RE: CCNA 2 and subnets
Yarrggh! Of course, that's (2^n) (*not* 2^(n-1) ) Maybe there *is* something to that aspartame story ;) - Tks | mailto:[EMAIL PROTECTED] BV | mailto:[EMAIL PROTECTED] Sr. Technical Consultant, SBM, A Gates/Arrow Co. Vox 770-623-3430 11455 Lakefield Dr. Fax 770-623-3429 Duluth, GA 30097-1511 = -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of Bob Vance Sent: Monday, January 22, 2001 10:35 PM To: CISCO_GroupStudy List (E-mail) Subject: CCNA 2 and subnets Sorry for the lame question, but I gotta know :| We know that subnet -1 (all ones) is valid to config in IOS and that 0 is OK with ip subnet-zero. For purposes of CCNA 2, do we assume that subnet 0 and -1 are valid, vs. CCNA 1 (where they were not) for questions like, "How many subnets can we have with this mask? " ? Does the test make it clear in preliminary text? The archives seem to have conflicting answers. The Cisco Press ICND book (McQuerry, 1-57870-111-2) doesn't address the issue head on, but simply shows tables with (2^(n-1))-2 subnets. The Cisco Press 640-507 Cert Guide (Odom, 0-7357-0971-8) clearly says that 2^(n-1) is correct and yet points out that 0 is only valid with "ip subnet-zero" ! Does anyone know the *definitive* answer for CCNA 2.0 ? - Tks | mailto:[EMAIL PROTECTED] BV | mailto:[EMAIL PROTECTED] Sr. Technical Consultant, SBM, A Gates/Arrow Co. Vox 770-623-3430 11455 Lakefield Dr. Fax 770-623-3429 Duluth, GA 30097-1511 = _ FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: CCNA 2 and subnets
Bob, Howard answered this question for me a while back so I'll try to answer it for you now. This question is probobaly more in depth than you realize, but the question comes down to why did they used to say the equation for finding the amount of valid subnets is 2^#of hosts -2? And why now do we not -2? Well the short answer is -we used to use Classfull addressing. With classfull the reason we used the -2 was because it was a bad idea to use the all 0's or all 1's subnets(highly discouraged is I believe the terminology)When an all 0's subnet update was sent to a classfull router it would not be able to decipher it from the entire network. This is because in clasfull the masks aren't sent with the updates therefore when the classfull mask is placed on say 192.168.0.0/28 it would change it to /24 because again the mask wasn't sent. Which would end up causing some issues obviously. The other one was the all 1's subnets. I'll just make an example. If you think along the same lines as the all 0's. Again in a classfull environment a broadcast for a particular subnet would be interpreted as a broadcast for the entire network. 192.168.0.255/28 has different meaning than 192.168.0.255/24. 3Coms website has the best explaination I have found The article is called: Understanding IP addressing: Everything You Ever Wanted To Know by Chuck Semeria. Cisco, Microsoft, and the RFC's seem to dance around the topic. Brian From: "Bob Vance" [EMAIL PROTECTED] Reply-To: "Bob Vance" [EMAIL PROTECTED] To: "CISCO_GroupStudy List \(E-mail\)" [EMAIL PROTECTED] Subject: RE: CCNA 2 and subnets Date: Tue, 23 Jan 2001 08:24:37 -0500 Yarrggh! Of course, that's (2^n) (*not* 2^(n-1) ) Maybe there *is* something to that aspartame story ;) - Tks | mailto:[EMAIL PROTECTED] BV | mailto:[EMAIL PROTECTED] Sr. Technical Consultant, SBM, A Gates/Arrow Co. Vox 770-623-3430 11455 Lakefield Dr. Fax 770-623-3429 Duluth, GA 30097-1511 = -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of Bob Vance Sent: Monday, January 22, 2001 10:35 PM To: CISCO_GroupStudy List (E-mail) Subject: CCNA 2 and subnets Sorry for the lame question, but I gotta know :| We know that subnet -1 (all ones) is valid to config in IOS and that 0 is OK with ip subnet-zero. For purposes of CCNA 2, do we assume that subnet 0 and -1 are valid, vs. CCNA 1 (where they were not) for questions like, "How many subnets can we have with this mask? " ? Does the test make it clear in preliminary text? The archives seem to have conflicting answers. The Cisco Press ICND book (McQuerry, 1-57870-111-2) doesn't address the issue head on, but simply shows tables with (2^(n-1))-2 subnets. The Cisco Press 640-507 Cert Guide (Odom, 0-7357-0971-8) clearly says that 2^(n-1) is correct and yet points out that 0 is only valid with "ip subnet-zero" ! Does anyone know the *definitive* answer for CCNA 2.0 ? - Tks | mailto:[EMAIL PROTECTED] BV | mailto:[EMAIL PROTECTED] Sr. Technical Consultant, SBM, A Gates/Arrow Co. Vox 770-623-3430 11455 Lakefield Dr. Fax 770-623-3429 Duluth, GA 30097-1511 = _ FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] _ Get your FREE download of MSN Explorer at http://explorer.msn.com _ FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: CCNA 2 and subnets
