[c-nsp] Multicast distribution over backbone

[Phil Mayers]

On 01/12/10 13:31, Alexander Clouter wrote:

>> Designate one router as the RP. Configure PIM-SM each router. Configure
>> them all with the same RP.
>>
>> You only need MSDP to pass source info between PIM-SM RPs.
>>
> All our core routers are RPs with the same 'anycasted' address so we
> have resilence.  We use MSDP to then make sure everything is then
> sync'ed up:

Sure. We do the same thing with our RPs (although we make use of the 
JunOS anycast-rp stuff to avoid having to run MSDP). Best to get a 
single RP working first though ;o)

One thing: Personally I'd be a bit cautious about making *every* router 
an RP. One unfortunate side effect of being an RP is the CPU-processing 
of the encaps/decaps traffic. This is particularly noticeable if you 
don't have:

ip pim [vrf NAME] register-rate-limit N

...on every *other* router, as high-bandwidth transmitter can punt lots 
of packets/sec to the RP CPU for brief periods until the (s,g) state is 
built.

For this reason we use separate routers as RPs. Our main RPs are two 
Juniper M7i (which have tunnel services PICs so to the encaps/decaps in 
hardware) but we also use an old Cisco 2691 with appropriate IOS as the 
RP for 239.0.0.0/8 inside our firewall, for boring reasons relating to 
lack of jumbo frames on the firewalls, fragmentation of PIM register 
packets containing full-size packets, and differing IOS/JunOS behaviour.

Obviously it depends on your traffic patterns and which routers you're 
using. There is no one-size-fits-all.