two trains that use the transit station, so you split the tracks to allow for space for two trains. For an IP address range that would be splitting the 255 space in half which would give you:

Code: 
Address Space #1: 192.168.1.0 to 192.168.1.127
Address Space #2: 192.168.1.128 to 192.168.1.255
Given this, the subnet mask of this is /25 (255.255.255.128) because if you look at the generalization of the bits between the two address spaces, only the left-most bit in the last octet is different, meaning 25 bits are for the network address, and the last 7 bits are used for host addresses.
Code: 
Address Space #1 First IP = 192.168.1.0   192.168.1.[COLOR=Red]0[/COLOR]0000000
Address Space #1 Last  IP = 192.168.1.127 192.168.1.[COLOR=Red]0[/COLOR]1111111

Address Space #2 First IP = 192.168.1.128 192.168.1.[COLOR=Red]1[/COLOR]0000000
Address Space #2 Last  IP = 192.168.1.255 192.168.1.[COLOR=Red]1[/COLOR]1111111
When you're inside one of the trains, your view is limited to what you can see from within the train. Similar to being inside the subnet mask, if your subnet mask limits you to a particular range that is all you can see, but if you have a subnet mask that encompasses the entire subnet then you'll see everything.

The security comes in when you do stuff like port-security and ACLs on switch ports, that prevent a user from changing their IP and subnet to whatever they want.
Click to expand...

Ok, that makes sense. So subnetting really doesn't give you much security if the users can change their subnet mask. I guess that's where GPOs come into affect as well.
 
Another thing, does anyone have an easy way for figuring out ranges when they are above 255 hosts? IE if the range starts at 10.0.0.0 and has 1022 hosts per subnet, what's the simplest way of "dividing" that up between octets?
 
/usr/home said:
Another thing, does anyone have an easy way for figuring out ranges when they are above 255 hosts? IE if the range starts at 10.0.0.0 and has 1022 hosts per subnet, what's the simplest way of "dividing" that up between octets?
Click to expand...


Do it in 2s. Find 2 ^ n >= 1022, closest would be 1024 which is 10 bits. Which means its a /22 per subnet. Which means it'll be 10.0.0000 00XX.XXXX XXXX is useably per subnet, where X is a bit that can be 0 or 1. So, then you know 22 bits are for network,

Code: 
 10.0.0.0 to 10.0.3.255 -->10.0.[B][COLOR=Red]0000 00[/COLOR][/B]XX.XXXX XXXX

10.0.4.0 to 10.0.7.255 -->10.0.[COLOR=Red][B]0000 01[/B][/COLOR]XX.XXXX XXXX

10.0.8.0 to 10.0.11.255 -->10.0.[B][COLOR=Red]0000 10[/COLOR][/B]XX.XXXX XXXX
etc.

The red is where you'll be changing the network address, until you hit the second octet.

After a while, this stuff just comes to you, although the adding up of numbers is still slow on me. :p
 
Last edited:
ShadowStriker said:
Do it in 2s. Find 2 ^ n >= 1022, closest would be 1024 which is 10 bits. Which means its a /22 per subnet. Which means it'll be 10.0.0000 00XX.XXXX XXXX is useably per subnet, where X is a bit that can be 0 or 1. So, then you know 22 bits are for network,

10.0.0.0 to 10.0.3.255
10.0.4.0 to 10.0.15.255
etc.

After a while, this stuff just comes to you, although the adding up of numbers is still slow on me. :p
Click to expand...

Yeah, but how do you add those numbers easily and quickly? Is there a simple way? like adding 512 or 1024 to 10.0.0.0. Well I suppose adding 512 to 10.0.0.0 would give you 10.0.1.255. Adding 8192 is more difficult though.
 
/usr/home said:
Yeah, but how do you add those numbers easily and quickly? Is there a simple way? like adding 512 or 1024 to 10.0.0.0. Well I suppose adding 512 to 10.0.0.0 would give you 10.0.1.255. Adding 8192 is more difficult though.
Click to expand...


In each octet, each bit represents a binary position,

From least significant to most significant (right to left)

Code: 
Bit 0 --> 1
Bit 1 --> 2
Bit 2 --> 4
Bit 3 --> 8
Bit 4 --> 16
Bit 5 --> 32
Bit 6 --> 64
Bit 7 --> 128
So, you can see that if you only use Bit 0, there are 2 (you take that number add 0 because you start at 0 not 1) possible IPs, but one is network and one is broadcast.

