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Anycast & Multicast
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  • 1. Anycast address overview
    • Types of Addresses in IPv6/IPv4
      • Unicast – one to one
      • Multicast – one to many
      • Broadcast – one to all ( only in IPv4 )
      • Anycast – one to one of many ( Only in IPv6)
    • A new type in IPv6. Not defined for IPv4
    • It is assigned to more than one interface
    • Refers to one among many address
      • A packet sent to an anycast address is routed to the nearest interface with that address.
  • 2. Anycast address & use
    • Allocated from unicast address space
      • Link local, site local, global
    • It is an unicast address assigned to many interfaces
    • Nodes with anycast address must be explicitly configured to receive anycast packets.
    • Used to identify
      • a set of routers of an ISP
      • a set of routers in a subnet
      • A set of routers providing entry to a routing domain
  • 3. Anycast address restrictions
    • Cannot be used as a source address
    • Cannot be assigned to a host
    • May be assigned to a router only
  • 4. Multicasting
    • One to many addressing
    • Delivery of packets to many destinations
      • Interactive conferencing
      • Dissemination of mail
      • News to multiple recepients
      • Webcasts to multiple registered recipients
      • Location of servers by clients
  • 5. IPv4 multicast address Class D
    • Range from 224.0.0.0 through 239.255.255.255
    • A set of hosts listening to a IP multicast address is called a host group
    • A host group can span multiple networks
    • Membership to a host group is dynamic
    • No restriction on number of hosts to a group
    • Non member can send a message to a group
    1 1 1 0 28 bit multicast gp ID
  • 6. Special multicast addresses
    • 224.0.0.0 Reserved; not used
    • 224.0.0.1 All devices on the subnet
    • 224.0.0.2 All routers on the subnet
    • 224.0.0.11 Mobile agents (for Mobile IP)
    • 224.0.0.12 DHCP Server / Relay Agent
  • 7. Ethernet Multicast address
    • Host group to multicast source
      • IP : group IP address
      • MAC : next hop address
    • Multicast source to Host group
      • IP : group IP address
      • MAC : Ethernet multicast address
  • 8. Mapping of class D IP address into Ethernet Multicast Address
    • IANA has allotted 01:00:5e:00:00:00 through 01:00:5e:7f:ff:ff for multicast
    • Lower order 23 bits if gp id copied to ethernet address
    • Eg1: 224.128.64.32 (hex e0.80.40.20) maps to hex 01:00:5e:00:40:20
    • Eg2 : 224.0.64.32 (hex e0.00.40.20) also maps to hex 01:00:5e:00:40:20
    IEEE 802 address
  • 9. IPv6 Multicast address
    • Format prefix : FF
    • Flags: 000T
      • T= 0: well known permanent
      • T=1: temporary
    • Scope: 0 to 15
      • 0: reserved
      • 1: interface local
      • 2: link local
      • 3 : reserved
      • 4 : admin local
      • 5 : site local
      • 8 : org local
      • E : global
      • F : reserved
    Multicast address structure
  • 10. IPv6 Multicast address
    • Group ID – Identifies the multicast group and is unique within the scope
      • Two well known group IDs
        • 1 : all nodes
        • 2 : all routers
    • Examples:
      • FF01::1 (interface-local scope all-nodes multicast address)
      • FF02::1 (link-local scope all-nodes multicast address)
      • FF01::2 (interface-local scope all-routers multicast address)
      • FF02::2 (link-local scope all-routers multicast address)
      • FF05::2 (site-local scope all-routers multicast address)
  • 11. Mapping IPv6 Multicast Addresses to Ethernet Addresses When sending IPv6 multicast packets on an Ethernet link, the corresponding destination MAC address is 33-33-mm-mm-mm-mm where mm-mm-mm-mm is a direct mapping of the last 32 bits of the IPv6 multicast address, as shown in Figure above
  • 12. Solicited node multicast address
    • Format: FF02:0:0:0:0:1:FFXX:XXXX
    • It is formed by taking the lower order 24 bits of ( unicast or anycast )
    • When A node n1 which wants to find MAC address of node n2, it will send neighbor solicitation message with solicited multicast address to n2.
    • Node n2 will reply with neighbor advertisement message
  • 13. An IPv6 Node’s multi cast addresses
    • For example, a host with the Ethernet MAC address of 00-AA-00-3F-2A-1C (link-local address of FE80::2AA:FF:FE3F:2A1C) registers the following multicast MAC addresses with the Ethernet adapter:
    •           The address of 33-33-00-00-00-01, which corresponds to the link-local scope all-nodes multicast address of FF02::1.
    •           The address of 33-33-FF-3F-2A-1C, which corresponds to the solicited-node address of FF02::1:FF3F:2A1C. Remember that the solicited-node address is the prefix FF02::1:FF00:0/104 and the last 24-bits of the unicast IPv6 address.