Transcender / Subnetting

borsky

Hi

Here are some of the answers/explanation I read in Transcender and think they are not correct. What do you think?

1. "...DNS servers cannot resolve single-part names to IP addresses"

(single-part: I have never seen this expression before it might refer to single label, unqualified names.)

2."...You should not create the same Active-Directory integrated zone on domain controllers for different domains because those zones would not be automatically synchronized"
(Two domains: A and B. Dns zones are active-dir-integrated in both domains. Dns in A can resolve names in both domains, but Dns in B can only resolve names in B. You want users in B to be able to resolve names in both domains.
Transcender's answer:In B implement a secondary zone for A)

Source: Trancender 70-218 question A52 and B23

I also found two incorrect answers about subnetting one of wich has been corrected. The other one is this:
Question A24: you plan to set up 4 subnets with up to 20 host on each. You'll use 192.168.0.0/24 private addr. Which subnet mask should you assign?
a. 255.255.255.192
b. 255.255.255.224

What is your suggestion?

Webmaster

Transcender has recently send me a full 70-218 TranscenderPak to review and I'm currently using it to study for the exam myself...
I couldn't find the first two questions yet... (will get back on these later today, I need to see them first to be sure...) but I've seen the subnetting question and I think you should just read the explanation carefully necause it makes very clear why the answer is 255.255.255.224 (224 = 128+64+32 = 3 bits = 2 x 2 x 2 = 8 -2 = 6 subnets allowed.)
255.255.255.192 would allow for only 2 subnets...

DNS cannot resolve single-part names to IP addresses... the server needs the FQDN including the domain(s), that's for sure..... with only the host part it wouldn't know were to look (in which zone...)

More later...

Johan

borsky

Subnetting:
you don't have to subtract 2 when calculating the number of subnets. Only when you calculate the total number of subnets on a given portion of the network you need to do the deduction of 2.
For creating 4 subnets you only need two bits and make the following addresses:192.168.0.0, (00)
0.64, (01)
0.128 (10)
0.192 (11)

DNS can resolve single-part names using WINS lookup, or it can append connection specific suffixes to the single-label names as it is configured by default.
By the way I wrote an email to Transcender about these and they told me to run an update. I did it and still got the wrong answers. Now they told me to check the update dates (go to Help and select About ManageCert 2000) and it should be 11/06/2003 but mine is 11/06/2002. Later on they sent me another mail saying 11/06/2002 is fine and updated.
Can you tell me what the date is on yours ?

Webmaster

borsky wrote:

Subnetting:
you don't have to subtract 2 when calculating the number of subnets. Only when you calculate the total number of subnets on a given portion of the network you need to do the deduction of 2.
For creating 4 subnets you only need two bits and make the following addresses:192.168.0.0, (00)
0.64, (01)
0.128 (10)
0.192 (11)

No. You DO have to substract the two. There are ways around this in Cisco (I believe its the ip subnet-zero command) but when you calculate subnets in general (as well as Comptia or MS) you DO have to substract the two. Who or what source told you otherwise?

DNS can resolve single-part names using WINS lookup, or it can append connection specific suffixes to the single-label names as it is configured by default.

Yes, who is DNS in this case why can the connection specific suffixes be appended?

I think they mean (at least that's what you posted) DNS servers can not resolve single part names, this is very logical if you understand how a the DNS db is build (it needs to now the located the zone where the A record is located, therefore it needs the FQDN, if the 'DNS' uses WINS it uses the WINS server not the DNS server. I agree this question is a bit ambigious, but it doesn't seem incorrect, BUT i haven't read the full question in my version yet...

Can you tell me what the date is on yours ?

11/06/2002

More later...

borsky

As far as the subnetting question concerned I am still not convinced.
Please check Transcender 70-216 question C20 it is a good explanation and it supports my point of view on this.

Webmaster

www.groupstudy.com/notes/notepages/Subnetting.PDF

www.techtutorials.com/tutorials/networking/subnetting.shtml

http://infocenter.cramsession.com/techlibrary/PDFFile/520.pdf

www.learntosubnet.com

And some subnetting exams I once wrote for another site:
www.certyourself.com/exams/ccna/ccstart.php?excode=ccna7

