Tag Archives: Tweak Multicast

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 (224.0.1.129)
You have to Deny the host adjacent in this case was 10.101.201.43

access-list CSC_FILTER_PIM standard deny host 10.101.201.43

interface Ethernet0/0
description CSC
nameif CSC-LON9
security-level 55
ip address 10.111.201.41 255.255.255.248 standby 10.111.201.42
pim neighbor-filter CSC_FILTER_PIM
igmp static-group 224.0.1.129

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

10.101.201.41 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 10.101.201.41/29
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 10.101.201.41 (this system)

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

fw01/sec/act# sh mroute 10.101.100.13 224.0.1.129

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

(10.101.100.13, 224.0.1.129), 3w3d/00:03:29, flags: SFJT
Incoming interface: INSIDE
RPF nbr: 10.101.100.13
Inherited Outgoing interface list:
CSC-LON9, Forward, 3w3d/never