cisco has a pretty good website out there too http://www.cisco.com/techtools/ip_addr.html "Brian Lodwick" [EMAIL PROTECTED] 01/23/01 01:16PM Bob, Howard answered this question for me a while back so I'll try to answer it for you now. This question is probobaly more in depth than you realize, but the question comes down to why did they used to say the equation for finding the amount of valid subnets is 2^#of hosts -2? And why now do we not -2? Well the short answer is -we used to use Classfull addressing. With classfull the reason we used the -2 was because it was a bad idea to use the all 0's or all 1's subnets(highly discouraged is I believe the terminology)When an all 0's subnet update was sent to a classfull router it would not be able to decipher it from the entire network. This is because in clasfull the masks aren't sent with the updates therefore when the classfull mask is placed on say 192.168.0.0/28 it would change it to /24 because again the mask wasn't sent. Which would end up causing some issues obviously. The other one was the all 1's subnets. I'll just make an example. If you think along the same lines as the all 0's. Again in a classfull environment a broadcast for a particular subnet would be interpreted as a broadcast for the entire network. 192.168.0.255/28 has different meaning than 192.168.0.255/24. 3Coms website has the best explaination I have found The article is called: Understanding IP addressing: Everything You Ever Wanted To Know by Chuck Semeria. Cisco, Microsoft, and the RFC's seem to dance around the topic. Brian From: "Bob Vance" [EMAIL PROTECTED] Reply-To: "Bob Vance" [EMAIL PROTECTED] To: "CISCO_GroupStudy List \(E-mail\)" [EMAIL PROTECTED] Subject: RE: CCNA 2 and subnets Date: Tue, 23 Jan 2001 08:24:37 -0500 Yarrggh! Of course, that's (2^n) (*not* 2^(n-1) ) Maybe there *is* something to that aspartame story ;) - Tks| mailto:[EMAIL PROTECTED] BV | mailto:[EMAIL PROTECTED] Sr. Technical Consultant, SBM, A Gates/Arrow Co. Vox 770-623-3430 11455 Lakefield Dr. Fax 770-623-3429 Duluth, GA 30097-1511 = -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of Bob Vance Sent: Monday, January 22, 2001 10:35 PM To: CISCO_GroupStudy List (E-mail) Subject: CCNA 2 and subnets Sorry for the lame question, but I gotta know :| We know that subnet -1 (all ones) is valid to config in IOS and that 0 is OK with ip subnet-zero. For purposes of CCNA 2, do we assume that subnet 0 and -1 are valid, vs. CCNA 1 (where they were not) for questions like, "How many subnets can we have with this mask? " ? Does the test make it clear in preliminary text? The archives seem to have conflicting answers. The Cisco Press ICND book (McQuerry, 1-57870-111-2) doesn't address the issue head on, but simply shows tables with (2^(n-1))-2 subnets. The Cisco Press 640-507 Cert Guide (Odom, 0-7357-0971-8) clearly says that 2^(n-1) is correct and yet points out that 0 is only valid with "ip subnet-zero" ! Does anyone know the *definitive* answer for CCNA 2.0 ? - Tks| mailto:[EMAIL PROTECTED] BV | mailto:[EMAIL PROTECTED] Sr. Technical Consultant, SBM, A Gates/Arrow Co. Vox 770-623-3430 11455 Lakefield Dr. Fax 770-623-3429 Duluth, GA 30097-1511 = _ FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] _ Get your FREE download of MSN Explorer at http://explorer.msn.com _ FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] _ FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: CCNA 2 and subnets
Using Cisco's website try to find out why the all 1's and all 0's subnet's are strongly discouraged in a classfull environment. Brian From: "Lowell Sharrah" [EMAIL PROTECTED] To: [EMAIL PROTECTED],[EMAIL PROTECTED], [EMAIL PROTECTED] Subject: RE: CCNA 2 and subnets Date: Tue, 23 Jan 2001 13:45:41 -0500 cisco has a pretty good website out there too http://www.cisco.com/techtools/ip_addr.html "Brian Lodwick" [EMAIL PROTECTED] 01/23/01 01:16PM Bob, Howard answered this question for me a while back so I'll try to answer it for you now. This question is probobaly more in depth than you realize, but the question comes down to why did they used to say the equation for finding the amount of valid subnets is 2^#of hosts -2? And why now do we not -2? Well the short answer is -we used to use Classfull addressing. With classfull the reason we used the -2 was because it was a bad idea to use the all 0's or all 1's subnets(highly discouraged is I believe the terminology)When an all 0's subnet update was sent to a classfull router it would not be able to decipher it from the entire network. This is because in clasfull the masks aren't sent with the updates therefore when the classfull mask is placed on say 192.168.0.0/28 it would change it to /24 because again the mask wasn't sent. Which would end up causing some issues obviously. The other one was the all 1's subnets. I'll just make an example. If you think along the same lines as the all 0's. Again in a classfull environment a broadcast for a particular subnet would be interpreted as a broadcast for the entire network. 