RE: 802.1Q or ISL
No problem Tom, and thank you for informing me about the 1522 frame size workgroup. Maybe they should make it a configurable variable so the administrators can set the maximum frame size them self, but leave the default to 1518 (and minimum to 64). Take care, Ole Ole Drews Jensen Systems Network Manager CCNA, MCSE, MCP+I RWR Enterprises, Inc. [EMAIL PROTECTED] http://www.insync.net/~drews/ccnp -Original Message- From: Tom Walstrom [mailto:[EMAIL PROTECTED]] Sent: Friday, September 08, 2000 7:17 PM To: [EMAIL PROTECTED] Subject: Re: 802.1Q or ISL Ole, Thanks for straightening me out. I was misled by the Exam Cram book. On reading more about 802.1q in the Clark/Hamilton Cisco Lan Switching book I see that 4 bytes are added. Interestingly, they note that the IEEE has formed a workgroup 802.3ac to extend ethernet maximum frame size to 1522 octets to take care of the baby giant issue. Thanks again for increasing my understanding. Tom "Ole Drews Jensen" [EMAIL PROTECTED] wrote in message 2019FB428FD3D311893700508B71EBFB2C5B5D@RWR_MAIL_SVR">news:2019FB428FD3D311893700508B71EBFB2C5B5D@RWR_MAIL_SVR... Thanks for your reply Tom, However, according to the book I'm reading, the 802.1Q DOES change the frame size by adding 4 bytes into it. Take care, Ole Ole Drews Jensen Systems Network Manager CCNA, MCSE, MCP+I RWR Enterprises, Inc. [EMAIL PROTECTED] http://www.insync.net/~drews/ccnp -Original Message- From: Tom Walstrom [mailto:[EMAIL PROTECTED]] Sent: Friday, September 08, 2000 6:30 AM To: Ole Drews Jensen; [EMAIL PROTECTED] Subject: RE: 802.1Q or ISL Ole, ISL encapsulates the frame adding, as you said, a 26 byte header and a 4 byte CRC trailer. 802.1Q frame-tagging does not change the frame size (hence its interoperability, because it appears as a standard ethernet frame to non-802.1Q devices), but does modify the existing frame with VLAN identification information. I would suspect that the real reason to deploy ISL is that it runs one spanning tree per vlan where 802.1Q runs only one spanning tree. Also ISL allows bonding into etherchannels. Seems like this would be more likely to make a difference on the network. I would think you would only do 802.1Q where interoperability was the issue, like with a Catalyst 4000 which I believe only supports 802.1Q. Maybe some switch guru could further illuminate this issue. Regards, Tom -Original Message- From: Ole Drews Jensen [mailto:[EMAIL PROTECTED]] Sent: Thursday, September 07, 2000 1:38 PM To: '[EMAIL PROTECTED]' Subject: 802.1Q or ISL Just a thought. - Digging through another book towards the light at the end of the tunnel, I have now added VLAN Trunc Links to my knowledge. That has brought this question up in my mind, so I would like to hear some feedback on this subject. I know that much of this depends on the average frame sizes, so lets say that I have analyzed my network, and the average frame size is 800. Lets also say that we are only dealing with Cisco Catalyst switches in this scenario. The question is, what would be least resource-waste to use as a trunking link : ISL or 802.1Q??? The 802.1Q has to break the frame open to modify it, but it adds only 4 bytes to each frame. The ISL does not have to break the frame open because it simply encapsulates it into a new one, but it adds 30 bytes to each frame. Any comments on this? Thanks, Ole ~~ Ole Drews Jensen Systems Network Manager CCNA, MCSE, MCP+I RWR Enterprises, Inc. [EMAIL PROTECTED] ~~ ___ UPDATED Posting Guidelines: http://www.groupstudy.com/list/guide.html FAQ, list archives, and subscription info: http://www.groupstudy.com Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] **NOTE: New CCNA/CCDA List has been formed. For more information go to http://www.groupstudy.com/list/Associate-Announcement.html _ UPDATED Posting Guidelines: http://www.groupstudy.com/list/guide.html FAQ, list archives, and subscription info: http://www.groupstudy.com Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] **NOTE: New CCNA/CCDA List has been formed. For more information go to http://www.groupstudy.com/list/Associates.html _ UPDATED Posting Guidelines: http://www.groupstudy.com/list/guide.html FAQ, list archives, and subscription info: http://www.groupstudy.com Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] **NOTE: New CCNA/CCDA List has been formed. For more information go to http://www.groupstudy.com/list/Associates.html _ UPDATED Posting Guidelines: http://www.g
RE: 802.1Q or ISL
Ole, ISL encapsulates the frame adding, as you said, a 26 byte header and a 4 byte CRC trailer. 802.1Q frame-tagging does not change the frame size (hence its interoperability, because it appears as a standard ethernet frame to non-802.1Q devices), but does modify the existing frame with VLAN identification information. I would suspect that the real reason to deploy ISL is that it runs one spanning tree per vlan where 802.1Q runs only one spanning tree. Also ISL allows bonding into etherchannels. Seems like this would be more likely to make a difference on the network. I would think you would only do 802.1Q where interoperability was the issue, like with a Catalyst 4000 which I believe only supports 802.1Q. Maybe some switch guru could further illuminate this issue. Regards, Tom -Original Message- From: Ole Drews Jensen [mailto:[EMAIL PROTECTED]] Sent: Thursday, September 07, 2000 1:38 PM To: '[EMAIL PROTECTED]' Subject: 802.1Q or ISL Just a thought. - Digging through another book towards the light at the end of the tunnel, I have now added VLAN Trunc Links to my knowledge. That has brought this question up in my mind, so I would like to hear some feedback on this subject. I know that much of this depends on the average frame sizes, so lets say that I have analyzed my network, and the average frame size is 800. Lets also say that we are only dealing with Cisco Catalyst switches in this scenario. The question is, what would be least resource-waste to use as a trunking link : ISL or 802.1Q??? The 802.1Q has to break the frame open to modify it, but it adds only 4 bytes to each frame. The ISL does not have to break the frame open because it simply encapsulates it into a new one, but it adds 30 bytes to each frame. Any comments on this? Thanks, Ole ~~ Ole Drews Jensen Systems Network Manager CCNA, MCSE, MCP+I RWR Enterprises, Inc. [EMAIL PROTECTED] ~~ ___ UPDATED Posting Guidelines: http://www.groupstudy.com/list/guide.html FAQ, list archives, and subscription info: http://www.groupstudy.com Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] **NOTE: New CCNA/CCDA List has been formed. For more information go to http://www.groupstudy.com/list/Associate-Announcement.html _ UPDATED Posting Guidelines: http://www.groupstudy.com/list/guide.html FAQ, list archives, and subscription info: http://www.groupstudy.com Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: 802.1Q or ISL
