From: Geert Nijs (Geert.Nijs@simac.be)
Date: Fri Jan 04 2008 - 12:29:06 ARST
Kubrat,
They will NOT do the same.
The command "ip pim spt-threshold" applies to SPARSE MODE groups only and it determines when the sparse mode group switches from the 'shared' tree (via the RP) to the
'direct' tree (directly to the source). This is determined by the throughput of the group ie if the stream is more then x kbps, you switch from 'shared' tree to 'direct' tree (i think by default, spt-threshold is 0, meaning immediatly starting from the first packet that an edge router receives, it will send a join towards the source to join the 'direct' tree. It actually has to wait for this first packet to detect the source ip address :-) because the edge router has no way of knowing this beforehand.
The sink RP method is used to determine which groups will run in SPARSE mode or which groups will run in DENSE mode.
Actually, when no RP is known, the group will fall back to DENSE mode automatically. By configuring a local sink RP, you actually define a local RP for ALL groups, so
that a local RP is ALWAYS known. Because there is always a local RP (loopback), DENSE mode fallback is impossible and all groups are always SPARSE mode.
Using auto-rp you then override the RP with some real RP for some limited number of groups only.
As you can see, this is something completely different.....
regards,
Geert Nijs
________________________________________
From: nobody@groupstudy.com [nobody@groupstudy.com] On Behalf Of Kubrat Vapzarov [kvapzarov@yahoo.com]
Sent: 04 January 2008 13:19
To: ccielab@groupstudy.com
Subject: Sink RP for Auto RP
Hello Group,
I have a question about multicast routing with Auto-RP. According to some Cisco documents in order to prevent the multicast groups (other than 224.0.1.39 and .40) from operating in dense mode, a sink RP must be configured. Something like this:
ip pim rp-address 1.1.1.1 20
ip pim send-rp-announce Loopback0 scope 32 group-list 10
ip pim send-rp-discovery Loopback0 scope 32
access-list 10 permit 224.0.0.0 15.255.255.255
access-list 20 deny 224.0.1.39
access-list 20 deny 224.0.1.40
access-list 20 permit 224.0.0.0 15.255.255.255
However, there is a command "ip pim spt-threshold" whose "infinity" option will do the same, or so I think.
My question is do these two different configurations achieve the same or are they different and how?
Kubrat
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