192.168.0.255/28 has different meaning than 192.168.0.255/24. 3Coms website has the best explaination I have found The article is called: Understanding IP addressing: Everything You Ever Wanted To Know by Chuck Semeria. Cisco, Microsoft, and the RFC's seem to dance around the topic. Brian From: "Bob Vance" [EMAIL PROTECTED] Reply-To: "Bob Vance" [EMAIL PROTECTED] To: "CISCO_GroupStudy List \(E-mail\)" [EMAIL PROTECTED] Subject: RE: CCNA 2 and subnets Date: Tue, 23 Jan 2001 08:24:37 -0500 Yarrggh! Of course, that's (2^n) (*not* 2^(n-1) ) Maybe there *is* something to that aspartame story ;) - Tks| mailto:[EMAIL PROTECTED] BV | mailto:[EMAIL PROTECTED] Sr. Technical Consultant, SBM, A Gates/Arrow Co. Vox 770-623-3430 11455 Lakefield Dr. Fax 770-623-3429 Duluth, GA 30097-1511 = -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of Bob Vance Sent: Monday, January 22, 2001 10:35 PM To: CISCO_GroupStudy List (E-mail) Subject: CCNA 2 and subnets Sorry for the lame question, but I gotta know :| We know that subnet -1 (all ones) is valid to config in IOS and that 0 is OK with ip subnet-zero. For purposes of CCNA 2, do we assume that subnet 0 and -1 are valid, vs. CCNA 1 (where they were not) for questions like, "How many subnets can we have with this mask? " ? Does the test make it clear in preliminary text? The archives seem to have conflicting answers. The Cisco Press ICND book (McQuerry, 1-57870-111-2) doesn't address the issue head on, but simply shows tables with (2^(n-1))-2 subnets. The Cisco Press 640-507 Cert Guide (Odom, 0-7357-0971-8) clearly says that 2^(n-1) is correct and yet points out that 0 is only valid with "ip subnet-zero" ! Does anyone know the *definitive* answer for CCNA 2.0 ? - Tks| mailto:[EMAIL PROTECTED] BV | mailto:[EMAIL PROTECTED] Sr. Technical Consultant, SBM, A Gates/Arrow Co. Vox 770-623-3430 11455 Lakefield Dr. Fax 770-623-3429 Duluth, GA 30097-1511 = _ FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] _ Get your FREE download of MSN Explorer at http://explorer.msn.com _ FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] _ Get your FREE download of MSN Explorer at http://explorer.msn.com _ FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: CCNA 2 and subnets
Thanks. I think that I pretty well understand the technical aspects. I know that I can use subnet -1 and subnet 0 in a Cisco environment (with "ip subnet-zero"). My question was of a practical nature: Does the CCNA 2.0 certification test assume that we can use 0 and -1 or does it assume that we cannot. E.g., if encountered on the CCNA 2.0 cert test, what is the answer to the following question: Given the Class C network, 192.168.1.0, what mask is needed to provide for 7 subnets? The "real" answer (in the sense of what could be configured on the Cisco routers and irrespective of any restrictions that hosts on those subnets might have) would be 255.255.255.224, even without "ip subnet-zero". The CCNA 1.0 answer would have been 255.255.255.240 What is the answer expected by CCNA 2.0 ? (Or maybe they scrupulously avoid those particular questions :) And, as I said, the ICND book still subtracts 2. - Tks | mailto:[EMAIL PROTECTED] BV | mailto:[EMAIL PROTECTED] Sr. Technical Consultant, SBM, A Gates/Arrow Co. Vox 770-623-3430 11455 Lakefield Dr. Fax 770-623-3429 Duluth, GA 30097-1511 = -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of Brian Lodwick Sent: Tuesday, January 23, 2001 1:17 PM To: [EMAIL PROTECTED]; [EMAIL PROTECTED] Subject: RE: CCNA 2 and subnets Bob, Howard answered this question for me a while back so I'll try to answer it for you now. This question is probobaly more in depth than you realize, but the question comes down to why did they used to say the equation for finding the amount of valid subnets is 2^#of hosts -2? And why now do we not -2? Well the short answer is -we used to use Classfull addressing. With classfull the reason we used the -2 was because it was a bad idea to use the all 0's or all 1's subnets(highly discouraged is I believe the terminology)When an all 0's subnet update was sent to a classfull router it would not be able to decipher it from the entire network. This is because in clasfull the masks aren't sent with the updates therefore when the classfull mask is placed on say 192.168.0.0/28 it would change it to /24 because again the mask wasn't sent. Which would end up causing some issues obviously. The other one was the all 1's subnets. I'll just make an example. If you think along the same lines as the all 0's. Again in a classfull environment a broadcast for a particular subnet would be interpreted as a broadcast for the entire network. 