Thanks for your reply Tom, However, according to the book I'm reading, the 802.1Q DOES change the frame size by adding 4 bytes into it. Take care, Ole Ole Drews Jensen Systems Network Manager CCNA, MCSE, MCP+I RWR Enterprises, Inc. [EMAIL PROTECTED] http://www.insync.net/~drews/ccnp -Original Message- From: Tom Walstrom [mailto:[EMAIL PROTECTED]] Sent: Friday, September 08, 2000 6:30 AM To: Ole Drews Jensen; [EMAIL PROTECTED] Subject: RE: 802.1Q or ISL Ole, ISL encapsulates the frame adding, as you said, a 26 byte header and a 4 byte CRC trailer. 802.1Q frame-tagging does not change the frame size (hence its interoperability, because it appears as a standard ethernet frame to non-802.1Q devices), but does modify the existing frame with VLAN identification information. I would suspect that the real reason to deploy ISL is that it runs one spanning tree per vlan where 802.1Q runs only one spanning tree. Also ISL allows bonding into etherchannels. Seems like this would be more likely to make a difference on the network. I would think you would only do 802.1Q where interoperability was the issue, like with a Catalyst 4000 which I believe only supports 802.1Q. Maybe some switch guru could further illuminate this issue. Regards, Tom -Original Message- From: Ole Drews Jensen [mailto:[EMAIL PROTECTED]] Sent: Thursday, September 07, 2000 1:38 PM To: '[EMAIL PROTECTED]' Subject: 802.1Q or ISL Just a thought. - Digging through another book towards the light at the end of the tunnel, I have now added VLAN Trunc Links to my knowledge. That has brought this question up in my mind, so I would like to hear some feedback on this subject. I know that much of this depends on the average frame sizes, so lets say that I have analyzed my network, and the average frame size is 800. Lets also say that we are only dealing with Cisco Catalyst switches in this scenario. The question is, what would be least resource-waste to use as a trunking link : ISL or 802.1Q??? The 802.1Q has to break the frame open to modify it, but it adds only 4 bytes to each frame. The ISL does not have to break the frame open because it simply encapsulates it into a new one, but it adds 30 bytes to each frame. Any comments on this? Thanks, Ole ~~ Ole Drews Jensen Systems Network Manager CCNA, MCSE, MCP+I RWR Enterprises, Inc. [EMAIL PROTECTED] ~~ ___ UPDATED Posting Guidelines: http://www.groupstudy.com/list/guide.html FAQ, list archives, and subscription info: http://www.groupstudy.com Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] **NOTE: New CCNA/CCDA List has been formed. For more information go to http://www.groupstudy.com/list/Associate-Announcement.html _ UPDATED Posting Guidelines: http://www.groupstudy.com/list/guide.html FAQ, list archives, and subscription info: http://www.groupstudy.com Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: 802.1Q or ISL
Thanks for your reply Tom, However, according to the book I'm reading, the 802.1Q DOES change the frame size by adding 4 bytes into it. Take care, Ole From the horse's mouth, 802.1Q: 9.1 Overview Tagging a frame requires: a) The addition of a Tag Header to the frame. This header is inserted immediately following the Desti-nation MAC address and Source MAC address (and Routing, if present) fields of the frame to be transmitted; To return to your original question, Ole, when you speak of optimizing resource use, what do you consider the scarce resource? Other than in the martini-soaked brain (if I may use the term) of an overly zealous salesdroid, you can't optimize for everything at once. Save me from "specialists in all cars, foreign and domestic." Some optimizations could include: Bandwidth overhead Frame length Overhead frames (BPDU, for example) Latency in the switch Input serialization Processing Internal forwarding Output serialization Ease of use Interoperability Which do you want to optimize? -Original Message- From: Tom Walstrom [mailto:[EMAIL PROTECTED]] Sent: Friday, September 08, 2000 6:30 AM To: Ole Drews Jensen; [EMAIL PROTECTED] Subject: RE: 802.1Q or ISL Ole, ISL encapsulates the frame adding, as you said, a 26 byte header and a 4 byte CRC trailer. 802.1Q frame-tagging does not change the frame size (hence its interoperability, because it appears as a standard ethernet frame to non-802.1Q devices), but does modify the existing frame with VLAN identification information. I would suspect that the real reason to deploy ISL is that it runs one spanning tree per vlan where 802.1Q runs only one spanning tree. Also ISL allows bonding into etherchannels. Seems like this would be more likely to make a difference on the network. I would think you would only do 802.1Q where interoperability was the issue, like with a Catalyst 4000 which I believe only supports 802.1Q. Maybe some switch guru could further illuminate this issue. Regards, Tom -Original Message- From: Ole Drews Jensen [mailto:[EMAIL PROTECTED]] Sent: Thursday, September 07, 2000 1:38 PM Just a thought. - Digging through another book towards the light at the end of the tunnel, I have now added VLAN Trunc Links to my knowledge. That has brought this question up in my mind, so I would