1 / 43

CSCI 6433 Internet Protocols Class 7

CSCI 6433 Internet Protocols Class 7. David C. Roberts. Topics. Internet Multicasting MPLS. IP Datagram Messaging. Unicast: datagram from one source device to one recipient device Broadcast: datagram from one source to all recipients on a network

onawa
Download Presentation

CSCI 6433 Internet Protocols Class 7

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. CSCI 6433Internet ProtocolsClass 7 David C. Roberts

  2. Topics • Internet Multicasting • MPLS

  3. IP Datagram Messaging • Unicast: datagram from one source device to one recipient device • Broadcast: datagram from one source to all recipients on a network • Multicast: datagram from one source to a collection of recipient devices

  4. Functions Needed • Multicast addressing • Class D of IPv4 addresses • Multicast group management • IGMP—Internet Group Management Protocol • Multicast datagram routing • Multicast routing protocols are employed

  5. Group Management • IGMP, Internet Group Management Protocol, is used to manage groups

  6. Multicast addressing • ARP is designed for unicast only • ARP for multicast would be very inefficient • Direct mapping to data link layer multicast groups is used • 23 of the 28 bits in the multicast group address in Ethernet are used

  7. Routing • Routing is complicated! • Must create multiple copies of the datagram for multicasting • Routers need special algorithms to handle these multiple copies with efficiency • Routers must be able to handle datagrams to a multicast group even if the source is not a group member

  8. IP Multicast • Group address—each group has a unique class D address, permanent or temporary • Number of groups—addresses for up to 228 simultaneous multicast groups • Dynamic group membership—host can join, leave a group any time • Hardware—can use hardware multicast • Internetwork forwarding—multicast routers needed to forward multicast between networks • Transmission—any host can send to any group

  9. Building Blocks • Multicast addressing scheme • Effective notification and delivery mechanisms • Internetwork forwarding facility

  10. The Concept • Multicast addresses • One IP multicast address per group • Addresses useful worldwide • Notification and delivery mechanism • Inform routers about groups • Transfer multicast packets to hosts • Internetwork forwarding • Efficient routing along shortest paths • Don’t route to networks with no group members

  11. IP Multicast Addresses

  12. Permanent IPv4 Multicast Addresses

  13. Permanent IPv6 Multicast Addresses

  14. Multicast Semantics • Multicast address only a destination address • No ICMP error messages generated about multicast datagrams • TTL field in an multicast datagram is honored Question: what happens when I ping a multicast address? Why?

  15. Multicast Routing • Not all routers are multicast routers • Host does not know which are multicast • Host sends packet using local network multicast address • Multicast routers listen for all multicast datagrams, route them appropriately • Host does not have to address multicast datagram to a multicast router • Multicast capability is provided by routers, not hosts

  16. Multicast Scope • Scope of a multicast group—range of group members • All on same network: scope is restricted to one network • All in same organization: scope limited to one organization • Methods of controlling scope: • TTL controls the range • Administrative scoping: routers forbidden to forward to the restricted space

  17. Host Participation Possible levels of participation of a host in multicasting: For an application to multicast, host must have an API for application to declare intent to join or leave a multicast group. Host must track application participation in groups, remember that it leaves a group when all applications leave.

  18. IGMP—Internet Group Management Protocol • IGMP carries group membership information • Thought of as a part of IP, like ICMP • IGMP is required for all machines that receive IP multicast • Phase 1: host joins a group, sends IGMP message to multicast address declaring membership • Phase 2: multicast routers poll hosts to determine whether any are still members of each group, stops advertising to other routers after no response to several polls

  19. IGMP Implementation • All communications between hosts and multicast routers use IGMP • Every 125 seconds, multicast routers poll all groups for membership information, not just one • Multicast routers on a single network choose just one to do all polling • Hosts don’t all respond to a query at the same time • Each host listens for responses from other hosts in the group, suppresses unnecessary response traffic Question: Why are hosts listening? What would they not send?

