CCNA Study Group

Magic Johnson

Haha! Thought I was going mad for a minute!

xnx

I've updated my previous posts on last page with an answer and explanation, sorry for any confusion caused earlier.

xnx

cpartin wrote: »

Answer is 172.144.0.0/12.

The /16 is a typo. Think about it this way, you can't summarize 2 large subnets with a smaller one so that answer fails a quick sanity check. Question is a bit tricky since the IP addresses given are in the middle of the subnet.

172.148.0.0/13 = 172.144.0.0 - 172.151.255.255
172.156.0.0/13 = 172.152.0.0 - 172.159.255.255

Range to summarize is therefore 172.144.0.0 - 172.159.255.255.

Edit: Original logic didn't work for all cases.

Please check my earlier post, a route summary includes the lowest address in range in the summary

anywho

Going back to original question, my shortcut to avoid binary is this:

1. Determine "block size" by subtracting larger interesting octet from smaller one. "Block size" can only be a power of 2.

2. In this question, I have to use 16 because 8 won't include 172.156 network. So the network address given the range and block size is 172.144.0.0

3. To determine subnet, subtract "block size" from 256 (256-16=240). 240 goes in the interesting octet, so 255.240.0.0 = /12

cpartin

Xnx, check your network boundaries. 172.148.0.0/12 doesn't cover 172.148.0.0 - 172.164.0.0, it's 172.144.0.0 - 172.159.255.255. See below how IOS auto corrects it.

R1(config-if)#ip summary-address eigrp 10 172.[B]148[/B].0.0 255.240.0.0
R1(config-if)#do show run int fast 0/0
Building configuration...


Current configuration : 138 bytes
!
interface FastEthernet0/0
 no ip address
 ip summary-address eigrp 10 172.[B]144[/B].0.0 255.240.0.0 5

Also I found this site to double check, I was starting to get confused lol.

http://asecuritysite.com/ip/routesum

Magic Johnson

I can pretty much do /16 and above without even thinking, but below that it gets a bit cloudy.

cpartin

Anywho, that's exactly how I do it as well. One thing you have to keep in mind though is whether you cross network boundaries.

See the below summarizations. Both are contiguous /13s, but have different sized summaries. /13+/13 doesn't always equal /12 lol.

172.144.0.0/13 + 172.152.0.0/13 = 172.144.0.0/12
172.152.0.0/13 + 172.160.0.0/13 = 172.128.0.0/10

xnx

cpartin wrote: »

Xnx, check your network boundaries. 172.148.0.0/12 doesn't cover 172.148.0.0 - 172.164.0.0, it's 172.144.0.0 - 172.159.255.255. See below how IOS auto corrects it.

R1(config-if)#ip summary-address eigrp 10 172.[B]148[/B].0.0 255.248.0.0
R1(config-if)#do show run int fast 0/0
Building configuration...


Current configuration : 138 bytes
!
interface FastEthernet0/0
 no ip address
 ip summary-address eigrp 10 172.[B]144[/B].0.0 255.248.0.0 5

Also I found this site to double check, I was starting to get confused lol.

http://asecuritysite.com/ip/routesum

You've entered a /13 mask here instead of a /12 in your IOS Config

255=8
240 = 4

Jon_Cisco

cpartin wrote: »

http://asecuritysite.com/ip/routesum

Great set of posts. We might all be confused but that's how learning happens.

My guess is the original question had a typo in the answer that made us all start second guessing ourselves. I'm gonna try out that routesum link. Might be nice for checking my math.

@magic I thought I was going mad too and I'm thinking of testing next week!

Magic Johnson

Jon_Cisco wrote: »

Great set of posts. We might all be confused but that's how learning happens.

My guess is the original question had a typo in the answer that made us all start second guessing ourselves. I'm gonna try out that routesum link. Might be nice for checking my math.

@magic I thought I was going mad too and I'm thinking of testing next week!

Lol just be safe in the knowledge that there are no typos in the exam!

In fact mate you'd be surprised at how many typos/wrong terms are used in the learning materials. There were a couple in Odoms that really made me question my sanity and learning methods!

cpartin

xnx wrote: »

You've entered a /13 mask here instead of a /12 in your IOS Config

255=8
240 = 4

Nice catch, I totally screwed that up. Same output though.

