Ralf Lübben <[EMAIL PROTECTED]> wrote:
> Hello,
>
> I'm new to XORP.
>
> At the moment I'm trying to extend PIM. For it I need to understand how the
> switch between the different phases in PIM (RP Tree -> Register Stop ->
> Shortest Path Tree) is done.
The switch to the SPT can be initiated by either:
(a) the last-hop router that is connected to the receiver. If the
last-hop router sends (S,G) Join toward the source, it will
start receiving the packets from S on the SPT (i.e., it won't
need the RP for that anymore). Note that the rest of the
receivers might continue to receive the packets on the RP Tree
(unless their last-hop routers also send (S,G) Join toward the
source).
(b) By the RP for the multicast group G.
The RP sends (S,G) Join toward the S, and once it starts
receiving the packets on the SPT the switch is completed.
If the RP receives a PIM Register for that source, it will send
PIM Register Stop to suppress further PIM Register
encapsulation.
Note that in this case only the path from S to the RP is
affected. The receivers will continue to receive the packets on
the RP Tree.
Typically, the switch to the SPT is bandwidth-triggered. E.g., if
the bandwidth for a particular (S,G) is above a pre-defined
threshold, the last-hop router (or the RP) will initiate SPT switch.
In XORP the threshold is configured by the following statement:
switch-to-spt-threshold {
/* approx. 1K bytes/s (10Kbps) threshold */
disable: false
interval: 100
bytes: 102400
}
The threshold in the above configuration is 10Kbps.
If you set "bytes" to 0, the switch will be initiated right after
the first packet is forwarded.
Implementation-wise, have a look in file pim/pim_mre_data.cc method
PimMre::is_switch_to_spt_desired_sg()
This is the procedure that tests whether the SPT switch should be
initiated.
Please search the rest of the PIM-SM code for that method to see how
it is used and in what places.
It is difficult to give you further recommendations without knowing
what exactly you are trying to extend in PIM-SM.
> I saw that all packets are forwarded to the PIM process if the flag
> VIFF_REGISTER is set.
> But I can't find the code where the flag is reset, so that multicast packets
> are no longer forwarded from the kernel to the PIM process.
The VIFF_REGISTER flag is permanent and is used to indicate the
so-called register_vif. That register_vif is used for communication
between the UNIX kernel and XORP. For example, all PIM Register
encapsulated packets received by the kernel (in the RP) are passed
to the userland process such that they appear they have arrived on
the register_vif.
In other words, you shouldn't try to manipulate the VIFF_REGISTER
flag.
Hope that helps,
Pavlin
> Maybe someone can give me a hint.
>
> Thanks in advance.
>
> Regards,
> Ralf
>
> _______________________________________________
> Xorp-hackers mailing list
> [email protected]
> http://mailman.ICSI.Berkeley.EDU/mailman/listinfo/xorp-hackers
_______________________________________________
Xorp-hackers mailing list
[email protected]
http://mailman.ICSI.Berkeley.EDU/mailman/listinfo/xorp-hackers
