4: Multicast Routing 2 Inter-Domain Routing

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4: Multicast Routing 2

Inter-Domain Routing

Technologie-Zentrum Informatik

Typical Intra-Domain Multicast Architecture

S

R

DATA

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Connecting Multicast-Domains

Intra-Domain Intra-Domain

S

R

S

MBR

Inter-Domain Multicast Routing

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Issues:

y Address clashes

y Finding active sources

y Broadcast/prune vs explicit join

y SSM vs ASM/SFM

y Parallel paths

y (Multicast) Route changes

y Support for distribution tree optimizations `

2 different approaches:

y Create shared tree in multicast border routers

(3)

Generic MBR Architecture

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Only one routing protocol for each interface

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Components change forwarding entry for “their” interface

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Single incoming interface per forwarding entry

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Components typically have separate multicast routing table

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Event-driven communication between components and routing logic

DVMRP MOSPF PIM-SM CBT

IGMP Protocol components

Shared forwarding cache

Network interfaces Routing logic (S1,G1) → (iif, { oif, ... }) ... Technologie-Zentrum Informatik

MBR routing process

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On incoming data, the dispatcher determines the iif owner

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iif owner may drop incoming packet

(e.g. not in scope boundaries, RPF check failed, etc.)

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Creation of (S,G) entry triggers alert for outgoing interfaces

→ enable flooding

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Deletion of (S,G) entry trigger alert for incoming interface

→ prune/leave

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Adding outgoing interface to (S,G) entry triggers alert for incoming

interface

→ join/graft

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Create (,) entries for externally-reached sources towards tree root

y Owned by routing logic (“interop dispatcher”)

y Clear state after prunes

y Create entries for joins

(4)

Applicability to Existing Protocols

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Dense-mode

y

Components are wildcard-receivers for internal sources

y

Wildcard-receivers for external sources if no domain-wide reports

available

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Sparse-mode

y

MBRs need to be on shared distribution tree

→ create wildcard entries for every group at every RP/Core

y

Act as DR for external sources

Example: Sender in PIM-SM-Domain

R

S

R

RP

PIM-SM

DVMRP

R

(5)

Example: Sender in PIM-SM-Domain

R

S

R

RP

PIM-SM

DVMRP

R

PIM-SM Router Operation

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MBR encapsulates data from external sources in Register message

y Use B-Bit to avoid multiple registrations

y RP sends data downstream `

Downstream router operation:

y Look for specific routing state (S,G) or (*,G) → forward downstream

y Look for matching (*,*,RP) entry

→ forward packets if data arrived on incoming interface

y Otherwise, drop packets `

MBR treated as group member

y Gets multicast data from senders within PIM-SM-domain

y Forwards to DVMRP-domain

(6)

Example: Sender in DVMRP-Domain

S

R

RP

PIM-SM

DVMRP

encapsulated data packet sent via unicast to RP

R

Overlay Routing Architecture

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Sparse-Mode approach relies on shared tree

y

Slow convergence in case of route changes

y

External single point of failure (due to unidirectional tree)

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BGMP: Border Gateway Multicast Protocol

y

Like BGP-4 for unicast routing

y

Can use any M-IGP (DVMRP, MOSPF, CBT, PIM, …)

y

Bidirectional routing tree → build global multicast RIB

y

SSM only on demand

y

Worse loop prevention (no RPF checks)

(7)

R

Domain D allocated root domain for G

IGMP join for group G

Report to border routers BGMP join Technologie-Zentrum Informatik Domain B

Domain Hierarchies in BGMP

Domain A Domain C

R

S

Multicast data

for group G

(8)

BGMP Routing

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Join/Prune is distributed to allocated root domain

y BGMP for communication between border routers

y Specific multicast routing protocol for interior communication `

Data is sent to multicast group as usual

y Border routers forward to next hop for specified group

y Forwarded downstream from root domain `

Must support specific M-IGP protocols

y Deal with RPF-checks

y Tree optimizations Technologie-Zentrum Informatik Domain B

Domain Hierarchies in BGMP

Domain A Domain C

R

S

Multicast data

for group G

encapsulate data to make RPF check succeed

(9)

R

S

Multicast data

for group G

source-specific join prune other branches

Technologie-Zentrum Informatik Domain B

Domain Hierarchies in BGMP

Domain A Domain C

R

S

Multicast data

for group G

data sent along optimized SPT

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Address Allocation

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MALLOC (RFC 2908)

y Overall allocation architecture

y Scope, lifetime, timeliness, resource management, … `

MASC (RFC 2909)

y Claim set of address prefixes

y CIDR-like aggregation for routers `

MZAP (RFC 2776)

y Announce information about local zone hierarchy

y To be used for address claims `

MADCAP (RFC 2730)

y Allocate multicast address for instant use

→ support dynamic groups such as ad-hoc-networks

y Similar to DHCP

4: Multicast Routing 2 Inter-Domain Routing