Post on 20-Jan-2016
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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.
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Fig 5-45
IPv4
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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
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Fig 4.45
Fig 4.46
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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
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Fig 4.47
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Fig 4.48
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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
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Fig 4.50(IGMP member query and membership report)
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Fig 4.51
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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
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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
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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
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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