RE: Ethernet or FastEthernet [7:35245]
Great answer. One minor thing. ISL came first. It was designed by Kalpana years ago. Cisco bought Kalpana in the mid-1990s. Priscilla At 10:53 AM 2/14/02, Oleg Oz wrote: >Mike, yes the IEEE802.1Q does insert the VLAN tag into the frame (ISL >encapsulates the frame.) I am going to try and get this part right. The max >frame size for an ethernet frame is 1518, however if you are going to insert >the 801.1Q Vlan tag you would require an additional 4 bytes. > > 2 bytes for Length/Type = 802.1Q Tag Type > 2 bytes for Tag Control Information) > > Bringing the grand total to 1522. I belive that the older chip sets >supported a max of 1518 (later the standard was changed to support 1522.) >So, I belive that the age on the hardware has a bit to do with this as the >change to the frame size (or the IEEE standard change) did not occur until >sometime in '98. > > Now Cisco's ISL came along and decided to take it a bit further. >Cisco's implementation encapsulates the frame (the original 1518 byte frame) >and by doing so adds 30 more bytes. This 1548 byte max. frame again presents >a problem to older Ethernet chip sets. > > So you may find certine Ethernet HW that will support the 1522 byte >size and not the 1548 byte size (I am pretty sure of this but will not swear >to it) and hence some hardware will support 802.1Q and not ISL. > > I hope I am not wrong about this. > > Oleg Oz... > > >http://www.techfest.com/networking/lan/ethernet2.htm >http://www.cisco.com/warp/public/473/741_4.html Priscilla Oppenheimer http://www.priscilla.com Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=35449&t=35245 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: Ethernet or FastEthernet [7:35245]
At 09:38 AM 2/14/02, Michael Williams wrote: >Oleg Oz wrote: > > The originally ethernet > > chips used in cisco network modules only supported a fixed > > frame size. When ISL/802.1Q came along, the hardware needed to > > support some additional space to accomadate the VLAN info. > >I could see this as being an explanation. But doesn't Dot1Q fit into a >standard ethernet frame? I believe so, whereas ISL adds into to the >ethernet frame making it bigger. This would explain why older (or even >newer) hardware may support Dot1Q but not ISL. Both ISL and IEEE 802.1Q can confuse older chipsets because the resulting frame can be longer than 1518 bytes. Whether these frames will confuse a chipset or not depends on the age of the chipset, and also on whether the chipset checks the length before it checks the header. ISL encapsulates an Ethernet frame, adding a 26-byte ISL header to the front of the frame, and a 4-byte CRC to the end of the frame. The first 48 bits, which would normally contain an ordinary destination address, contain a 40-bit "address," a 4-bit Type, and 4-bit User field used for priority. The first 40 bits are 0x01-00-0C-00-00. A recipient that doesn't understand ISL takes a look at those 40 bits with the next 8 bits and sees a multicast address that it doesn't understand. The recipient should just drop the packet. The exact behavior depends on the chipset, however. A good chip would just say "hey, it's not for me, get rid of it." A bad chip would say "Yikes this is way too long" and report an error, crash perhaps, or do something unpredictable. Now, the IEEE 802.1Q crowd has the advantage that they can influence IEEE specifications. They added four bytes, inserting them where a length/type field would appear normally. They were able to reserve a type field (0x8100) so that all recipients can determine if they should understand the frame or not. The first two bytes of the 802.1Q insertion are actually the Tag Protocol Identifier (TPID). The TPID is set to 0x8100. Because this number is bigger than the maximum size of an Ethernet frame, a recipient knows that the frame is not a standard 802.3 frame and that the field is not an 802.3 length field. If the recipient supports 802.1Q, it continues to process the rest of the insertion as an 802.1Q header. If the recipient does not support 802.1Q, it sees the two TPID bytes as an unsupported EtherType and should drop the frame. On the other hand, a bad chipset might barf. To support IEEE 802.1Q and avoid the need to drop and report "baby giants," the IEEE 802.3ac VLAN Tag Task Force received approval in September 1998 for extending the Ethernet maximum frame size to 1522 bytes. Priscilla Priscilla Oppenheimer http://www.priscilla.com Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=35447&t=35245 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: Ethernet or FastEthernet [7:35245]
