Ethernet

Description:

Protocol suite:Ethernet
Type:CSMA/CD Data Link and Physical Layer.

The Ethernet is a local area network (LAN) set of protocols which serves the physical and data link layers. Ethernet utilizes a linear bus or star topology. Ethernet served as the basis for the IEEE 802.3 standard.

The Ethernet deals with the low level - Physical and Data Link Layers. 

The Data Link Layer is divided into two sublayers:

Ethernet uses CSMA/CD when transmitting packets. The Carrier Sense Multiple Access with Collision Detection (CSMA/CD) is an algorithm, for transmitting and receiving packets over a common network hardware medium, by aiding in avoiding transmission collisions. The network is checked for other transmissions; when the way is clear, the computer transmissions can begin. If a collision is detected the packet is retransmitted later.

Address resolution protocol (ARP) is a TCP/IP protocol used to map IP network addresses to a hardware interface physical addresses.

Reverse address resolution protocol (RARP) is a TCP/IP protocol used to map hardware interface physical addresses to IP network addresses.

Some of the listed RFCs for Ethernet implement the Simple Network Management Protocol (SNMP).


Ethernet frame.

Preamble Ethernet 802.3 packet Data FCS

Preamble. 8 bytes.
For synchronization, this indicates that the frame is about to begin. Included is the Start Frame Delimiter field that ends with two1s.

Ethernet 802.3 Packet format.

00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15
 

Destination Address

 

 

Source Address

 

EtherType
Data
:::

Destination Address. 6 bytes.
The address(es) are specified for a unicast, multicast (subgroup), or broadcast (an entire group).

Source Address. 6 bytes.
The address is for a unicast (single computer or device).

EtherType. 16 bits.
Which upper layer protocol will utilized the Ethernet frame.

Data. variable, 46-1500 bytes.

FCS, Frame Check Sequence. 4 bytes.
Error checking with a Cycle Redundancy Check (CRC) value.


Ethernet 802.2 LLC Packet format:

00 01 02 03 04 05 06 07
DSAP
SSAP
Control

LLC, Link Layer Control.
The Logical Link Control (LLC) consists of the DSAP, SSAP, and Control fields. The function is to establish paths to the SAP addresses for the Network Layer protocol services. This part gets inserted into the data field.

DSAP, Destination Service Access Point. 8 bits.
The destination network layer, protocol type of the packet.

SSAP, Source Service Access Point. 8 bits.
The source network layer, protocol type of the packet.

Control. 8 bits.


Ethernet SNAP Packet format:

00 01 02 03 04 05 06 07
Organization
Code
EtherType

Ethernet SNAP. Organization Code and Ethertype fields follow the LLC fields.

Organization Code. 3 bytes.
Which organization assigned the Ethernet Type field.

EtherType. 2 bytes.
Defines which upper layer protocol will utilize the Ethernet frame.

Value EtherTypes
0x0800 IP.
0x0806 ARP, Address Resolution Protocol.
0x8035 RARP, Reverse Address Resolution Protocol.
0x809B AppleTalk.
0x80F3 AppleTalk ARP.
0x8137 NetWare IPX/SPX.

Glossary:

Address Mapping.
(RFC 894, page 2) Mappings between 32-bit Internet addresses and 48-bit Ethernet addresses could be accomplished through the Address Resolution Protocol (ARP) [RFC 826]. Internet addresses are assigned arbitrarily on some Internet network. Each host's implementation must know its own Internet address and respond to Ethernet Address Resolution packets appropriately. It should also use ARP to translate Internet addresses to Ethernet addresses when needed.

Managed Objects.
(RFC 2358, page 3) Managed objects are accessed via a virtual information store, termed the Management Information Base or MIB. Objects in the MIB are defined using the subset of Abstract Syntax Notation One (ASN.1) [Information processing systems - Open Systems Interconnection - Specification of Abstract Syntax Notation One (ASN.1), International Organization for Standardization, International Standard 8824, December 1987.] defined in the SMI [RFC 1902]. In particular, each object object type is named by an OBJECT IDENTIFIER, an administratively assigned name. The object type together with an object instance serves to uniquely identify a specific instantiation of the object. For human convenience, we often use a textual string, termed the descriptor, to refer to the object type.

SNMP, Network Management Framework.
(RFC 2358 , pages 2 and 3) The SNMP Network Management Framework consists of several components. For the purpose of this specification, the applicable components of the Framework are the SMI and related documents [RFC 1902, RFC 1903, RFC 1904], which define the mechanisms used for describing and naming objects for the purpose of management. The Framework permits new objects to be defined for the purpose of experimentation and evaluation.


RFCs:

[RFC 826] An Ethernet Address Resolution Protocol.

[RFC 894] A Standard for the Transmission of IP Datagrams over Ethernet Networks.

[RFC 895] A Standard for the Transmission of IP Datagrams over Experimental Ethernet Networks.

[RFC 1029] A MORE FAULT TOLERANT APPROACH TO ADDRESS RESOLUTION FOR A MULTI-LAN SYSTEM OF ETHERNETS.

[RFC 1089] SNMP over Ethernet.

[RFC 1369] Implementation Notes and Experience for The Internet Ethernet MIB.

[RFC 1643] Definitions of Managed Objects for the Ethernet-like Interface Types.

[RFC 1972] A Method for the Transmission of IPv6 Packets over Ethernet Networks.

[RFC 2358] Definitions of Managed Objects for the Ethernet-like Interface Types.


Obsolete RFCs:

[RFC 1284] Definitions of Managed Objects for the Ethernet-like Interface Types.

[RFC 1398] Definitions of Managed Objects for the Ethernet-like Interface Types.

[RFC 1623] Definitions of Managed Objects for the Ethernet-like Interface Types.

[RFC 1650] Definitions of Managed Objects for the Ethernet-like Interface Types using SMIv2.


References:

Chappell, Laura and Dan Hakes. Novell's Guide to NetWare LAN Analysis (First Edition). Sybex Inc. and Novell Press, 1993.

Chappell, Laura and Dan Hakes. Novell's Guide to NetWare LAN Analysis (Second Edition). Sybex Inc. and Novell Press, 1994.

Naugle, Matthew. Network Protocol Handbook. McGraw-Hill, Inc., 1994.

Networking Technologies. Novell Inc.