CCNA Study Group

--chris--

Magic Johnson wrote: »

1-1 = 1 address to 1 host. I got confused a bit with Dynamic Nat thinking well there is multiple addresses so that must be many to 1 but no. 1 to Many = 1 public IP shared between many hosts.

So then dynamic NAT can not have concurrent connections? Thats what I read by having a 1:Many connection. If there is only one public IP that is being dynamically matched to a pool of internal private IP's then once that one public is used up there are not more outbound internet connections?

Magic Johnson

--chris-- wrote: »

So then dynamic NAT can not have concurrent connections? Thats what I read by having a 1:Many connection. If there is only one public IP that is being dynamically matched to a pool of internal private IP's then once that one public is used up there are not more outbound internet connections?

Dynamic NAT is a pool of public IPs that get assigned on a first come first served basis. This is a one to one mapping i.e one client gets one public IP address.

PAT is many clients using one public IP address and port address translation up to around 65k connections can be made.

--chris--

Magic Johnson wrote: »

Dynamic NAT is a pool of public IPs that get assigned on a first come first served basis. This is a one to one mapping i.e one client gets one public IP address.

PAT is many clients using one public IP address and port address translation up to around 65k connections can be made.

Ah ok, that's what I was thinking. I had a hard time putting into words. It is possible to exhaust the public pool of IP's with dynamic NAT correct?

Magic Johnson

--chris-- wrote: »

Ah ok, that's what I was thinking. I had a hard time putting into words. It is possible to exhaust the public pool of IP's with dynamic NAT correct?

Oh yes absolutely. You can put only 2 public IPs in the NAT pool and the first two clients that wanted to go on the web and get NAT'd would use them up for as long as needed. The next time a different client needed an address there wouldn't be one, and the request would fail.

You can see the attraction of PAT straight away!

Jon_Cisco

latest update

I passed my CCENT last week with a score of 960. I did a lot of studying over the last 9 months and crammed with practice tests for the last two weeks. Overall the questions are not difficult so much as wide ranged. I know I screwed up in one of the simulations and I knew what they wanted to but command I knew was not available. When studying it's probably worth looking for two ways to verify each thing. I did panic a little as time was wasting. After 10 minutes I took an educated guess without confirming the answer on the router. I finished the test with 7 minutes left so I am glad I didn't waste any more time there. Next exam I might even guess quicker as time management it important also.

This week I am taking my final for Networking IV of the netacad. After the final I plan to take at least a week off of studying. Then I'm watching CBT nuggets for ICND2 and reading Wendell Odem's ICND2 book. I expect to test in June.

This is a great thread and it's good to see it still going after so much time has passed.

Good Luck to everyone!

Agent47

Hey everyone, just checking in and glad to see you all still studying and hanging in there! Congratulations if you've passed your exam recently! Well deserved. If you haven't yet, you will. Keep it right here and stay motivated! I wanted to paste a good/simple explanation on route summarization. With just these few steps now I finally understand. The books get way too wordy for me, this is more simplified and to the point. With a little bit of practice, these can be belted out. This method seems like a relatively fast way to do it also. Let me know if this works for you.



Step 1
List all routes that need to be summarized in dotted decimal format from lowest to highest, then list their matching subnet broadcast addresses based on the given mask.

Example Network Range:
10.3.4.0/24 - 10.3.7.0/24



Subnet ID

Broadcast ID



10.3.4.0

10.3.4.255



10.3.5.0

10.3.5.255



10.3.6.0

10.3.6.255



10.3.7.0

10.3.7.255








Step 2
Write the network ID of the smallest network and the broadcast of the largest network.

Example:


Subnet ID

Broadcast ID



10.3.4.0

10.3.4.255



10.3.5.0

10.3.5.255



10.3.6.0

10.3.6.255



10.3.7.0

10.3.7.255









Step 3
Determine the starting subnet mask.

Take the original subnet mask and subtract 1 as the starting point. This will determine whether or not our range of addresses will be included in the final answer.

Example: 24 - 1 = 23

Now we have /23

Step 4
Take the lowest subordinate subnet ID and find the network ID and broadcast with the mask from Step 3.