192.168.0.255/28 has different meaning than 192.168.0.255/24. 3Coms website has the best explaination I have found The article is called: Understanding IP addressing: Everything You Ever Wanted To Know by Chuck Semeria. Cisco, Microsoft, and the RFC's seem to dance around the topic. Brian From: "Bob Vance" [EMAIL PROTECTED] Reply-To: "Bob Vance" [EMAIL PROTECTED] To: "CISCO_GroupStudy List \(E-mail\)" [EMAIL PROTECTED] Subject: RE: CCNA 2 and subnets Date: Tue, 23 Jan 2001 08:24:37 -0500 Yarrggh! Of course, that's (2^n) (*not* 2^(n-1) ) Maybe there *is* something to that aspartame story ;) - Tks | mailto:[EMAIL PROTECTED] BV | mailto:[EMAIL PROTECTED] Sr. Technical Consultant, SBM, A Gates/Arrow Co. Vox 770-623-3430 11455 Lakefield Dr. Fax 770-623-3429 Duluth, GA 30097-1511 = -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of Bob Vance Sent: Monday, January 22, 2001 10:35 PM To: CISCO_GroupStudy List (E-mail) Subject: CCNA 2 and subnets Sorry for the lame question, but I gotta know :| We know that subnet -1 (all ones) is valid to config in IOS and that 0 is OK with ip subnet-zero. For purposes of CCNA 2, do we assume that subnet 0 and -1 are valid, vs. CCNA 1 (where they were not) for questions like, "How many subnets can we have with this mask? " ? Does the test make it clear in preliminary text? The archives seem to have conflicting answers. The Cisco Press ICND book (McQuerry, 1-57870-111-2) doesn't address the issue head on, but simply shows tables with (2^(n-1))-2 subnets. The Cisco Press 640-507 Cert Guide (Odom, 0-7357-0971-8) clearly says that 2^(n-1) is correct and yet points out that 0 is only valid with "ip subnet-zero" ! Does anyone know the *definitive* answer for CCNA 2.0 ? - Tks | mailto:[EMAIL PROTECTED] BV | mailto:[EMAIL PROTECTED] Sr. Technical Consultant, SBM, A Gates/Arrow Co. Vox 770-623-3430 11455 Lakefield Dr. Fax 770-623-3429 Duluth, GA 30097-1511 = _ FAQ,
RE: CCNA 2 and subnets
I think he means on the exam only is it -2 or not for the subnet. I'd like to know too since The two books say something different as Bob mentioned. At 06:54 PM 1/23/2001 +, Brian Lodwick wrote: Using Cisco's website try to find out why the all 1's and all 0's subnet's are strongly discouraged in a classfull environment. Brian From: "Lowell Sharrah" [EMAIL PROTECTED] To: [EMAIL PROTECTED],[EMAIL PROTECTED], [EMAIL PROTECTED] Subject: RE: CCNA 2 and subnets Date: Tue, 23 Jan 2001 13:45:41 -0500 cisco has a pretty good website out there too http://www.cisco.com/techtools/ip_addr.html "Brian Lodwick" [EMAIL PROTECTED] 01/23/01 01:16PM Bob, Howard answered this question for me a while back so I'll try to answer it for you now. This question is probobaly more in depth than you realize, but the question comes down to why did they used to say the equation for finding the amount of valid subnets is 2^#of hosts -2? And why now do we not -2? Well the short answer is -we used to use Classfull addressing. With classfull the reason we used the -2 was because it was a bad idea to use the all 0's or all 1's subnets(highly discouraged is I believe the terminology)When an all 0's subnet update was sent to a classfull router it would not be able to decipher it from the entire network. This is because in clasfull the masks aren't sent with the updates therefore when the classfull mask is placed on say 192.168.0.0/28 it would change it to /24 because again the mask wasn't sent. Which would end up causing some issues obviously. The other one was the all 1's subnets. I'll just make an example. If you think along the same lines as the all 0's. Again in a classfull environment a broadcast for a particular subnet would be interpreted as a broadcast for the entire network. 192.168.0.255/28 has different meaning than 192.168.0.255/24. 