R1(config-if)#ip summary-address eigrp 10 172.148.0.0 255.240.0.0
R1(config-if)#do show run int fast 0/0
Building configuration...


Current configuration : 138 bytes
!
interface FastEthernet0/0
 no ip address
 ip summary-address eigrp 10 172.144.0.0 255.240.0.0 5

Long story short, don't feel bad everyone, this stuff is confusing lol.

cpartin

What I did for my CCNA prep was visit this site and drill for 10-15 min a day. Apparently I need to go back and practice some more!

subnettingquestions.com - Free Subnetting Questions and Answers Randomly Generated Online

xnx

cpartin wrote: »

What I did for my CCNA prep was visit this site and drill for 10-15 min a day. Apparently I need to go back and practice some more!

subnettingquestions.com - Free Subnetting Questions and Answers Randomly Generated Online

I love this site, my highest score was 19 before the 'enter key' functionality was brought in

xnx

Just realised my mistake in earlier post too, I couldn't add 16 to 144. *facepalm*

Agent47

Thank you all for your responses, glad this got everyone thinking . I'm going to go through and re-read them to see how I can apply your suggestions. I printed out all of the summaries and written labs from Lammle's book so I believe that question is from chapter 6. Will send another update once I get a little practice in.

ME when I finally figure out route summarization and ACL's:

https://www.youtube.com/watch?v=SXHxxj1oBeI

Have a good day and thanks again!

--chris--

Just finished Odoms chapter on sumerization. I am feeling very overwhelmed on the whole sumerization & VLSM subject. Is that something that I just need to practice more to get comfortable with?

davenull

I was struggling with summarization and especially VLSM for a bit too.

For VLSM, the breakthrough came when I realized that different subnet masks basically define different block sizes, the "floor" and the "ceiling" of a subnet, but that the pool of addresses still remains the same. You are just cutting up the same pie in different size slices.

For summarization, I just imagine it in my head in binary, I'm going from left to right looking for the first bit that is different, then the bit before that defines the new mask. There might be an easier way, but it works for me so far.

xnx

I found summarisation slightly difficult too when I first learnt it, now I just think of the range of addresses that need to be summarised and the mask that'll allow an increment to go up to a network that both address ranges.

e.g 172.16.2.0
172.16.5.0

Lowest network is 172.16.0.0 and we need to go up in a increment of 8 on 3rd octet to cover the 172.16.5.0 network.

So 172.16.0.0/21 will go up in 8's on the 3rd octet and cover 172.16.0.0 to 172.16.7.0 but NOT the 172.16.8.0 network as that's the start of a new block.

Magic Johnson

Just finished EIGRP, now onto troubleshooting routing protocols! More than half way through now.

--chris--

xnx wrote: »

I found summarisation slightly difficult too when I first learnt it, now I just think of the range of addresses that need to be summarised and the mask that'll allow an increment to go up to a network that both address ranges.

e.g 172.16.2.0
172.16.5.0

Lowest network is 172.16.0.0 and we need to go up in a increment of 8 on 3rd octet to cover the 172.16.5.0 network.

So 172.16.0.0/21 will go up in 8's on the 3rd octet and cover 172.16.0.0 to 172.16.7.0 but NOT the 172.16.8.0 network as that's the start of a new block.

davenull wrote: »

I was struggling with summarization and especially VLSM for a bit too.

For VLSM, the breakthrough came when I realized that different subnet masks basically define different block sizes, the "floor" and the "ceiling" of a subnet, but that the pool of addresses still remains the same. You are just cutting up the same pie in different size slices.

For summarization, I just imagine it in my head in binary, I'm going from left to right looking for the first bit that is different, then the bit before that defines the new mask. There might be an easier way, but it works for me so far.

Thanks, the both of ya. These ideas have helped me, quite a bit in fact.

Jon_Cisco

I scheduled my CCENT for this Friday.

For review I have been skimming Odems chapters for the last week (didn't have time to read the book) and taking a practice test each night.
I keep a list of terms I don't know or understand while testing and look up the topics at the end of the test.

My original learning was the Netacad and CBT Nuggets.

Magic Johnson

Jon_Cisco wrote: »

I scheduled my CCENT for this Friday.

