Lan ethernet multicast
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LAN (Ethernet), Multicast. Why Multicast. When sending same data to multiple receivers better bandwidth utilization less host/router processing quicker participation Application Video/Audio broadcast (One sender) Video conferencing (Many senders) Real time news distribution

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Lan ethernet multicast

LAN (Ethernet), Multicast


Why multicast

Why Multicast

  • When sending same data to multiple receivers

    • better bandwidth utilization

    • less host/router processing

    • quicker participation

  • Application

    • Video/Audio broadcast (One sender)

    • Video conferencing (Many senders)

    • Real time news distribution

    • Interactive gaming

    • Cluster computing


Ip multicast service model

IP multicast service model

  • Invented by Steve Deering (PhD. 1991)

    • It’s a different way of routing datagrams

  • RFC1112 : Host Extensions for IP Multicasting - 1989

  • Senders transmit IP datagrams to a "host group"

  • “Host group” identified by a class D IP address

  • Members of host group could be present anywhere in the Internet

  • Members join and leave the group and indicate this to the routers

  • Senders and receivers are distinct: i.e., a sender need not be a member

  • Routers listen to all multicast addresses and use multicast routing protocols to manage groups


Class d multicast ip addresses

Class D: Multicast IP addresses


Ip multicast addresses

IP Multicast Addresses


Igmp joining a group

IGMP – Joining a group

  • Example : R joins to Group 224.2.0.1

  • R sends IGMP Membership-Reportto 224.2.0.1

  • DR receives it. DR will start forwarding packets for 224.2.0.1 to Network A

  • DR periodically sends IGMP Membership-Queryto 224.0.0.1 (ALL-SYSTEMS.MCAST.NET)

  • R answers IGMP Membership-Reportto 224.2.0.1

IGMP Membership-Report

R

Network A

DR

Data to 224.2.0.1

Network B

R: ReceiverDR: Designated Router


Igmp leaving a group

IGMP – Leaving a group

  • Example : R leaves from a Group 224.2.0.1

  • R sends IGMP Leave-Group to 224.0.0.2 (ALL-ROUTERS.MCAST.NET)

  • DR receives it.

  • DR stops forwarding packets for 224.2.0.1 to Network A if no more 224.2.0.1 group members on Network A.

IGMP Leave-Group

R

Network A

DR

Data to 224.2.0.1

Network B

R: ReceiverDR: Designated Router


Rpf reverse path forwarding

RPF(reverse path forwarding)

  • Simple algorithm developed to avoid duplicate packets on multi-access links

  • RPF algorithm takes advantage of the IP routing table to compute a multicast tree for each source.

  • RPF check

    • When a multicast packet is received, note its source (S) and interface (I)

    • If I belongs to the shortest path from S, forward to all interfaces except I

    • If test in step 2 is false, drop the packet

  • Packet isneverforwarded back out the RPF interface!


Protocol independent multicast

Protocol Independent Multicast

  • PIM : Protocol Independent Multicast

    • Independent of particular unicast routing protocol

    • Most popular multicast routing protocol today

  • PIM supports both dense (DM) and sparse (SM) mode operation

    • Opt out (NACK) type (DM)

      • Start with “broadcasting” then prune brunches with no receivers, to create a distribution tree

      • Lots of wasted traffic when there are only a few receivers and they are spread over wide area

    • Opt in (ACK) type (SM)