3Coms website has the best explaination I have found The article is called: Understanding IP addressing: Everything You Ever Wanted To Know by Chuck Semeria. Cisco, Microsoft, and the RFC's seem to dance around the topic. Brian From: "Bob Vance" [EMAIL PROTECTED] Reply-To: "Bob Vance" [EMAIL PROTECTED] To: "CISCO_GroupStudy List \(E-mail\)" [EMAIL PROTECTED] Subject: RE: CCNA 2 and subnets Date: Tue, 23 Jan 2001 08:24:37 -0500 Yarrggh! Of course, that's (2^n) (*not* 2^(n-1) ) Maybe there *is* something to that aspartame story ;) - Tks| mailto:[EMAIL PROTECTED] BV | mailto:[EMAIL PROTECTED] Sr. Technical Consultant, SBM, A Gates/Arrow Co. Vox 770-623-3430 11455 Lakefield Dr. Fax 770-623-3429 Duluth, GA 30097-1511 = -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of Bob Vance Sent: Monday, January 22, 2001 10:35 PM To: CISCO_GroupStudy List (E-mail) Subject: CCNA 2 and subnets Sorry for the lame question, but I gotta know :| We know that subnet -1 (all ones) is valid to config in IOS and that 0 is OK with ip subnet-zero. For purposes of CCNA 2, do we assume that subnet 0 and -1 are valid, vs. CCNA 1 (where they were not) for questions like, "How many subnets can we have with this mask? " ? Does the test make it clear in preliminary text? The archives seem to have conflicting answers. The Cisco Press ICND book (McQuerry, 1-57870-111-2) doesn't address the issue head on, but simply shows tables with (2^(n-1))-2 subnets. The Cisco Press 640-507 Cert Guide (Odom, 0-7357-0971-8) clearly says that 2^(n-1) is correct and yet points out that 0 is only valid with "ip subnet-zero" ! Does anyone know the *definitive* answer for CCNA 2.0 ? - Tks| mailto:[EMAIL PROTECTED] BV | mailto:[EMAIL PROTECTED] Sr. Technical Consultant, SBM, A Gates/Arrow Co. Vox 770-623-3430 11455 Lakefield Dr. Fax 770-623-3429 Duluth, GA 30097-1511 = _ FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] _ Get your FREE download of MSN Explorer at http://explorer.msn.com _ FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] _ Get your FREE download of MSN Explorer at http://explorer.msn.com _ FAQ,
Re: CCNA 2 and subnets
At the CCNA level we're still teaching 2^n-2, but we also clarify the difference between the "classroom" and the "real world." Tom Lisa, Instructor, CCNA, CCAI Community College of Southern Nevada Cisco Regional Networking Academy Bob Vance wrote: Sorry for the lame question, but I gotta know :| We know that subnet -1 (all ones) is valid to config in IOS and that 0 is OK with ip subnet-zero. For purposes of CCNA 2, do we assume that subnet 0 and -1 are valid, vs. CCNA 1 (where they were not) for questions like, "How many subnets can we have with this mask? " ? Does the test make it clear in preliminary text? The archives seem to have conflicting answers. The Cisco Press ICND book (McQuerry, 1-57870-111-2) doesn't address the issue head on, but simply shows tables with (2^(n-1))-2 subnets. The Cisco Press 640-507 Cert Guide (Odom, 0-7357-0971-8) clearly says that 2^(n-1) is correct and yet points out that 0 is only valid with "ip subnet-zero" ! Does anyone know the *definitive* answer for CCNA 2.0 ? - Tks| mailto:[EMAIL PROTECTED] BV | mailto:[EMAIL PROTECTED] Sr. Technical Consultant, SBM, A Gates/Arrow Co. Vox 770-623-3430 11455 Lakefield Dr. Fax 770-623-3429 Duluth, GA 30097-1511 = _ FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] _ FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: CCNA 2 and subnets
For CCNA 2.0 exam x^2 -1 is the correct answer. I did get a question on the similar lines I answered it based on this, it must be correct since I got a 100% for that topic. ""Bob Vance"" [EMAIL PROTECTED] wrote in message 002d01c08573$2af4e680$[EMAIL PROTECTED]">news:002d01c08573$2af4e680$[EMAIL PROTECTED]... Thanks. I think that I pretty well understand the technical aspects. I know that I can use subnet -1 and subnet 0 in a Cisco environment (with "ip subnet-zero"). My question was of a practical nature: Does the CCNA 2.0 certification test assume that we can use 0 and -1 or does it assume that we cannot. E.g., if encountered on the CCNA 2.0 cert test, what is the answer to the following question: Given the Class C network, 192.168.1.0, what mask is needed to provide for 7 subnets? The "real" answer (in the sense of what could be configured on the Cisco routers and irrespective of any restrictions that hosts on those subnets might have) would be 255.255.255.224, even without "ip subnet-zero". The CCNA 1.0 answer would have been 255.255.255.240 What is the answer expected by CCNA 2.0 ? (Or maybe they scrupulously avoid those particular questions :) And, as I said, the ICND book still subtracts 2. - Tks | mailto:[EMAIL PROTECTED] BV | mailto:[EMAIL PROTECTED] Sr. Technical Consultant, SBM, A Gates/Arrow Co. Vox 770-623-3430 11455 Lakefield Dr. Fax 770-623-3429 Duluth, GA 30097-1511 = -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of Brian Lodwick Sent: Tuesday, January 23, 2001 1:17 PM To: [EMAIL PROTECTED]; [EMAIL PROTECTED] Subject: RE: CCNA 2 and subnets Bob, Howard answered this question for me a while back so I'll try to answer it for you now. This question is probobaly more in depth than you realize, but the question comes down to why did they used to say the equation for finding the amount of valid subnets is 2^#of hosts -2? And why now do we not -2? Well the short answer is -we used to use Classfull addressing. With classfull the reason we used the -2 was because it was a bad idea to use the all 0's or all 1's subnets(highly discouraged is I believe the terminology)When an all 0's subnet update was sent to a classfull router it would not be able to decipher it from the entire network. This is because in clasfull the masks aren't sent with the updates therefore when the classfull mask is placed on say 192.168.0.0/28 it would change it to /24 because again the mask wasn't sent. Which would end up causing some issues obviously. The other one was the all 1's subnets. I'll just make an example. If you think along the same lines as the all 0's. Again in a classfull environment a broadcast for a particular subnet would be interpreted as a broadcast for the entire network. 192.168.0.255/28 has different meaning than 192.168.0.255/24. 3Coms website has the best explaination I have found The article is called: Understanding IP addressing: Everything You Ever Wanted To Know by Chuck Semeria. Cisco, Microsoft, and the RFC's seem to dance around the topic. Brian From: "Bob Vance" [EMAIL PROTECTED] Reply-To: "Bob Vance" [EMAIL PROTECTED] To: "CISCO_GroupStudy List \(E-mail\)" [EMAIL PROTECTED] Subject: RE: CCNA 2 and subnets Date: Tue, 23 Jan 2001 08:24:37 -0500 Yarrggh! Of course, that's (2^n) (*not* 2^(n-1) ) Maybe there *is* something to that aspartame story ;) - Tks | mailto:[EMAIL PROTECTED] BV | mailto:[EMAIL PROTECTED] Sr. Technical Consultant, SBM, A Gates/Arrow Co. Vox 770-623-3430 11455 Lakefield Dr. Fax 770-623-3429 Duluth, GA 30097-1511 = -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of Bob Vance Sent: Monday, January 22, 2001 10:35 PM To: CISCO_GroupStudy List (E-mail) Subject: CCNA 2 and subnets Sorry for the lame question, but I gotta know :| We know that subnet -1 (all ones) is valid to config in IOS and that 0 is OK with ip subnet-zero. For purposes of CCNA 2, do we assume that subnet 0 and -1 are valid, vs. CCNA 1 (where they were not) for questions like, "How many subnets can we have with this mask? " ? Does the test make it clear in preliminary text? The archives seem to have conflicting answers. The Cisco Press ICND book (McQuerry, 1-57870-111-2) doesn't address the issue head on, but simply shows tables with (2^(n-1))-2 subnets. The Cisco Press 640-507 Cert Guide (Odom, 0-7357-0971-8) clearly says that 2^(n-1) is correct and yet points out that 0 is only valid with "ip subnet-zero" ! Does anyone know the *d
RE: CCNA 2 and subnets - Yikes
Yikes !!! For CCNA 2.0 exam x^2 -1 is the correct answer. So, you're saying that subnet -1 (all ones) is assumed to be allowed (which is true for Cisco routers), and subnet 0 is *not*, in the absence an explicit "ip subnet-zero". That's worse than I thought (or better, since it's correct ;) !!! - Tks | mailto:[EMAIL PROTECTED] BV | mailto:[EMAIL PROTECTED] Sr. Technical Consultant, SBM, A Gates/Arrow Co. Vox 770-623-3430 11455 Lakefield Dr. Fax 770-623-3429 Duluth, GA 30097-1511 = -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of Gopinath Pulyankote Sent: Tuesday, January 23, 2001 6:01 PM To: [EMAIL PROTECTED] Subject: Re: CCNA 2 and subnets For CCNA 2.0 exam x^2 -1 is the correct answer. I did get a question on the similar lines I answered it based on this, it must be correct since I got a 100% for that topic. ""Bob Vance"" [EMAIL PROTECTED] wrote in message 002d01c08573$2af4e680$[EMAIL PROTECTED]">news:002d01c08573$2af4e680$[EMAIL PROTECTED]... Thanks. I think that I pretty well understand the technical aspects. I know that I can use subnet -1 and subnet 0 in a Cisco environment (with "ip subnet-zero"). My question was of a practical nature: Does the CCNA 2.0 certification test assume that we can use 0 and -1 or does it assume that we cannot. E.g., if encountered on the CCNA 2.0 cert test, what is the answer to the following question: Given the Class C network, 