Title: Ethernet
1Ethernet
2Direct connection point-to-point
datagram
rcving node
link layer protocol
sending node
adapter (NIC)
adapter (NIC)
3Direct connection broadcast
Metcalfes Ethernet Sketch (1973)
- Ethernet dominant LAN technology
- cheap 30 for 100Mbs!
- first widely used LAN technology
- simpler, cheaper than token LANs and ATM
- kept up with speed race 10, 100, 1000 Mbps
4Ethernet Format Physical Layer
- Each bit has a transition
- Allows clocks in sending and receiving nodes to
synchronize to each other - no need for a centralized, global clock among
nodes!
5Ethernet Format Framing
- Preamble (clearing your throat)
- 8 bytes, allows sender/receiver clocks to
synchronize - Destination/Source Address (hey Paul, Tom here)
- 6 bytes each
- Type
- 2 bytes, indicates higher layer protocol
- 0x0800 is IP, 0x0806 is ARP
- Data 46-1500 bytes
- FCS (CRC)
- catches most transmission errors - errored frames
dropped
6Ethernet Packet Structure
- 14 byte header
- 2 addresses
Graphic Source Network Computing Magazine August
7, 2000
7Ethernet Physical Layer Packet Structure
Graphic Source Network Computing Magazine August
7, 2000
8Ethernet Addressing
- 6 byte address (unique to each adapter)
- Example 08-0b-db-e4-b1-02
- 248 281 trillion can produce 100 million LAN
devices every day for 2000 years! - Interpretation of address
- Upper 24 bits OUI (Organizationally Unique
Identifier) - Lower 24 bits Organization-assigned portion
- Unicast lowest bit of first byte is 0
- Multicast lowest bit of first byte is 1
- Broadcast ff-ff-ff-ff-ff-ff
- Adaptor accept frame if and only if
- Destination address matches adapter address, or
- Destination address is broadcast, or
- Destination address is multicast and adapter has
been configured to accept it
9Ethernet Media sharing
- CSMA/CD (the polite conversationalist)
- carrier sense dont transmit if you sense
someone else transmitting - collision detection abort your transmission if
you sense someone else transmitting - random access wait random time before attempting
a retransmission
10Ethernet Technologies
- 10Base2
- 10Mbps, 200 meters max cable length
- thin coaxial cable in a bus topology
- repeaters connect multiple segments
- 10BaseT / 100BaseT fast ethernet
- 10/100Mbps, Twisted pair
- Nodes connect to a hub in star topology
- Gigabit Ethernet
- 1Gbps, fibre or copper
- Extending from LAN to MAN
- 10 Gbps Ethernet now!
- High data speed larger distance increasing
number of devices per LAN gt switching
11Twisted Pair Wire Map
- EIA/TIA 568B (UGA Standard)
12Standard vs Crossover Cables
Card-to-Hub Wiring (Standard Cable)
RD
TD
TD-
RD-
RD
TD
TD-
RD-
Card-to-Card (Hub-to-Hub) Wiring (Crossover Cable)
TD (RD)
TD (RD)
TD- (RD-)
TD- (RD-)
RD (TD)
RD (TD)
RD- (TD-)
RD- (TD-)
13Power over Ethernet (PoE)
http//www.nwfusion.com/news/2003/1124infrapoe.htm
l
14Ethernet
- Most popular LAN technology nowadays 10Mb/s -
1Gb/s - Each host has unique 48bit MAC address (factory
assigned) - Frames sent to MAC addresses
- Broadcasts widely used
- To find destination MAC address, ARP protocol is
used
15ARP finding the MAC Address
RFC 826 Address Resolution Protocol, 1982
16ARP frame format
17IP Ethernet Multicast Address Mapping
- IP multicast addresses (class D) range from
224.0.0.1 to 239.255.255.255 and map to Ethernet
destination MAC addresses as shown below
18Multicast Addresses
- Multicast revises addresses to be protocol
specific high byte, least bit is 1 if
multicast. - Applications that use multicast
- Imagecast
- AppleTalk zones
- One-to-many IP video broadcasting
- Service location protocol (SLP)
19IGMP Snooping
- Internet Group Management Protocol (IGMP - RFC
2236) used to manage IP multicast traffic - Application wishing to receive traffic for
specific IP multicast address sends out an ICMP
join request (or a leave request to stop
receiving multicast) - Switches that employ IGMP snooping listen for
IGMP join/leave requests to decide when to send a
specific multicast frame to a port
20Switching (same as Bridging)
- Goals
- traffic isolation
- transparent operation
- plug-and-play
- Operation
- store and forward Ethernet frames
- examine frame header and selectively forward
frame based on MAC dest address - when frame is to be forwarded on segment, uses
CSMA/CD to access segment
21Switching Tables
22Spanning Tree Protocol
23Spanning tree protocol (IEEE 802.1d)
- Every bridge has bridge-id
- bridge-id 2-byte priority 6-byte MAC addr
- Question MAC address of bridge??
- Every port of bridge has
- port-id 1-byte priority 1-byte port-number
- port-cost inversely proportional to link speed
- Bridge with lowest bridge-id is root bridge
- On each LAN segment, bridge with lowest path cost
to root is designated bridge (use bridge-id and
port-id to break ties) - A bridge forwards frames through a port only if
it is a designated bridge for that LAN segment
24STP terminology
- Port roles
- Root port (switch port leading to root)
- Designated port (LAN port leading to root)
- Alternate / backup port (anything else)
- Port states
- Blocking (no send/rcv, except STP bpdus)
- Listening (prepare for learning/forwarding)
- Learning (learn MAC addr but no forwarding)
- Forwarding (send/rcv frames)
- Can disable STP on port or switch
- All frames are forwarded
- BPDUs?
