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Most modern Ethernet installations use Ethernet switches as opposed to hubs. Although the wiring is identical to hubbed Ethernet, switched Ethernet has several advantages over shared medium Ethernet including greater bandwidth and simplified wiring. Switched networks typically have a star topology, even though they still implement a single Ethernet "cloud" from the viewpoint of attached machines.
Initially, Ethernet switches work like Ethernet hubs, with all traffic being echoed to all ports. However, as the switch "learns" the end-points associated with each port, it ceases to send non-broadcast traffic to ports other than the intended destination. In this way, Ethernet switching can allow the full wire speed of Ethernet to be used by any given pair of ports on a single switch.
Since packets are typically only delivered to the port they are intended for, traffic on a switched Ethernet is slightly less public than on shared-medium Ethernet. However, as it is easy to subvert switched Ethernet systems by means such as ARP spoofing and MAC flooding , as well as for the network administrators to use monitoring functions to copy traffic from the network, switched Ethernet should still be regarded as an insecure network technology.
Frames are the format of data packets on the wire.
There are five types of Ethernet frame:
The different frame types have different formats and MTU values, but can coexist on the same physical medium.
The most common Ethernet Frame format, type II
The original Xerox Version 1 Ethernet had a 16 bit length field, although the maximum length of a packet was 1500 bytes. This length field was soon re-used in Xerox's Version 2 Ethernet as a label field, with the convention that values between 0 and 1500 indicated the use of the original Ethernet format, but higher values indicated what became known as an EtherType, and the use of the new frame format. This is now supported in the IEEE 802 protocols using the SNAP header.
| EtherType | Protocol |
| 0x0800 | IP Internet Protocol ( IPv4) |
| 0x0806 | Address Resolution Protocol ( ARP) |
| 0x8035 | Reverse Address Resolution Protocol ( RARP) |
| 0x809b | AppleTalk (Ethertalk) |
| 0x80f3 | Appletalk Address Resolution Protocol (AARP) |
| 0x8137 | Novell IPX (alt) |
| 0x8138 | Novell |
| 0x86DD | Internet Protocol, Version 6 ( IPv6) |
Type field (EtherType) for some common protocols
Novell Netware used this frame type by default until the mid nineties, and since Netware was very widespread back then (while IP was not) at some point in time most of the world's Ethernet traffic ran over "raw" 802.3 carrying IPX. Since Netware 4.10 Netware now defaults to IEEE 802.x with LLC (Netware Frame Type Ethernet_802.2) when using IPX. There is a Classical Series of Usenet Postings by Novell's Don Provan that have found their way into numerous FAQs and are widely considered the definitive answer to the Novell Frame Type jungle.
The 802.x variants of Ethernet are not in widespread use on common networks currently, with the exception of large corporate Netware installations that have not yet migrated to Netware over IP. The most common type used today is Ethernet Version 2, as it is used by most Internet Protocol-based networks, with its EtherType set to 0x0800. There exists a well defined standard for encapsulating IP traffic in IEEE 802.3 frames with LLC/SNAP headers, but it is commonly not supported.
IP Version 6 over Ethernet is also standardized based on IEEE 802.x. with LLC/SNAP.
Novell IPX is probably the only network protocol that supports all 4 current frame types.| Politics | Business | Finance |
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