Tag Archives: PIM

Tweak multicast on Cisco ASA without RP

This came as a customer request, where they required to send multicast for testing purposes to their own customers but without using a RP. A Cisco ASA is segregating the environment acting as Layer 3 between the multicast sender and receivers. The first step was disabling the snooping on the switching to let the traffic going through, and last but not least setup a static group on the ASA to flood the interface outwards to the receivers. The challenge was the PIM, which has to be enabled but can’t have a neighbourship otherwise the interface is not going to flood the multicast out, so how do we make this work?

I’m running code Cisco ASA 9.1(7) with multicast-routing enabled

Because i have the firewall connect to a DMZ switch i have to disable the IGMP snooping on the switch

no ip igmp snooping vlan 2201

Setup a Filter to not allow the neighbourship but having the PIM enabled, and the static group to force the ASA to join particular multicast address (
You have to Deny the host adjacent in this case was

access-list CSC_FILTER_PIM standard deny host

interface Ethernet0/0
description CSC
nameif CSC-LON9
security-level 55
ip address standby
pim neighbor-filter CSC_FILTER_PIM
igmp static-group

If a PIM neighbourship was established, that needs to expire before the interface starts flooding the traffic, if you see Nbr Count=0 you are almost there

fw01/sec/act# show pim interface

Address Interface PIM Nbr Hello DR DR
Count Intvl Prior CSC-LON9 on 0 30 1 this system

fw01/sec/act# sh igmp interface CSC-LON9
CSC-LON9 is up, line protocol is up
Internet address is
IGMP is enabled on interface
Current IGMP version is 2
IGMP query interval is 125 seconds
IGMP querier timeout is 255 seconds
IGMP max query response time is 10 seconds
Last member query response interval is 1 seconds
Inbound IGMP access group is:
IGMP limit is 500, currently active joins: 0
Cumulative IGMP activity: 1 joins, 0 leaves
IGMP querying router is (this system)

Now the interface is forwarding the multicast, if you see Null you missed something

fw01/sec/act# sh mroute

Multicast Routing Table
Flags: D – Dense, S – Sparse, B – Bidir Group, s – SSM Group,
C – Connected, L – Local, I – Received Source Specific Host Report,
P – Pruned, R – RP-bit set, F – Register flag, T – SPT-bit set,
J – Join SPT
Timers: Uptime/Expires
Interface state: Interface, State

(,, 3w3d/00:03:29, flags: SFJT
Incoming interface: INSIDE
RPF nbr:
Inherited Outgoing interface list:
CSC-LON9, Forward, 3w3d/never