25STP operation
- BPDU carries 4-tuple
- ltroot-id, root-cost, bridge-id, port-idgt
- Store rcvd and send 4-tuple for each port
- port with best rcvd 4-tuple is root port
- root bridge has no such port
- if send 4-tuple better than rcv 4-tuple, port is
designated port - rest of the ports are alternate/backup ports
- Various timers
26Spanning tree example
DP
DP
DP
RP
DP
RP
RP
DP
DP
DP
DP
DP
root
RP
DP
DP
27New Spanning Tree Protocol versions
- Implementation of
- Rapid Spanning Tree Protocol 802.1w (RSTP)
- Per VLAN Spanning Tree 802.1q (PVST )
- Multiple Spanning Tree 802.1s (MST)
- Load balancing across links
- BPDU guard
- Root Guard and
- Uni-Directional Link Detection (UDLD)
28Evolution of Spanning Tree
- The following developments in Spanning Tree
Protocol are examined - Per-VLAN Spanning Tree (PVST) is a
Cisco-proprietary implementation requiring ISL
trunk encapsulation. - PVST provides Layer 2 load balancing for the
VLAN on which it runs. - MST (IEEE 802.1s) extends the IEEE 802.1w Rapid
Spanning Tree (RST) algorithm to multiple
spanning-trees. - Enhanced PVST or Multiple Instance of Spanning
Tree Protocol (MISTP), a compromise between PVST
and MST.
29802.1w Rapid Spanning Tree Protocol
- The IEEE 802.1w specification, Rapid Spanning
Tree Protocol, provides for subsecond
reconvergence of STP after failure of one of the
uplinks in a bridged environment. - 802.1w provides the structure on which the 802.1s
features such as multiple spanning tree operates. - There are only three port states left in RSTP
corresponding to the three possible operational
states Learning ,Forwarding and Discarding. - Rapid Transition to Forwarding State is the most
important feature introduced by 802.1w - RSTP actively confirms safe port transition to
forwarding without relying on timers - There is now a real feedback mechanism that
takes place between RSTP-compliant bridges. - In order to achieve fast convergence on a port,
the protocol relies upon two new variables edge
ports and link type.
30Virtual LANs
- LAN (broadcast domain) grows large
- departments or workgroups not happy with big
broadcast domain - Security (eavesdropping)
- Bandwidth consumed by flooding/multicasting
- Split LAN into multiple broadcast domains
- Multiple physical LANs?
- Too expensive!
- People move all the time!
- VLAN logical partition of LAN
31Virtual LANs
32VLANs IEEE 802.1q
destination addr
source addr
data
FCS
type
3-bit priority 1-bit CFI 12-bit VLAN id
VLAN protocol id 0x8100
- Tagged Ethernet frames contain VLAN-id
- Switch adds/removes tag when forwarding frames
between trunk and non-trunk ports - Complications
- Hosts and legacy switches do not understand VLAN
tags - Tag insertion/removal requires FCS recomputation
- Frame length increases beyond legacy MTU
33VLAN Standard IEEE 802.1q
CFI-Canonical Format Identifier
(Ethernet/TokenRing)
34The 802.3 (legacy) and 802.1Q Ethernet frame
formats
35L2 Tunneling
The default system MTU for traffic on the switch
is 1500 bytes. You can configure the switch to
support larger frames by using the system mtu
global configuration command. Because the 802.1Q
tunneling feature increases the frame size by 4
bytes when the metro tag is added, you must
configure all switches in the service-provider
network to be able to process larger frames by
increasing the switch system MTU size to at least
1504 bytes. The maximum allowable system MTU for
Catalyst 3550 Gigabit Ethernet switches is 2000
bytes the maximum system MTU for Fast Ethernet
switches is 1546 bytes.
36Some Switches Support Priorities
37802.1p Prioritization
- Eight levels of prioritization - p0 (lowest)
through p7 (highest) - 802.1p example
38StoreForward vs Cut Through Switching
- The following diagram depicts the differences
between store-and-forward and cut-through
switching - Switches should employ store-and-forward
exclusively (cut-through propagates bad packets)
39(No Transcript)
40Gigabit Ethernet over Fiber
41Wave Division Multiplexing
DWDM 1528 to 1560 nm erbium doped fiber
amplifiers (EDFA) EDFA every 60km, regeneration
every 500km
42(No Transcript)
43Erbium doped fiber amplifiers
- A pump laser injects a high intensity pulse of
light exciting the erbium and causing the erbium
atoms to release their stored energy. - The EDFA amplifies all the wavelengths to the
same level (gain flatness). - DWDM 1528 to 1560 nm EDFA every 60km,
regeneration every 500km
44(No Transcript)
45Configuration Example
- interface GigabitEthernet2/9
- description NISN/NASA
- mtu 9216
- no ip address
- speed nonegotiate
- switchport
- switchport trunk encapsulation dot1q
- switchport trunk allowed vlan 210-213,217-226,231
,232 - switchport mode trunk
- switchport nonegotiate
- interface GigabitEthernet2/10
- description GEMnet
- mtu 9216
- no ip address
- speed nonegotiate
- switchport
- switchport trunk encapsulation dot1q
- switchport trunk allowed vlan 167-169,231
- switchport mode trunk
WKN 20040414