like to hear some feedback on this subject. I know that much of this depends on the average frame sizes, so lets say that I have analyzed my network, and the average frame size is 800. Lets also say that we are only dealing with Cisco Catalyst switches in this scenario. The question is, what would be least resource-waste to use as a trunking link : ISL or 802.1Q??? The 802.1Q has to break the frame open to modify it, but it adds only 4 bytes to each frame. The ISL does not have to break the frame open because it simply encapsulates it into a new one, but it adds 30 bytes to each frame. Any comments on this? Thanks, Ole **NOTE: New CCNA/CCDA List has been formed. For more information go to http://www.groupstudy.com/list/Associate-Announcement.html _ UPDATED Posting Guidelines: http://www.groupstudy.com/list/guide.html FAQ, list archives, and subscription info: http://www.groupstudy.com Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: 802.1Q or ISL
I hate martini Howard. Anyway, I believe I mean the latency in the switch. It's kind of, what would be the fastest thing to do: A) Put a large overcoat on and button 30 buttons. or B) Take your coat off, put a vest on with 4 buttons, and put the coat back on - (no buttons on the coat). Now consider a line of 1000 guests waiting for you to do A or B on them. What method would be the fastest to get these people out the door so you could go to bed? Have a great weekend, Ole ~~ Ole Drews Jensen Systems Network Manager CCNA, MCSE, MCP+I RWR Enterprises, Inc. [EMAIL PROTECTED] ~~ -Original Message- From: Howard C. Berkowitz [mailto:[EMAIL PROTECTED]] Sent: Friday, September 08, 2000 9:34 AM To: [EMAIL PROTECTED] Subject: RE: 802.1Q or ISL Thanks for your reply Tom, However, according to the book I'm reading, the 802.1Q DOES change the frame size by adding 4 bytes into it. Take care, Ole From the horse's mouth, 802.1Q: 9.1 Overview Tagging a frame requires: a) The addition of a Tag Header to the frame. This header is inserted immediately following the Desti-nation MAC address and Source MAC address (and Routing, if present) fields of the frame to be transmitted; To return to your original question, Ole, when you speak of optimizing resource use, what do you consider the scarce resource? Other than in the martini-soaked brain (if I may use the term) of an overly zealous salesdroid, you can't optimize for everything at once. Save me from "specialists in all cars, foreign and domestic." Some optimizations could include: Bandwidth overhead Frame length Overhead frames (BPDU, for example) Latency in the switch Input serialization Processing Internal forwarding Output serialization Ease of use Interoperability Which do you want to optimize? -Original Message- From: Tom Walstrom [mailto:[EMAIL PROTECTED]] Sent: Friday, September 08, 2000 6:30 AM To: Ole Drews Jensen; [EMAIL PROTECTED] Subject: RE: 802.1Q or ISL Ole, ISL encapsulates the frame adding, as you said, a 26 byte header and a 4 byte CRC trailer. 802.1Q frame-tagging does not change the frame size (hence its interoperability, because it appears as a standard ethernet frame to non-802.1Q devices), but does modify the existing frame with VLAN identification information. I would suspect that the real reason to deploy ISL is that it runs one spanning tree per vlan where 802.1Q runs only one spanning tree. Also ISL allows bonding into etherchannels. Seems like this would be more likely to make a difference on the network. I would think you would only do 802.1Q where interoperability was the issue, like with a Catalyst 4000 which I believe only supports 802.1Q. Maybe some switch guru could further illuminate this issue. Regards, Tom -Original Message- From: Ole Drews Jensen [mailto:[EMAIL PROTECTED]] Sent: Thursday, September 07, 2000 1:38 PM Just a thought. - Digging through another book towards the light at the end of the tunnel, I have now added VLAN Trunc Links to my knowledge. That has brought this question up in my mind, so I would like to hear some feedback on this subject. I know that much of this depends on the average frame sizes, so lets say that I have analyzed my network, and the average frame size is 800. Lets also say that we are only dealing with Cisco Catalyst switches in this scenario. The question is, what would be least resource-waste to use as a trunking link : ISL or 802.1Q??? The 802.1Q has to break the frame open to modify it, but it adds only 4 bytes to each frame. The ISL does not have to break the frame open because it simply encapsulates it into a new one, but it adds 30 bytes to each frame. Any comments on this? Thanks, Ole **NOTE: New CCNA/CCDA List has been formed. For more information go to http://www.groupstudy.com/list/Associate-Announcement.html _ UPDATED Posting Guidelines: http://www.groupstudy.com/list/guide.html FAQ, list archives, and subscription info: http://www.groupstudy.com Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] **NOTE: New CCNA/CCDA List has been formed. For more information go to http://www.groupstudy.com/list/Associate-Announcement.html _ UPDATED Posting Guidelines: http://www.groupstudy.com/list/guide.html FAQ, list archives, and subscription info: http://www.groupstudy.com Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: 802.1Q or ISL
