Comments on: Identifying Ethernet Header Types http://bradhedlund.com/2007/11/19/identifying-ethernet-header-types/ Studies in Data Center Networking, Virtualization, Computing Wed, 16 May 2012 06:59:43 +0000 hourly 1 http://wordpress.org/?v=3.3.2 By: naxidavid http://bradhedlund.com/2007/11/19/identifying-ethernet-header-types/comment-page-1/#comment-8727 naxidavid Thu, 16 Feb 2012 09:12:08 +0000 http://www.bradhedlund.com/articles/5/identifying-ethernet-header-types/#comment-8727 In order to allow some packets using Ethernet v2 framing and some packets using the original version of 802.3 framing to be used on the same Ethernet segment, EtherType values must be greater than or equal to 1536 (0x0600). That value was chosen because the maximum length of the payload field of an Ethernet 802.3 frame is 1500 octets (0x05DC). Thus if the field's value is greater than or equal to 1536, the frame must be an Ethernet v2 frame, with that field being a type field.[3] If it's less than or equal to 1500, it must be an IEEE 802.3 frame, with that field being a length field. Values between 1500 and 1536, exclusive, are undefined.[4] This convention allows software to determine whether a frame is an Ethernet II frame or an IEEE 802.3 frame, allowing the coexistence of both standards on the same physical medium. http://en.wikipedia.org/wiki/Ethernet_frame#Ethernet_frame_types In order to allow some packets using Ethernet v2 framing and some packets using the original version of 802.3 framing to be used on the same Ethernet segment, EtherType values must be greater than or equal to 1536 (0×0600). That value was chosen because the maximum length of the payload field of an Ethernet 802.3 frame is 1500 octets (0x05DC). Thus if the field’s value is greater than or equal to 1536, the frame must be an Ethernet v2 frame, with that field being a type field.[3] If it’s less than or equal to 1500, it must be an IEEE 802.3 frame, with that field being a length field. Values between 1500 and 1536, exclusive, are undefined.[4] This convention allows software to determine whether a frame is an Ethernet II frame or an IEEE 802.3 frame, allowing the coexistence of both standards on the same physical medium.
http://en.wikipedia.org/wiki/Ethernet_frame#Ethernet_frame_types

]]> By: owlman http://bradhedlund.com/2007/11/19/identifying-ethernet-header-types/comment-page-1/#comment-3026 owlman Fri, 12 Nov 2010 08:26:09 +0000 http://www.bradhedlund.com/articles/5/identifying-ethernet-header-types/#comment-3026 Ethernet is a type of self-clocking synchronous serial communication. On the wire, the Ethernet signal has an embedded clock, so the hardware knows exactly when the first and last bits arrive (because no clock information means no data). It simply has to count the bits, then divide by 8 to get the byte count of the frame. http://en.wikipedia.org/wiki/Manchester_code I think 35 years ago when they invented Ethernet it was quite expensive hardware-wise to count the bits, so they included the length in the frame for easier processing... Ethernet is a type of self-clocking synchronous serial communication. On the wire, the Ethernet signal has an embedded clock, so the hardware knows exactly when the first and last bits arrive (because no clock information means no data). It simply has to count the bits, then divide by 8 to get the byte count of the frame.

http://en.wikipedia.org/wiki/Manchester_code

I think 35 years ago when they invented Ethernet it was quite expensive hardware-wise to count the bits, so they included the length in the frame for easier processing…

]]> By: Thomas B. http://bradhedlund.com/2007/11/19/identifying-ethernet-header-types/comment-page-1/#comment-2765 Thomas B. Mon, 01 Nov 2010 18:08:43 +0000 http://www.bradhedlund.com/articles/5/identifying-ethernet-header-types/#comment-2765 This is probably obvious to everyone else, but I can't seem to figure it out. If Type/Length indicates a Type, how do you determine the Length? Do you just look for an interframe gap or something? This is probably obvious to everyone else, but I can’t seem to figure it out. If Type/Length indicates a Type, how do you determine the Length? Do you just look for an interframe gap or something?

]]> By: Internetwork Expert .org » Identifying Ethernet Multicast http://bradhedlund.com/2007/11/19/identifying-ethernet-header-types/comment-page-1/#comment-2 Internetwork Expert .org » Identifying Ethernet Multicast Wed, 21 Nov 2007 21:52:43 +0000 http://www.bradhedlund.com/articles/5/identifying-ethernet-header-types/#comment-2 [...] like there are 3 different Ethernet header formats, there are also 3 different types of Ethernet [...] [...] like there are 3 different Ethernet header formats, there are also 3 different types of Ethernet [...]

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