If you take up to Bit 5 (including), you'll have have 64 possible hosts (minus two for network and broadcast) (trick is to look at next bit position and that's how many hosts are possible, since if you add Bit 1 + Bit 2 + ... + Bit 5 you get 63, then add zero'th and you get 64.

I think I might still have some notes I had at home from when I started learning this, I'll have a look and see. (I have some stuff from what I was studying in my last semester here at the bottom under Advanced Switching Networks about security for ports and stuff.
 
Last edited:
Maybe I'm describing it funny, or I'm just not getting your explanation.

Say I have a range of 8192 hosts in each subnet and I need to figure out the ranges for all the subnets, for example, 4. Figuring out 64 hosts per subnet is easy, just add 64 in the last octet. But if you have 8192 to add, it's obviously greater than 255 and you have to start adding in the second last octet. I can do one octet adding fine, but it's when it gets to the second and higher octets that I'm not understanding... :(
 
/usr/home said:
Maybe I'm describing it funny, or I'm just not getting your explanation.

Say I have a range of 8192 hosts in each subnet and I need to figure out the ranges for all the subnets, for example, 4. Figuring out 64 hosts per subnet is easy, just add 64 in the last octet. But if you have 8192 to add, it's obviously greater than 255 and you have to start adding in the second last octet. I can do one octet adding fine, but it's when it gets to the second and higher octets that I'm not understanding... :(
Click to expand...

Ah, I think I know what you mean. You're having problems transitioning from finding the ranges between one octet subnets and subnets that span multiple octets.

Okay, so if you have 192.168.2.0/24 You know there are 24 network bits and 8 host bits.
What you have is this:
Code: 
1100 0000 . 1010 1000 . 0000 0010 . 0000 0000
From that, we know that 24 bits are network bits and 8 bits are host bits. Identifying network bits as red and host bits as green.

Code: 
[COLOR=Red]1100 0000 . 1010 1000 . 0000 0010[/COLOR] .[COLOR=Lime] 0000 0000[/COLOR]
Now, the range is essentially the IP addresses in-between the network address and the broadcast address of a subnet. The network address is where ALL HOST BITS ARE ZERO and the broadcast address is where ALL HOST BITS ARE ONE.

That means that this is a network address:
Code: 
[COLOR=Red]1100 0000 . 1010 1000 . 0000 0010[/COLOR] .[COLOR=Lime] 0000 0000[/COLOR]
IP adddress - 192.168.2.0/24

And that means that this is a broadcast address:
Code: 
[COLOR=Red]1100 0000 . 1010 1000 . 0000 0010[/COLOR] .[COLOR=Lime] 1111 1111[/COLOR]
IP address = 192.168.2.255/24

Giving us a range of 192.168.2.0 to 192.168.2.255 for that subnet.

For a subnet that uses more than one octet:

If we use 10.0.0.0/22, we know that 22 bits are used for network address and (32 - 22 = 10) bits are used for host address. That means we have a format where it looks like this.
Code: 
[COLOR=Red]0000 1010 . 0000 0000 . 0000 00[/COLOR][COLOR=Lime]00 . 0000 0000[/COLOR]
To get the network address of this range, we set all host bits to zero.

Code: 
[COLOR=Red]0000 1010 . 0000 0000 . 0000 00[/COLOR][COLOR=Lime]00 . 0000 0000[/COLOR]
IP address = 10.0.0.0 /22

To get the broadcast address we set all host bits to one.

Code: 
[COLOR=Red]0000 1010 . 0000 0000 . 0000 00[/COLOR][COLOR=Lime]11 . 1111 1111[/COLOR]
IP address = 10.0.3.255 /22

To get the next subnet, we ONLY look at the network bits, and say "We want the second subnet", so we figure out what the binary of 1 is, and then add it to the network part. (remember it starts at 0, so what we just did above was the zero'th subnet, we're doing the position 2 subnet now)

Code: 
[COLOR=Red]
 0000 1010 . 0000 0000 . 0000 00[/COLOR][COLOR=Lime]00 . 0000 0000
[/COLOR]+[COLOR=Red]0000 1010 . 0000 0000 . 0000 01[/COLOR]
So when we add them together we get this:

Code: 
[COLOR=Red]0000 1010 . 0000 0000 . 0000 01[/COLOR][COLOR=Lime]00 . 0000 0000[/COLOR]
IP address = 10.0.4.0 /22

Which also happens to be the network address of our second subnet.