Yes, it's true, .1Q adds 4 bytes. The TPID and TCI fields look like this: Tag Protocol Identifier (TPID) 2 bytes - fixed value of 0x8100 16 bits Tag Control Information (TCI) 2 bytes - User Prioroty 3 bits - Canonical FFormat Indicator (CFI) 1 bit - VLAN Identifier 12 bits An Ethernet frame of maximum size (1518 bytes) that gets tagged with .1Q VLAN info is now 4 bytes too big (1522 bytes). This frame is called a "baby giant". Switches can handle the frame correctly, but it may also generate an error statistic. This might not be a big deal unless you have lots of them and you have certain alarm thresholds set in your management system... One other thing - ISL will only encapsulate frames that exit the switch on a trunk port, while .1Q tags get added to all frames (as I recall... somebody might want to check me on this). Dale [=`) From: Ole Drews Jensen [EMAIL PROTECTED] Reply-To: Ole Drews Jensen [EMAIL PROTECTED] To: "'Tom Walstrom'" [EMAIL PROTECTED],Ole Drews Jensen [EMAIL PROTECTED], [EMAIL PROTECTED] Subject: RE: 802.1Q or ISL Date: Fri, 8 Sep 2000 07:40:46 -0500 Thanks for your reply Tom, However, according to the book I'm reading, the 802.1Q DOES change the frame size by adding 4 bytes into it. Take care, Ole Ole Drews Jensen Systems Network Manager CCNA, MCSE, MCP+I RWR Enterprises, Inc. [EMAIL PROTECTED] http://www.insync.net/~drews/ccnp -Original Message- From: Tom Walstrom [mailto:[EMAIL PROTECTED]] Sent: Friday, September 08, 2000 6:30 AM To: Ole Drews Jensen; [EMAIL PROTECTED] Subject: RE: 802.1Q or ISL Ole, ISL encapsulates the frame adding, as you said, a 26 byte header and a 4 byte CRC trailer. 802.1Q frame-tagging does not change the frame size (hence its interoperability, because it appears as a standard ethernet frame to non-802.1Q devices), but does modify the existing frame with VLAN identification information. I would suspect that the real reason to deploy ISL is that it runs one spanning tree per vlan where 802.1Q runs only one spanning tree. Also ISL allows bonding into etherchannels. Seems like this would be more likely to make a difference on the network. I would think you would only do 802.1Q where interoperability was the issue, like with a Catalyst 4000 which I believe only supports 802.1Q. Maybe some switch guru could further illuminate this issue. Regards, Tom -Original Message- From: Ole Drews Jensen [mailto:[EMAIL PROTECTED]] Sent: Thursday, September 07, 2000 1:38 PM To: '[EMAIL PROTECTED]' Subject: 802.1Q or ISL Just a thought. - Digging through another book towards the light at the end of the tunnel, I have now added VLAN Trunc Links to my knowledge. That has brought this question up in my mind, so I would like to hear some feedback on this subject. I know that much of this depends on the average frame sizes, so lets say that I have analyzed my network, and the average frame size is 800. Lets also say that we are only dealing with Cisco Catalyst switches in this scenario. The question is, what would be least resource-waste to use as a trunking link : ISL or 802.1Q??? The 802.1Q has to break the frame open to modify it, but it adds only 4 bytes to each frame. The ISL does not have to break the frame open because it simply encapsulates it into a new one, but it adds 30 bytes to each frame. Any comments on this? Thanks, Ole ~~ Ole Drews Jensen Systems Network Manager CCNA, MCSE, MCP+I RWR Enterprises, Inc. [EMAIL PROTECTED] ~~ ___ UPDATED Posting Guidelines: http://www.groupstudy.com/list/guide.html FAQ, list archives, and subscription info: http://www.groupstudy.com Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] **NOTE: New CCNA/CCDA List has been formed. For more information go to http://www.groupstudy.com/list/Associate-Announcement.html _ UPDATED Posting Guidelines: http://www.groupstudy.com/list/guide.html FAQ, list archives, and subscription info: http://www.groupstudy.com Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] _ Get Your Private, Free E-mail from MSN Hotmail at http://www.hotmail.com. Share information about yourself, create your own public profile at http://profiles.msn.com. **NOTE: New CCNA/CCDA List has been formed. For more information go to http://www.groupstudy.com/list/Associate-Announcement.html _ UPDATED Posting Guidelines: http://www.groupstudy.com/list/guide.html FAQ, list archives, and subscription info: http://www.groupstudy.com Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: 802.1Q or ISL
But I think it's more like: A: Pull a big trash bag over their head B: Stuff a lunch bad in their shirt pocket and then after either case, weigh them (CRC). Again, you might want to consider how often you will do each thing. You may only need to pull bags over the heads of 250 people going out the front door, and ignore the other 750 people who are going into different rooms of the house - as opposed to stuffing lunch bags in the pockets of all 1000 regardless of where they are going... Dale [=`) From: Ole Drews Jensen [EMAIL PROTECTED] Reply-To: Ole Drews Jensen [EMAIL PROTECTED] To: "'Howard C. Berkowitz'" [EMAIL PROTECTED], [EMAIL PROTECTED] Subject: RE: 802.1Q or ISL Date: Fri, 8 Sep 2000 10:05:41 -0500 I hate martini Howard. Anyway, I believe I mean the latency in the switch. It's kind of, what would be the fastest thing to do: A) Put a large overcoat on and button 30 buttons. or B) Take your coat off, put a vest on with 4 buttons, and put the coat back on - (no buttons on the coat). Now consider a line of 1000 guests waiting for you to do A or B on them. What method would be the fastest to get these people out the door so you could go to bed? Have a great weekend, Ole ~~ Ole Drews Jensen Systems Network Manager CCNA, MCSE, MCP+I RWR Enterprises, Inc. [EMAIL PROTECTED] ~~ -Original Message- From: Howard C. Berkowitz [mailto:[EMAIL PROTECTED]] Sent: Friday, September 08, 2000 9:34 AM To: [EMAIL PROTECTED] Subject: RE: 802.1Q or ISL Thanks for your reply Tom, However, according to the book I'm reading, the 802.1Q DOES change the frame size by adding 4 bytes into it. Take care, Ole From the horse's mouth, 802.1Q: 9.1 Overview Tagging a frame requires: a) The addition of a Tag Header to the frame. This header is inserted immediately following the Desti-nation MAC address and Source MAC address (and Routing, if present) fields of the frame to be transmitted; To return to your original question, Ole, when you speak of optimizing resource use, what do you consider the scarce resource? Other than in the martini-soaked brain (if I may use the term) of an overly zealous salesdroid, you can't optimize for everything at once. Save me from "specialists in all cars, foreign and domestic." Some optimizations could include: Bandwidth overhead Frame length Overhead frames (BPDU, for example) Latency in the switch Input serialization Processing Internal forwarding Output serialization Ease of use Interoperability Which do you want to optimize? -Original Message- From: Tom Walstrom [mailto:[EMAIL PROTECTED]] Sent: Friday, September 08, 2000 6:30 AM To: Ole Drews Jensen; [EMAIL PROTECTED] Subject: RE: 802.1Q or ISL Ole, ISL encapsulates the frame adding, as you said, a 26 byte header and a 4 byte CRC trailer. 