PIM-Networkshop 2003-14

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- or How an IPv4 Multicast Packet gets from sender to receiver

A Day in the Life of aMulticast Flow

Gorry Fairhurst

[email protected] to Networkshop, YorkApril 2003

Updated July 2003 (rev. 14)

Supporting multicast on the LAN


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[email protected] of Aberdeen (c) 2003

Overview

ReceiverSource

RP

Rendezvous

Point

DesignatedRouter

ReceiveRouter

Terminology

Part 1: Starting Multicast Applications

Part 2: Network Delivery

Part 3: Stopping Multicast Applications


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Three key thingsIGMP tells a Receive Router which flows to receive

Overview

RP's tell PIM Routers about Sources

Join/Prune used to build trees

ReceiverSource

RP

Rendezvous

Point

DesignatedRouter

ReceiveRouter


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Designated Router (DR) = router sending from source IGMP = Internet Group Management Protocol (IPv4)

PIM = Protocol Independent Multicast routing protocol Receiver = end host / pc that wishes to receive Receive Router = last-hop router delivering to receiver

Rendezvous Point (RP) = a router that knows source Source = end host / pc that send

Transit Router = multicast router in the network

Terminology


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Tree - the multicast delivery path

from the Source to one or more receivers from a Rendezvous Point to one or more receivers

TIB - Tree Information Base (multicast routing table) Join - Routing message to create a Tree entry Prune - Routing message to delete a Tree entry

Multicast Jargon List


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PIM Message TypesPIM Messages

0: HELLO1: REGISTER (includes tunnelled packet)2: REGISTER STOP3: JOIN/PRUNE4: Bootstrap Router (BSR) - SM Only

5: ASSERT6: GRAFT - DM Only7: GRAFT-ACK - DM Only8: CANDIDATE RP-ADVERTISEMENT (with BSR)

Common PIM Flags (displayed by "mroute")

C Connected - One or members wish to receive flow for Group GF Register - This DR has a local Source for Group GJ Join - Router has sent a Join message for this flowP Pruned - Router does not need to forward flow for Group GT Tree - Router is receiving directly from the Source (S,G)

Note: This presentation looks only at PIM-SM (not PIM-DM or PIM-SSM)


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Terminology

Part 1: Starting Multicast Applications

Part 2: Network Delivery

Part 3: Stopping Multicast Applications


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User starts program

Program registers with OS Packets flow to Receiver

Receivers / Clients


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Tree Information Base (TIB)

OS Sends IGMP Report

Router enables LAN interface

Receive Router (IGMP Querier)

Receiver

IGMPReport

224.2.132.76

X

Receive Router forwards packets to Receiver

X XXX

OS enables Ethernet Interface

OS send IGMP-Reportfor Group(s)

Router creates TIB entry


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IPv4 Multicast Addresses

Class D IP Multicast Address32 bits starting with bit pattern 1110224.0.0.0-239.255.255.255

224.0.0.X are reserved

IPv6IPv6 has similar address allocations

[RFC 3171]

28 bit group destination address


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Mapping to Ethernet MAC

Class D IPv4 destination address

224.0.0.0-239.255.255.255

1110

28 bits32 bits

0 1 - 00 - 5 E - 7F - FF - FF

48 bits

5 bit overlap

23 bits

MAC hardware destination address

One L2 (MAC) addressmay carry multiple L3 (IPv4) addresses

[RFC1122]


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Multicast IP Packet Decode

ETHER

Packet size = 218 bytesDestination = 1:0:5e:2:dc:3e, (multicast) (01-00-5e-02-dc-3e)Source = 0:d0:bb:f7:c6:c0,Ethertype = 0800 (IPv4)IP

Version = 4, Header length = 20 bytesType of service = 0x00Total length = 204 bytes (00cc)ID = 57862, Flags = 0x00, Frags = 0Time To Live = 113 seconds/hopsProtocol = 17 (UDP)Header checksum = a1a9

Source address = 132.185.132.118Destination address = 224.2.220.62No optionsUDP

Source port = 31106 (7982)Destination port = 31106 (7982)Length = 184 (00b8)Checksum = 08a0

