VRRP & GLBP – Kung.dk

VRRP (open standard) and GLBP (Cisco, with load balancing) – the FHRP siblings of HSRP.

VRRP facts

Topic	VRRP
Standard	Open standard (RFC 5798)
Multicast	224.0.0.18 · IP protocol 112
Virtual IP / MAC	1 per group · `0000.5e00.01XX`
Roles	Master / Backup
Priority / Timers	100 (0–255) · Advertisement 1 s
Versions	VRRPv2 (IPv4), VRRPv3 (IPv4+IPv6)

When to use: multivendor networks, when an open standard or vendor-independence is required. Avoid: pure Cisco environments where HSRP is already standard. Pros: open RFC, widely supported, same architecture as HSRP. Cons: less common in Cisco-only shops, fewer Cisco-specific integrations.

VRRP configuration

Router A (master) / Router B (backup), VLAN 10, virtual gateway 10.10.10.254:

interface vlan 10
 ip address 10.10.10.1 255.255.255.0
 vrrp 10 ip 10.10.10.254
 vrrp 10 priority 110
 vrrp 10 preempt
!
interface vlan 10
 ip address 10.10.10.2 255.255.255.0
 vrrp 10 ip 10.10.10.254
 vrrp 10 priority 100
 vrrp 10 preempt

vrrp version 3                              ! v2 = IPv4, v3 = IPv4+IPv6
vrrp 10 preempt delay minimum 60            ! preemption with delay
track 1 interface GigabitEthernet1/0/1 line-protocol
 vrrp 10 track 1 decrement 20               ! tracking: lower priority when uplink fails
vrrp 10 timers advertise 1                  ! default advertisement = 1 s
vrrp 10 authentication text mypassword      ! clear-text (CCNA)
vrrp 10 authentication md5 key-string mysecretkey   ! MD5 (CCNP)

Verification: show vrrp, show vrrp brief. Typical faults: ❌ no master → different VRRP group · wrong master → priority · doesn’t take over → missing preempt · flapping → mismatched timers · no adjacency → VLAN mismatch · auth failure · traffic stops on link failure → missing tracking.

GLBP facts

Topic	GLBP
Standard	Cisco proprietary
Multicast	224.0.0.102 · UDP 3222
Virtual MACs	Multiple per group
Roles	AVG / AVF
Priority / Timers	100 (0–255) · Hello 3 s / Hold 10 s

AVG (Active Virtual Gateway): controls the group and assigns the virtual MAC addresses
AVF (Active Virtual Forwarder): forwards traffic for its virtual MAC
Several routers can be active simultaneously

When to use: gateway redundancy and load balancing, multiple gateways actively used, Cisco-only, when you want to avoid multiple HSRP groups. Avoid: multivendor, when simplicity/troubleshooting matters. Pros: redundancy + load balancing, efficient gateway use. Cons: proprietary, more complex, rarer in practice.

GLBP configuration

interface vlan 10
 ip address 10.10.10.1 255.255.255.0
 glbp 10 ip 10.10.10.254
 glbp 10 priority 110
 glbp 10 preempt
!
interface vlan 10
 ip address 10.10.10.2 255.255.255.0
 glbp 10 ip 10.10.10.254
 glbp 10 priority 100
 glbp 10 preempt

Load-balancing methods:

glbp 10 load-balancing round-robin    ! default
glbp 10 load-balancing weighted
glbp 10 load-balancing host-dependent

Tracking: track 1 interface … + glbp 10 track 1 decrement 20. Timers: glbp 10 timers 1 3. Authentication: glbp 10 authentication text … / md5 key-string ….

Verification: show glbp, show glbp brief – output shows AVG state plus every forwarder’s state. Typical faults: only one router forwarding → wrong load-balancing method · wrong AVG → missing preempt · flapping → timers · traffic stops on link failure → missing tracking · no active forwarders → VLAN mismatch · auth failure → mismatched authentication.

Tagged ccnp, fhrp