Ethernet on DataLink
Layer (Layer 2)
Data Link layer user MAC address for addressing, basically a
hexadecimal number is burnt on Network Interface Card of the device can be PC,
router, etc.
All the Layer 2 devices are coordinated on the basis of MAC
addresses further layer3 devices are also coordinated on the basis of Layer2
MAC address at each interface provided.
MAC addressed is defined in the form of - 00-21-5C- 23- 67 –
DB
1.
It is a 48 bits long code(6 bytes)
2.
First 24 bits is the OUI (Organizational Unique
Identifier)
3.
Last 24 bits are Vendor Assigned.
OKH-MAX_R1#sh interfaces
Gi1/1
GigabitEthernet1/1 is up,
line protocol is up (connected)
Hardware is C7600 1Gb 802.3, address is 0022.5518.3fc0 (bia 0022.5518.3fc0)
Description: *** L3 LINK TO PE2-OKHLA
OKH_MAX-R2 ***
Internet address is 10.181.128.65/30
Ethernet Frame Types:
·
Ethernet_II
·
802.3_Ethernet
Frame Fields
·
Preamble in the form of 1010
·
Start Frame Delimiter 11
·
Destination Address
·
Source Address
·
Length or Type Field (length for 802.3 and Type
for Ethernet _II)
·
Data
·
Frame Check Sequence (FCS)
Duplex and Speed:
Duplex is basically the way how Ethernet frame will
communicate between sender and receiver.
Duplex can be further classified as Half Duplex and Full
Duplex.
Half Duplex is one way communication between two devices for
example walky talky communication.
Full Duplex Communications is basically communication
between two devices in both ways for example a telephone conversation. In Full
Duplex Communication:
·
No collision takes place during the
communication
·
Dedicated switch port can be assigned for fast
and reliable communication.
·
Network Card and switches must have provision
for full duplex communication.
·
Point to Point communication takes place during
the communications.
Speeds is basicaaly the rate at which frames travels over
the communication media. The ports assigned at Switches or NIC’s are capable of
varying speeds, or can be auto negotiated to get the packet pass on.
Speeds can be classified as:
·
10 Mb/s – Ethernet
·
100Mb/s- Fast Ethernet
·
1000Mb/s- Gigabit Ethernet
·
10000Mb/s- 10 Gigabit Ethernet.
Note: If we have speed and duplex mismatches between sender
and receiver, the communication between the two ports is not possible.
Cables: In Point to
point communication , layer 1 devices need to be categorized on the basis of
standards defined by IEEE. The cable can be categorized as:
1.
Straight through cable: Straight cable is used
to connect different devices like a switch can be connected to router, computer
can be connected to hub, computer to switch. The both ends of a straight
through cable are same.
2.
Crossover Cable: Cross Over cable has been
connected to similar devices like router to router, switch to switch, hub to
hub, etc.
3.
Rolled Cable:
Host to console of Router or switch. Both end of rolled cable are
exactly opposites.
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