802.1Q frame-tagging does not change the frame size (hence its interoperability, because it appears as a standard ethernet frame to non-802.1Q devices), but does modify the existing frame with VLAN identification information. I would suspect that the real reason to deploy ISL is that it runs one spanning tree per vlan where 802.1Q runs only one spanning tree. Also ISL allows bonding into etherchannels. Seems like this would be more likely to make a difference on the network. I would think you would only do 802.1Q where interoperability was the issue, like with a Catalyst 4000 which I believe only supports 802.1Q. Maybe some switch guru could further illuminate this issue. Regards, Tom -Original Message- From: Ole Drews Jensen [mailto:[EMAIL PROTECTED]] Sent: Thursday, September 07, 2000 1:38 PM Just a thought. - Digging through another book towards the light at the end of the tunnel, I have now added VLAN Trunc Links to my knowledge. That has brought this question up in my mind, so I would like to hear some feedback on this subject. I know that much of this depends on the average frame sizes, so lets say that I have analyzed my network, and the average frame size is 800. Lets also say that we are only dealing with Cisco Catalyst switches in this scenario. The question is, what would be least resource-waste to use as a trunking link : ISL or 802.1Q??? The 802.1Q has to break the frame open to modify it, but it adds only 4 bytes to each frame. The ISL does not have to break the frame open because it simply encapsulates it into a new one, but it adds 30 bytes to each frame. Any comments on this? Thanks, Ole **NOTE: New CCNA/CCDA List has been formed. For more information go to http://www.groupstudy.com/list/Associate-Announcement.html _ UPDATED Posting Guidelines: http://www.groupstudy.com/list/guide.html FAQ, list archives, and subscription info: http://www.groupstudy.com Report miscondu
RE: 802.1Q or ISL
C ) Offer them a Martini on there way out :) flem --- Ole Drews Jensen [EMAIL PROTECTED] wrote: I hate martini Howard. Anyway, I believe I mean the latency in the switch. It's kind of, what would be the fastest thing to do: A) Put a large overcoat on and button 30 buttons. or B) Take your coat off, put a vest on with 4 buttons, and put the coat back on - (no buttons on the coat). Now consider a line of 1000 guests waiting for you to do A or B on them. What method would be the fastest to get these people out the door so you could go to bed? Have a great weekend, Ole ~~ Ole Drews Jensen Systems Network Manager CCNA, MCSE, MCP+I RWR Enterprises, Inc. [EMAIL PROTECTED] ~~ -Original Message- From: Howard C. Berkowitz [mailto:[EMAIL PROTECTED]] Sent: Friday, September 08, 2000 9:34 AM To: [EMAIL PROTECTED] Subject: RE: 802.1Q or ISL Thanks for your reply Tom, However, according to the book I'm reading, the 802.1Q DOES change the frame size by adding 4 bytes into it. Take care, Ole From the horse's mouth, 802.1Q: 9.1 Overview Tagging a frame requires: a) The addition of a Tag Header to the frame. This header is inserted immediately following the Desti-nation MAC address and Source MAC address (and Routing, if present) fields of the frame to be transmitted; To return to your original question, Ole, when you speak of optimizing resource use, what do you consider the scarce resource? Other than in the martini-soaked brain (if I may use the term) of an overly zealous salesdroid, you can't optimize for everything at once. Save me from "specialists in all cars, foreign and domestic." Some optimizations could include: Bandwidth overhead Frame length Overhead frames (BPDU, for example) Latency in the switch Input serialization Processing Internal forwarding Output serialization Ease of use Interoperability Which do you want to optimize? -Original Message- From: Tom Walstrom [mailto:[EMAIL PROTECTED]] Sent: Friday, September 08, 2000 6:30 AM To: Ole Drews Jensen; [EMAIL PROTECTED] Subject: RE: 802.1Q or ISL Ole, ISL encapsulates the frame adding, as you said, a 26 byte header and a 4 byte CRC trailer. 802.1Q frame-tagging does not change the frame size (hence its interoperability, because it appears as a standard ethernet frame to non-802.1Q devices), but does modify the existing frame with VLAN identification information. I would suspect that the real reason to deploy ISL is that it runs one spanning tree per vlan where 802.1Q runs only one spanning tree. Also ISL allows bonding into etherchannels. Seems like this would be more likely to make a difference on the network. I would think you would only do 802.1Q where interoperability was the issue, like with a Catalyst 4000 which I believe only supports 802.1Q. Maybe some switch guru could further illuminate this issue. Regards, Tom -Original Message- From: Ole Drews Jensen [mailto:[EMAIL PROTECTED]] Sent: Thursday, September 07, 2000 1:38 PM Just a thought. - Digging through another book towards the light at the end of the tunnel, I have now added VLAN Trunc Links to my knowledge. That has brought this question up in my mind, so I would like to hear some feedback on this subject. I know that much of this depends on the average frame sizes, so lets say that I have analyzed my network, and the average frame size is 800. Lets also say that we are only dealing with Cisco Catalyst switches in this scenario. The question is, what would be least resource-waste to use as a trunking link : ISL or 802.1Q??? The 802.1Q has to break the frame open to modify it, but it adds only 4 bytes to each frame. The ISL does not have to break the frame open because it simply encapsulates it into a new one, but it adds 30 bytes to each frame. Any comments on this? Thanks, Ole **NOTE: New CCNA/CCDA List has been formed. For more information go to http://www.groupstudy.com/list/Associate-Announcement.html _ UPDATED Posting Guidelines: http://www.groupstudy.com/list/guide.html FAQ, list archives, and subscription info: http://www.groupstudy.com Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] **NOTE: New CCNA/CCDA List has been formed. For more information go to http://www.groupstudy.com/list/Associate-Announcement.html _ UPDATED Posting Guidelines: http://www.groupstudy.com/list/guide.html FAQ, list archives, and subscription info: http://www.groupstudy.com Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] __ Do You Yahoo!? Yahoo! Mail - Free email you can a
