RE: IP Address Calculation [1:1010]
Part of the learning experience, as frustrating as it may be at times, is learning to separate the several grades of accurate from the several grades of inaccurate. One does this by reading from at least two sources, and asking questions on the forums. There are many wonderful sources out there, and ALL of them contain errors, ranging from fat finger kinds of things to total off the wall stuff. What is particularly frustrating is that for many of the middle of the road terminology or definitional "errors" there may not be "right" answers in the strict sense of the term. Kinda like reading a dictionary and finding that a word has several meanings, some of which may not be directly related. When I took my first Cisco training courses several years ago, the instructor's use of the term "bits of subnetting" ( and therefore I presume Cisco's as well, seeing as these were official Cisco courses ) referred to any bits IN ADDITION TO the number of classful mask bits. I.e. if we were asked to subnet 172.16.0.0 with 12 bits of subnetting, we were expected to know, or at least figure out, that the mask in question would be 255.255.255.240 Some sources word it in this way: subnetting is moving / adding mask bits to the right, while supernetting / aggregating is subtracting mask bits to the left. The assumption is that you are beginning with the classful mask. As always, you should be writing these things out in binary and looking at the ones and the zeros in relation to eachother. At first it can seem like learning Sanscrit. But once it clicks, you will never be confused again. In terms of test taking, particularly when you are sitting in the room, my recollection is that if you understand the principals of subnetting, you will not become confused by the wording of the questions and the answer choices given. Hey, Leigh Anne, when's the book due? Chuck -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]] On Behalf Of Leigh Anne Chisholm Sent: Thursday, November 23, 2000 3:22 PM To: JL; [EMAIL PROTECTED]; [EMAIL PROTECTED]; [EMAIL PROTECTED] Subject:RE: IP Address Calculation [1:1010] Mitsunori: I was looking through the Sybex CCNA Study Guide 2nd edition, and couldn't find the question you reference--I assume it's from a different book in their CCNA series... I recently completed a project with Sybex that is due out in January. The one thing my editor and I really worked on was ensuring that the terminology used was correct and that didn't confuse the test taker. In my opinion, when I read "12-bit subnet mask" I assume exactly that -- there are 12 bits in the subnet mask. If I as the author of the test question wanted you to calculate a subnet where you would tack on 12 bits of subnetting to the subnet mask, I would use the terminology "12 bits of subnetting". Travis was on the right track when he said that "a subnet is the 'borrowed bits'". Those borrowed bits are "the bits of subnetting". Often you can deduce the response being sought by looking at the options available. In this case, the author of the question is looking for a 28 bit subnet mask response. Same applies for whether when determining the number of networks or hosts available, whether ip subnet zero is expected as a response or not. For the CCNA exam, the formula to calculate hosts is always 2^n-2 (no ip subnet zero). It's really unfortunate that a question such as this exists, but sometimes we authors don't think about terminology... I got caught on BRI - I thought it was Basic Rate ISDN. My editor pointed out BRI is actually Basic Rate Interface. I checked with CCITT (the organization responsible for ISDN standards). Sure enough, she was correct! As an author, I feel that it's very important for authors to think about how someone less experienced will interpret a question. In this case, I'd say Sybex dropped the ball - but as long as they keep the editor I worked with on the CCNA Virtual Test Center project, I'd expect the number of errors or unclear statements to decrease drastically. If Sybex can keep people THAT good (and as long as my editor IS the editor), I'd definitely recommend their future Cisco reference materials! As you work through your CCNA, a great reference is certificationzone.com. CertificationZone strives for an extremely high level of technical accuracy and that really benefits the beginner because you DON'T learn things that are wrong. Been there, done that--it's no fun. It's so hard to unlearn things you've learned wrong... I've also heard good things about ccprep.com (to plug someone I'm not affiliated with...) Yes, both sites charge for their services, but you get what you pay for with Internet sites... -- Leigh Anne -----Original Message- From: [EMAIL PROTECTED] [mailto:[EMAI
