Multicast Flashcards
Multicast Address Ranges
1) Local Scope - 224.0.0.0 - 224.0.0.225 - reserved by IANA for network protocols use
2) Global Scope - 224.0.1.0 - 238.255.255.255 - allocated dynamically throughout the Internet
3) Administratively scoped - 239.0.0.0 - 239.255.255.255 - reserved for use inside private domains
4) RFC 5771
Multicast Models
1) One-to-many, where one sender sends data to many receivers
2) Many-to-Many, where a host can simultaneously be a sender and a receiver
3) Many-to-one, where many receivers are sending data back to one sender
4) Few-to-many
Multicast Service Model Components
1) Senders sent to a multicast address
2) Receivers express an interest in a multicast address
3) Routers deliver traffic from the senders to the receivers
Multicast Service Model Characteristics
1) Host extensions for IP Multicasting
2) Each Multicast group is identified by a Class D IP address
3) Members join and leave the group and indicate this to the routers
4) Routers listen to all multicast addresses and use multicast routing protocols to manage groups
Multicast Host Extensions
1) RFC 1112 specifies the host extensions for IP to support multicast
2) IP multicast allows hosts to join a group that receives multicast packets
3) It allows users to dynamically register (join or leave multicast groups) based on the applications they use
4) It uses IP datagrams to transmit data
Multicast Listener Discovery (MLD)
- messages to join or leave IPv6 multicast groups
Multicast Protocol Traits
1) Multicast network routers are distinct from source and receiver segments
2) Sources simply start sending data without any indication and first-hop routers forward data
3) Receivers report their membership to last-hop routers
4) Last-hop (leaf) routers communicate group membership to the network
Shortest Path Tree (SPT)
Internet Group Management Protocol (IGMP)
1) permits hosts to communicate their desire to receive multicast traffic to the IP multicast router
2) IGMPv1 documented in RFC1112
3) IGMPv2 documented in RFC2236
4) IGMPv3 documented in RFC3376
IGMPv1
1) documented in RFC1112
2) multicast routers periodically (every 60-120s) send membership quieries to the all-hosts multicast (224.0.0.1) to solicit which multicast groups are active
3) Hosts send membership reports with a TTL of 1 to the multicast address of the group it wants to join
4) report suppression is used among group members to prevent membership report storm
IGMPv2
1) Group specific queries - allows the router to query a single multicast group instead of all hosts
2) Leave-group message - allows hosts to tell the router that they are leaving the group, thereby reducing the leave latency
3) Querier election mechanism - the lowest unicast IP address of the IGMPv2-capable routers will be elected as the querier; all routers are initialized as queriers by default, but relinquish the role if a lower IP is heard
4) Query-interval response time - helps control the burstiness of reports
5) Backwards compatible with IGMPv1
IGMPv3
1) Adds support for source filtering, which enables the host to tell the router which sources to expect traffic from
Source Trees
1) route at the source, and the branches form a spanning-tree through the network to the receivers
2) aka Shortest Path Tree (SPT) because it uses the shortest path
3) Notation (S, G), where S = Source, and G = Group
Shared Trees
1) use a single common root placed at some chosen point in the network, called the rendezvous point (RP)
2) Notation (*, G), where * = All sources, and G = Group
3) Sources send traffic to the RP first, and then cascade down to hosts, unless the host is between the source and RP, in which case it will be service directly
Reverse Path Forwarding (RPF)
1) when a multicast packet is received on the router interface, the router uses the source addr to verify that the packet is not in a loop; it checks that the interface on which the packet arrived is the same as the interface indicated by the routing table