RE: 802.1Q or ISL
Trivia Q... where the TPID value of 0x8100 come from? --- Dale Holmes [EMAIL PROTECTED] wrote: Yes, it's true, .1Q adds 4 bytes. The TPID and TCI fields look like this: Tag Protocol Identifier (TPID) 2 bytes - fixed value of 0x8100 16 bits Tag Control Information (TCI) 2 bytes - User Prioroty 3 bits - Canonical FFormat Indicator (CFI) 1 bit - VLAN Identifier 12 bits = -/--- Erick B. / http://berk.dhs.org [EMAIL PROTECTED] / CCNP+Security+NetRanger / Nortel NCSE, CCIE Writ. -/--- __ Do You Yahoo!? Yahoo! Mail - Free email you can access from anywhere! http://mail.yahoo.com/ **NOTE: New CCNA/CCDA List has been formed. For more information go to http://www.groupstudy.com/list/Associate-Announcement.html _ UPDATED Posting Guidelines: http://www.groupstudy.com/list/guide.html FAQ, list archives, and subscription info: http://www.groupstudy.com Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: 802.1Q or ISL
Good question since the info I have shows the value to be 08-00 and is only 1 byte Maybe we should ask Howard to verify since he evidently has the IEEE Standards doc. Karen E Young Network Engineer ELF Technologies, Inc [EMAIL PROTECTED] "Erick B." erickbe@yahoTo: Dale Holmes [EMAIL PROTECTED], o.com [EMAIL PROTECTED], [EMAIL PROTECTED], [EMAIL PROTECTED] Sent by: cc: nobody@groupsSubject: RE: 802.1Q or ISL tudy.com 09/08/2000 01:18 PM Please respond to "Erick B." Trivia Q... where the TPID value of 0x8100 come from? --- Dale Holmes [EMAIL PROTECTED] wrote: Yes, it's true, .1Q adds 4 bytes. The TPID and TCI fields look like this: Tag Protocol Identifier (TPID) 2 bytes - fixed value of 0x8100 16 bits Tag Control Information (TCI) 2 bytes - User Prioroty 3 bits - Canonical FFormat Indicator (CFI) 1 bit - VLAN Identifier 12 bits = -/--- Erick B. / http://berk.dhs.org [EMAIL PROTECTED] / CCNP+Security+NetRanger / Nortel NCSE, CCIE Writ. -/--- __ Do You Yahoo!? Yahoo! Mail - Free email you can access from anywhere! http://mail.yahoo.com/ **NOTE: New CCNA/CCDA List has been formed. For more information go to http://www.groupstudy.com/list/Associate-Announcement.html _ UPDATED Posting Guidelines: http://www.groupstudy.com/list/guide.html FAQ, list archives, and subscription info: http://www.groupstudy.com Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] **NOTE: New CCNA/CCDA List has been formed. For more information go to http://www.groupstudy.com/list/Associate-Announcement.html _ UPDATED Posting Guidelines: http://www.groupstudy.com/list/guide.html FAQ, list archives, and subscription info: http://www.groupstudy.com Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: 802.1Q or ISL
Well, On Ethernet, the tag is 4 bytes. 2 bytes TPID and 2 byte TCI. On FDDI and Token Ring, the tag is 10 bytes. 8 byte TPID and 2 byte TCI. Is 802.1q a final standard now or still draft (been awhile since I checked)? -E Good question since the info I have shows the value to be 08-00 and is only byte Maybe we should ask Howard to verify since he evidently has the IEEE Standards doc. Karen E Young __ Do You Yahoo!? Yahoo! Mail - Free email you can access from anywhere! http://mail.yahoo.com/ **NOTE: New CCNA/CCDA List has been formed. For more information go to http://www.groupstudy.com/list/Associates.html _ UPDATED Posting Guidelines: http://www.groupstudy.com/list/guide.html FAQ, list archives, and subscription info: http://www.groupstudy.com Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: 802.1Q or ISL
You're right. I wasn't paying attention. Took a closer look at the format on my source and saw it was mislabeled. Here goes with the corrected info: 2 octet TPID with a value of 08-00. 2 octet TCI (Tag Control Information) consiting of 3 bits = user priority 1 bit = CFI (Canonical Format Indicator) 12 bits = VID (VLAN Identifier) if CFI = 1 then there will be an additional 4-32 octets for the Embeded RIF in the following format: 2 octets length/type field 2 octet RC (Route Control) field consisting of 3 bit = routing type 5 bit = length field 1 bit = direction bit 6 bit = LF (Largest Frame) field 1 bit = NCFI (Non-Canonical Format Indicator) - 0=MAC address info is in non-canonical format, 1=MAC address info is in canonical format. 0-28 octets of route descriptors. http://www.protocols.com/pbook/lan2.htm#VLAN Karen E Young Network Engineer ELF Technologies, Inc [EMAIL PROTECTED] Ole Drews Jensen To: "'[EMAIL PROTECTED]'" [EMAIL PROTECTED], OJensen@mail"Erick B." [EMAIL PROTECTED] 1.rwr.com cc: [EMAIL PROTECTED], [EMAIL PROTECTED], Ole Drews Jensen [EMAIL PROTECTED], [EMAIL PROTECTED] 09/08/2000 Subject: RE: 802.1Q or ISL 01:59 PM How can 08-00 be only one byte ??? Ole ~~ Ole Drews Jensen Systems Network Manager CCNA, MCSE, MCP+I RWR Enterprises, Inc. [EMAIL PROTECTED] ~~ -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]] Sent: Friday, September 08, 2000 3:52 PM To: Erick B. Cc: [EMAIL PROTECTED]; [EMAIL PROTECTED]; [EMAIL PROTECTED]; [EMAIL PROTECTED] Subject: RE: 802.1Q or ISL Good question since the info I have shows the value to be 08-00 and is only 1 byte Maybe we should ask Howard to verify since he evidently has the IEEE Standards doc. Karen E Young Network Engineer ELF Technologies, Inc [EMAIL PROTECTED] "Erick