IP: Addresses and Forwarding

1
?????
????????????? ???
2
??? ??????
3
1 ?????

• ???????????????????????????????????
• ?????????????????????????????????????
• ????????????????????????????????

4
1 ?????
Src
Src
??????????????????
5
2 ?????

• ????????(one-to-many)?????
• ??
• ??/????/????/?????????
• ????(Distance learning)
• ????????(routing updates)
• ????(Teleconferencing ,audio, video, shared
  whiteboard, text editor)
• ???????????(Distributed interactive gaming or
  simulations)
• ????(Content distribution) ????(Software
  distribution)
• Web????(Web-cache updates )
• ?????(Database replication)

6
3 ???????????

• ??(Broadcast)
• ??????????????????
• ????(Simple), ??????(inefficient)
• ??????????????????
• ????????CPU??
• ???????broadcast storms
• ???????(Replicated Unicast)
• ??????????????????
• ??????????????????
• ???????????,
• ?????(Reliability gt per-receiver state, separate
  sessions/processes at sender)

7
4 IP???????
???? Service model
Hosts
??????????(IGMP)
Routers
?????? Multicast routing protocols
8
5 IP ???? RFC 1112

• ???(?)?????????
• ?????group address??????
• ?IP??????????????????
• ??????????????(any size)
• ???????????????
• ????(Group membership)???????(not explicitly
  known)
• ?????????????????????(Receivers can join/leave
  at will)

9
5 IP ???? RFC 1112

• ?????????(Distribution tree,????? )???????
• ??????,??????????????????
• ?????????????(?????????????????????,??????????????
  ???(multicast delivery tree changes dynamically)

10
6 IP ????

• IP????D?IP??(Class D IP addresses)
• 224.0.0.0 239.255.255.255
• ??????(Address allocation)
• IANA????????? (Well-known 224.0.0.x and
  224.0.1.x )???????????(Transient multicast
  addresses),??????
• ??????????????(host group)
• IP?????????(flat address space)

1
1
1
0
Group ID
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IP???????????

• ??????
• ?????? Join-IP-Multicast-Group(group-address,
  interface)
• ????Leave-IP-Multicast-Group(group-address,
  interface)
• ?????,??????IP????( normal IP-receive
  operation)???????

12
7 IP??????????????

• ???(Ethernet)??????802??
• ??????(Direct mapping! ?unicast??! ??ARP???.)

LAN multicast address
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IP Multicast Architecture
Service model
Hosts
Host-to-router protocol(IGMP)
Routers
Multicast routing protocols(various)
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8 ????????(Internet Group Management Protocol)

• IGMP ???????????????????signaling protocol?
• ?? ???????????????????(keep router up-to-date
  with group membership of entire LAN)
• ??,???????????????,???????????????

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IGMP???????
Q
Routers
Hosts

• ????????????????querier
• ????????????????IGMP (Membership Query message)
  ???????(all-systems group ,224.0.0.1)
• ???????????,?????????(random timers,010 ?)

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IGMP???????(cont.)
Q
Routers
G
G
G
G
Hosts

• ?????????,??????????????(Membership Report)??G
• ???????????,????????
• ????????????????,???????????(??),???????????????

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IP Multicast Architecture
Service model
Hosts
Host-to-router protocol(IGMP)
Routers
Multicast routing protocols
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9 ????(Multicast Routing)

• ?????????????????????????????
• ????????????????????? (detected by IGMP)
• ??????????????(Multicast service model makes it
  hard)
• ??????
• ???????(Dynamic join/leave)

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??????????

• ????????????
• ??????????????
• ???????????????
• ????????? DVMRP, PIM-DM
• ?????????????
• ?????????????????,??????????????
• ?????????????,????Dijkstra??????????????,???????
• ???? MOSPF

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???????????
G
G
S
G
21
??(Flooding)
G
G
S
G
22
??(Pruning)
G
G
Prune (s,g)
Prune (s,g)
S
G
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??(Grafting)
G
G
G
Report (g)
Graft (s,g)
Graft (s,g)
S
G
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?????
G
G
G
S
G
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????????(Distance-Vector Multicast Routing)

• DVMRP ??????
• ???????? (like RIP)
• ?????????
• DVMRP ??????? if
• The packet arrived from the link used to reach
  the source of the packet
• ??????? RPF
• ?????????????
• ????????????,???????