192.168.1.0, what mask is needed to provide for 7 subnets? The "real" answer (in the sense of what could be configured on the Cisco routers and irrespective of any restrictions that hosts on those subnets might have) would be 255.255.255.224, even without "ip subnet-zero". The CCNA 1.0 answer would have been 255.255.255.240 What is the answer expected by CCNA 2.0 ? (Or maybe they scrupulously avoid those particular questions :) And, as I said, the ICND book still subtracts 2. - Tks | mailto:[EMAIL PROTECTED] BV | mailto:[EMAIL PROTECTED] Sr. Technical Consultant, SBM, A Gates/Arrow Co. Vox 770-623-3430 11455 Lakefield Dr. Fax 770-623-3429 Duluth, GA 30097-1511 = -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of Brian Lodwick Sent: Tuesday, January 23, 2001 1:17 PM To: [EMAIL PROTECTED]; [EMAIL PROTECTED] Subject: RE: CCNA 2 and subnets Bob, Howard answered this question for me a while back so I'll try to answer it for you now. This question is probobaly more in depth than you realize, but the question comes down to why did they used to say the equation for finding the amount of valid subnets is 2^#of hosts -2? And why now do we not -2? Well the short answer is -we used to use Classfull addressing. With classfull the reason we used the -2 was because it was a bad idea to use the all 0's or all 1's subnets(highly discouraged is I believe the terminology)When an all 0's subnet update was sent to a classfull router it would not be able to decipher it from the entire network. This is because in clasfull the masks aren't sent with the updates therefore when the classfull mask is placed on say 192.168.0.0/28 it would change it to /24 because again the mask wasn't sent. Which would end up causing some issues obviously. The other one was the all 1's subnets. I'll just make an example. If you think along the same lines as the all 0's. Again in a classfull environment a broadcast for a particular subnet would be interpreted as a broadcast for the entire network. 192.168.0.255/28 has different meaning than 192.168.0.255/24. 3Coms website has the best explaination I have found The article is called: Understanding IP addressing: Everything You Ever Wanted To Know by Chuck Semeria. Cisco, Microsoft, and the RFC's seem to dance around the topic. Brian From: "Bob Vance" [EMAIL PROTECTED] Reply-To: "Bob Vance" [EMAIL PROTECTED] To: "CISCO_GroupStudy List \(E-mail\)" [EMAIL PROTECTED] Subject: RE: CCNA 2 and subnets Date: Tue, 23 Jan 2001 08:24:37 -0500 Yarrggh! Of course, that's (2^n) (*not* 2^(n-1) ) Maybe there *is* something to that aspartame story ;) - Tks | mailto:[EMAIL PROTECTED] BV | mailto:[EMAIL PROTECTED] Sr. Technical Consultant, SBM, A Gates/Arrow Co. Vox 770-623-3430 11455 Lakefield Dr. Fax 770-623-3429 Duluth, GA 30097-1511 = -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of Bob Vance Sent: Monday, January 22, 2001 10:35 PM To: CISCO_GroupStudy List
RE: CCNA 2 and subnets - Yikes
I just took the ccna test v.2.0 in Dec, and there was NOT a question that discussed ip subnet zero or even one that could be remotely associated with that. The only subnetting questions were very basic. I think I only had one or two questions about subnetting, and if I remember correctly they were along the lines of "If you had this address...162.53.21.12 and you need no more than 126 hosts on this subnet, what mask would you use" and the answer is 255.255.255.128. The subnetting part, IF you understand subnetting, it is the least of your worries. It is very basic and deals with class c, and possibly a class b, but like I said, these are the questions you will breeze through. Make sure you understand the concepts of broadcast and collision domains(VLANS) and router commands and ipx, and access lists as these are covered much more than subnetting. Don't get stuck on one thing. There is not much along the subnetting lines that you are going to half to sit and figure much out. My two sheets of paper I took in with me were still blank when I came out. I just finished the academy and believe it or not, we studied for v.2.0. In out classes, it was still (2^x)-2 for usable subnets. We were taught the first and the last are not used. I am sure there is more than that, but I don't know about that yet but I am understanding the ccna is similiar to kindergarten of routing technology, but as far as your v.2.0 test, I wouldn't worry about those things yet. I didn't see them on my test. The ace busters I had were about telnetting sessions and going back and forth between different sessions, as in what command does that and since we