All things related to multicast

[Leonard Giuliano <>]

If 194.82.152.254 is originating SAs for which it hasn't received PIM 
registers, then it is breaking the laws of MSDP.

Are you certain that it is not receiving registers, though?  Could a bad 
RP mapping misconfig or leaked BSR/AutoRP msg be making it to the DR for
62.217.124.105 such that it really is sending registers to 194.82.152.254?


On Wed, 11 Mar 2015, Zenon Mousmoulas wrote:

| Yes, that router appears to be originating SAs while it is practically 
| certain that it is not the RP or the DR for the particular S,Gs and it 
| has just discovered them via MSDP. So it appears to be reflecting a 
| large portion of the SAs it is originating (which added up to 590 the 
| last time I checked). I can't think of any case where such a behavior 
| would make sense; it rather seems like misconfiguration or a bug. What 
| do you think?
| 
| 10 ?????? 2015, 17:03, ??/?? "Leonard Giuliano" 
<>
 ????????????:
| 
| > 
| > Hmm, what do you mean by "reflector"?  A router should only originate an 
| > SA if it is the local RP and receives a PIM register for the source (or 
| > the source is directly connected and the router is the RP and DR on that 
| > interface).  If the router is not the local RP, it should not originate 
| > the SAs.  From RFC 3618:
| > 
| > 6. Intermediate MSDP Peers
| > 
| >   Intermediate MSDP speakers do not originate periodic SA messages on
| >   behalf of sources in other domains.  In general, an RP MUST only
| >   originate an SA for a source which would register to it, and ONLY RPs
| >   may originate SA messages.  Intermediate MSDP speakers MAY forward SA
| >   messages received from other domains.
| > 
| > 
| > On Tue, 10 Mar 2015, Zenon Mousmoulas wrote:
| > 
| > | Hi Leonard,
| > | 
| > | thanks, yes I figured out that a) I can't filter based on originator 
(not that it would make much sense in general) and b) peer-rpf check does not 
consider SA source. They are accepted, perhaps even before rule 4, because 
the peer is indeed the next hop to the originator. So, to catch such cases, 
one would need to write MSDP import policies that would reject SAs for 
sources within one's own address space, which in general should not appear 
outside one's own PIM domain.
| > | 
| > | What I didn't understand however is why that MSDP originator would act 
as a "reflector", i.e. if there would be any legitimate explanation for such 
a behavior.
| > | 
| > | Thanks for your insight,
| > | Z.
| > | 
| > | 9 ?????? 2015, 23:33, ??/?? "Leonard Giuliano" 
<>
 ????????????:
| > | 
| > | > Zenon,
| > | > 
| > | > You can filter SAs based on source, group or peer, but not originator.
| > | > 
| > | > As to the question of whether they should pass peer-rpf, do a "show 
route 
| > | > detail" on the peer (62.40.124.89) as well as the originator 
| > | > (194.82.152.254).  The results can then be compared against the rpf 
rules 
| > | > in sect 10.1.3 in RFC 3618.  You'll probably see it accepted bc of 
rule 
| > | > iv: 62.40.124.89 resides in the AS path in the best path for 
| > | > 194.82.152.254.  
| > | > 
| > | > MSDP peer-rpf doesn't care about the source; rather, it only cares 
about 
| > | > the peer with respect to the originator.  Put another way, MSDP will 
NOT 
| > | > decide if it's OK for 194.82.152.254 to originate an SA with source 
| > | > 233.21.32.32; it WILL decide if 62.40.124.89 is the peer who should 
be 
| > | > allowed to advertise SAs with the originator of 194.82.152.254.
| > | > 
| > | > 
| > | > Hope this helps,
| > | > Lenny
| > | > 
| > | > On Sat, 28 Feb 2015, Zenon Mousmoulas wrote:
| > | > 
| > | > | While investigating an issue with PIM register messages being 
dropped by 
| > | > | our RP routers (due to misconfiguration), I noticed that some S,G 
state 
| > | > | for local sources was mysteriously still present on the RP, even 
though 
| > | > | register messages were being dropped. I then realized this state 
was 
| > | > | triggered by MSDP SAs such as the following, which seem to be 
originated 
| > | > | by some system in the UK. I can't think of a valid scenario where 
it 
| > | > | could be an originator for what is certainly a foreign (in terms of 
a 
| > | > | PIM domain) S,G. Such SAs are being accepted by the router -- I'm 
not 
| > | > | sure at this stage if they should pass peer-rpf-check or not.
| > | > | 
| > | > | Group address   Source address  Peer address    Originator      
Flags
| > | > | 233.21.32.32    62.217.124.105  62.40.124.89    194.82.152.254  
Accept
| > | > | 233.21.32.234   62.217.124.105  62.40.124.89    194.82.152.254  
Accept
| > | > | 
| > | > | Given these oddities about 194.82.152.254, which seems to act as a 
MSDP 
| > | > | reflector (currently for up to 590 SAs), I wanted to see if I could 
drop 
| > | > | such SAs in the MSDP import policy statement. However there doesn't 
seem 
| > | > | to be a match condition for originator, at least not on JunOS 13.3. 
I 
| > | > | wonder if there is any other way to do this?
| > | > | 
| > | > | Regards,
| > | > | Z.
| > | > | 
| > |
|