FHRP Hardware Limitations

FHRP Protocols such as VRRP or HSRP might support many groups but that doesn't mean your hardware does as well.

For example, take a look at this ISR4331 router:

R1#show standby capability 
ISR4331/K9                                    * indicates hardware may support HSRP
                                              |
Interface          Type                       H  Potential Max Groups per subin
Gi0/0/0            27  ISR4331-3x1GE          *  15   (0x7F2F563A6AD0, 0x7F2F563A6AD0)
Gi0/0/1            27  ISR4331-3x1GE          *  15   (0x7F2F563A6AD0, 0x7F2F563A6AD0)
Gi0/0/2            27  ISR4331-3x1GE          *  15   (0x7F2F563A6AD0, 0x7F2F563A6AD0)
GigabitEthernet0   27  RP management port     *  4096 (0x7F2F52BBFBC0, 0x7F2F56271900)
LIIN0              27  LIIN                      -   
Loopback0          96  Loopback                  -   
Vlan1              156 Ethernet SVI           *  4096 (0x7F2F52BBFBC0, 0x7F2F5C4F7C20)

This router supports up to 15 standby groups on its GigabitEthernet interface and 4096 on its Vlan1 interface.

Gigabit Interface

Let's try this. I'll configure an IP address:

R1(config)#interface GigabitEthernet 0/0/0
R1(config-if)#ip address 192.168.1.1 255.255.255.0

I'll be able to create 15 groups:

R1(config-if)#standby 1 ip 192.168.1.254
R1(config-if)#standby 2 ip 192.168.1.253
R1(config-if)#standby 3 ip 192.168.1.252
R1(config-if)#standby 4 ip 192.168.1.251
R1(config-if)#standby 5 ip 192.168.1.250
R1(config-if)#standby 6 ip 192.168.1.249
R1(config-if)#standby 7 ip 192.168.1.248
R1(config-if)#standby 8 ip 192.168.1.247
R1(config-if)#standby 9 ip 192.168.1.246
R1(config-if)#standby 10 ip 192.168.1.245
R1(config-if)#standby 11 ip 192.168.1.244
R1(config-if)#standby 12 ip 192.168.1.243
R1(config-if)#standby 13 ip 192.168.1.242
R1(config-if)#standby 14 ip 192.168.1.241
R1(config-if)#standby 15 ip 192.168.1.240

Once I try to create number 16 I get an error:

R1(config-if)#standby 16 ip 192.168.1.239
% Warning: Interface MAC address filter only supports 15 additional addresses   
% and 15 HSRP groups are already configured.  The HSRP MAC address may not be   
% added to the MAC address filter if the group becomes active.

VLAN Interface

Let's test the VLAN interface:

R1(config)#default interface GigabitEthernet 0/0/0
Interface GigabitEthernet0/0/0 set to default configuration

R1(config)#interface Vlan 1
R1(config-if)#ip address 192.168.1.1 255.255.255.0

I can create plenty of standby groups:

R1(config)#interface Vlan 1
R1(config-if)#standby 1 ip 192.168.1.254
R1(config-if)#standby 2 ip 192.168.1.253
R1(config-if)#standby 3 ip 192.168.1.252
R1(config-if)#standby 4 ip 192.168.1.251
R1(config-if)#standby 5 ip 192.168.1.250
R1(config-if)#standby 6 ip 192.168.1.249
R1(config-if)#standby 7 ip 192.168.1.248
R1(config-if)#standby 8 ip 192.168.1.247
R1(config-if)#standby 9 ip 192.168.1.246
R1(config-if)#standby 10 ip 192.168.1.245
R1(config-if)#standby 11 ip 192.168.1.244
R1(config-if)#standby 12 ip 192.168.1.243
R1(config-if)#standby 13 ip 192.168.1.242
R1(config-if)#standby 14 ip 192.168.1.241
R1(config-if)#standby 15 ip 192.168.1.240
R1(config-if)#standby 16 ip 192.168.1.239
R1(config-if)#standby 17 ip 192.168.1.238
R1(config-if)#standby 18 ip 192.168.1.237
R1(config-if)#standby 19 ip 192.168.1.236
R1(config-if)#standby 20 ip 192.168.1.235

4096 are supported, if needed.