RE: IP Address Calculation [1:1010]
Mitsunori: I was looking through the Sybex CCNA Study Guide 2nd edition, and couldn't find the question you reference--I assume it's from a different book in their CCNA series... I recently completed a project with Sybex that is due out in January. The one thing my editor and I really worked on was ensuring that the terminology used was correct and that didn't confuse the test taker. In my opinion, when I read "12-bit subnet mask" I assume exactly that -- there are 12 bits in the subnet mask. If I as the author of the test question wanted you to calculate a subnet where you would tack on 12 bits of subnetting to the subnet mask, I would use the terminology "12 bits of subnetting". Travis was on the right track when he said that "a subnet is the 'borrowed bits'". Those borrowed bits are "the bits of subnetting". Often you can deduce the response being sought by looking at the options available. In this case, the author of the question is looking for a 28 bit subnet mask response. Same applies for whether when determining the number of networks or hosts available, whether ip subnet zero is expected as a response or not. For the CCNA exam, the formula to calculate hosts is always 2^n-2 (no ip subnet zero). It's really unfortunate that a question such as this exists, but sometimes we authors don't think about terminology... I got caught on BRI - I thought it was Basic Rate ISDN. My editor pointed out BRI is actually Basic Rate Interface. I checked with CCITT (the organization responsible for ISDN standards). Sure enough, she was correct! As an author, I feel that it's very important for authors to think about how someone less experienced will interpret a question. In this case, I'd say Sybex dropped the ball - but as long as they keep the editor I worked with on the CCNA Virtual Test Center project, I'd expect the number of errors or unclear statements to decrease drastically. If Sybex can keep people THAT good (and as long as my editor IS the editor), I'd definitely recommend their future Cisco reference materials! As you work through your CCNA, a great reference is certificationzone.com. CertificationZone strives for an extremely high level of technical accuracy and that really benefits the beginner because you DON'T learn things that are wrong. Been there, done that--it's no fun. It's so hard to unlearn things you've learned wrong... I've also heard good things about ccprep.com (to plug someone I'm not affiliated with...) Yes, both sites charge for their services, but you get what you pay for with Internet sites... -- Leigh Anne -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of JL Sent: November 23, 2000 11:37 AM To: [EMAIL PROTECTED] Subject: RE: IP Address Calculation [1:1010] It's important to remember your default mask for all 3 address ranges when looking at a question like this. A class B address has a default mask of 16 bits, so if " You have an IP address of 172.16.4.58 with a 12-bit subnet mask." you would add an additional 12 bits to the default mask and from there determine your valid hosts. 16 bits (default mask) + 12 bits (additional bits) = 28 = 255.255.255.240; then 256 - 240 = 16. You will have valid ranges in multiples of 16, 1-16, 17-32, 33-48, 49-64, etc... you do have to remember to leave out the high and low addresses (network and broadcast) leaving 14 valid host id's per subnet. Using a 172.16.4.58/28 notation would accomplish the same thing and is just an easier way to say "I have a class B address with a 12 bit subnet mask". I personally struggled with subnetting before it finally clicked, it's just important to remember that there are only just so many combinations available. I would suggest approaching this from multiple different angles until you find the one that clicks for you, once it does you'll be amazed at how simple it all seems. Gragg Vaill MCP CCNA NOS Contractor Sprint ION NOC Kansas City, Ks. -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of Timothy R Estes Sent: Thursday, November 23, 2000 8:19 AM To: [EMAIL PROTECTED] Subject: Re: IP Address Calculation [1:1010] Group, That's pretty confusing. (IMHO). If we are going to refer to subnet masks with the /30 notation, then we need to stick to it. How would we know if someone meant with, or without the default mask included? my $0.02 Timothy Estes CCNA Tampa FL ""Travis O'Hara"" wrote in message news:[EMAIL PROTECTED]... > Hi, > > It's important to understand the wording > > 172.16.4.58 is a Class B address. A subnet is the 'borrowed bits' from the > host portion of the address. In this case it is stated as being 12bits > > So by default it has a 16 bit network
