All things related to multicast

[Leonard Giuliano <>]

You can always just put in filters that block SAs containing your sources 
from coming in from external peers if you are sure they should never send 
you those.  That would essentially be like anti-spoofing SA filters and 
would block your SAs from coming in from all other bad originators, not 
just this one.

But to be honest, having a few extra SAs floating around out there isn't 
the worst thing in the world.  The thing to worry about is if the SAs 
aren't making it out to the world (if indeed you want the world to see 
them).  Having extra guys originating them isn't going to do any real harm 
other than creating a little extra state.  And extra state isn't something 
to lose sleep over unless it becomes a large amount- in which case the 
per-source/per-peer/per-instance SA policers should protect you.

-Lenny

On Wed, 11 Mar 2015, Zenon Mousmoulas wrote:

| I will check the logs once more just to be absolutely sure, but yes I am 
fairly certain that no RP leakage etc. was involved -- the DR was sending PIM 
register to our RP, for which it has a static mapping, and it had no 
knowledge of other RPs.
| 
| The thing is, if this speaker is indeed breaking the laws of MSDP, what can 
other routers do to protect their networks from the unintended consequences 
of that speaker's actions (such as input case), other than perhaps 
"anti-spoofing" filters.
| 
| 11 ?????? 2015, 17:10, ??/?? "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.
| > | > | > | 
| > | > |
| > |
|