slides16 Flashcards
Unicast
• 1-to-1 data flow; one source, one destination • Most current IP traffic is unicast
Broadcast
• 1-to-many data flow; one source, “all” destinations
• Broadcast is simple: a single packet read by all hosts on
the local network
• Reduces traffic on the local network as (for most link layers) we don’t have copies of mostly-identical packets, one for each destination, but just one packet that is read by every host
• Scales well (locally): it is independent of the number of destination hosts
• Don’t have to know how many destination hosts there are
Limited broadcast
The address 255.255.255.255 sends to all hosts on the local network. A packet with this address is never forwarded by a router. Useful when you don’t know the local network address
Multicast
For sending a single packet to multiple hosts, not necessarily all hosts
Host groups can cross multiple networks and there is no limit on the size of a group (and generally you can’t know how big the group is)
In IPv4, class D (224.0.0.0 to 239.255.255.255) addresses are used for multicast
How are multicast groups formed
The process of joining and leaving groups is governed by the Internet Group Management Protocol (IGMP)
A host that wishes to join a multicast group provided by a server sends an IGMP message towards the server
The routers on the path to the server take note and so know to route multicast packets for this group towards the joining host
The server itself is not interested or involved in the IGMP message
ttl used if hosts dont let server know they are out
alternative mechanism multicast
The 239.0.0.0/8 range is assigned by RFC 2365 for private use within an organization. From the RFC, packets destined to administratively scoped IPv4 multicast addresses do not cross administratively defined organizational boundaries, and administratively scoped IPv4 multicast addresses are locally assigned and do not have to be globally unique. The RFC also discusses structuring the 239.0.0.0/8 range to be loosely similar to the scoped IPv6 multicast address range described in RFC 1884.
IGMP
The Internet Group Management Protocol (IGMP) is a communications protocol used by hosts and adjacent routers on IPv4 networks to establish multicast group memberships. IGMP is an integral part of IP multicast.
difference broadcast multicast
- a multicast will only be read and processed by a subset of machines
- a broadcast is limited to the local network, while a multicast can spread far and wide
IPv6 broadcast
IPv6 does not implement traditional IP broadcast, and therefore does not define broadcast addresses. In IPv6, the same result can be achieved by sending a packet to the link-local all nodes multicast group which is analogous to IPv4 broadcast
Simple Service Discovery Protocol
The Simple Service Discovery Protocol (SSDP) is a network protocol based on the Internet Protocol Suite for advertisement and discovery of network services and presence information. It accomplishes this without assistance of server-based configuration mechanisms, such as DHCP or DNS, and without special static configuration of a network host
multicast DNS
In computer networking, the multicast DNS (mDNS) protocol resolves host names to IP addresses within small networks that do not include a local name server. It is a zero-configuration service, using essentially the same programming interfaces, packet formats and operating semantics as the unicast Domain Name System (DNS).
wat Most big providers do to provide content everywhere
having many local distribution points containing identical data
content delivery network
A content delivery network or content distribution network (CDN) is a geographically distributed network of proxy servers and their data centers. The goal is to provide high availability and high performance by distributing the service spatially relative to end-users. CDNs serve a large portion of the Internet content today, including web objects (text, graphics and scripts), downloadable objects (media files, software, documents), applications (e-commerce, portals), live streaming media, on-demand streaming media, and social media sites.[1]
why multicast is not being picked up more
Routing companies want to avoid supporting multicast, claiming undue complexity to support it: A router must keep a record of all multicast paths passing through it, so routers on popular paths (e.g., in internet exchanges) might need to keep a large amount of data
Anycast
Anycast in IPv6 sends a single packet to a single destination chosen out of several possible destinations
For example, replicated Web servers: have many servers around the world with identical content and the same anycast address. A browser would get pages from the closest server, thus sharing load
The reply would be unicast
