I've been reading through various Multicast Forwarding over GRE (i.e. enable PIM Sparse on the Interesting Interface on each router, and the GRE Tunnel), and can see that this allows you to use the pre-allocated 224.0.1.40 Multicast subnet.
(Source: https://supportforums.cisco.com/thread/2168826)
My intent here is to try and run HSRP between two routers with a shared Subnet (i.e. RouterA has an Fa1/0 as 10.230.108.2/28 -
HSRP 10.230.108.1; RouterB has an Fa1/0 as 10.230.108.3/28 - HSRP 10.230.108.1) - however that Shared Subnet is actually a Resilient (Active/Passive) pair of ASA Firewalls, hence I don't have a common Broadcast Domain for the HSRP -> 224.0.0.2 Multicast "Hello" messages to traverse.
RouterA and RouterB have a /30 routed interface between them, and some Track objects/IP SLA which enables the WAN -> Firewall and Firewall -> WAN Failover to occur (big hint: turn CEF off or watch your Sunday afternoon disappear in a cloud of "Why are you routing there when the RIB table says you go here?!" smoke).
It seems to be possible to forward Multicast across a GRE Tunnel, connected to both RouterA and RouterB so can this be extended to forward HSRP Multicast packets to 224.0.0.2, without needing common Switched infrastructure between RouterA and Router B?
RouterA
ip pim bidir-enable
ip multicast-routing
!
interface FastEthernet0/0
description *** ASA Failover Link ***
ip address 10.182.179.225 255.255.255.252
duplex auto
speed auto
!
interface FastEthernet1/0
description *** Link to ASA (Primary HA) ***
ip address 10.230.108.2 255.255.255.240
no ip redirects
no ip proxy-arp
ip pim sparse-dense-mode
ip route-cache flow
no ip mroute-cache
duplex auto
speed auto
standby 1 ip 10.230.108.1
standby 1 priority 110
standby 1 preempt
!
interface Tunnel1
ip unnumbered FastEthernet1/0
ip pim sparse-dense-mode
tunnel source FastEthernet0/0
tunnel destination 10.182.179.226
end
RouterB
ip pim bidir-enable
ip multicast-routing
!
ip mroute 10.230.108.2 255.255.255.255 Tunnel1
ip mroute 10.182.179.224 255.255.255.252 Tunnel1
ip mroute 10.230.108.0 255.255.255.240 Tunnel1
!
interface FastEthernet0/0
description *** ASA Failover Link ***
ip address 10.182.179.226 255.255.255.252
duplex auto
speed auto
!
interface FastEthernet1/0
description *** Link to ASA (Primary HA) ***
ip address 10.230.108.3 255.255.255.240
no ip redirects
no ip proxy-arp
ip pim sparse-dense-mode
ip route-cache flow
no ip mroute-cache
duplex auto
speed auto
standby 1 ip 10.230.108.1
standby 1 preempt
!
interface Tunnel1
ip unnumbered FastEthernet1/0
ip pim sparse-dense-mode
tunnel source FastEthernet0/0
tunnel destination 10.182.179.225
end