For review I have been skimming Odems chapters for the last week (didn't have time to read the book) and taking a practice test each night.
I keep a list of terms I don't know or understand while testing and look up the topics at the end of the test.

My original learning was the Netacad and CBT Nuggets.

Good luck!

ednard

I miss studying for my CCNA Had to postpone it until I finish my second year at Uni, and I'm hoping to take my Composite in September, can't wait.

Magic Johnson

Feeling very overwhelmed with STP and EIGRP at the moment. I've not even hit WAN protocols yet (the part people say is the hardest!). Self doubt creeping in. Hopefully my new job kicks me back in to action.

--chris--

Magic Johnson wrote: »

Feeling very overwhelmed with STP and EIGRP at the moment. I've not even hit WAN protocols yet (the part people say is the hardest!). Self doubt creeping in. Hopefully my new job kicks me back in to action.

I know the feeling. I have finished Lammles book and have two chapters left in Odoms book, yet feel very far away from being ready for the exam.

The one thing that has made me feel better is to realize my 12 month goal for CCNA is just a self imposed goal. I only disappoint myself if I don't get this done in 12 months, no one else. Its not like I lose my job if I don't get it in that time period. You see where I am going with this?

Once I take some pressure of myself and look at things again I feel renewed hope and the self doubt starts to go away because i know given enough time anyone can learn this stuff.

--chris--

Question on NAT/PAT (more or less, am I right?):

Static NAT and Dynamic NAT require a 1:1 relationship of inside local address's to inside global addresses right? While PAT is the only translation technique that can do a Many:1?

Magic Johnson

--chris-- wrote: »

Question on NAT/PAT (more or less, am I right?):

Static NAT and Dynamic NAT require a 1:1 relationship of inside local address's to inside global addresses right? While PAT is the only translation technique that can do a Many:1?

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.

Magic Johnson

--chris-- wrote: »

I know the feeling. I have finished Lammles book and have two chapters left in Odoms book, yet feel very far away from being ready for the exam.

The one thing that has made me feel better is to realize my 12 month goal for CCNA is just a self imposed goal. I only disappoint myself if I don't get this done in 12 months, no one else. Its not like I lose my job if I don't get it in that time period. You see where I am going with this?

Once I take some pressure of myself and look at things again I feel renewed hope and the self doubt starts to go away because i know given enough time anyone can learn this stuff.

I planned to have my CCNA by the end of April. That's way out the window, don't even think I'll have it by May. I can make my target June, would be nice to be certified for my birthday.

I'm the same, it's a self-imposed deadline.

Really enjoying GNS3 at the moment though, it just 'feels' miles better than PT or Boson Netsim.

Magic Johnson

Magic Johnson wrote: »

Really enjoying GNS3 at the moment though, it just 'feels' miles better than PT or Boson Netsim.

And sweet fate, with a cruel twist of her Valyrian steel knife, stabs me right in the back and breaks my base topology config that had taken me 4 hours this morning to set up.

ARGH.

EDIT: Ok fixed got my topology back (was stored on network instead of local, was causing errors) but I didn't copy my running configs over to startup and I didn't realise GNS3 doesn't save the running configs when you save the project! D'oh!!!

jeffgibbs

Magic Johnson wrote: »

Feeling very overwhelmed with STP and EIGRP at the moment. I've not even hit WAN protocols yet (the part people say is the hardest!). Self doubt creeping in. Hopefully my new job kicks me back in to action.

I know how you feel I was really hoping to have finished CCNA up by the end of April. Now it looks like I wont be taking the test untill maybe the end of June. EIGRP threw me for a loop as well . I suppose that may be partly just lack of familiarity with it. I have worked professionally with OSPF so its had extra reinforcement in my brain, but never EIGRP.

I thought I understood STP untill the Per Vlan bridge election process was "explained to me" I understand it when I read it but looking at in in a network and everything gets kind of hazy. STP itself is simple. Its the sometmes complex networks we build that complicates it and makes your mind hurt. I am of course paraphraseing Jeremy for CBT Nuggets here.

I think the solution for me is probably more labs to reinforce the reading and videos. Hang in there. Remember it was by persistance that the snail made it to the Ark.


Jeff