I hope these will convince you, I've calculated subnets untill my head started spinning for my certs and took many late afternoons teaching others... You are probably making the most common mistake in subnetting

borsky

There is a big misunderstanding about this and I noticed even some books are incorrect about it. Here are my reasons:
It is clear why we have to subtract 2 when calculating host numbers. It is because the host ID can't have all 0's and 1's. All 0's on the host ID equals the network ID (Net ID:192.168.1.0/24 where the first possible host ID is 192.168.1.1) and all 1's on the host ID is the loopback address of the (sub)network.
Now please tell why should you subtract to when calculating the network ID?
E.g you need 2 subnets, you borrow 1 bit. 192.168.0.0 is the Network addr. Two subnets will be: 192.168.0.0/25 (where the first host is 192.168.0.1 the last is 0.127) and 192.168.0.128/25 (where the first host is 192.168.0.129 and the last is 0.255)
Now if you can give me any satisfactory reason - apart from your book - why I am wrong I will be grateful.
By the wy if you check 70-216 Transcender question C20 it has a good explanation.
I have done 216 and spent some time with subnetting. Now I realized that sources are not always reliable even Transcender.

Webmaster

Just read the links provided above...

10000000 is not valid... this would result in a (sub)network address of 0s or all 1s which is not valid (like I said in some cases it is, Cisco routers using the correct routing protocol can handle it)

Again just read the links above, it is explained in at least 3 of them, carefully read the first line in the Cramsession's Quick and Dirty Subnetting Guide...

(I don't have the 70-216 Transcender by the way) And don't have this from just a book, I've designed large networks with dosens of subnets and encountered it in several exams... I know subnetting... It's just one of those things you have to do over and over again untill it sticks... there's some in the 70-216 and maybe 218 exam but wait untill you decide to take cisco exams...

The formula for calculating subnets is: 2^n-2, where "n" is the number of subnet bits.

borsky

I checked one of your sources and I am shocked!
Anyway here is my final proof from Microsoft, check it out.

http://support.microsoft.com/default.aspx?scid=kb;EN-US;164015


In this case, you divide your network into four subnets by using a subnet mask that makes the network address larger and the possible range of host addresses smaller. In other words, you are 'borrowing' some of the bits usually used for the host address, and using them for the network portion of the address. The subnet mask 255.255.255.192 gives you four networks of 62 hosts each. This works because in binary notation, 255.255.255.192 is the same as 1111111.11111111.1111111.11000000. The first two digits of the last octet become network addresses, so you get the additional networks 00000000 (0), 01000000 (64), 10000000 (12 and 11000000 (192). (Some administrators will only use two of the subnetworks using 255.255.255.192 as a subnet mask. For more information on this topic, see RFC 1878.) In these four networks, the last 6 binary digits can be used for host addresses.

Using a subnet mask of 255.255.255.192, your 192.168.123.0 network then becomes the four networks 192.168.123.0, 192.168.123.64, 192.168.123.128 and 192.168.123.192. These four networks would have as valid host addresses:
192.168.123.1-62
192.168.123.65-126
192.168.123.129-190
192.168.123.193-254

Remember, again, that binary host addresses with all ones or all zeros are invalid, so you cannot use addresses with the last octet of 0, 63, 64, 127, 128, 191, 192, or 255.

You can see how this works by looking at two host addresses, 192.168.123.71 and 192.168.123.133. If you used the default Class C subnet mask of 255.255.255.0, both addresses are on the 192.168.123.0 network. However, if you use the subnet mask of 255.255.255.192, they are on different networks; 192.168.123.71 is on the 192.168.123.64 network, 192.168.123.133 is on the 192.168.123.128 network.

Good Luck!

Webmaster

Good Luck!

I checked one of your sources and I am shocked!

and dosens of online sources will tell you the same... these are just a few...

I'm almost giving up but... we actually have a subnetting TechNote coming up for the Net+, CCNA and 70-216 exam... makes this discussion worthwhile... just remember what I keep saying: that this what MS says only goes if all your routing equipment and the routing protocol supports it...

Here's an excerpt from a page at cisco clearing it all up: the use of the ip subnet-zero command to allow Subnet Zero and the All-Ones Subnet

""Traditionally, it was strongly recommended that subnet zero and the all-ones subnet not be used for addressing. According to RFC 950 , "It is useful to preserve and extend the interpretation of these special (network and broadcast) addresses in subnetted networks. This means the values of all zeros and all ones in the subnet field should not be assigned to actual (physical) subnets." This is the reason why network engineers required to calculate the number of subnets obtained by borrowing three bits would calculate 23-2 (6) and not 23 (8 ). The "-2" takes into account that subnet zero and the all-ones subnet are not used traditionally.""

The word "traditionally" obviously explains....

I'll be sure to give the extra information needed to determine the actual possible amount of subnets that can be assigned to physical segments in our upcoming subnetting practice questions...

borsky

Well, here is what RFC1878 says about this. The question is now which is considered to be auhtentic source.

http://www.faqs.org/rfcs/rfc1878.html

Webmaster

borsky wrote:

Well, here is what RFC1878 says about this. The question is now which is considered to be auhtentic source.