RTP180B of Data

0: 0100 5e02 dc3e 00d0 bbf7 c6c0 08004500

16: 00cc e206 0000 7111 a1a9 84b9 8476 e002

32: dc3e7982 7982 00b8 08a0 8005 dbc6 d721

48: 69c0 0752 bb5f fe39 3600 8808 b120 8933

64: 6219 9118 5128 ffc8 1321 bc10 933e aa2380: 3233 ba00 e892 a00c 1a3c 0a28 37ab 012d

96: aca5 4819 9088 0b39 64ba 43a0 b9a8 04b3

112: 88b8 4bf8 3940 d024 0a98 8b0b 1703 0a3a

128: 8820 a381 a21f 3bc0 9298 e893 90bd 042a

144: 0a88 3287 59ab e980 1211 4002 2208 98b1

160: 7039 0b26 e898 99ab b118 a1aa a702 9ac4

176: 9128 ca21 7822 2971 090a 2194 98d0 27bb

192: 0958 8092 993f b3b0 2922 337a 0f88 8810

208: 8a29 0183 fb15 b888 0d4c

IPv4 Multicast packet sent to Group 224.2.220.62


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IGMP Query

Router updates TIB entry


Receiver

IGMP

Report

IGMPQuery

224.2.132.76 CHECK

Receive Router continues to forward packets to Receiver

Router sends IGMP-Queryto LAN

Receiver (or another computer) responds


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* TCPdump: Receiver Joining

IGMPReport

16:00:35.401923 churchward.erg.abdn.ac.uk > 224.2.132.76: igmp v2 report 224.2.132.76 [ttl 1]

16:00:35.594515 source.x.ac.uk.64276 > 224.2.132.76.49280: udp 986 (ttl 127)



....



16:00:44.370493 churchward.erg.abdn.ac.uk > 224.2.132.76: igmp v2 report 224.2.132.76 [ttl 1]




Data flows from Source to requested Group

Receiver enables Group (G) at Ethernet interfaceReceiver send IGMP Membership Reportfor (G)

Receiver resends IGMP Membership Reportfor (G)- in case first report was lost

IGMPReport


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gate#show ip igmp groupIGMP Connected Group Membership

Group Address Interface Uptime Expires Last Reporter

239.255.255.255 FastEthernet0 2d02h 00:02:38 139.133.204.131

239.255.255.250 FastEthernet0 2d02h 00:02:40 139.133.204.220

224.2.132.76 FastEthernet0 2d02h 00:02:58 139.133.204.110

224.255.222.239 FastEthernet0 2d02h 00:02:59 139.133.204.110

233.2.171.1 FastEthernet0 2d02h 00:02:46 139.133.204.118

224.2.127.254 FastEthernet0 2d02h 00:02:38 139.133.204.131

224.0.1.75 FastEthernet0 2d02h 00:02:38 139.133.204.131224.0.1.40 FastEthernet0 2d02h never 139.133.204.210

* Router IGMP Table

IGMPReport

IGMPQuery


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TerminologyPart 1: Starting Multicast ApplicationsPart 2: Network DeliveryPart 3: Stopping Multicast Applications


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The Multicast Tree

XX

X

Source

Receiver 1

Receiver 2


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Pruning

Routers Prune flows when there are noJoins

Joining / Pruning the Tree

X

XX

Source

Receiver 1

Receiver 2

Joining

Routers do not forward flows until aJoin is receivedRouters sendJoin if they wish to receive a flow


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* Multicast Delivery

Source

RP

Each network has at least one Rendezvous Point (RP) RouterRP knows the address of SourcesRP can forward packets on behalf of sources

Sources send packets to a Designated Router (DR)DR tells RP the addresses of active local Sources

Rendezvous Point

SourceDesignated

Router

DRText


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Sending to the LAN DR

Send unicast PIM-Registerto RP

PIM Designated Router (DR)