Mike, yes the IEEE802.1Q does insert the VLAN tag into the frame (ISL encapsulates the frame.) I am going to try and get this part right. The max frame size for an ethernet frame is 1518, however if you are going to insert the 801.1Q Vlan tag you would require an additional 4 bytes. 2 bytes for Length/Type = 802.1Q Tag Type 2 bytes for Tag Control Information) Bringing the grand total to 1522. I belive that the older chip sets supported a max of 1518 (later the standard was changed to support 1522.) So, I belive that the age on the hardware has a bit to do with this as the change to the frame size (or the IEEE standard change) did not occur until sometime in '98. Now Cisco's ISL came along and decided to take it a bit further. Cisco's implementation encapsulates the frame (the original 1518 byte frame) and by doing so adds 30 more bytes. This 1548 byte max. frame again presents a problem to older Ethernet chip sets. So you may find certine Ethernet HW that will support the 1522 byte size and not the 1548 byte size (I am pretty sure of this but will not swear to it) and hence some hardware will support 802.1Q and not ISL. I hope I am not wrong about this. Oleg Oz... http://www.techfest.com/networking/lan/ethernet2.htm http://www.cisco.com/warp/public/473/741_4.html Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=35404&t=35245 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: Ethernet or FastEthernet [7:35245]
Oleg Oz wrote: > The originally ethernet > chips used in cisco network modules only supported a fixed > frame size. When ISL/802.1Q came along, the hardware needed to > support some additional space to accomadate the VLAN info. I could see this as being an explanation. But doesn't Dot1Q fit into a standard ethernet frame? I believe so, whereas ISL adds into to the ethernet frame making it bigger. This would explain why older (or even newer) hardware may support Dot1Q but not ISL. >From the responses I've seen posted in this thread, it seems that even an entire group of Cisco "experts" (hehe) are having trouble nailing down exactly what the facts are. Mike W. Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=35396&t=35245 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: Ethernet or FastEthernet [7:35245]
I also belive that it is possible to run isl/802.1Q over ethernet. I seem to remember reading that the limiting factor was the age of the ethernet hardware. The originally ethernet chips used in cisco network modules only supported a fixed frame size. When ISL/802.1Q came along, the hardware needed to support some additional space to accomadate the VLAN info. This was a problem with older ethernet chips sets however the newer hardware supports this. The chip sets used on the FE board did not have this problem because they were already designed to allow for a larger frame. Can anyone verify my recollection??? Oleg Oz.. Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=35311&t=35245 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: Ethernet or FastEthernet [7:35245]
I had read (and understood) that you needed FastEthernet for ISL trunking. I'm not for sure about Dot1Q though. It appears from the post from MADMAN, that you can indeed perform Dot1Q on Ethernet ports. But I still think FastEthernet I read a post in this thread that on a 2900 switch someone set it for 10-half and didn't receive an error when setting up ISL trunking. However, it appears from that post that he's using a 2900(XL) switch (because of the 'switchport trunk' IOS command). If that's the case, then regardless of speed/duplex settings, that port is still (technically) a FastEthernet port, and therefore capable of ISL trunking. That's my take on it.. Mike W. Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=35307&t=35245 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: Ethernet or FastEthernet [7:35245]
