Định tuyến Multicast routing

Định tuyến multicast routing

Multicast Routing

Wed 28 MAY 2003

» Multiple unicast

Wast Network bandwidth,

Registering mechanism.

» Multiple addresses in a packet

Can be only one instance( why Can? ),

Limited size of packet limits the max number of recipient Much more processing in a router(List of Addresses)

O nly partially help in the bandwidth wasting problem of

the previous method

» Multicast address

The sender does not need to know the recipients,

Implementation (Cont’s)

• Saving the network link bandwidth is left to the routers,

• the group does not have any physical or geographical boundaries

• Hosts that are interested in receiving data flowing to a particular group must join the group using IGMP

Internet Group Management Protocol

• IGMP provides the means for a host to inform its attached router

• Given that, the scope of IGMP interaction is limited to a host and its attached router

• Another protocol is clearly required to coordinate the multicast-

router throughout the internet, that accomplished by the

network-layered multicast routing algorithms such as PIM , DVMRP and

MOSPT

• Router queries the local hosts for m-cast group

membership info

• Hosts respond with membership reports: actually, the

first host which responds, speaks for all

IGMP protocol

• IGMPv1, there are just two different type of IGMP message:

Membership QUERY and Membership REPORT

When there is no reply to three consecutive IGMP membership queries, the router times out group an stops forwarding traffic

directed toward group

• IGMPv2, there are four types.basically the same as version 1

the main difference:

1) The hosts communicate to the local multicast router when intention to leave the group

2) The router then sends out a group-specific query and

determines whether there are any remaining host

IP Multicast Addresses

• Multicast addresses specify an arbitrary group of IP hosts that

have joined the group and want to receive traffic sent to this

group

• The Internet Assigned Numbers Authority (IANA) controls the

assignment of IP multicast addresses

• all IP multicast group addresses will fall in the range of 224.0.0.0

Routing protocol Multicast

• Problem: find the best (e.g., min cost) tree which interconnects all the members

Multicast Tree Option

• GROUP SHARED TREE: single tree for all senders(entire multicast group); bidirectional links

• SOURCE BASED TREE: each source is the root of its

own tree connecting to all members; thus separate trees

Group Shared Tree

• Uses a single common root placed at some chosen point in the

network (rendezvous point)

• Source must send their traffic to the root, and then the traffic is

forwarded down the shared tree to reach all receivers

• Message are replicated only where the tree branch

• Member can any time join or leave, so the distribution trees must be dynamically update.(Prune,graft)

• finding a minimum cost tree is known as the Steiner tree

problem ( NP-complete )

• Alternate: Center-based approach

- under some circumstances,the paths might not be the optimal paths

- Network designers must carefully consider the placement of the

RP when implementing an environment with only shared trees.

Source-based Tree

• Source is the root of the multicast tree and whose branches form

a spanning tree through the network to the receivers

• Also known as Short Path Tree(SPT) because tree uses the

shortest path through the network

• SPT creating the optimal path between the source and receivers This guarantees the minimum amount of network latency

• Routers must maintain the state of each link (link-state)

• A simpler multicasting routing algorithm,need much less link

state information, is the Reverse Path Forwarding(RPF).

Reverse Path forwarding

• RPF makes use of the existing unicast routing table

• A router forwards a multicast packet only if it is received on the

up stream interface

Multicast Routing Algorithms and Protocols

• Flooding

a router that receives a packet with multicast

destination address, simply sends to all interfaces, expect the interface where the packet came to the router.

News: uses a article path history

OSPF: uses link state database

Using a list of last seen packets would need a lot of

memory in current high speed routers and the checking

local host……… 0 local network segment 1 site……… 15 region……… 31 country……… 48 continent(Europe)…… 63 world ……… 127

Multicast Routing Alg.s and Prot.s (Cont’s)

• Spanning tree

Building a logical network on top of the real network

by creating a loopless graph between all nodes resolves the looping problem in flooding

Multicast Routing Alg.s and Prot.s (Cont’s)

• RPF and Prunes

When the first packet in a multicast transmission

reaches the end leaves in the routing tree, the leaf router sends a pruning message upstream if it does not have

any group members attached to it Likewise, if a any

router in the tree receives a prune message from all of its downstream interfaces it sends a prune message

upstream The purpose of the prune message is to

prevent sending unneeded following packets in that

group to the pruned branch.

There is still a one bad point the first packet in a group

is always flooded in the whole network.

Multicast Routing Alg.s and Prot.s (Cont’s)

• Steiner trees

The idea of steiner trees is to build an overlay network that connects all nodes in a group with minimum total

number of links

It is not usually suitable in real networks

The computing of the tree is hard and it must be done

again each time a node joins or leaves a group.

• Core-based trees

Each multicast group has a core,

Routing protocol Multicast

Protocol Independent Multicast(PIM)

Why independent?

Independent of the underlying unicast routing protocol

EIGRP, OSPF, BGP, or static routes.

• Dense mode

many or most of routers in the area need to be involved in routing multicast datagram

• Sparse mode

with respect to total number of routers

Dense Mode PIM Example

Source

Receiver 2 Receiver 1

Dense Mode PIM Example

Initial Flood of Data and Creation of State Source

Dense Mode PIM Example

Prune to Non-RPF Neighbor Source

Prune

Receiver 2 Receiver 1

Dense Mode PIM Example

C and D Assert to Determine Forwarder for the LAN, C Wins Source

Dense Mode PIM Example

I Gets Pruned E’s Prune is Ignored G’s Prune is Overridden Source

Prune

Receiver 2 Receiver 1

Dense Mode PIM Example

Dense Mode PIM Example

Source

Receiver 2 Receiver 1

Sparse Mode PIM Example

Link Data Control

Sparse Mode PIM Example

B

E

C Creates (*, G) State, Sends

(*, G) Join to the RP

C

RP Join

Sparse Mode PIM Example

Sparse Mode PIM Example

B

E

A Sender Registers to the

RP

C Register

Sparse Mode PIM Example

Receiver 1

B

E

Forwards Data Down the Shared Tree

Sends Joins Towards the Source

C

Receiver 2

Sparse Mode PIM Example

C Register-Stop

Sparse Mode PIM Example

C

Receiver 2 (

S, G) Join

Sparse Mode PIM Example

B

E

It Sends Prunes Up the RP tree for the Source RP Deletes (S, G) OIF and Sends Prune Towards the Source

C

(

S, G) RP Bit Prune (

S, G) Prune

Sparse Mode PIM Example

Receiver 1

B

E

E Creates State and Sends (*, G) Join

C

Receiver 2 (*,

G) Join

Sparse Mode PIM Example

B

E

List of Both (*, G) and (S, G) Data from Source Arrives at E

C

Sparse Mode PIM Example

Receiver 1

B

E

D Sends Registers, RP Sends Joins

RP Forwards Data to Receivers

through Shared Tree

C

Receiver 2

Source 2 Register

Hope be useful

Thanks Hassan Salmani