Source139.133.204.31

139.133.204.31: 224.2.132.76

Reg

PIM Designated Router (DR) maybe IGMP Querier

DR receives flows from local Source

Creates a TIB entry


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Telling the RP about a Source

RP

DR

139.133.204.31: 224.2.132.76

Source DR stops registering (for a while)XX

DR waits for a PIM-Join

STOP

Reg

139.133.204.31

Source DR does not forward flows

RP updates TIB

Send a PIM-Registerto the RP

RP sends PIM-Register-STOP

Source


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All DRs must know the RP address PIM-Registermessages sent to RP Packets UNICAST to RP

Messages include a complete packet DR resends a PIM-Registerafter a timeout

RPs can forward packets (shared tree) Generally do not forward packets Receiving Router Joins to DR

e.g. ~ 1 sec.

* Facts about RPs


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Mar 7 16:20:15: 2d02h: PIM: Send v2 Data-header Register to 146.97.36.9

for 139.133.204.31, group 224.2.132.76

Mar 7 16:20:15: 2d02h: PIM: Received v2 Register-Stop on Ethernet0 from 146.97.36.9

for source 139.133.204.31, group 224.2.132.76

Mar 7 16:20:15: 2d02h: PIM: Clear register flag to 146.97.36.9

for (139.133.204.31/32, 224.2.132.76)

Registering with the RP

Reg

STOP

DR

RP RP = 146.97.36.9

Source = 139.133.204.31Group = 224.2.132.76


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Receiving via the RP

RP

DR

139.133.204.31: 224.2.132.76

RP sends (S,G) PIM-Jointo Source DR

X

X

Packets forwarded via the RP

Receive Router

139.133.204.31

Receive Router sends (*,G) PIM-Jointo RPRP updates TIB

Source DR forwards flow via RPReceiver


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[email protected] of Aberdeen (c) 2003 Joining

Routers do not forward until they receive aJoin Routers canJoin before Source sends a flow

Routers canJoin before Source Registers with RP Pruning Routers Prune flows when there are noJoins

Routers continue to send (~ 3 secs) after Prune Allows other routers toJoin (continue receiving)

Routers delete inactive flows (after ~ 3 mins)

* Facts about Join / Prune


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[email protected] of Aberdeen (c) 2003gate#show ip mroute

IP Multicast Routing Table

Flags: D - Dense, S - Sparse, C - Connected, L - Local, P - Pruned

R - RP-bit set, F - Register flag, T - SPT-bit set, J - Join SPT

M - MSDP created entry, X - Proxy Join Timer Running

A - Candidate for MSDP Advertisement

Outgoing interface flags: H - Hardware switched

Timers: Uptime/Expires

Interface state: Interface, Next-Hop or VCD, State/Mode

...

(139.133.204.31, 224.2.132.76), 2d02h/00:03:29, flags: CFT

Incoming interface: FastEthernet0, RPF nbr 0.0.0.0

Outgoing interface list:

Tunnel0, Forward/Sparse, 2d02h/00:03:17 (ttl-threshold 24)

...

(139.133.204.31, 224.2.132.76), 2d02h/00:03:29, flags: CFT

Incoming interface: FastEthernet0, RPF nbr 0.0.0.0

Outgoing interface list:

Ethernet2, Forward/Sparse, 00:00:11/00:02:57Tunnel0, Forward/Sparse, 2d02h/00:03:18 (ttl-threshold 24)

* Joining 224.2.132.76

After aJoin from a Receiver on Local LAN


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Receiving from Source

RP 139.133.204.31: 232.2.132.76

Source DR forwards packets to Receiver

X

X

Packets forwarded on shortest path

Join

139.133.204.31

Receive Router discovers Source address

Receive Router sends (S,G) PIM-Jointo Source

RP sends a PIM-Pruneto Source DR

Receive Router sends a PIM-Pruneto RP

Source

Receive

Router

DR

Receiver


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Finding a Remote Source

DRX X

Local RP needed

to know Source!