Some platfors support it on 10M ethernet with the right IOS: C2611A#conf t Enter configuration commands, one per line. End with CNTL/Z. C2611A(config)#inter e0/1.1 C2611A(config-subif)#enc C2611A(config-subif)#encapsulation ? dot1Q IEEE 802.1Q Virtual LAN sdeIEEE 802.10 Virtual LAN - Secure Data Exchange Dave "Schneider, Matt" wrote: > > In the book that I read it says that you can only use fast ethernet or gig > ethernet > > -Original Message- > From: Colin [mailto:[EMAIL PROTECTED]] > Sent: Tuesday, February 12, 2002 8:20 PM > To: [EMAIL PROTECTED] > Subject: Ethernet or FastEthernet [7:35245] > > Hello > > I have been doing some reading on VLANs and Trunking and have read > conflicting information. Can you use a 10Mbs Ethernet interface when > running ISL or 801.1q or does the interface have to be FastEthernet? > Some books/articles I've read say you must use at least a FastEthernet > interface and others say you can use an Ethernet interface. Note: this > is for my CCNP lab studies, not a production network. > > Thanks > Colin -- David Madland Sr. Network Engineer CCIE# 2016 Qwest Communications Int. Inc. [EMAIL PROTECTED] 612-664-3367 "Emotion should reflect reason not guide it" Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=35300&t=35245 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: Ethernet or FastEthernet [7:35245]
Hi Colin, I have configured a port on a 2900 for 10Mbit and half duplex, and it lets me issue the command 'switchport trunk encapsulation isl' without any problems. On CatOS switches, you can issue the command 'show port capabilities', which will tell you the capabilities of each port. Regards, georg Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=35287&t=35245 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: Ethernet or FastEthernet [7:35245]
In the book that I read it says that you can only use fast ethernet or gig ethernet -Original Message- From: Colin [mailto:[EMAIL PROTECTED]] Sent: Tuesday, February 12, 2002 8:20 PM To: [EMAIL PROTECTED] Subject: Ethernet or FastEthernet [7:35245] Hello I have been doing some reading on VLANs and Trunking and have read conflicting information. Can you use a 10Mbs Ethernet interface when running ISL or 801.1q or does the interface have to be FastEthernet? Some books/articles I've read say you must use at least a FastEthernet interface and others say you can use an Ethernet interface. Note: this is for my CCNP lab studies, not a production network. Thanks Colin Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=35277&t=35245 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: Ethernet or FastEthernet [7:35245]
Even if Enet is available, it is not recomenned on Enet. Depends on the traffic you have on the trunk. Colin wrote: > Hello > > I have been doing some reading on VLANs and Trunking and have read > conflicting information. Can you use a 10Mbs Ethernet interface when > running ISL or 801.1q or does the interface have to be FastEthernet? > Some books/articles I've read say you must use at least a FastEthernet > interface and others say you can use an Ethernet interface. Note: this > is for my CCNP lab studies, not a production network. > > Thanks > Colin -- Ishrat Nadeem Zahid CCNP Cisco Systems,Inc. Chelmsford, MA 01824 Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=35251&t=35245 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: Ethernet or FastEthernet [7:35245]
a 2610 or 11 can do it over eth. ""Colin"" wrote in message [EMAIL PROTECTED]">news:[EMAIL PROTECTED]... > Hello > > I have been doing some reading on VLANs and Trunking and have read > conflicting information. Can you use a 10Mbs Ethernet interface when > running ISL or 801.1q or does the interface have to be FastEthernet? > Some books/articles I've read say you must use at least a FastEthernet > interface and others say you can use an Ethernet interface. Note: this > is for my CCNP lab studies, not a production network. > > Thanks > Colin Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=35248&t=35245 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: Ethernet or FastEthernet [7:35245]
ISL requires Fast ethernet. J -Original Message- From: Colin [mailto:[EMAIL PROTECTED]] Sent: Tuesday, February 12, 2002 8:20 PM To: [EMAIL PROTECTED] Subject: Ethernet or FastEthernet [7:35245] Hello I have been doing some reading on VLANs and Trunking and have read conflicting information. Can you use a 10Mbs Ethernet interface when running ISL or 801.1q or does the interface have to be FastEthernet? Some books/articles I've read say you must use at least a FastEthernet interface and others say you can use an Ethernet interface. Note: this is for my CCNP lab studies, not a production network. Thanks Colin Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=35247&t=35245 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
