GateD Configuration Guide - PIM Configuration

# 6.3.2 Multicast Routing Protocols

## 4. Core-Based Trees Protocol (CBT)

Traditional multicast routing mechanisms (e.g. DVMRP and MOSPF) were in intended for use within regions where groups are densely populated or bandwidth is universally plentiful. When groups, and senders to these groups, are distributed sparsely across a wide area, these "dense mode" schemes do not perform efficiently. Core Based Trees (CBT) like PIM-SM provides a mechanism for creating shared delivery trees for multicast groups. Shared trees allow for a single tree per multicast group (*,G) instead of trees based in each source-group pair (S,G).

Multicasting Protocols require two different functions in order to create the source based trees or group based tree:

- a set of routes used to calculate the Reverse Path Forwarding, and
- a mechanism by which to build trees.

CBT depends on existing multicast routing to provide a route to do the Reverse Path Forwarding. In contrast, DVMRP passes this set of routes within the protocol.

An overview of PIM can be found in the document Core Based Trees (CBT) Multicast - Multicast Architecture. A detailed protocol specification can be found in the document:

Core Based Trees (CBT) Multicast - Protocol Specification.

## The CBT Statement

    cbt yes | no | on | off [ {

        interface interface_list cbt_options ;
        traceoptions trace_options ;
        mfc-timeout sec ;
        dr-interval sec ;
        dr-timeout sec ;
        directroute [on|off] cbt_dr_group ;

    } ] ;

> interface interface_list cbt_options

> Enables or disables, and configures CBT on an interface by interface basis.

> > The possible optional cbt parameters are:

> > > disable

> > > > Specifies that CBT packets received via the specified interface will be ignored. The default is to listen to CBT on all multicast capable interfaces.

enable

> > This is the default. This argument may be necessary when `disable` is used on a wildcard interface descriptor.

echomode [echo-by-router | echo-by-group]

> This method determines if this router will send an echo through this interface for the group or for the router.

traceoptions trace_options

Specifies the tracing options for PIM. (See Trace Statements and the PIM specific tracing options below.)

mfc-timeout sec

Length of time that a child will remain part of the tree. Default =180 seconds.

dr-interval sec

Interval that a neighbor router for IGMP querier to send IGMP Host Membership Query.

    dr-timeout sec

Interval that a neighbor router is remember after receiving an IGMP Host query. Also defined as IGMP Host Query Interval.

directroute [on|off]

[group-addr-start host] [group-addr-end host]

[core_address

{

> [address cbt-type]

> [primary-core | secondary-core target-core]];

> }; The directroute configures a CBT router with knowledge of the CBT core for a group of multicast addresses. The multicast group addresses are configured by the start and of a range of group addresses. The CBT core is configured by the address of the core router and its type (primary, secondary or target).

> group-addr-start host

> Start of the range of multicast group addresses that have a direct route from this router.

> group-addr-end host

> End of the range of multicast group addresses that have a direct route from this router.

> core-address [address cbttype [primary-core| secondary-core |target-core]

> The core-addresses specify the addresses of the CBT routers that will service these range of multicast groups (group-addr-start to group-addr-end). CBT allows for three types of core to be specified: primary, secondary, and target core. The core-address command also indicates what type of core the CBT router and group addresses are.

###

### Tracing options

Packet tracing options (which may be modified with `detail`, `send` or `recv`):

packets - CBT packets

join - PIM Join packets

quit - PIM Quit packets

echo - PIM echo packets

assert - PIM Graft and Graft Ack packets

## Sample PIM configurations

See the sample multicast router configurations.

Last updated April 26, 1997