Enterasys Networks X-PeditionTM manual Describing the XSR’s PIM-SM v2 Features

Describing the XSR’s PIM-SM v2 Features

Behavior of Group Members Among Older Version Group Members

An IGMPv3 host may be situated in a network where hosts have not yet been upgraded to IGMPv3. A host may allow its IGMPv3 Membership Record to be suppressed by either a Version 1 or Version 2 Membership Report

Behavior of Multicast Routers Among Older Version Queriers

IGMPv3 routers may be sited on a network where at least one router on the network has not yet been upgraded to IGMPv3 with these requirements:

•If older versions of IGMP exist on routers, the querier must use the lowest IGMP version present on the network. This must be assured administratively; routers that desire to be compatible with IGMPv1 and IGMPv2 must have a configuration option to act in IGMPv1 or IGMPv2 compatibility modes which can be set with the ip igmp version command. When in IGMPv1 mode, routers must send Periodic Queries with a Max Resp Code of 0 and truncated at the Group Address field (i.e., 8-bytes long), and must ignore Leave Group messages. They should also log receipt of IGMPv2 or IGMPv3 queries. When in IGMPv2 mode, routers must send Periodic Queries truncated at the Group Address field (i.e., 8-bytes long), and should also log receipt of IGMPv3 queries. They also must fill in the Max Resp Time in the Max Resp Code field; that is, the exponential algorithm described is not used.

•If you do not explicitly configure a router to use IGMPv1 or IGMPv2 and it receives an IGMPv1 Query or IGMPv2 General Query, it should log a warning.

Behavior of Multicast Routers Among Older Version Group Members

IGMPv3 routers may be placed on a network where there are hosts that have not yet been upgraded to IGMPv3 but for compatibility with older version hosts, IGMPv3 routers must operate in version 1 and version 2 compatibility modes. IGMPv3 routers keep a record of compatibility mode by group, which is determined by the Group Compatibility Mode variable from one of three states: IGMPv1, IGMPv2 or IGMPv3. This variable is kept per group record and is dependent on the version of Membership Reports heard for that group as well as the Older Version Host Present timer for the group.

Describing the XSR’s PIM-SM v2 Features

PIM-SM is a sparse-mode multicast routing protocol that uses a receiver-initiated process to build and maintain the MDT, as specified in draft-ietf-pim-sm-v2-new-05. A router running PIM-SM joins the construction of a MDT only when at least one of the hosts on its subnet requests membership in the specific multicast group. PIM-SM supports both shared and shortest-path trees (SPT) and can convert from shared to shortest-path tree based on network status to optimize multicast performance.

PIM-SM relies on another protocol to discover and collect network topology data and fill the Multicast Routing Information Base (MRIB). The MRIB is used by PIM-SM to learn how to reach other PIM-SM enabled routers. MRIB can derive from the unicast routing table filled by unicast routing protocols, such as RIP and OSPF, or it can be filled by another routing protocol tailored for multicast, such as MBGP. MRIB is also used to check against incoming multicast packets to ensure loop-free forwarding.

PIM-SM behavior can be described in three phases. Since senders and receivers can join or leave at any time, all phases may occur in parallel.

XSR User’s Guide 7-7