Hi,
I am re-learning multicast for the 3-4th time in the past 10 years now so
I'm rusty.
IOS XR machine (ASR9k). PIM-SSM (group in ff38::/96)
multicast-source--R1--R2--R3--client
This is R3:
multicast-routing
address-family ipv6
interface-inheritance disable
interface all enable
I enable the interface in "router pim" and "router mld", and everything is
fine, client can receive multicast stream after MLD join, mrib of course
looks great.
Why can't I now disable PIM? Why is PIM needed on a client-only interface
wherefrom I don't need any multicast sourced, just want clients to be able
to MLD join streams from elsewhere. If I disable PIM, mrib still looks
almost the same, but there is no multicast being forwarded out that
interface towards the client.
I really would like to avoid having to run PIM on thousands of
(sub)interfaces, which on top of everything needs to be protected with an
ACL because I don't want my customers to be able to establish a PIM
session with my router.
Without PIM:
#show mrib ipv6 route <source-IPv6-address>
Mon Feb 9 15:17:16.770 CET
IP Multicast Routing Information Base
Entry flags: L - Domain-Local Source, E - External Source to the Domain,
C - Directly-Connected Check, S - Signal, IA - Inherit Accept,
IF - Inherit From, D - Drop, ME - MDT Encap, EID - Encap ID,
MD - MDT Decap, MT - MDT Threshold Crossed, MH - MDT interface handle
CD - Conditional Decap, MPLS - MPLS Decap, MF - MPLS Encap, EX - Extranet
MoFE - MoFRR Enabled, MoFS - MoFRR State, MoFP - MoFRR Primary
MoFB - MoFRR Backup, RPFID - RPF ID Set
Interface flags: F - Forward, A - Accept, IC - Internal Copy,
NS - Negate Signal, DP - Don't Preserve, SP - Signal Present,
II - Internal Interest, ID - Internal Disinterest, LI - Local Interest,
LD - Local Disinterest, DI - Decapsulation Interface
EI - Encapsulation Interface, MI - MDT Interface, LVIF - MPLS Encap,
EX - Extranet, A2 - Secondary Accept, MT - MDT Threshold Crossed,
MA - Data MDT Assigned, LMI - mLDP MDT Interface, TMI - P2MP-TE MDT
Interface
IRMI - IR MDT Interface
(<source>,<group>)
RPF nbr: fe80::da67:d9ff:fe4b:510c Flags:
Up: 00:00:09
Incoming Interface List
HundredGigE0/0/0/0 Flags: A, Up: 00:00:09
Outgoing Interface List
TenGigE0/2/0/3.2021 Flags: LI, Up: 00:00:09
When I enable PIM, I get:
Outgoing Interface List
TenGigE0/2/0/3.2021 Flags: F NS LI, Up: 00:01:59
Now everything works as it should.
and when I disable PIM, it goes back to:
Outgoing Interface List
TenGigE0/2/0/3.2021 Flags: LI, Up: 00:02:36
F means "Forward", so it's pretty obvious that the forwarding plane stops
the forwarding of this multicast group without PIM enabled on the
interface. I just don't understand why.
Could someone please enlighten me?
--
Mikael Abrahamsson email: [email protected]
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