Multicast routing issues when a subinterface is configured

matthubach · ‎10-02-2014

Strange issue here. Cisco and the vendor are unable to help so far...

Most of our layer 3 lives on core switches. However, we have a couple sites off our WAN connected via Cisco routers. In these offices, we can not get paging to work.

I setup a lab and have finally determined what is at least causing the issue. My lab "branch" has the same problems, but I can resolve the problem by removing the sub-interface off the router.

On my LAN side of the router, with this config, everything works fine.

#--- THIS WORKS ---#

R1#
ip pim rp-address 192.168.251.254
!
gig 0/0 (connects to SW1 g0/1)
ip address 10.254.253.254 255.255.255.0
ip pim sparse-dense mode

SW1#
gig 0/1 (connects to R1 g0/0)
!no config - default VLAN1
--------------------

When I apply this config...everything breaks. The phone goes off

#--- THIS DOES NOT WORK ---#
R1#
ip pim rp-address 192.168.251.254
!
gig 0/0 (connects to SW1 g0/1)
no ip
gig 0/0.777 (connects to SW1 g0/1)
ip address 10.254.253.254 255.255.255.0
ip pim sparse-dense mode

SW1#
gig 0/1 (connects to R1 g0/0)
sw mode trunk
sw trunk encap dot1q
!
int vlan 777
ip address 10.254.253.1 255.255.255.0
ip pim sparse-dense mode
!
int vlan 778
ip address 10.254.251.1 255.255.255.0
ip pim sparse-dense mode
!
gig 0/17 (phone port)
switch access vlan 778 (keeping it simple for now)
----------------------------

I have tried this on 2 different model routers, each with different IOS versions. The same issues follow each router. What is it about the sub interfaces?

Any insight? Calling all multicast experts! Thanks!

Akash Agrawal · ‎10-02-2014

Hi,

creating sub-interface should not create any difference here. Only difference i can see earlier switch was working in l2 mode now it is participating in multicast routing as SVI is configured and pim neighborship established. Have you configured RP address on SW1. Please share below outputs from both devices

- running config

- show ip mroute <group>

- show ip pim rp address mapping

Regards,

Akash

Walter Astori · ‎10-03-2014

On the router R1, try to add the following command :

gigabit0/0.777
encapsulation dot1q

matthubach · ‎10-03-2014

Thanks Akash, I thought you were on to something there. However, I configured the RP address on SW1 and the results were the same. The phone goes off hook,but no audio.

I will work on getting you the results from the commands you want. I will provide them when paging is working and when paging is not working. Give me a bit...

Mat

James Boothe · ‎05-01-2018

What ever happened with this? I am having strange issues with some phone models going off hook but not playing audio as well...did you get this resolved?