Red Hat Fedora 5 Unleashed

The Foundation Summary is a collection of information that provides a convenient review of many key concepts in this chapter. If you are already comfortable with the topics in this chapter, this summary can help you recall a few details. If you just read this chapter, this review should help solidify some key facts. If you are doing your final preparation before the exam, this information is a convenient way to review the day before the exam.

  • IP multicast addresses range from 224.0.0.0 to 239.255.255.255 (highest 4 bits are always

    1110).

  • Multicast MAC addresses always start with 0100.5e (next bit is always 0). The lower 28 bits of the IP address are mapped over into the lower 23 bits of the MAC address.

  • RPF decides whether a multicast packet can be forwarded: If it arrived on an interface where the source can be found, it is forwarded; if not, it is dropped.

  • IGMP is the protocol used to join and leave (as well as to maintain) multicast groups.

  • PIM is a multicast routing protocol used to build multicast tree topologies.

    Table 15-4. A Comparison of PIM Modes

     

    Multicast Flows

    Tree Construction

    Tree Refinements

    Dense Mode

    (S,G)

    Root to leaves; source is the root, recipients are leaf nodes

    First flood, then prune

    Sparse Mode

    (*,G)

    Leaves to root; RP is the root, source can be anywhere, recipients are leaf nodes

    Group extended from recipients toward RP; pruning only when member leaves group

    Sparse-Dense Mode

    (S,G) or (*,G)

    Hybrid on a per-group basis

    Not applicable

    Table 15-5. IP PIM Multicast Configuration Commands

    Command Syntax

    Task

    ip multicast-routing

    Enables multicast routing

    ip pim dense-mode

    Enables PIM dense mode on an interface

    ip pim sparse-mode

    Enables PIM sparse mode on an interface

    ip pim sparse-dense-mode

    Enables PIM sparse-dense mode

    ip pim rp-address ip-address [access-list] [override]

    Defines a PIMv1 RP

    ip pim send-rp-discovery scope ttl

    Defines a PIMv1 Auto-RP mapping agent

    ip pim send-rp-announce type mod/num scope ttl group-list access-list

    Identifies the PIMv1 Auto-RP RP routers

    ip pim bsr-candidate type mod/num hash-mask-length [priority]

    Defines a PIMv2 BSR

    ip pim rp-candidate type mod/num ttl group-list access-list

    Identifies the PIMv2 candidate RP routers

    ip pim border

    Defines a PIMv2 border router

  • IGMP snooping allows a switch to intercept IGMP messages to learn of group members and their port locations.

  • CGMP allows a router to relay IGMP join and leave requests to Layer 2 switches. The switches then learn of group members and their port locations.

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