If we set all the host bits to one, we get the broadcast address of the second subnet.

Code: 
[COLOR=Red]0000 1010 . 0000 0000 . 0000 01[/COLOR][COLOR=Lime]11 . 1111 1111[/COLOR]
IP address = 10.0.7.255

And then we now know that the subnet is from 10.0.4.0 to 10.0.7.255
 
The fastest way, for me, was remembering how many hosts can be in a subnet. Don't forget that 2 address cannot be used by hosts, so if you're deciding on a network size, add 2 to the total host count before doing any calculations.

/24 is where most people start, and they either work forwards or backwards.

Memorizing /24-/30 makes things very easy instead of working it out in your head, but I guess that will come with exposure.

One way that helped me was ordering the bits (read left to right):
# of bits:
0 = 0
1st = 128 or 2^7
2nd = 64 or 2^6
3rd = 32 or 2^5

when you memorize it that way you can quickly understand how many hosts can be within a subnet. For example a /25, or 255.255.255.128, can have a total of 128 address or 128-2 = 126 hosts. Following this lets say you have a /26, or 255.255.255.192 (remember this is a 2nd bit so 128 + 64 = 192), but you automatically know that because it is a 2nd bit, or 64, then it has 64 addresses or 62 hosts.

Ex.
/24 = 255.255.255.0 = .00000000 = #bits: 0
/25 = 255.255.255.128 = .10000000 = #bits: 1
/26 = 255.255.255.192 = .11000000 = #bits: 2

If you want to move from the /24 subnet to something smaller you pretty much double the previous number of address that the subnet could have. So /24 = 256 address then /23 = 512. Likewise you keep going so /21 = 2048 (255.255.248.0)
 
The Cisco Press book I used had binary workgrids that they wanted you to use. I found that more tedious than visualizing it. Outside of an exam, you could also use Windows Calculator which has binary options.
 
ShadowStriker said:
Ah, I think I know what you mean. You're having problems transitioning from finding the ranges between one octet subnets and subnets that span multiple octets.

Okay, so if you have 192.168.2.0/24 You know there are 24 network bits and 8 host bits.
What you have is this:
Code: 
1100 0000 . 1010 1000 . 0000 0010 . 0000 0000
From that, we know that 24 bits are network bits and 8 bits are host bits. Identifying network bits as red and host bits as green.

Code: 
[COLOR=Red]1100 0000 . 1010 1000 . 0000 0010[/COLOR] .[COLOR=Lime] 0000 0000[/COLOR]
Now, the range is essentially the IP addresses in-between the network address and the broadcast address of a subnet. The network address is where ALL HOST BITS ARE ZERO and the broadcast address is where ALL HOST BITS ARE ONE.

That means that this is a network address:
Code: 
[COLOR=Red]1100 0000 . 1010 1000 . 0000 0010[/COLOR] .[COLOR=Lime] 0000 0000[/COLOR]
IP adddress - 192.168.2.0/24

And that means that this is a broadcast address:
Code: 
[COLOR=Red]1100 0000 . 1010 1000 . 0000 0010[/COLOR] .[COLOR=Lime] 1111 1111[/COLOR]
IP address = 192.168.2.255/24

Giving us a range of 192.168.2.0 to 192.168.2.255 for that subnet.

For a subnet that uses more than one octet:

If we use 10.0.0.0/22, we know that 22 bits are used for network address and (32 - 22 = 10) bits are used for host address. That means we have a format where it looks like this.
Code: 
[COLOR=Red]0000 1010 . 0000 0000 . 0000 00[/COLOR][COLOR=Lime]00 . 0000 0000[/COLOR]
To get the network address of this range, we set all host bits to zero.

Code: 
[COLOR=Red]0000 1010 . 0000 0000 . 0000 00[/COLOR][COLOR=Lime]00 . 0000 0000[/COLOR]
IP address = 10.0.0.0 /22

To get the broadcast address we set all host bits to one.

Code: 
[COLOR=Red]0000 1010 . 0000 0000 . 0000 00[/COLOR][COLOR=Lime]11 . 1111 1111[/COLOR]
IP address = 10.0.3.255 /22

To get the next subnet, we ONLY look at the network bits, and say "We want the second subnet", so we figure out what the binary of 1 is, and then add it to the network part. (remember it starts at 0, so what we just did above was the zero'th subnet, we're doing the position 2 subnet now)

Code: 
[COLOR=Red]
 0000 1010 . 0000 0000 . 0000 00[/COLOR][COLOR=Lime]00 . 0000 0000
[/COLOR]+[COLOR=Red]0000 1010 . 0000 0000 . 0000 01[/COLOR]
So when we add them together we get this:

Code: 
[COLOR=Red]0000 1010 . 0000 0000 . 0000 01[/COLOR][COLOR=Lime]00 . 0000 0000[/COLOR]
IP address = 10.0.4.0 /22

Which also happens to be the network address of our second subnet.

