Configuring Time-To-Live
Time-To-Live (TTL) works in this bearings aloof like it does in added acquisition environments.
Simply put, any packet that comes in with a college TTL than the one configured will be
forwarded and the TTL amount decreased by one. TTL is bidding as a cardinal that signifies the
number of router hops. The absence amount of TTL is 0. A TTL of aught agency that every packet
is forwarded. Configuring the TTL absolute is done on a per-interface basis. To configure a value
other than the default, blazon the afterward in interface mode:
DallasR1>(config-if)#ip multicast ttl-threshold ttl-value
Example 11-3 demonstrates how to configure the TTL absolute application the ip multicast ttlthreshold
command.
Debugging Multicast
Many abeyant commands can be acclimated back debugging multicast. We will go over a brace of
the best important here. You can acquisition affidavit on added debugging commands at CCO
(www.cisco.com).
The aboriginal command of significance, appearance ip pim neighbor, displays the PIM acquaintance table as
demonstrated beforehand in Example 11-1.
Another accordant command, appearance ip mroute, shows the entries in the multicast acquisition table.
The accepted syntax for this command is as follows:
DallasR1> appearance ip mroute [group-name | group-address] [source] [summary] [count]
[active kbps]
Example 11-4 demonstrates achievement generated by the appearance ip mroute command.
Routing entries are categorized as (S,G). S is the antecedent and G is the destination multicast
group. The added affectionate of access is a (*,G), which is an access fabricated by the Designated Router on
behalf of a host that wants to accompany a group. The G is the accumulation multicast address.
Another advantageous debugging apparatus is to abduction all multicast packets to the animate awning through
the alter facility. As is the case back application any alter command, you charge exercise caution
because this is a CPU-intensive task.
Example 11-3 ip multicast ttl-threshold Configures the TTL Absolute on a Router Interface
DallasR1>#show running-config
hostname DallasR1>
!
!
ip multicast routing
!
interface VLAN100
ip pim sparse-dense-mode
ip multicast ttl-threshold 16
382 Chapter 11: Configuring Multicast Networks
To log all IP multicast packets accustomed and transmitted by a router, access the following
command in EXEC mode:
DallasR1>#debug ip mpacket [detail] [access-list] [group]
Example 11-5 shows sample achievement generated by arising this command.
Configuring Internet Accumulation Management Protocol (IGMP)
Internet Accumulation Management Protocol (IGMP) is an important allotment of IP that charge be supported
by all multicast hosts on a network. Multicast routers use IGMP to accumulate clue of multicast hosts
on a network.
Although two versions of IGMP are available, adaptation 1 and adaptation 2, IGMP adaptation 2 is the
default in all Cisco routers active IOS Release 11.3(2)T and later.
To configure the multicast router to accompany a accurate multicast group, access the following
command in the accordant interface agreement mode:
DallasR1>(config-if)#ip igmp join-group group-address
where group-address is the multicast abode of the group.
One way to verify the multicast accumulation is to affair a ping to the defined accumulation address. All
configured routers should acknowledge to the ping.