[Xorp-users] Multicast problem

[Ben Greear]

Pavlin Radoslavov wrote:
> Ben Greear <greearb at candelatech.com> wrote:
>
>   
>> Ok, the MFC was being set up, but it seems xorp continues to
>> receive and transmit packets.  I'm thinking I don't really know
>> how multicast routing is supposed to work :)
>>     
>
> Yes, this is how PIM-SM is suppose to work.
> The sender's multicast data packets are encapsulated in PIM Register
> messages by the DR (Designated Router) for the sender's subnet,
> and then are unicast to the RP. On Linux the encapsulation happens
> in user-space (in the XORP PIM-SM process); on BSD the IPv4
> encapsulation can happen in kernel (IPv6 BSD doesn't have the kernel
> support to do that).
> The user-space data encapsulation is probably the reason for the
> long latency you were seeing.
>
> However, if the RP sends source-specific (S,G) toward the DR, then
> the multicast data packets will be forwarded natively (without the
> PIM Register encapsulation overhead).
> In XORP you can control when the RP sends the DR by using the
> following configuration inside the pimsm4 or pimsm6 block:
>
>         switch-to-spt-threshold {
>             /* approx. 1K bytes/s (10Kbps) threshold */
>             disable: false
>             interval: 100
>             bytes: 102400
>         }
>
> If you set "bytes" to 0 for example, then the RP should send the
> (S,G) Join right after the first PIM Register for that socket is
> received by the RP. In your case where performance is critical
> you might want to set "bytes" to 0.
>   
What is the benefit of setting it to something larger than 0 ?

Thanks,
Ben

-- 
Ben Greear <greearb at candelatech.com> 
Candela Technologies Inc  http://www.candelatech.com