Singlewire Informacast Paging Gateway for a L3 switched site with multiple VLANs

[edguidry]

Hello,

We are going to install paging gateways.  In the past, I have dealt with environments with a single voice VLAN.  I simply put the gateway on the voice VLAN.  Now I am at an environment that will have sites with multiple voice VLANs.  My question for a Layer 3 switching site, can I get away with one paging gateway and rely on multicast to propagate to all voice VLANs for the site? 

Thanks,

Eddie

[Jonathan Schulenberg]

That depends on whether the L3 switches in the site are licensed and configured for multicast routing. If it is, then you can use a single paging gateway. If not then you would need one per layer two broadcast domain (aka VLAN).

Multicast is a significant topic but if you're unfamiliar with it you'll want to configure Any Source Multicast (ASM) with PIM sparse-mode as the routing protocol amongst the layer three routers/switches, a Rendezvous Point (RP) on one of the routers/switches, and IGMP snooping on the layer two portion of the network. You would also need to either manually configure the RP on each layer three switch/router, a Bootstrap Router (BSR) or the older Auto-RP feature for each switch to discover the RP.

The configuration varies by hardware platform but here's a good starting point: http://www.cisco.com/c/en/us/support/docs/ip/ip-multicast/9356-48.html

PS- Be mindful of the switch licensing. IP Base is typically restricted to PIM Stub Mode, a Cisco-proprietary variant of PIM that aligns with - and depends on - EIGRP Stub Mode. Essentially it can only be the last hop before the multicast receiver. It cannot be the source or an intermediate hop.

[edguidry]

Jonathan, thanks for this.  3850 switches running Universal code.