Transcript CS335 Networking & Network Administration

CS335
Networking &
Network Administration
Tuesday, April 13, 2010
LANs and data link layer





Physical layer specifies electrical, mechanical,
procedural, and functional requirements for
activating, maintaining, and deactivating the
physical link
Physical layer specifies voltage levels, data rates,
maximum transmission distances, and physical
connectors
Data link layer (layer 2) communicates with upper
layers through Logical Link Control (LLC)
Uses framing to group the bits of data
Uses MAC Address to identify devices
LAN standards

Media Access Control (MAC) (IEEE802.3)


The MAC sublayer defines how to transmit frames on the
physical wire. It handles physical addressing associated
with each device, network topology definition, and line
discipline
Logical Link Control (LLC) (IEEE802.2)

Logically identifies different protocol types and then
encapsulates them. A type code or a service access point
(SAP) identifier performs the logical identification. The type
of LLC frame used by an end station depends on what
identifier the upper layer protocol expects.
Hardware Addressing






Physical address
Hardware address
MAC address (media access control)
When a sender transmits a frame the sender
and receiver MAC address are in the frame
header
Source address field
Destination address field
NICS


LAN Hardware handles details of sending
and receiving frames (NIC)
Independent of the processor
NICS





If a frame is addressed to the NIC, the NIC
accepts the frame and passes it on to the
CPU
Otherwise it discards the frame
Checks CRC and discards frames with errors
NICs have
The computer therefore is isolated from
activity because the NIC isolates the CPU
from unnecessary frames
Format of a physical address


Static – hardware manufacturer assigns a
unique physical address to all devices
Advantages


Ease of use and permanence
Unique, no conflicts
Format of a physical address


Configurable – customer assigns an address
manually (switches or jumpers) or
electronically with nonvolatile memory like
EPROM
Advantages


Address remains the same
Can be smaller
Format of a physical address


Dynamic – automatically assigns a physical address
when the station boots, ex. Current time of day,
check to see if that address is taken, different
address every time it boots
Advantages



Eliminates need for hardware manufacturers to coordinate
assigning addresses
Addresses can be smaller
Disadvantage


Lack of permanence
Potential conflict
Unicast


A single packet is sent from a source to a
destination
Uses the MAC address
Broadcasting


Data sent to all devices on the network, not a
single destination physical address
Broadcast address is a reserved address of
each network



EX. 10.10.10.0 subnet mask 255.255.255.0, the
broadcast address is 10.10.10.255
Broadcast address is usually reserved as all 1’s
When a frame is sent to the broadcast
address each computer on the network
receives a copy
Multicasting




Broadcasting is inefficient
Computers waste CPU time deciding if a
broadcast frame is necessary
Sends a single frame over the network and
allows a specific subset of nodes to receive
the transmission
The source addresses by using a multicast
address
Frame headers and format



Two parts
Frame header has a fixed size
Size of the data area is determined by the
type of data being sent
Example frame format




Ethernet frame format
64 bit preamble contains alternating 0’s and
1’s to allow synchronizing signals
Ethernet uses 48 bit addresses (6 byte)
16 bit frame type
Frame types
Network Analyzers



NIC is in promiscuous mode so it receives
copies of all frames
Can choose what kind of frames to report
Can graph results
Next



http://cs.eou.edu/CSMM/twelch/networkdevic
es.ppt
This next link covers much of what we are
covering, use it to further review the basics
and extend your knowledge
http://www.erg.abdn.ac.uk/users/gorry/eg356
1/road-map.html