RE: IP Address Calculation [1:1010]
It's important to remember your default mask for all 3 address ranges when looking at a question like this. A class B address has a default mask of 16 bits, so if " You have an IP address of 172.16.4.58 with a 12-bit subnet mask." you would add an additional 12 bits to the default mask and from there determine your valid hosts. 16 bits (default mask) + 12 bits (additional bits) = 28 = 255.255.255.240; then 256 - 240 = 16. You will have valid ranges in multiples of 16, 1-16, 17-32, 33-48, 49-64, etc... you do have to remember to leave out the high and low addresses (network and broadcast) leaving 14 valid host id's per subnet. Using a 172.16.4.58/28 notation would accomplish the same thing and is just an easier way to say "I have a class B address with a 12 bit subnet mask". I personally struggled with subnetting before it finally clicked, it's just important to remember that there are only just so many combinations available. I would suggest approaching this from multiple different angles until you find the one that clicks for you, once it does you'll be amazed at how simple it all seems. Gragg Vaill MCP CCNA NOS Contractor Sprint ION NOC Kansas City, Ks. -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of Timothy R Estes Sent: Thursday, November 23, 2000 8:19 AM To: [EMAIL PROTECTED] Subject: Re: IP Address Calculation [1:1010] Group, That's pretty confusing. (IMHO). If we are going to refer to subnet masks with the /30 notation, then we need to stick to it. How would we know if someone meant with, or without the default mask included? my $0.02 Timothy Estes CCNA Tampa FL ""Travis O'Hara"" wrote in message news:[EMAIL PROTECTED]... > Hi, > > It's important to understand the wording > > 172.16.4.58 is a Class B address. A subnet is the 'borrowed bits' from the > host portion of the address. In this case it is stated as being 12bits > > So by default it has a 16 bit network mask a Class a has 8 and a Class C 24 > > 255 255 00 > = 16Bit netmask > |---| |---| > network host > > 255 255 255 240 > = 16bit netmask + 12bit subnet mask + > 4bit host portion > |---| |---||--| > networksubnet host > > > 172.16.4.58 255.255.255.240 is the ip address and network mask > > (anyone got a better way of explaining this bit?) > As networks must start on a border of the subnet that they are divisible by > (anyone got a better way of explaining this bit?) > > we can figure out the the network address for this IP address with this > subnet mask starts at 172.16.4.48 (this is not a host address it's a > network/cable/segment address) first available host address is 172.16.4.49 > your network size is 16 IP addresses so counting from and including > 172.16.4.48 you reach 172.16.4.63. The last address of the network is > discarded as being a host address as well as this will be used as the > broadcast address for the network so the available IP's assignable to hosts > are 172.16.4.49-62 > > That explanation probably sounds as clear as mud but hopefully it's helpful. > It's important to read the questions carefully for the syntax they use and > how it is applied to the subject. > > Trav. > > > -Original Message- > > From: Mitsunori Sagae [mailto:[EMAIL PROTECTED]] > > Sent: Thursday, 23 November 2000 3:46 PM > > To: [EMAIL PROTECTED] > > Subject: IP Address Calculation [1:1010] > > > > > > Hi, and I am kinda lost with the following question on CCNA > > sybex book. > > It's on the Ch4 Review question, and says > > > > You have an IP address of 172.16.4.58 with a 12-bit subnet > > mask. What are > > your valid hosts? > > > > The answer to this question is 172.16.4.49 to 172.16.4.62 > > but I can never get this result, > > > > Can someone help me on this, explaining the logic behind it? > > > > Thanks > > > > mitzs > > > > > > > > > > Message Posted at: > > http://www.groupstudy.com/form/read.php?f=1&i=1010&t=1010 > > -- > > You are reading GroupStudy's Associate Mailing List. To > > unsubscribe follow > > the directions on http://www.groupstudy.com/list/Associates.html > > > > > > > Message Posted at: > http://www.groupstudy.com/form/read.php?f=1&i=1011&t=1010 > -- > You are reading GroupStudy's Associa