Network 10.3.4.0 /23 - 10.3.5.255 Broadcast

(/23 does not work because it does not include all Subnet IDs defined in Step 1)

Repeat Step 3 & 4: Subtract one more from the Subnet Mask 23 - 1 = /22

Recalculate the network and broadcast using /22.

Result:
Network: 10.3.4.0
Broadcast: 10.3.7.255

WINNER - The /22 subnet mask includes all subnets listed in Step 1!




[TH="align: left"] Original Source[/TH]

Agent47

Binary

Mask

Increment

Class (A/B/C)



00000000

0

256

8

16

24



10000000

128

128

9

17

25



11000000

192

64

10

18

26



11100000

224

32

11

19

27



11110000

240

16

12

20

28



11111000

248

8

13

21

29



11111100

252

4

14

22

30



11111110

254

2

15

23

31



11111111

255

1












Hexadecimal



1

0001



2

0010



3

0011



4

0100



5

0101



6

0110



7

0111



8

1000



9

1001



(10) A

1010



(11) B

1011



(12) C

1100



(13) D

1101



(14) E

1110



(15) F

1111

Technoracer

I just passed my ICND2 exam, with a score of 973. This is a good website to practice your skills: DansCourses.com | Computer Networking Classes Taught by Dan Alberghetti.

--chris--

Agent47 wrote: »

Binary
Mask
Increment
Class (A/B/C)


00000000

0

256

8

16

24



10000000
128
128
9
17
25


11000000
192
64
10
18
26


11100000
224
32
11
19
27


11110000
240
16
12
20
28


11111000
248
8
13
21
29


11111100
252
4
14
22
30


11111110
254
2
15
23
31


11111111

255

1












Hexadecimal


1
0001


2
0010


3
0011


4
0100


5
0101


6
0110


7
0111


8
1000


9
1001


(10) A
1010


(11) B
1011


(12) C
1100


(13) D
1101


(14) E
1110


(15) F
1111

NICE!!! I Just finished Odoms book on lunch today and read the exam prep section. Time to hit subnetting hard and memorize these tables. I have about 40 videos in Chris Bryant's Udemy series left as well.

Still not as confident as I want to be, but better than I was last week.

Agent47

Congrats to Technoracer & Jon_Cisco!! Chris sounds like you are getting really close. Yes, definitely memorize this table because honestly, it makes things SOOO much quicker when you can just look it up. I write it out every time I practice subnetting just for the sake of doing it. Do alot of practice questions too, will help you to regulate your time.

Technoracer

Agent47 wrote: »

Congrats to Technoracer & Jon_Cisco!! Chris sounds like you are getting really close. Yes, definitely memorize this table because honestly, it makes things SOOO much quicker when you can just look it up. I write it out every time I practice subnetting just for the sake of doing it. Do alot of practice questions too, will help you to regulate your time.

Thank You Agent47!!! I hope you do well on your exam.

--chris--

Agent47 wrote: »

Congrats to Technoracer & Jon_Cisco!! Chris sounds like you are getting really close. Yes, definitely memorize this table because honestly, it makes things SOOO much quicker when you can just look it up. I write it out every time I practice subnetting just for the sake of doing it. Do alot of practice questions too, will help you to regulate your time.

This will be my game plan for the next week on lunch (maybe more if I need it).

Also I am getting stuck on these types of problems, this is CIDR stuff right?

Enter the last valid host on the network 172.30.192.0/18:

Agent47

Thanks Technoracer, Im trying to stay motivated...............I keep getting off track and my cert expires this October. *sigh*

--chris-- wrote: »

This will be my game plan for the next week on lunch (maybe more if I need it).

Also I am getting stuck on these types of problems, this is CIDR stuff right?

Enter the last valid host on the network 172.30.192.0/18:

Hey Chris, this is kind of a long explanation but I hope it helps one way or the other.

Yes, CIDR is just the short version of a dotted decimal mask.

In regards to your example:

An IP address can be part of 5 classes but we only deal with 3.

The ip ranges for class A,B and C are:
A (8-15): 1-126
B (16-23): 128-191
C (24-30): 192-223

You have a class B IP with a class B Mask
172.30.192.0 /18

The CIDR (Classless Inter-Domain Routing) dotted decimal equivalent of /18 = 255.255.192.0

The Block, Increment or Magic Number (as people like to call it) for this particular mask is 64.

