
39
PIM Source-Specific Mode (PIM-SSM)
PIM source-specific mode (PIM-SSM) is a multicast protocol that forwards multicast traffic from a single source to a subnet. In the
other versions of protocol independent multicast (PIM), a receiver subscribes to a group only. The receiver receives traffic not just
from the source in which it is interested but from all sources sending to that group. PIM-SSM requires that receivers specify the
sources in which they are interested using IGMPv3 include messages to avoid receiving unwanted traffic.
PIM-SSM is more efficient than PIM-SM because it immediately creates shortest path trees (SPT) to the source rather than first
using shared trees. PIM-SM requires a shared tree rooted at the RP because IGMPv2 receivers do not know about the source
sending multicast data. Multicast traffic passes from the source to the receiver through the RP, until the receiver learns the source
address, at which point it switches to the SPT. PIM-SSM uses IGMPv3. Because receivers subscribe to a source and group, the RP
and shared tree is unnecessary; only SPTs are used. On Dell Networking systems, it is possible to use PIM-SM with IGMPv3 to
achieve the same result, but PIM-SSM eliminates the unnecessary protocol overhead.
PIM-SSM also solves the multicast address allocation problem. Applications must use unique multicast addresses because if multiple
applications use the same address, receivers receive unwanted traffic. However, global multicast address space is limited. Currently
GLOP/EGLOP is used to statically assign Internet-routable multicast addresses, but each autonomous system number yields only
255 multicast addresses. For short-term applications, an address could be leased, but no global dynamic multicast address allocation
scheme has been accepted yet. PIM-SSM eliminates the need for unique multicast addresses because routing decisions for (S1, G1)
are independent from (S2, G1). As a result, subnets do not receive unwanted traffic when multiple applications use the same address.
Implementation Information
•
The Dell Networking implementation of PIM-SSM is based on RFC 3569.
•
The Dell Networking OS reduces the number of control messages sent between multicast routers by bundling Join and Prune
requests in the same message.
Important Points to Remember
•
The default SSM range is 232/8 always. Applying an SSM range does not overwrite the default range. Both the default range
and SSM range are effective even when the default range is not added to the SSM ACL.
•
Extended ACLs cannot be used for configuring SSM range. Be sure to create the ACL first and then apply it to the SSM range.
•
The default range is always supported, so range can never be smaller than the default.
Configure PIM-SSM
Configuring PIM-SSM is a two-step process.
1.
Configure PIM-SSM.
2.
Enable PIM-SSM for a range of addresses.
Related Configuration Tasks
•
Use PIM-SSM with IGMP Version 2 Hosts
640
PIM Source-Specific Mode (PIM-SSM)
Summary of Contents for S4048-ON
Page 1: ...Dell Configuration Guide for the S4048 ON System 9 9 0 0 ...
Page 146: ...Figure 14 BFD Three Way Handshake State Changes 146 Bidirectional Forwarding Detection BFD ...
Page 522: ...Figure 87 Configuring Interfaces for MSDP 522 Multicast Source Discovery Protocol MSDP ...
Page 523: ...Figure 88 Configuring OSPF and BGP for MSDP Multicast Source Discovery Protocol MSDP 523 ...
Page 528: ...Figure 91 MSDP Default Peer Scenario 1 528 Multicast Source Discovery Protocol MSDP ...
Page 529: ...Figure 92 MSDP Default Peer Scenario 2 Multicast Source Discovery Protocol MSDP 529 ...
Page 530: ...Figure 93 MSDP Default Peer Scenario 3 530 Multicast Source Discovery Protocol MSDP ...
Page 633: ...Policy based Routing PBR 633 ...
Page 777: ...Figure 119 Single and Double Tag TPID Match Service Provider Bridging 777 ...
Page 778: ...Figure 120 Single and Double Tag First byte TPID Match 778 Service Provider Bridging ...