41902 Lecture Notes - Lecture 13: Ethernet Frame, Mac Address, Network Layer
Network Fundamentals
Chapter 6.4: LANs
Addressing, ARP
- 32-bit IP address: network-layer address for interface used for network-layer
forwarding
- MAC (LAN/Physical/Ethernet) address: is used locally to get frame from one interface
to another physically-connected interface (same network in IP addressing sense). 48-
bit MAC address (for most LANs) burned in NIC ROM, also sometimes software settable
- LAN addresses and ARP: Each adapter on LAN has a unique LAN address. MAC address
allocation administered by IEEE. Manufacturer buys portion of MAC address space (to
assure uniqueness).
- MAC address (like an ID) is portable and can move LAN card from one LAN to
another. IP hierarchal address (like a postal address) is not portable; address
depends on IP subnet to which node it attached.
- ARP table: each IP node (host, router) on LAN has table. IP/MAC address
mappings for some nodes: <IP address; MAC address; TTL>
- TTL (Time To Live): time after which address mapping will be forgotten
(typically 20 min). EXAMPLES IN POWERPOINT
Ethernet
- Is a doiat ied LAN teholog. Has a sigle hip, ultiple speeds. Was the fist
widely used LAN technology. Simpler and cheap. Good speed - (10Mbp-10Gbps)
- Physical topology:
- Bus: popular through mid 90s. All nodes in same collision domain (can collide
with each other)
- Star: used toda. Atie sith i ete. Eah spoke us a sepaate
Ethernet protocol (nodes do not collide with each other).
- A sending adapter encapsulates IP datagrams (or other network layer protocol packets)
in Ethernet frame [structure]:
- Preamble: 7 bytes with pattern 10101010 followed by one byte pattern with
10101011. Used to synchronise receiver and sender clock rates.
- Unreliable/Connectionless:
- Connectionless: no handshaking between sending and receiving NICs
- Unreliable: eeiig NIC does’t sed aks o aks to sedig NIC. Data i
dropped frames is recovered only if initial sender uses higher layer rdt (e.g.
TCP), otherwise dropped data is lost
- Etheet’s MAC potool: uslotted C“MA/CD ith ia akoff
Switches
- Ethernet Switch - Link layer device: takes an active role
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
32-bit ip address: network-layer address for interface used for network-layer forwarding. Mac (lan/physical/ethernet) address: is used locally to get frame from one interface to another physically-connected interface (same network in ip addressing sense). 48- bit mac address (for most lans) burned in nic rom, also sometimes software settable. Lan addresses and arp: each adapter on lan has a unique lan address. Manufacturer buys portion of mac address space (to assure uniqueness). Mac address (like an id) is portable and can move lan card from one lan to another. Ip hierarchal address (like a postal address) is not portable; address depends on ip subnet to which node it attached. Arp table: each ip node (host, router) on lan has table. Ip/mac address mappings for some nodes: Ttl (time to live): time after which address mapping will be forgotten (typically 20 min). All nodes in same collision domain (can collide with each other)