      • Forward only to the hosts which explicitly joined to the group

      • Latency of join propagation


Pim dm overview

PIM DM overview

  • Assumes that you have lots of folks who want to be part of a group

  • Based on broadcast and prune

    • Ideal for dense group

  • Source tree created on demand based on RPF rule

  • If the source goes inactive, the tree is torn down

  • Easy “plug-and-play” configuration

  • Branches that don’t want data are pruned


Pim dm overview1

PIM DM overview

  • Grafts used to join existing source tree

  • Asserts used to determine the forwarder for multi-access LAN

  • Non-RPF point-2-point links are pruned as a consequence of initial flooding


Pim dm 1 initial flood of data

PIM-DM(1)Initial flood of data

S

Source

A

B

G

F

C

D

H

I

E

R1

R2

Receiver 1

Receiver 2


Pim dm 2 prune non rpf p2p link

PIM-DM(2)prune non-RPF p2p link

S

IGMP PIM-Prune

Source

A

B

G

F

C

D

H

I

E

R1

R2

Receiver 1

Receiver 2


Pim dm 3 c and d assert to determine forwarder for the lan c wins

PIM-DM(3)C and D Assert to DetermineForwarder for the LAN, C Wins

S

IGMP PIM-Assertwith its own IP address

Source

A

B

G

F

C

D

H

I

E

R1

R2

Receiver 1

Receiver 2


Pim dm 4 i e g send prune h send join to override g s prune

PIM-DM(4)I, E, G send PruneH send Join to override G’s Prune

S

IGMP PIM-Prune

Source

IGMP PIM-Join

A

B

G

F

C

D

H

I

E

R1

R2

Receiver 1

Receiver 2


Lan ethernet multicast

PIM-DM(5)I Gets PrunedE’s Prune is Ignored (since R1 is a receiver)G’s Prune is Overridden (due to new receiver R2)

S

Source

A

B

G

F

C

D

H

I

E

R1

R2

Receiver 1

Receiver 2


Pim dm 6 new receiver i send graft

PIM-DM(6)New Receiver, I send Graft

S

IGMP PIM-Graft

Source

A

B

G

F

C

D

H

I

E

R1

R2

Receiver 1

R3

Receiver 2

Receiver 3


Pim dm 6 new branch

PIM-DM(6)new branch

S

IGMP PIM-Graft

Source

A

B

G

F

C

D

H

I

E

R1

R2

Receiver 1

R3

Receiver 2

Receiver 3


Multicast scope control ttl boundaries

Multicast Scope Control:TTL Boundaries

to keep multicast traffic within an administrative domain, e.g., for privacy or resource reasons

the rest of the Internet

TTL threshold set oninterfaces to these links,greater than the diameterof the admin. domain

an administrative domain


Direct connection broadcast

Direct connection: broadcast

  • Shared media

Metcalfe’s 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, 10000 Mbps

  • wireless options


10mb s ethernet physical layer

10Mb/s Ethernet 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!


Ethernet format framing

Ethernet Format: Framing

  • Preamble: (synchronization)

    • 8 bytes, allows sender/receiver clocks to synchronize

  • Destination/SourceAddress: (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


Ethernet packet structure

Ethernet Packet Structure

  • 14 byte header

  • 2 addresses


Ethernet addressing

Ethernet Addressing

  • 6 byte address (unique to each adapter)

    • Example: 08-0b-db-e4-b1-02

    • 2^48 = 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


Ethernet media sharing

CSMA/CD (the polite conversationalist)

carrier sense: don’t 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

Ethernet Media sharing


Ethernet technologies

nodes

hub

Ethernet 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 available

  • High data speed + larger distance + increasing number of devices per LAN => switching


Twisted pair wire map

Twisted Pair Wire Map

  • EIA/TIA 568B (UGA Standard)


Standard vs crossover cables

Standard 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-)


Power over ethernet poe

Power over Ethernet (PoE)

http://www.nwfusion.com/news/2003/1124infrapoe.html


Ethernet

Most popular LAN technology nowadays 10Mb/s - 1Gb/s

Each host has unique 48bit MAC address (factory assigned)

Frames sent to MAC addresses

To find destination MAC address, ARP protocol is used

IP: 10.0.0.10

MAC: 00:00:aa:aa:aa:aa

IP: 10.0.0.11

MAC: 00:00:bb:bb:bb:bb

A

B

IP: 10.0.0.12

MAC: 00:00:cc:cc:cc:cc

IP: 10.0.0.13

MAC: 00:00:dd:dd:dd:dd

C

D

Ethernet frame

Dest

MAC

Source

MAC

IP packet

DestIP

SourceIP

Data

Ethernet


Arp finding the mac address

ARP Query

Host A

Host B

Broadcast

Host B

MAC ?

