1

Changes in IPv6– Expanded addressing capabilities (32 to 128 bits), anycast address– A streamlined 40-byte header– Flow labeling and priority– Fig 4.44

IPv6 (from ch 4 of Computer Networking by Jim Kurose and Keith Ross, 2002.

2

Fig 5-45

IPv4

3

IPv6 vs IPv4– Fragmentation/reassembly: IPv6 does not allow for fragmentation and re

assembly at intermediate routers.– Header checksum: IPv4 header checksum needed to be recomputed at e

very router.– Options: next headers pointer in IPv6

ICMP for IPv6– Packet too big, unrecognized IPv6 options error codes– IGMP

Transitioning from IPv4 to IPv6– Flag day– Dual-stack: DNS to determine whether another node is IPv6 or IPv4– Tunneling

4

Fig 4.45

Fig 4.46

5

Unicast vs multicast The sending of a packet from one sender to multiple rece

ivers with a single send operation. Network-layer aspects of multicast Handle multicast groups

– One-to-all unicast– Application-level multicast– Explicit multicast at the network layer

How to identify the receivers of a multicast datagram?– Address indirection: a single identifier is used for the group of rec

eivers -> class D How to address a datagram sent to these receivers?

Multicast routing

6

Fig 4.47

7

Fig 4.48

8

IGMP– Group membership protocol– Locally between a host and an attached router– Means for a host to inform its attached router that an application runnin

g one the host wants to join a specific multicast group– Joining a multicast group is receiver-driven

Network-layer multicast algorithms (PIM, DVMRP, MOSPF)– Coordinate the multicast routers so that multicast datagrams are routed

to their final destinations Table 4.4

9

Fig 4.50(IGMP member query and membership report)

10

Fig 4.51

11

The goal of multicast routing is to find a tree of links that connects all of the routers that have attached hosts belonging to the multicast group.

Fig 4.52

Multicast routing: the general case

12

Two approaches: whether a single “group-shared” tree is used to distribute the traffic for all senders in the group, or whether a source-specific routing tree is constructed for each individual sender.

Fig 4.53

13

Multicast routing using a group-shared tree– Fig 4.54

– Steiner tree problem: None of the existing Internet multicast routing algs has been based on this approach: information about all links is needed, rerun whenever link costs change, and performance.

– Center-based approach: center node, rendezvous point or core: how to select the center

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Multicast routing using a source-based tree– Reverse path forwarding (RPF)– Fig 4.56

– If there were thousands of routers downstream from D, … -> pruning

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DVMRP: Distance Vector Multicast Routing Protocol– Source-based trees with reverse path forwarding and pruning– Small fraction of the Internet routers are multicast-capable -> Tun

neling, e.g., Mbone– Fig 4.57

Multicast routing in the Internet

16

PIM: Protocol Independent Multicast– Dense mode: a flood-and-prune reverse path

forwarding– Sparse mode: a center-based approach– The ability to switch from a group-shared tree to a

source-specific tree after joining the rendezvous point.

– UUNet Multicast Open Shortest Path First (MOSPF) DVMRP has been the de facto inter-AS

multicast routing protocol

Multicast routing in the Internet