Nah, this should not be questioned... both are authentic... they don't contradict eachother.

Like I've said in pretty much every post in this topic... you don't have to substract the 2 subnets if all your routing hardware and software supports it... especically the routing protocol... in modern cisco routing environments using a routing protocol that supports CIDRand Subnet Zero and the All-Ones Subnet (using the ip subnet-zero command) the 2 are not substracted, this ofcourse would be a waste of addresses when it's not neccesary.

So the conclusion should be that you need additonal info when answering subnetting questions... (it's getting about time I actually read the Transcender questions to see the full wording....)

Anyway, I agree this isn't explained or mentioned well enough in any of the well-known online subnetting resources I provided and they could all use an update...

Webmaster

[I've removed you other new topic, please don't start this discussion all over again in a new topic, just reply on this one , there is enough information provided by you and me in the previous post in this topic to clear this up, otherwise I'm sure this post will]

In traditional subnetting you have to substract the 2. (this is the way it is described in most books, tutorials and online references, especially those related to certification) If your network equipment supports it and an appropriate routing protocol is being used (e.g. OSPF, RIPv2, EIGRP) you do not have to substract the 2, allowing you to assign the Subnet Zero and the All-Ones Subnet.

As mentioned in RFC1878 (to which you posted a link):
"""For the sake of completeness within this memo, tables 2-1 and 2-2
illistrate some options for subnet/host partions within selected
block sizes using calculations which exclude all-zeros and all-ones
subnets [2]. Many vendors only support subnetting based upon this
premise. This practice is obsolete! Modern software will be able to
utilize all definable networks.
"""
I agree most modern networks use a routing protocol that supports it, but in traditional subnetting this is not implied. (that's why I said once or twice that you need more information to answer a subnetting question.)

Back to the Transcender question this discussion started with (question 24 in my version), it is a simple subnetting question asking to design an IP addressing scheme for your company's network. Besided that it doesn't provide any information except the private network address+subnet and the desired amount of subnets+hosts.
I would go for the traditional way (since I don't have any information about the network) and substract the 2, so I share Transcenders' opinion and would choose 255.255.255.224 as correct allowing for 6 subnets.

Would it say"for your company's network with Windows 2000 based routers (Ripv2 or OSPF) etc. etc." I would agree and wouldn't substract the 2 because they can be assigned. (yes, I agree this is a Windows 2000 exam..., nevertheless...)
In reality you should still choose 255.255.255.224 allowing for some growth

And last but not least one of the references that comes with Transcenders' explanation, most probably the one they based their question on, carefully read the last paragraph of this excerpt, because the network gives absolutely no info about the network, the hardware, software and routing protocols used, that's why you should go for the traditional method:

www.microsoft.com/windows2000/techinfo/reskit/en-us/cnet/cnbb_tcp_rlgr.asp

""""RFC 950 forbade the use of the subnetted network IDs where the bits being used for subnetting are set to all 0's (the all-zeros subnet) and all 1's (the all-ones subnet). The all-zeros subnet caused problems for early routing protocols and the all-ones subnet conflicts with a special broadcast address called the all-subnets directed broadcast address.

However, RFC 1812 now permits the use of the all-zeros and all-ones subnets in a CIDR*-compliant environment. CIDR-compliant environments use modern routing protocols that do not have a problem with the all-zeros subnet and the all-subnets directed broadcast is no longer relevant.

The all-zeros and all-ones subnets may cause problems for hosts or routers operating in a classful mode. Before you use the all-zeros and all-ones subnets, verify that they are supported by your hosts and routers. Windows 2000 and Windows NT support the use of the all-zeros and all-ones subnets."""" (again, yes, I agree this is a Windows 2000 exam..., nevertheless...)

Source: Windows 2000 Server Resource Kit
* CIDR = Classless InterDomain Routing.

I hope this is finally a satisfying answer, sorry it took me so long I'm sure at least our subnetting TechNote will benifit from this 'debate' Thanks.

Webmaster

On a side note: Microsoft would probably want you to assume the entire network is Windows based

borsky

Thank you Webmaster indeed. It was very educational.

I did not know about the older method of calculating subnets, and it is probably due to the fact that I never had to do it that way since I started MCSE.
As I probably mentioned earlier I found Transcender 216 very helpful to understand subnetting and in that there were no questions and explanation where subnets were calculated in the "old" way or let alone mentioned that it is possible. Since I saw that particular question in 218 I became uncertain about what Microsoft requires in the exam when it comes to calculate subnets.

So thanx again for the better understanding!

Borsky