only had the basic telnet command explained, this is one of the questions I missed. Still got an 892, but I guess what I'm saying is you need to concentrate more on the concepts of vlans and domains. The test is conceptual in the true sense of the word. Access list...don't forget to study ipx and access list. That is real important. When are you taking the test? Do you have time for one more study guide? I have a good one if you want to look at it. Good Luck!! Jennifer Cribbs [EMAIL PROTECTED] -Original Message- From: Bob Vance [SMTP:[EMAIL PROTECTED]] Sent: Tuesday, January 23, 2001 7:28 PM To: CISCO_GroupStudy List (E-mail) Subject: RE: CCNA 2 and subnets - Yikes Yikes !!! For CCNA 2.0 exam x^2 -1 is the correct answer. So, you're saying that subnet -1 (all ones) is assumed to be allowed (which is true for Cisco routers), and subnet 0 is *not*, in the absence an explicit "ip subnet-zero". That's worse than I thought (or better, since it's correct ;) !!! - Tks| mailto:[EMAIL PROTECTED] BV | mailto:[EMAIL PROTECTED] Sr. Technical Consultant, SBM, A Gates/Arrow Co. Vox 770-623-3430 11455 Lakefield Dr. Fax 770-623-3429 Duluth, GA 30097-1511 = -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of Gopinath Pulyankote Sent: Tuesday, January 23, 2001 6:01 PM To: [EMAIL PROTECTED] Subject: Re: CCNA 2 and subnets For CCNA 2.0 exam x^2 -1 is the correct answer. I did get a question on the similar lines I answered it based on this, it must be correct since I got a 100% for that topic. ""Bob Vance"" [EMAIL PROTECTED] wrote in message 002d01c08573$2af4e680$[EMAIL PROTECTED]">news:002d01c08573$2af4e680$[EMAIL PROTECTED]... Thanks. I think that I pretty well understand the technical aspects. I know that I can use subnet -1 and subnet 0 in a Cisco environment (with "ip subnet-zero"). My question was of a practical nature: Does the CCNA 2.0 certification test assume that we can use 0 and -1 or does it assume that we cannot. E.g., if encountered on the CCNA 2.0 cert test, what is the answer to the following question: Given the Class C network, 192.168.1.0, what mask is needed to provide for 7 subnets? The "real" answer (in the sense of what could be configured on the Cisco routers and irrespective of any restrictions that hosts on those subnets might have) would be 255.255.255.224, even without "ip subnet-zero". The CCNA 1.0 answer would have been 255.255.255.240 What is the answer expected by CCNA 2.0 ? (Or maybe they scrupulously avoid those particular questions :) And, as I said, the ICND book still subtracts 2. - Tks | mailto:[EMAIL PROTECTED] BV | mailto:[EMAIL PROTECTED] Sr. Technical Consultant, SBM, A Gates/Arrow Co. Vox 770-623-3430 11455 Lakefield Dr. Fax 770-623-3429 Duluth, GA 30097-1511 = -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of Brian Lodwick Sent: Tuesday, J
Re: CCNA 2 and subnets
The way I've always read it, with both Microsoft and Cisco texts, is that even though subnet zero is supported by nearly everything these days, it's not recommended as not everything does support it (not that I've ever heard of something not, but perhaps an old UNIX host or something). I think for any test I'd go with the "book" answer and ditch the 0s 1s subnets. -- Jason Roysdon, CCNP+Security/CCDP, MCSE, CNA, Network+, A+ List email: [EMAIL PROTECTED] Homepage: http://jason.artoo.net/ Cisco resources: http://r2cisco.artoo.net/ ""Bob Vance"" [EMAIL PROTECTED] wrote in message 001901c084ed$68539e80$[EMAIL PROTECTED]">news:001901c084ed$68539e80$[EMAIL PROTECTED]... Sorry for the lame question, but I gotta know :| We know that subnet -1 (all ones) is valid to config in IOS and that 0 is OK with ip subnet-zero. For purposes of CCNA 2, do we assume that subnet 0 and -1 are valid, vs. CCNA 1 (where they were not) for questions like, "How many subnets can we have with this mask? " ? Does the test make it clear in preliminary text? The archives seem to have conflicting answers. The Cisco Press ICND book (McQuerry, 1-57870-111-2) doesn't address the issue head on, but simply shows tables with (2^(n-1))-2 subnets. The Cisco Press 640-507 Cert Guide (Odom, 0-7357-0971-8) clearly says that 2^(n-1) is correct and yet points out that 0 is only valid with "ip subnet-zero" ! Does anyone know the *definitive* answer for CCNA 2.0 ? - Tks | mailto:[EMAIL PROTECTED] BV | mailto:[EMAIL PROTECTED] Sr. Technical Consultant, SBM, A Gates/Arrow Co. Vox 770-623-3430 11455 Lakefield Dr. Fax 770-623-3429 Duluth, GA 30097-1511 = _ FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] _ FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