Host B

IP

ARP Response

Unicast

Host B

MAC

Host B

IP

ARP: finding the MAC Address

RFC 826: Address Resolution Protocol, 1982


Arp frame format

ARP frame format


Multicast o ne to many communication

R

R

S

S

R

R

R

R

Multicast: one to many communication

  • IP multicast

  • Application level one to many communication

  • multiple unicasts


Ip ethernet multicast address mapping

1110

00000001

00000000

01011110

0

IP & 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

32-bit Class D IP Address

Low-order 23 bits of multicast

Not mapped

Group ID copied to Enet address

48-bit Ethernet Address


Multicast addresses

high

byte

Multicast(1)

Local(1)/global(0)

administration

48 bit address

Multicast Addresses

  • Multicast revises addresses to be protocol specific: high byte, least bit is “1” if multicast.

  • Applications that use multicast

    • One-to-many IP video broadcasting

    • Computing clusters in Grids


Ethernet multicast addresses

Ethernet Multicast Addresses

01-00-5E-00-00-00


Switching same as bridging

Switching (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


Switching tables

E0: 0260.8c01.1111

E0: 0260.8c01.2222

E1: 0260.8c01.3333

E1: 0260.8c01.4444

0260.8c01.1111

0260.8c01.3333

E0

E1

0260.8c01.2222

0260.8c01.4444

Switching Tables


Spanning tree protocol

X

Y

Segment 1

Broadcast

Segment 2

Spanning Tree Protocol


Spanning tree protocol ieee 802 1d

Spanning tree protocol (IEEE 802.1d)

  • Every bridge has bridge-id

    • bridge-id = 2-byte priority + 6-byte MAC addr

      • MAC address is 00:A0:C5:12:34:56

      • bridge ID is 8000:00A0:C512:3456

  • 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


Stp terminology

STP 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?


Stp operation

STP operation

  • BPDU carries 4-tuple:

    • <root-id, root-cost, bridge-id, port-id>

  • 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


Spanning tree example

Spanning tree example

DP

DP

DP

RP

DP

RP

RP

DP

DP

DP

DP

DP

root

RP

DP

DP


Lan ethernet multicast

New 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;

    • Uni-Directional Link Detection (UDLD)


Lan ethernet multicast

802.1w 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.


Virtual lans

Virtual 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


Lan ethernet multicast

Virtual LANs


Vlans ieee 802 1q

VLANs: IEEE 802.1q

destination

addr

source

addr

data

FCS

type

  • “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

3-bit priority

1-bit CFI

12-bit VLAN id

VLAN protocol id

= 0x8100


Vlan standard ieee 802 1q

VLAN Standard: IEEE 802.1q

CFI-Canonical Format Identifier (Ethernet/TokenRing)


The 802 3 legacy and 802 1q ethernet frame formats

The 802.3 (legacy) and 802.1Q Ethernet frame formats


L2 tunneling

L2 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.


Some switches support priorities

Some Switches Support Priorities


802 1p prioritization

VLAN/802.1p Switch

FS

Internal Queues:

FS

VS

VS

VS

p7:

p0:

FS

FS

VS

VS

VS

L2 Switch

VS

VS

802.1p Prioritization

  • Eight levels of prioritization - p0 (lowest) through p7 (highest)

  • 802.1p example


Gigabit ethernet over fiber

Gigabit Ethernet over Fiber


Switch configuration 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 FastEthernet0/7

description ASSA

switchport access vlan 210

no ip address

speed 10

Switch Configuration Example


Igmp snooping

IGMP 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


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