Lets look at the IP:

172.A.B.C

The very first octet (172 in this case) determines your class. This tells you which octet (to the right) to look at next.

So, we look at the third octet:

172.39.192.0

Since we have an increment of 64 we start from 0 and double it until we get past the number in the third octet. These are your subnets (listing these numbers can help you figure out what subnet an ip belongs to but I digress).

0, 64, 128, 192, 256

ok

Now we know that 172.39.192.0 is the actual subnet and that the next subnet will be 172.39.256.0.

As a result:

The valid host range will be 172.39.192.1 - 172.39.255.254


172.39.192.1 is the first valid host and 172.39.255.254 is the last valid host because 172.39.192.0 is the subnet number and 172.39.255.255 is the broadcast number. These are IP's that cannot be assigned to hosts so we subtract 2 from the valid hosts (UNLESS the question mentions something about the ip subnet-zero command).


Subnettingquestions.com & Subnetting.net are great resources for practice. Also helps to have a subnetting calculator to check your work if you're just starting out.

Boom plackity klow.
Heh.

--chris--

Agent47 wrote: »

Thanks Technoracer, Im trying to stay motivated...............I keep getting off track and my cert expires this October. *sigh*



Hey Chris, this is kind of a long explanation but I hope it helps one way or the other.

Yes, CIDR is just the short version of a dotted decimal mask.

In regards to your example:

An IP address can be part of 5 classes but we only deal with 3.

The ip ranges for class A,B and C are:
A (8-15): 1-126
B (16-23): 128-191
C (24-30): 192-223

You have a class B IP with a class B Mask
172.30.192.0 /18

The CIDR (Classless Inter-Domain Routing) dotted decimal equivalent of /18 = 255.255.192.0

The Block, Increment or Magic Number (as people like to call it) for this particular mask is 64.

Lets look at the IP:

172.A.B.C

The very first octet (172 in this case) determines your class. This tells you which octet (to the right) to look at next.

So, we look at the third octet:

172.39.192.0

Since we have an increment of 64 we start from 0 and double it until we get past the number in the third octet. These are your subnets (listing these numbers can help you figure out what subnet an ip belongs to but I digress).

0, 64, 128, 192, 256

ok

Now we know that 172.39.192.0 is the actual subnet and that the next subnet will be 172.39.256.0.

As a result:

The valid host range will be 172.39.192.1 - 172.39.255.254


172.39.192.1 is the first valid host and 172.39.255.254 is the last valid host because 172.39.192.0 is the subnet number and 172.39.255.255 is the broadcast number. These are IP's that cannot be assigned to hosts so we subtract 2 from the valid hosts (UNLESS the question mentions something about the ip subnet-zero command).


Subnettingquestions.com & Subnetting.net are great resources for practice. Also helps to have a subnetting calculator to check your work if you're just starting out.

Boom plackity klow.
Heh.

That you very much. I spent an hour in Lammles book last night going over his method of subnetting, I think it works much better for me (and is similar to what you posted above). I have retained more about the subnetting in just the one day I have really focused on it than I have in all the last 2 months I have been working on the CCENT.

For me subnetting was one of those things I needed to pass over until I see how its used and why its used, then I came back to it and it makes much more sense.

--chris--

Agent47 wrote: »

Heh.

Just wanted to drop by and say thanks again! I spent 90 minutes on this today, the first 60 minutes I got almost every question wrong. The last 30 minutes it started to click and I was answering all of them correctly! Feels good!

I am using subnetting.net for practice.

edit: I have figured out my next weak spot. The questions that go like this:

You have 172.30.0.0 /23. How many subnets and how many hosts will this support?

I got it right once, bombed 3 other times.

Agent47

--chris-- wrote: »

Just wanted to drop by and say thanks again! I spent 90 minutes on this today, the first 60 minutes I got almost every question wrong. The last 30 minutes it started to click and I was answering all of them correctly! Feels good! I am using subnetting.net for practice. edit: I have figured out my next weak spot. The questions that go like this: You have 172.30.0.0 /23. How many subnets and how many hosts will this support? I got it right once, bombed 3 other times.

