lan (ethernet), multicast
DESCRIPTION
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 - PowerPoint PPT PresentationTRANSCRIPT
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LAN (Ethernet), Multicast
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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
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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
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Class D: Multicast IP addresses
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IP Multicast Addresses
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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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IGMP – Joining a groupExample : R joins to Group 224.2.0.1
• R sends IGMP Membership-Reportabout 224.2.0.1 to 224.0.0.2 (ALL-ROUTERS.MCAST.NET)
• DR receives it. DR will start forwarding packets for 224.2.0.1 to Network A
• DR periodically sends IGMP Membership-Query to 224.0.0.1 (ALL-SYSTEMS.MCAST.NET)
• R answers IGMP Membership-Report about 224.2.0.1
R
R: ReceiverDR: Designated Router
Data to 224.2.0.1
IGMP Membership-Report
Network A
Network B
DR
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IGMP – Leaving a groupExample : 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.
Data to 224.2.0.1
R
DR
R: ReceiverDR: Designated Router
IGMP Leave-Group
Network A
Network B
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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
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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
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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
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PIM-DM(1)Initial flood of data
Source
Receiver 2
Receiver 1
S
R1
A
R2
B
C D F
G
H
IE
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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 check1. When a multicast packet is received, note its source (S) and interface (I)
2. If I belongs to the shortest path from S, forward to all interfaces except I
3. If test in step 2 is false, drop the packet
• Packet is nevernever forwarded back out the RPF interface!
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PIM-DM(2)prune non-RPF p2p link
Source
Receiver 2
Receiver 1
S
R1
A
R2
B
C D F
G
H
IE
IGMP PIM-Prune
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PIM-DM(3) C and D Assert to Determine
Forwarder for the LAN, C Wins
Source
Receiver 2
Receiver 1
S
R1
A
R2
B
C D F
G
H
IE
IGMP PIM-Assertwith its own IP address
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PIM-DM(4)I, E, G send Prune
H send Join to override G’s Prune
Source
Receiver 2
Receiver 1
S
R1
A
R2
B
C D F
G
H
IE
IGMP PIM-PruneIGMP PIM-Join
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PIM-DM(5)I Gets Pruned
E’s Prune is Ignored (since R1 is a receiver)G’s Prune is Overridden (due to new receiver R2)
Source
Receiver 2
Receiver 1
S
R1
A
R2
B
C D F
G
H
IE
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PIM-DM(6)New Receiver, I send Graft
Source
Receiver 2
Receiver 1
S
R1
A
R2
B
C D F
G
H
IE
IGMP PIM-Graft
Receiver 3
R3
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PIM-DM(6)new branch
Source
Receiver 2
Receiver 1
S
R1
A
R2
B
C D F
G
H
IE
IGMP PIM-Graft
Receiver 3
R3
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Multicast Scope Control:TTL Boundaries
to keep multicast traffic within an administrative domain, e.g., for privacy or resource reasons
an administrative domain
TTL threshold set oninterfaces to these links,greater than the diameterof the admin. domain
the rest of the Internet
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Direct connection: broadcast• Shared media
Metcalfe’s EthernetSketch (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
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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!
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Ethernet Format: Framing
• Preamble: (synchronization)– 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
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Ethernet Packet Structure
•14 byte header•2 addresses
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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
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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
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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
hub
nodes
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Twisted Pair Wire Map
• EIA/TIA 568B (UGA Standard)
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Standard vs Crossover CablesCard-to-Hub Wiring
(Standard Cable)
Card-to-Card (Hub-to-Hub) Wiring(Crossover Cable)
TD+TD- RD-
RD+
RD+
RD-
TD+
TD-
TD+ (RD+)TD- (RD-)
RD+ (TD+)
RD- (TD-)
TD+ (RD+)
TD- (RD-)RD+ (TD+)
RD- (TD-)
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Power over Ethernet (PoE)
http://www.nwfusion.com/news/2003/1124infrapoe.html
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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: 10.0.0.13
MAC: 00:00:dd:dd:dd:dd
IP: 10.0.0.12
MAC: 00:00:cc:cc:cc:cc
IP: 10.0.0.11
MAC: 00:00:bb:bb:bb:bb
A
DC
B
DestMACDestMAC
SourceMACSourceMAC
DestIPDestIP
SourceIPSourceIP DataData
Ethernet frame
IP packet
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ARP: finding the MAC Address
Host A Host BARP Query
ARP Response
BroadcastBroadcast Host BMAC ?Host BMAC ?
Host BIP
Host BIP
Host BMAC
Host BMAC
Host BIP
Host BIPUnicastUnicast
RFC 826: Address Resolution Protocol, 1982
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ARP frame format
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Multicast: one to many communication
• Application level one to many communication• multiple unicasts • IP multicast
S S
R
R
R
R
R
R
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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
00000001 00000000 01011110 0
1110
Low-order 23 bits of multicast
Group ID copied to Enet address
32-bit Class D IP Address
48-bit Ethernet Address
Not mapped
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• 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
Multicast Addresses
Multicast(1)
Local(1)/global(0)administration
48 bit address
highbyte
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Ethernet Multicast Addresses
01-00-5E-00-00-00
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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
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Switching Tables
0260.8c01.1111
0260.8c01.2222
0260.8c01.3333
0260.8c01.4444
E0 E1
E0: 0260.8c01.1111
E0: 0260.8c01.2222E1: 0260.8c01.3333E1: 0260.8c01.4444
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Spanning Tree Protocol
Broadcast
Segment 1
Segment 2
X Y
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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
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A
C
E
D
B
K
F
H
J
G
I
B5
B2
B3
B7
B4
B1
B6
Spanning tree example
rootDPDP
DPDP
DP
RP
DP
DP
DP
RP
RP
DPDP
DP
RP
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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?
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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)
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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
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Virtual LANs
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VLANs: IEEE 802.1q
• “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
destinationaddr
sourceaddr
data FCS
VLAN protocol id= 0x8100
3-bit priority1-bit CFI12-bit VLAN id
type
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VLAN Standard: IEEE 802.1q
CFI-Canonical Format Identifier (Ethernet/TokenRing)
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The 802.3 (legacy) and 802.1Q Ethernet frame formats
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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.
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Some Switches Support Priorities
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802.1p Prioritization• Eight levels of prioritization - p0 (lowest)
through p7 (highest)• 802.1p example
FS
VS
VS
VS
VS VS VS
VS
VS
FSFS
FSp7:
p0:
Internal Queues:
VLAN/802.1p Switch
L2 Switch
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Gigabit Ethernet over Fiber
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Switch Configuration Exampleinterface GigabitEthernet2/9
description NISN/NASAmtu 9216no ip addressspeed nonegotiateswitchportswitchport trunk encapsulation dot1qswitchport trunk allowed vlan 210-213,217-226,231,232switchport mode trunkswitchport nonegotiate
interface FastEthernet0/7 description ASSA switchport access vlan 210 no ip address speed 10