RP

DR

139.133.204.31: 224.2.132.76

JoinJoin

Join

X

Source DR forwards flow to Receiver

139.133.204.31

Receive Router sends (*,G) PIM-Jointo local RP

Local RP sends (S,G) PIM-Jointo Source

Note: Packets were not forwarded via the RP

Source

Receiver


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All RPs need to know address of all Sources

Inter-domain & Intra-domain

Two other protocols used in Inter-Domain PIM: Multicast Source Discovery Protocol - MSDP

Multi-Protocol BGP - MBGP

Connecting PIM Domains


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Terminology

Part 1: Starting Multicast ApplicationsPart 2: Network DeliveryPart 3: Stopping Multicast Applications


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Program sends signal to OS

Ethernet interface filters cleared

Send IGMP-Leave messageStop responding to IGMP-Queries

Application Ends

Receivers may "disappear"Program crashesComputer CrashesComputer disconnects from net...


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Pack Up & Go Home

Router stops forwarding flow


Receiver

224.2.132.76

X

Router prunes unwanted multicast group

Prune

IGMPQuery

CHECK

Send IGMP-Queryto check for ReceiversNo response indicates no members

PIM-Prunesent upstream


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Stopping a Source

Source continues to send to DR

Source DR

Source

139.133.204.31:224.2.132.76

Prune

X

Source DR stops forwarding

Source DR receives a PIM-Prune


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Multicast Flow (G= 224.2.132.76) forwarded by local DR

IGMP Leave Message from Receiver16:07:18.879773 churchward.erg.abdn.ac.uk > ALL-ROUTERS.MCAST.NET:

igmp leave 224.2.132.76 [ttl 1]

Multicast Flow (G= 224.2.132.76) STILL forwarded by local DR

IGMP Query16:07:41.026028 gate-erg.erg.abdn.ac.uk > ALL-SYSTEMS.MCAST.NET:

igmp query v2 [tos 0xc0] [ttl 1]

Multicast Flow (G= 224.2.132.76) STILL forwarded by local DR

Local DR STOPS forwarding Multicast Flow (G= 224.2.132.76)

Send PIM-Prune (G= 224.2.132.76) if no other local LANs require this

TCPDump ofIGMP-Leave


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Three key things

IGMP tells a Receive Router which flows to ReceiveRP's tell Receive Routers about Sources (via packets)

Join/Prune used to build trees

So Finally....

Multicast isn't hardIt is very different to unicast

Need to work with new "tools"


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Question & Answers

?


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[email protected] of Aberdeen (c) 2003 Networkshop 30 (Nottingham, 2002)

Jonathan Couzens, "Inter-Domain Multicast" , 2002.

G Fairhurst, "Multicast & LANs, p191-208, 2002.

RFCs

S. Deering, 'Host Extensions for IP Multicasting', RFC 1112, October 1989

W. Fenner, 'Internet Group Management Protocol, Version 2', RFC2236, November 1997

B. Cain, S. E. Deering, and A. Thyagarajan, 'Internet Group Management Protocol, Version 3', WORK IN PROGRESS (IETF MAGMA WG), 2003.

D. Estrin, D. Farinacci, A. Helmy, D. Thaler, S., Deering, M. Handley, V. Jacobson, C. Liu, P. Sharma, L. WeiProtocol Independent Multicast-Sparse Mode (PIM-SM): Protocol Specification", RFC2362, . June 1998

W Fenner, Mark Handley "Protocol Independent Multicast - Sparse Mode (PIM-SM): Protocol Specification(Revised)" draft-ietf-pim-sm-v2-new-06.txt , WORK IN PROGRESS (IETF PIM WG), 2003.

Books

K. Clark & K. Hamilton CISCO LAN Switching ISBN 1-57870-094-9, 1999

B.M. Edwards, L.A. Giuliano, B.R. Wright, Intedomain Multicast Routing: Practical Juniper and CISCO SystemsSolutions, ISBN 0-201-74612-3, 2002.

Kosiur, IP Multicasting, Wiley, ISBN 0-417-24359-0, 1998

B. Wilson, Developing IP Multicast Networks, CISCO Press, ISBN 1-57870-077-9, 2000.

Finding out more

PIM-Networkshop 2003-14

Documents

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