Hey Chris! You're very welcome! Keep practicing! At first subnetting is confusing but after dissecting it will start to make alot of sense. When you look back at the chart you will have this eureka moment. From there you should be able to solve these questions within 30 sec. I am glad that you are using the links, those will give you some confidence after a while!

As long as you got 1 right that's one more step in the right direction.

So subnets and hosts. With this type of question (I know you didn't ask but I really like subnetting lol), all you need to do is compare the mask thats given i.e. /23 to the default mask for the ip given which is /16 a class b mask.
Compare these masks in dotted decimal (you can do this quickly once you find your groove)

/16 = 1111 1111.1111 1111.0000 0000.0000 0000
/23 = 1111 1111.1111 1111.1111 1110.0000 0000

0 and 1's represent your subnets All 0's represent your hosts.

Remember, you need to calculate to the second power.




512
256
128
64
32
16
8
4
2
1


POWER:
9

8

7

6

5

4

3

2

1

0









Therefore:
128 Subnets (7 subnet bits)
510 Bits (9 purple bits but we subtract 2 to account for the subnet and broadcast addresses which cannot be assigned to a host)

--chris--

Agent47 wrote: »

Hey Chris! You're very welcome! Keep practicing! At first subnetting is confusing but after dissecting it will start to make alot of sense. When you look back at the chart you will have this eureka moment. From there you should be able to solve these questions within 30 sec. I am glad that you are using the links, those will give you some confidence after a while!

As long as you got 1 right that's one more step in the right direction.

So subnets and hosts. With this type of question (I know you didn't ask but I really like subnetting lol), all you need to do is compare the mask thats given i.e. /23 to the default mask for the ip given which is /16 a class b mask.
Compare these masks in dotted decimal (you can do this quickly once you find your groove)

/16 = 1111 1111.1111 1111.0000 0000.0000 0000
/23 = 1111 1111.1111 1111.1111 1110.0000 0000

0 and 1's represent your subnets All 0's represent your hosts.

Remember, you need to calculate to the second power.




512
256
128
64
32
16
8
4
2
1


POWER:
9

8

7

6

5

4

3

2

1

0









Therefore:
128 Subnets (7 subnet bits)
510 Bits (9 purple bits but we subtract 2 to account for the subnet and broadcast addresses which cannot be assigned to a host)

Another great explanation! Good stuff man! I did 4-5 of these, then realized all I needed to do was right down the powers of 2 up 12 on paper then simply look up what I needed to answer them. Once I did that I did another 20 or so in a few minutes time. Very simple once you grasp it!

The way I sped things up was by thinking like this:

Example:

172.16.0.0 /21 How many subs? How many hosts?

This is a class B or /16 by default. We now have a /21. Subtract the 16 from 21 to get 5, which is my subnet answer (2*2*2*2*2 = 32). Then subtract 21 from 32 which is 11, or 2*2*2*2*2*2*2*2*2*2*2 = 2048. Subtract 2 for the sub ID and the broadcast address = 2046.

Thanks a ton! Again!

Magic Johnson

MAN. Started my new job yesterday, I think these guys expect a lot from me. I spend the morning in the NOC today. It's mostly VOIP I'm doing in terms of installs, my boss wants me to configure the routers and switches before installing them and set up how they want their call flows to work using Horizon. That's done at head office now they want to change that.

JeanM

Magic Johnson wrote: »

MAN. Started my new job yesterday, I think these guys expect a lot from me. I spend the morning in the NOC today. It's mostly VOIP I'm doing in terms of installs, my boss wants me to configure the routers and switches before installing them and set up how they want their call flows to work using Horizon. That's done at head office now they want to change that.

Why do you think they expect a lot from you, is it because you have to come up with the design part? Or are you just configuring the routers/switches per the configs that engineer is providing to you?

--chris--

Ran into something that stumped me:





Enter the first valid host on the network that the host 10.179.56.98/29 is a part of:









Given my logic I posted above, the difference between the default mask and the given mask is 21 bits. That cant be, right?

Magic Johnson

JeanM wrote: »

Why do you think they expect a lot from you, is it because you have to come up with the design part? Or are you just configuring the routers/switches per the configs that engineer is providing to you?