B." erickbe@yahoTo: Dale Holmes [EMAIL PROTECTED], o.com [EMAIL PROTECTED], [EMAIL PROTECTED], [EMAIL PROTECTED] Sent by: cc: nobody@groups Subject: RE: 802.1Q or ISL tudy.com 09/08/2000 01:18 PM Please respond to "Erick B." Trivia Q... where the TPID value of 0x8100 come from? --- Dale Holmes [EMAIL PROTECTED] wrote: Yes, it's true, .1Q adds 4 bytes. The TPID and TCI fields look like this: Tag Protocol Identifier (TPID) 2 bytes - fixed value of 0x8100 16 bits Tag Control Information (TCI) 2 bytes - User Prioroty 3 bits - Canonical FFormat Indicator (CFI) 1 bit - VLAN Identifier 12 bits = -/--- Erick B. / http://berk.dhs.org [EMAIL PROTECTED] / CCNP+Security+NetRanger / Nortel NCSE, CCIE Writ. -/--- __ Do You Yahoo!? Yahoo! Mail - Free email you can access from anywhere! http://mail.yahoo.com/ **NOTE: New CCNA/CCDA List has been formed. For more information go to http://www.groupstudy.com/list/Associate-Announcement.html _ UPDATED Posting Guidelines: http://www.groupstudy.com/list/guide.html FAQ, list archives, and subscription info: http://www.groupstudy.com Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] **NOTE: New CCNA/CCDA List has been formed. For more information go to http://www.groupstudy.com/list/Associates.html _ UPDATED Posting Guidelines: http://www.groupstudy.com/list/guide.html FAQ, list archives, and subscription info: http://www.groupstudy.com Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: 802.1Q or ISL
8100 used to be a Wellfleet EtherType. I guess since Wellfleet submerged into Bay Networks (with Synoptics) they don't need their EtherType anymore!? ;-) Priscilla At 01:18 PM 9/8/00, Erick B. wrote: Trivia Q... where the TPID value of 0x8100 come from? --- Dale Holmes [EMAIL PROTECTED] wrote: Yes, it's true, .1Q adds 4 bytes. The TPID and TCI fields look like this: Tag Protocol Identifier (TPID) 2 bytes - fixed value of 0x8100 16 bits Tag Control Information (TCI) 2 bytes - User Prioroty 3 bits - Canonical FFormat Indicator (CFI) 1 bit - VLAN Identifier 12 bits = -/--- Erick B. / http://berk.dhs.org [EMAIL PROTECTED] / CCNP+Security+NetRanger / Nortel NCSE, CCIE Writ. -/--- __ Do You Yahoo!? Yahoo! Mail - Free email you can access from anywhere! http://mail.yahoo.com/ **NOTE: New CCNA/CCDA List has been formed. For more information go to http://www.groupstudy.com/list/Associate-Announcement.html _ UPDATED Posting Guidelines: http://www.groupstudy.com/list/guide.html FAQ, list archives, and subscription info: http://www.groupstudy.com Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] Priscilla Oppenheimer http://www.priscilla.com **NOTE: New CCNA/CCDA List has been formed. For more information go to http://www.groupstudy.com/list/Associates.html _ UPDATED Posting Guidelines: http://www.groupstudy.com/list/guide.html FAQ, list archives, and subscription info: http://www.groupstudy.com Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: 802.1Q or ISL
Yes, 8100 is the TPID for 802.1Q (the Cisco Press BCMSN book - page 103). Have a great weekend, Ole Ole Drews Jensen Systems Network Manager CCNA, MCSE, MCP+I RWR Enterprises, Inc. [EMAIL PROTECTED] http://www.insync.net/~drews/ccnp -Original Message- From: Priscilla Oppenheimer [mailto:[EMAIL PROTECTED]] Sent: Friday, September 08, 2000 5:44 PM To: [EMAIL PROTECTED] Subject: RE: 802.1Q or ISL Looks like a typo maybe? 0800 would be IP! I think the 802.1q TPID is 8100 though the only page I could find on this topic is in German! http://einstein.offis.uni-oldenburg.de/lehre/Protokolle/08/index.htm Priscilla At 02:33 PM 9/8/00, [EMAIL PROTECTED] wrote: You're right. I wasn't paying attention. Took a closer look at the format on my source and saw it was mislabeled. Here goes with the corrected info: 2 octet TPID with a value of 08-00. 2 octet TCI (Tag Control Information) consiting of 3 bits = user priority 1 bit = CFI (Canonical Format Indicator) 12 bits = VID (VLAN Identifier) if CFI = 1 then there will be an additional 4-32 octets for the Embeded RIF in the following format: 2 octets length/type field 2 octet RC (Route Control) field consisting of 3 bit = routing type 5 bit = length field 1 bit = direction bit 6 bit = LF (Largest Frame) field 1 bit = NCFI (Non-Canonical Format Indicator) - 0=MAC address info is in non-canonical format, 1=MAC address info is in canonical format. 0-28 octets of route descriptors. http://www.protocols.com/pbook/lan2.htm#VLAN Karen E Young Network Engineer ELF Technologies, Inc [EMAIL PROTECTED] Ole Drews Jensen To: "'[EMAIL PROTECTED]'" [EMAIL PROTECTED], OJensen@mail"Erick B." [EMAIL PROTECTED] 1.rwr.com cc: [EMAIL PROTECTED], [EMAIL PROTECTED], Ole Drews Jensen [EMAIL PROTECTED], [EMAIL PROTECTED] 09/08/2000 Subject: RE: 802.1Q or ISL 01:59 PM How can 08-00 be only one byte ??? Ole ~~ Ole Drews Jensen Systems Network Manager CCNA, MCSE, MCP+I RWR Enterprises, Inc. [EMAIL PROTECTED] ~~ -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]] Sent: Friday, September 08, 2000 3:52 PM To: Erick B. Cc: [EMAIL PROTECTED]; [EMAIL PROTECTED]; [EMAIL PROTECTED]; [EMAIL PROTECTED] Subject: RE: 802.1Q or ISL Good question since the info I have shows the value to be 08-00 and is only 1 byte Maybe we should ask Howard to verify since he evidently has the IEEE Standards doc. Karen E Young Network Engineer ELF Technologies, Inc [EMAIL PROTECTED] "Erick B." erickbe@yahoTo: Dale Holmes [EMAIL PROTECTED], o.com [EMAIL PROTECTED], [EMAIL PROTECTED], [EMAIL PROTECTED] Sent by: cc: nobody@groups Subject: RE: 802.1Q or ISL tudy.com 09/08/2000 01:18 PM Please respond to "Erick B." Trivia Q... where the TPID value of 0x8100 come from? --- Dale Holmes [EMAIL PROTECTED] wrote: Yes, it's true, .1Q adds 4 bytes. The TPID and TCI fields look like this: Tag Protocol Identifier (TPID) 2 bytes - fixed value of 0x8100 16 bits Tag Control Information (TCI) 2 bytes - User Prioroty 3 bits - Canonical FFormat Indicator (CFI) 1 bit - VLAN Identifier 12 bits = -/--- Erick B. / http://berk.dhs.org [EMAIL PROTECTED] / CCNP+Security+NetRanger / Nortel NCSE, CCIE Writ. -/--- __ Do You Yahoo!? Yahoo! Mail - Free email you can access from anywhere! http://mail.yahoo.com/ **NOTE: New CCNA/CCDA List has been formed. For more information go to http://www.groupstudy.com/list/Associate-Announcement.html _ UPDATED Posting Guidelines: http://www.groupstudy.com/list/guide.html FAQ, list archives, and subscription info: http://www.groupstudy.com Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] **NOTE: New CCNA/CCDA List has been formed. For more information go to http://www.groupstudy.com/list/Associates.html _ UPDATED Posting Guidelines: http://www.groupstudy.com/list/guide.html FAQ, list archives, and subscription info: http://www.groupstudy