If we set all the host bits to one, we get the broadcast address of the second subnet.

Code: 
[COLOR=Red]0000 1010 . 0000 0000 . 0000 01[/COLOR][COLOR=Lime]11 . 1111 1111[/COLOR]
IP address = 10.0.7.255

And then we now know that the subnet is from 10.0.4.0 to 10.0.7.255
Click to expand...

Awesome! I think you got through to me on this one. I tried one quickly and got the right answer, I'll try some more here when I have some more downtime at work here. Thanks for all your patience and help.
 
/usr/home said:
Awesome! I think you got through to me on this one. I tried one quickly and got the right answer, I'll try some more here when I have some more downtime at work here. Thanks for all your patience and help.
Click to expand...

My lab book has 6 or so exercises for this. Figuring out the network, subnet mask and range. If you want me to scan them to PDF, I could probably do that. I'll even white out my answers for ya.
 
Maximus825 said:
My lab book has 6 or so exercises for this. Figuring out the network, subnet mask and range. If you want me to scan them to PDF, I could probably do that. I'll even white out my answers for ya.
Click to expand...

The more practice questions, the better. I have a ten hour flight there and back, so I'll have plenty of time to practice. I found a really good workbook online, it's about 85 pages long, I've been working through that. It doesn't tell you how to, just questions and a few examples.So far I'm catching on fairly well.
 
AMD_Gamer said:
Just checked it out and same thing. they just ask you to find :"the subnet and broadcast IPs" easy stuff.

Do you get design questions? like you need this many subnets with so many hosts?
Click to expand...

Wendell Odom has a few examples of practical questions in his book that will help you with that. Also learn to write out a subnet table from memory and do that first thing on your test. It will help with answering questions a lot faster. Ask your test proctor when you can start writing and go with it.
 
Langly said:
Wendell Odom has a few examples of practical questions in his book that will help you with that. Also learn to write out a subnet table from memory and do that first thing on your test. It will help with answering questions a lot faster. Ask your test proctor when you can start writing and go with it.
Click to expand...

Heh, all I wrote down when I did my CCNA was "128 64 32 16 8 4 2 1" And the proctor thought I was a weirdo since (I'm assuming) he doesn't know anything about subnetting. :p
 
Tomorrow is my CCENT exam. I'm nervous, but confident. Subnetting was an issue a while back, as I was overthinking it. I know my binary math (since I was a kid), and a few months ago everything just clicked and BOOM! I'm good at it now. I know my Cisco switch and router commands pretty well (CCNA level, anyway). I know my interfaces. I just hope I know it to Cisco's way. I've had a lot more hands on lately (of course, I went from using 3660's and 2600's to using Nexus and 2950's to Gb/10Gb switches).

Any advice on what to do any last minute study on?
 
Ur_Mom said:
Tomorrow is my CCENT exam. I'm nervous, but confident. Subnetting was an issue a while back, as I was overthinking it. I know my binary math (since I was a kid), and a few months ago everything just clicked and BOOM! I'm good at it now. I know my Cisco switch and router commands pretty well (CCNA level, anyway). I know my interfaces. I just hope I know it to Cisco's way. I've had a lot more hands on lately (of course, I went from using 3660's and 2600's to using Nexus and 2950's to Gb/10Gb switches).

Any advice on what to do any last minute study on?
Click to expand...
If you know your stuff, you should be fine. As long as you don't overthink things! Good luck!
 
Ur_Mom said:
Tomorrow is my CCENT exam. I'm nervous, but confident. Subnetting was an issue a while back, as I was overthinking it. I know my binary math (since I was a kid), and a few months ago everything just clicked and BOOM! I'm good at it now. I know my Cisco switch and router commands pretty well (CCNA level, anyway). I know my interfaces. I just hope I know it to Cisco's way. I've had a lot more hands on lately (of course, I went from using 3660's and 2600's to using Nexus and 2950's to Gb/10Gb switches).

Any advice on what to do any last minute study on?
Click to expand...

So how did you do today?
 
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