No no it's not design, they will specify what is required and I think they want me to build the config myself.

In terms of routing it's mostly DSL stuff, one default route over the dialer interface. They spec their sites so voice has it's own circuit, instead of data flowing over there too.

I've been given a deadline to finish my CCNA. They want me to help out the MPLS dep, the ISP dep, the support dep! So much experience I guess! They want me to become a guru in the VoIP solutions they offer, especially the reporting aspect.

I'm overwhelmed, to say the least. The Certification has definitely helped, but the real thing is miles different. Well not different, but much more in depth.

Agent47

--chris-- wrote: »

Ran into something that stumped me:





Enter the first valid host on the network that the host 10.179.56.98/29 is a part of:







Given my logic I posted above, the difference between the default mask and the given mask is 21 bits. That cant be, right?

Hi Chris,

In this case, look at the mask, then determine which octet to deal with which is the very last one since its a class c mask. List the subnets based on the block number. So /29 = increment or block of 8.

(these are all multiples of 8 ) 88, 96, 104

Therefore, the first valid host would be 10.179.56.97

The last valid host would be 10.179.56.102

The subnet the IP belongs to is 10.179.56.96

The broadcast 10.179.56.103

I personally don't think of the default mask on this type of question.

Agent47

Magic Johnson wrote: »

No no it's not design, they will specify what is required and I think they want me to build the config myself.

In terms of routing it's mostly DSL stuff, one default route over the dialer interface. They spec their sites so voice has it's own circuit, instead of data flowing over there too.

I've been given a deadline to finish my CCNA. They want me to help out the MPLS dep, the ISP dep, the support dep! So much experience I guess! They want me to become a guru in the VoIP solutions they offer, especially the reporting aspect.

I'm overwhelmed, to say the least. The Certification has definitely helped, but the real thing is miles different. Well not different, but much more in depth.

You are lucky lol. It all sounds scary but...........the experience you will get! I hope that you at least have another person to work with on these projects!

--chris--

Agent47 wrote: »

Hi Chris,

In this case, look at the mask, then determine which octet to deal with which is the very last one since its a class c mask. List the subnets based on the block number. So /29 = increment or block of 8.

(these are all multiples of 8 ) 88, 96, 104

Therefore, the first valid host would be 10.179.56.97

The last valid host would be 10.179.56.102

The subnet the IP belongs to is 10.179.56.96

The broadcast 10.179.56.103

I personally don't think of the default mask on this type of question.

You are right. That's the problem with doing these at work, sometimes I get distracted in the middle of them and come back to them later with poor results.

Starting next week I will start going over everything I have read in both Lammle's and Odom's books, but I feel like I dont know where to focus. After this 10 day block of nothing but subnetting I feel comfortable doing it now. I can do some in my head, the rest on paper in under 30 seconds.

Where should I focus after this? Labs? I feel weak on VLAN config but I am using GNS3 so I cant do much labbing with that. I feel unfocused, and dont like it!

Agent47

--chris-- wrote: »

You are right. That's the problem with doing these at work, sometimes I get distracted in the middle of them and come back to them later with poor results.

Starting next week I will start going over everything I have read in both Lammle's and Odom's books, but I feel like I dont know where to focus. After this 10 day block of nothing but subnetting I feel comfortable doing it now. I can do some in my head, the rest on paper in under 30 seconds.

Where should I focus after this? Labs? I feel weak on VLAN config but I am using GNS3 so I cant do much labbing with that. I feel unfocused, and dont like it!

Hi Chris,

Yeah, its kind of hard to get these done at work even with downtime. I need absolute silence when it comes to Cisco lol! Loss of focus is common but you can get it back. It's nice to look at the big picture but approach your studies piece by piece. You can do 1 of 2 things to start.

From lammles book, print out all of the "chapter summaries" and the lab questions at the end. I like this route because I find Lammle easier to follow. Then go chapter by chapter. Then on Odoms, I would print his practice questions also to fill in the gaps. I generally go to Odom for reference.

Or

Simply write down a list of topics you really struggle with and start there.

Set a goal for how many chapters you want to cover per week and move from set to set. Master these chapters and questions.