  20. Group Membership State

  21. IGMP Message Format

  22. Special Properties of Multicast Routing • Multicast routes can change simply because an application decides to leave or join a group • Multicast forwarding requires a router to examine more than the destination address • A multicast datagram may originate on a host that is not part of the group, and may be routed across networks with no group members attached

  23. Multicast Forwarding and Routing Dot, X are two different multicast groups

  24. Multicast Routing Paradigms • RPF—reverse path forwarding • Router looks up interface that leads to source address (interface I) • Forwards datagram over all interfaces other than I • If datagram arrived other than through I, discard it • RPF sends datagrams to networks with no members • TRPF—truncated reverse path forwarding • Uses list of multicast groups reachable through each interface • First, RPF is applied • Then, interfaces that do not lead to members of the group are skipped Multicast routing is based on the datagram’s source and destination addresses

  25. Consequences of TRPF Consider the case where a multicast datagram headed for host B is sent by host A

  26. Multicast Trees Number of copies received depends on the source

  27. Multicast Routing • TRPF doesn’t forward to network if it has no members of the group • Thus router must know about group membership • Membership information must be communicated across the Internet • Multicast design a tradeoff of routing traffic overhead and inefficient data transmission

  28. Reverse Path Multicasting • Basis: • First priority given to reach all group members rather than avoid retransmission • Presume that multicast routers have a routing table that is correct • Routing should improve performance where possible • Use RPF to send across all networks • Use RPM to identify routers that don’t reach members • Cease forwarding to routers that don’t reach members • RPM is called broadcast and prune strategy

  29. Where It’s Used • Multicasting is widely used within organizations for video and audio distribution • Use on the Internet has begun with Internet radio and television

  30. Summary • IP multicasting an abstraction of hardware multicasting • IP multicasting uses class D addresses • Hosts communicate group membership to multicast routers using IGMP • IGMP introduces periodic message from a multicast router and a reply for each group • Several protocols have been designed for multicast routing

  31. Multi-Protocol Label switching (mpls)

  32. Disadvantages of Table Routing • Takes log2 n probes to find an address in forwarding table of n entries • Array index can be performed in one step • Switching methods use a label from a packet as in index to a table that gives action to take

  33. Multi-Protocol Label Switching • Data packets are assigned labels • Packet-forwarding decisions made based on the label, no need to examine the packet • Can create end-to-end circuits across any transport medium with any protocol • Can carry many types of packets • Traffic management is improved • Loss of visibility to IT departments • Path labels identify virtual links between distant nodes, not necessarily endpoints

  34. MPLS Routers • Routers that carry MPLS traffic are called label switch routers (LSRs) • Entry and exit point routers are called label edge routers (LERs), which push an MPLS label onto a packet and pop it off an outgoing packet

  35. MPLS in the Stack MPLS is called a “layer 2.5” protocol

  36. Understanding MPLS • Instead of focusing on destinations, focus on packet flows • Instead of thinking about forwarding tables that are relatively static, think about a system that can change forwarding tables quickly Switching technologies like MPLS use the flow abstraction and create forwarding for flows rather than for destinations

  37. How It Works • Each packet is prefixed by an MPLS header, called a label stack with some number of these: • 20-bit label value • 3-bit traffic class field for QoS • 1-bit bottom of stack flag • 8-bit TTL field • Label edge router pushes label, pops at other edge of MPLS network • Label switch router routes based on the label only

  38. Label Distribution Protocol • LDP used to distribute labels between LERs and LSRs • LSRs exchange reachability and label information to build a complete diagram of the MPLS network • Label switch paths are used to create virtual paths through MPLS networks • LER determines forwarding class of a packet, pushes label into MPLS header • LSR looks at topmost label, does a label swap, push or pop to label stack

  39. Use of the Label Stack • Label swap • Label is swapped with a new label • Packet is forwarded along path of new label • Label push • New label pushed on top of existing label • Encapsulates packet in another layer of MPLS • Allows hierarchical routing of MPLS packets • Label pop • Label is removed from packet • May reveal an inner label • If label is last one, packet leaves MPLS tunnel • At egress router, only original payload remains, so that router must be able to process it

  40. Multi-Protocol Label Switching Use of labels to direct forwarding

  41. MPLS Encapsulation

  42. Traffic Engineering • Can use MPLS to define full mesh between two ISPs, can monitor traffic to other ISPs • Can use MPLS to use fastest routes for most critical traffic

  43. Summary • Indexing can be used instead of table lookup to determine routing, saving router time • Paths can be defined and engineered • MPLS prepends a header onto each message • LSRs along the route use labels to forward the datagram without lookups • MPLS was defined to save router time, is less important today because of faster routers • MPLS is mostly used today to provide VPNs

More Related