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DVMRP ?????

• ??????????????, ?????(count-to-infinity)?????(tran
  sient looping)
• ??????RIP?????. ???????????(scaling limitations)
  
• ????(S,G) ??,???????????!
• ??????????.

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Multicast Backbone (MBone)

• An overlay network of IP multicast-capable
  routers using DVMRP
• Tools sdr (session directory), vic, vat, wb

R
Host/router
MBone router
H
Physical link
Tunnel
Part of MBone
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Multicast OSPF (MOSPF)

• MOSPF?OSPF???,??????
• ???(Multicast-capable routers)????????( link
  state routing advertisements)
• ??????????????(Link-state packets include
  multicast group addresses to which local members
  have joined)
• ????????????????(??Dijkstra??)?????????????????

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MOSPF Example
Source 1
Z
W
Q
T
Receiver 1
Receiver 2
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Link Failure/Topology Change
Source 1
Z
X
W
Q
T
Receiver 1
Receiver 2
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Group Membership Change
Source 1
Z
Receiver 3
W
Q
T
Receiver 1
Receiver 2
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??? vs. ???

• ???(Source-based trees)
• ?????????????
• ???????(S,G) ??(state)??????
• Eg DVMRP, MOSPF, PIM-DM, PIM-SM
• ???(Shared trees)
• ???????????
• ???????????????????
• ????????(,G) ??( (,G) state at intermediate
  routers)
• Eg CBT, PIM-SM

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???(Source-based Trees)
Router
Source
S
Receiver
R
R
R
R
S
S
R
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???(Shared Tree)
Router
Source
S
Receiver
R
R
R
RP
R
S
S
R
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Shared vs. Source-Based Trees

• Source-based trees
• Shortest path trees low delay, better load
  distribution
• More state at routers (per-source state)
• ???????????????(Efficient in dense-area
  multicast)
• Shared trees
• Higher delay (bounded by factor of 2), traffic
  concentration
• Choice of core affects efficiency
• Per-group state at routers
• ?????????????(Efficient for sparse-area multicast)

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Core-based Routing Protocols

• Specify meeting place aka core or rendezvous
  point (RP)
• Sources send initial packets to core
• Receivers join group at core
• Requires mapping between multicast group address
  and meeting place
• Examples CBT, PIM-SM

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??????????Protocol Independent Multicast (PIM)

• Support for both shared and per-source trees
• Dense mode (per-source tree)
• Similar to DVMRP
• Sparse mode (shared tree)
• Core rendezvous point (RP)
• Independent of unicast routing protocol
• Just uses unicast forwarding table

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PIM Protocol Overview

• Basic protocol steps
• Routers with local members Join toward Rendezvous
  Point (RP) to join shared tree
• Routers with local sources encapsulate data in
  Register messages to RP
• Routers with local members may initiate
  data-driven switch to source-specific shortest
  path trees
• PIM v.2 Specification (RFC2362)

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PIM Example Build Shared Tree
Shared tree after R1,R2 join
Source 1
Join messagetoward RP
(,G)
(,G)
RP
(,G)
(,G)
(,G)
(,G)
Receiver 1
Receiver 3
Receiver 2
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Data Encapsulated in Register
Unicast encapsulated data packet to RP in Register
Source 1
(,G)
(,G)
RP
(,G)
(,G)
(,G)
(,G)
Receiver 1
Receiver 3
Receiver 2
RP de-capsulates, forwards down shared tree
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RP Send Join to High Rate Source
Shared tree
Source 1
Join messagetoward S1
(S1,G)
RP
Receiver 1
Receiver 3
Receiver 2
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Build Source-Specific Distribution Tree
Shared Tree
Source 1
Join messages
(S1, G)
(S1,G),(,G)
RP
(S1,G),(,G)
(S1,G),(,G)
Receiver 1
Receiver 3
Receiver 2
Build source-specific tree for high data rate
source
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Thank you !