Multicast PIM NBMA Mode

Lessons Discussion
17

Hi Hussein,

I just redid this lab on some real hardware and I think this is some Cisco VIRL quirk. When I run it on VIRL, I don’t need to use PIM nbma mode. On real hardware, I do need it.

Spoke1-VIRL#show version | include 15
Cisco IOS Software, IOSv Software (VIOS-ADVENTERPRISEK9-M), Version 15.6(3)M2, RELEASE SOFTWARE (fc2)
Spoke1-REAL#show version | include 15
Cisco IOS Software, 2800 Software (C2800NM-ADVENTERPRISEK9-M), Version 15.1(4)M7, RELEASE SOFTWARE (fc2)

Let’s join a group:

Spoke2(config)#interface gi0/0
Spoke2(config-if)#ip igmp join-group 239.3.3.3

The hub creates some entries.

Cisco VIRL:

Hub#
MRT(0): Create (*,239.3.3.3), RPF (unknown, 0.0.0.0, 0/0)
MRT(0): WAVL Insert interface: Tunnel0 in (* ,239.3.3.3) Successful
MRT(0): set min mtu for (3.3.3.3, 239.3.3.3) 0->1476
MRT(0): Add Tunnel0/239.3.3.3 to the olist of (*, 239.3.3.3), Forward state - MAC not built
MRT(0): Add Tunnel0/239.3.3.3 to the olist of (*, 239.3.3.3), Forward state - MAC not built
MRT(0): Set the PIM interest flag for (*, 239.3.3.3)

Real hardware:

Hub#
PIM(0): Received v2 Join/Prune on Tunnel0 from 172.16.123.2, to us
PIM(0): Join-list: (*, 239.3.3.3), RPT-bit set, WC-bit set, S-bit set
PIM(0): Check RP 3.3.3.3 into the (*, 239.3.3.3) entry
PIM(0): Adding register decap tunnel (Tunnel2) as accepting interface of (*, 239.3.3.3).
MRT(0): Create (*,239.3.3.3), RPF  /0.0.0.0
MRT(0): WAVL Insert interface: Tunnel0 in (* ,239.3.3.3) Successful
MRT(0): set min mtu for (3.3.3.3, 239.3.3.3) 0->1476
MRT(0): Add Tunnel0/239.3.3.3 to the olist of (*, 239.3.3.3), Forward state - MAC not built
PIM(0): Add Tunnel0/172.16.123.2 to (*, 239.3.3.3), Forward state, by PIM *G Join
MRT(0): Add Tunnel0/239.3.3.3 to the olist of (*, 239.3.3.3), Forward state - MAC not built

Then I send some traffic from spoke1:

Spoke1#ping 239.3.3.3 repeat 1000
Type escape sequence to abort.
Sending 1000, 100-byte ICMP Echos to 239.3.3.3, timeout is 2 seconds:

Reply to request 0 from 10.255.1.190, 40 ms
Reply to request 1 from 10.255.1.190, 13 ms
Reply to request 2 from 10.255.1.190, 13 ms

Here’s what the hub does:

Cisco VIRL:

Hub#
MRT(0): Reset the z-flag for (10.255.1.189, 239.3.3.3)
MRT(0): Create (10.255.1.189,239.3.3.3), RPF (unknown, 192.168.34.4, 1/0)
MRT(0): WAVL Insert interface: Tunnel0 in (10.255.1.189,239.3.3.3) Successful
MRT(0): set min mtu for (10.255.1.189, 239.3.3.3) 18010->1476
MRT(0): Add Tunnel0/239.3.3.3 to the olist of (10.255.1.189, 239.3.3.3), Forward state - MAC not built
MRT(0): Reset the z-flag for (172.16.123.1, 239.3.3.3)
MRT(0): (172.16.123.1,239.3.3.3), RPF install from  /0.0.0.0 to Tunnel0/172.16.123.1
MRT(0): Set the F-flag for (*, 239.3.3.3)
MRT(0): Set the F-flag for (172.16.123.1, 239.3.3.3)
MRT(0): Create (172.16.123.1,239.3.3.3), RPF (Tunnel0, 172.16.123.1, 110/1000)
MRT(0): Set the T-flag for (172.16.123.1, 239.3.3.3)
MRT(0): Update Tunnel0/239.3.3.3 in the olist of (*, 239.3.3.3), Forward state - MAC not built
MRT(0): Update Tunnel0/239.1.1.1 in the olist of (*, 239.1.1.1), Forward state - MAC not built

Real hardware:

Hub#
PIM(0): Received v2 Register on Tunnel0 from 172.16.123.1
     for 1.1.1.1, group 239.3.3.3
PIM(0): Adding register decap tunnel (Tunnel2) as accepting interface of (1.1.1.1, 239.3.3.3).
MRT(0): Reset the z-flag for (1.1.1.1, 239.3.3.3)
MRT(0): (1.1.1.1,239.3.3.3), RPF install from  /0.0.0.0 to Tunnel0/172.16.123.1
MRT(0): Create (1.1.1.1,239.3.3.3), RPF Tunnel0/172.16.123.1
PIM(0): Insert (1.1.1.1,239.3.3.3) join in nbr 172.16.123.1's queue
PIM(0): Building Join/Prune packet for nbr 172.16.123.1
PIM(0):  Adding v2 (1.1.1.1/32, 239.3.3.3), S-bit Join
PIM(0): Send v2 join/prune to 172.16.123.1 (Tunnel0)
PIM(0): Received v2 Register on Tunnel0 from 172.16.123.1
     for 1.1.1.1, group 239.3.3.3
MRT(0): Set the T-flag for (1.1.1.1, 239.3.3.3)
PIM(0): Removing register decap tunnel (Tunnel2) as accepting interface of (1.1.1.1, 239.3.3.3).
PIM(0): Installing Tunnel0 as accepting interface for (1.1.1.1, 239.3.3.3).
PIM(0): Received v2 Join/Prune on Tunnel0 from 172.16.123.2, to us
PIM(0): Join-list: (1.1.1.1/32, 239.3.3.3), S-bit set
PIM(0): Insert (1.1.1.1,239.3.3.3) join in nbr 172.16.123.1's queue
PIM(0): Building Join/Prune packet for nbr 172.16.123.1
PIM(0):  Adding v2 (1.1.1.1/32, 239.3.3.3), S-bit Join
PIM(0): Send v2 join/prune to 172.16.123.1 (Tunnel0)
PIM(0): Received v2 Register on Tunnel0 from 172.16.123.1
     for 1.1.1.1, group 239.3.3.3
PIM(0): Send v2 Register-Stop to 172.16.123.1 for 1.1.1.1, group 239.3.3.3

I need to add IP PIM nbma mode on my real hardware to make it work. The output of the debugs is a bit different but that’s probably related to the IOS version. There’s probably also something funny happening with the switch on VIRL.

About the pruning, without NBMA mode spokes don’t see each other prune messages so they won’t be able to send a prune override message. Once you enable NBMA mode, the hub treats each spoke as a seperate “connection” so it forwards prunes to all spokes, allowing spokes to send prune override messages.

Rene

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