Lammle has a simulator that goes according to the chapters (starts at ch 6 I think) so you can do the sim labs along with the chapters. Doing it towards the end of your ICND1 study isn't a bad idea either mainly because, since you know the material, labbing and memorizing IOS commands should be a lil easier.

Hope this helps!




PUSH THROUGH Y'ALL! PUSH IT!

--chris--

Agent47 wrote: »

Hi Chris,

Yeah, its kind of hard to get these done at work even with downtime. I need absolute silence when it comes to Cisco lol! Loss of focus is common but you can get it back. It's nice to look at the big picture but approach your studies piece by piece. You can do 1 of 2 things to start.

From lammles book, print out all of the "chapter summaries" and the lab questions at the end. I like this route because I find Lammle easier to follow. Then go chapter by chapter. Then on Odoms, I would print his practice questions also to fill in the gaps. I generally go to Odom for reference.

Or

Simply write down a list of topics you really struggle with and start there.

Set a goal for how many chapters you want to cover per week and move from set to set. Master these chapters and questions.

Lammle has a simulator that goes according to the chapters (starts at ch 6 I think) so you can do the sim labs along with the chapters. Doing it towards the end of your ICND1 study isn't a bad idea either mainly because, since you know the material, labbing and memorizing IOS commands should be a lil easier.

Hope this helps!




PUSH THROUGH Y'ALL! PUSH IT!

That lammle sim looks nice, I didn't bring that book to work but I will tomorrow! Ill run through those tomorrow.

Feeling 100% confident with all sub netting questions. Feels amazing! I am wondering now, do the ICND1/2 exams try to catch you in the wording of these subnetting questions or are they straight forward like the ones you see on Subnetting.net?

Agent47

Trust, Cisco exam questions are pretty straightforward. Just be careful, they are one shot. Once answered, that's it. Glad you're doing better on the subnetting questions!

mikerodriguez

Hey guys, started studying (again) for the CCNA exam lol. I should have already taken the test by now, but I always lose focus towards the end. I joined the forum (After lurking for a long while) to help motivate myself a bit more. Gimme a couple hours, I'll be editing with what I studied. Good luck to everybody in their studies.

EDIT: So 3:36 A.M., at work... Started reading Lammle's book from chapter 2 and am bit more than half way through. I'm thinking about reading the whole book and review key concepts with Odom's book, since it generally goes into more detail.

I'll get through chapter 2 today and stop at chapter 3... I'll continue with that tomorrow

Happy reading.

bugzy3188

Hey all, I figured I’d chime in seeing as how I am scheduled for the 200-120 next Friday. I have read Both the ICND1 and ICND 2 books by Wendell Odom (just finished tonight) and watched both of the series on CBT Nuggets supplementing my reading as I went. I am able to comfortably pass the practice material on the ICND1 exam but still have some work to do on the ICND2 side. Surprisingly I seem to have a solid grasp on Frame Relay and the other WAN technologies on the exam, it is the fine details of various topics that are killing me such as the specific LSA types for OSPF and how to recognize them, or how to calculate specific OSPF costs in relation to the various show commands provided. Luckily I have given myself a week to review, so I will be drilling down heavily in to such topics over the course of the next few days. Specifically; I have identified the following weak areas following my most recent practice exam:

• STP – I have the route port and designated port down, but need to memorize the specifics on how each is chosen and how the hellos work in detail
• IPV6 – link local addressing, global unicast, etc. I have a blurry picture of these items but really need some clarification
• OSPF - I have a fairly solid understanding on implementation, but when looking at a routing table or when asked what a specific cost is based on certain criteria, I struggle

I have heard that the practice exams with these books is actually a bit tougher than the actual exam, can anyone validate this or is this just not true entirely? The questions seem to require a great deal of precision, often times requiring 2 or 3 correct answers out of a group which really kills me. Either way, great thread, I will surely be checking back in before and after the exam!

Magic Johnson

The practice exams with the CISCO Press books are easier I would say. The Boson ones are harder. Overall the exam is probably somewhere in between the two.

The devil is in the detail, as they say. Prepare all the 'gotchas', as Odom puts it. They are killer. Know the outputs of commands, not only for the exam but for real world too. The sooner you can gather info the better, 'sh run' is laborious and may not show you the info you want.

Good luck!