Re: 802.1Q or ISL
Ole, Thanks for straightening me out. I was misled by the Exam Cram book. On reading more about 802.1q in the Clark/Hamilton Cisco Lan Switching book I see that 4 bytes are added. Interestingly, they note that the IEEE has formed a workgroup 802.3ac to extend ethernet maximum frame size to 1522 octets to take care of the baby giant issue. Thanks again for increasing my understanding. Tom "Ole Drews Jensen" [EMAIL PROTECTED] wrote in message 2019FB428FD3D311893700508B71EBFB2C5B5D@RWR_MAIL_SVR">news:2019FB428FD3D311893700508B71EBFB2C5B5D@RWR_MAIL_SVR... Thanks for your reply Tom, However, according to the book I'm reading, the 802.1Q DOES change the frame size by adding 4 bytes into it. Take care, Ole Ole Drews Jensen Systems Network Manager CCNA, MCSE, MCP+I RWR Enterprises, Inc. [EMAIL PROTECTED] http://www.insync.net/~drews/ccnp -Original Message- From: Tom Walstrom [mailto:[EMAIL PROTECTED]] Sent: Friday, September 08, 2000 6:30 AM To: Ole Drews Jensen; [EMAIL PROTECTED] Subject: RE: 802.1Q or ISL Ole, ISL encapsulates the frame adding, as you said, a 26 byte header and a 4 byte CRC trailer. 802.1Q frame-tagging does not change the frame size (hence its interoperability, because it appears as a standard ethernet frame to non-802.1Q devices), but does modify the existing frame with VLAN identification information. I would suspect that the real reason to deploy ISL is that it runs one spanning tree per vlan where 802.1Q runs only one spanning tree. Also ISL allows bonding into etherchannels. Seems like this would be more likely to make a difference on the network. I would think you would only do 802.1Q where interoperability was the issue, like with a Catalyst 4000 which I believe only supports 802.1Q. Maybe some switch guru could further illuminate this issue. Regards, Tom -Original Message- From: Ole Drews Jensen [mailto:[EMAIL PROTECTED]] Sent: Thursday, September 07, 2000 1:38 PM To: '[EMAIL PROTECTED]' Subject: 802.1Q or ISL Just a thought. - Digging through another book towards the light at the end of the tunnel, I have now added VLAN Trunc Links to my knowledge. That has brought this question up in my mind, so I would like to hear some feedback on this subject. I know that much of this depends on the average frame sizes, so lets say that I have analyzed my network, and the average frame size is 800. Lets also say that we are only dealing with Cisco Catalyst switches in this scenario. The question is, what would be least resource-waste to use as a trunking link : ISL or 802.1Q??? The 802.1Q has to break the frame open to modify it, but it adds only 4 bytes to each frame. The ISL does not have to break the frame open because it simply encapsulates it into a new one, but it adds 30 bytes to each frame. Any comments on this? Thanks, Ole ~~ Ole Drews Jensen Systems Network Manager CCNA, MCSE, MCP+I RWR Enterprises, Inc. [EMAIL PROTECTED] ~~ ___ UPDATED Posting Guidelines: http://www.groupstudy.com/list/guide.html FAQ, list archives, and subscription info: http://www.groupstudy.com Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] **NOTE: New CCNA/CCDA List has been formed. For more information go to http://www.groupstudy.com/list/Associate-Announcement.html _ UPDATED Posting Guidelines: http://www.groupstudy.com/list/guide.html FAQ, list archives, and subscription info: http://www.groupstudy.com Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] **NOTE: New CCNA/CCDA List has been formed. For more information go to http://www.groupstudy.com/list/Associates.html _ UPDATED Posting Guidelines: http://www.groupstudy.com/list/guide.html FAQ, list archives, and subscription info: http://www.groupstudy.com Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: 802.1Q or ISL
Ole Drews Jensen wrote: The question is, what would be least resource-waste to use as a trunking link : ISL or 802.1Q??? Strictly resource wise, clearly 802.1Q, provided all your devices support it (earlier cisco stuff doesn't). There was a BUGTRAQ report some time ago, however, reporting that due to the frame modification of the 802.1Q packets, that it was possible to rather trivially inject 802.1Q frames into the network destined for any arbitrary VLAN. This isn't as easy with ISL as it is harder to fake/generate a raw ISL packet. I don't know if this has been fixed or deemed a low-risk as I haven't heard anything else about it in months. In both cases, particularly ISL, you should realize that with many switches your interface statistics and SNMP MIBs will incorrectly report "giants" as line errors when in fact this is due to the addition of the ISL framing pushing the frame size the media MTU. Unless you have a "highly specialized ASIC" that is aware of this, your typical stock ASIC will report them as giants, although they are processed normally by the switch. The 29nnXL IOS-based switches suffer from this "false error reporting" although the "classic" Catalysts (2900, 5000, 5500) do not. Jeff Kell [EMAIL PROTECTED] **NOTE: New CCNA/CCDA List has been formed. For more information go to http://www.groupstudy.com/list/Associate-Announcement.html _ UPDATED Posting Guidelines: http://www.groupstudy.com/list/guide.html FAQ, list archives, and subscription info: http://www.groupstudy.com Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
