Lab Simulation 8 Guidelines This is a lab item in which tasks will be performed on virtual devices. - Refer to the Tasks tab to view the tasks for this lab item. - Refer to the Topology tab to access

GLBP Lab Explanation Overall Goal GLBP (Gateway Load Balancing Protocol) is Cisco's proprietary first-hop redundancy protocol. Unlike HSRP/VRRP which waste standby router bandwidth, GLBP simultaneously load-balances traffic across multiple gateways while providing redundancy. The

Submitted by rania.sa· Mar 6, 2026Infrastructure

Question

Lab Simulation 8 Guidelines This is a lab item in which tasks will be performed on virtual devices. - Refer to the Tasks tab to view the tasks for this lab item. - Refer to the Topology tab to access the device console(s) and perform the tasks. - Console access is available for all required devices by clicking the device icon or using the tab(s) above the console window. - All necessary preconfigurations have been applied. - Do not change the enable password or hostname for any device. - Save your configurations to NVRAM before moving to the next item. - Click Next at the bottom of the screen to submit this lab and move to the next question. - When Next is clicked, the lab closes and cannot be reopened. Topology Tasks Implement GLBP between DISTRO-SW1 and DISTRO-SW2 on VLAN100 for hosts connected to ACCESS-SW1 to achieve these goals: 1. Configure group 30 using the virtual IP address of 192.168.1.254. 2. Configure DISTRO-SW1 as the AVG using a priority value of 110. 3. If DISTRO-SW1 suffers a failure and recovers, ensure that it automatically resumes the AVG role after waiting for a minimum of 15 seconds. Answer: Note: The virtual IP address, priority, delay value ... may be different so please check the question carefully. DISTRO-SW1(config)#interface vlan 100 DISTRO-SW1(config-if)#glbp 1 ip 192.168.1.254 DISTRO-SW1(config-if)#glbp 1 priority 110 DISTRO-SW1(config-if)#glbp 1 preempt delay minimum 15 //Configures the router to preempt if it has a higher priority than the current active virtual forwarder after a delay of 15 seconds DISTRO-SW2(config)#interface vlan 100 DISTRO-SW2(config-if)#glbp 1 ip 192.168.1.254 DISTRO-SW2(config-if)#glbp 1 preempt Don't forget to save the configs DISTRO-SW1#, DISTRO-SW2#copy running-config startup-config

Explanation

GLBP Lab Explanation

Overall Goal

GLBP (Gateway Load Balancing Protocol) is Cisco's proprietary first-hop redundancy protocol. Unlike HSRP/VRRP which waste standby router bandwidth, GLBP simultaneously load-balances traffic across multiple gateways while providing redundancy. The goal here is to make both distribution switches actively forward traffic for VLAN 100 hosts, with DISTRO-SW1 as the Active Virtual Gateway (AVG) - the router that assigns MAC addresses and coordinates the group.

Note: The question says "group 30" but the answer uses glbp 1. Always use the group number from the actual lab screen - they deliberately vary it. The explanation below uses group 1 as shown in the answer.

Step-by-Step Breakdown

Steps 1 & 5 - interface vlan 100 (on both switches)

Both switches must enter the SVI (Switched Virtual Interface) for VLAN 100. GLBP operates at Layer 3 on an interface, so all GLBP commands are entered here. Skipping this puts commands on the wrong interface, breaking everything silently.

Step 2 - glbp 1 ip 192.168.1.254 (DISTRO-SW1)

This creates GLBP group 1 and sets the virtual IP address - the gateway IP that all VLAN 100 hosts will point to as their default gateway. Both routers share this single IP. The first router to issue this command typically becomes the AVG candidate.

If skipped: Hosts have no virtual gateway to route through; GLBP group never forms.

Step 3 - glbp 1 priority 110 (DISTRO-SW1 only)

The default GLBP priority is 100. Setting DISTRO-SW1 to 110 makes it win the AVG election (higher priority wins). DISTRO-SW2 stays at default 100, so it becomes the AVS (Active Virtual Secondary) - it still forwards traffic but defers to SW1 for group coordination.

If skipped: Both switches have equal priority (100); election outcome is non-deterministic and SW1 may not become AVG.

Step 4 - glbp 1 preempt delay minimum 15 (DISTRO-SW1)

This does two things:

Preempt - enables SW1 to reclaim the AVG role automatically after recovering from a failure (preemption is disabled by default in GLBP).
Delay minimum 15 - waits at least 15 seconds before preempting, giving routing protocols (OSPF, EIGRP) and STP time to reconverge before SW1 takes over, preventing a traffic blackhole.

If preempt is skipped: SW1 recovers but sits as standby forever; SW2 remains AVG indefinitely.
If delay is skipped: SW1 preempts immediately on recovery, potentially before its routing table is populated - packets drop.

Step 6 - glbp 1 ip 192.168.1.254 (DISTRO-SW2)

SW2 joins the same GLBP group with the same virtual IP. This is required for group membership - without it, SW2 is not part of GLBP and provides no redundancy or load balancing.

Step 7 - glbp 1 preempt (DISTRO-SW2)

SW2 needs preemption enabled so it can reclaim the AVG role if SW1 fails permanently and a new higher-priority router appears. Without this, in some failure/recovery scenarios the group gets stuck with an unexpected AVG.

Why no priority or delay on SW2? SW2 should remain subordinate (default priority 100), so no priority command is needed. No delay is specified here either - the exam only requires the minimum 15-second delay on SW1 per the task requirements.

Step 8 - copy running-config startup-config (both)

Saves configuration to NVRAM. Without this, a reboot wipes all GLBP config. This is always the final step in any Cisco lab.

What Breaks If Steps Are Out of Order

Mistake	Consequence
Setting priority before `glbp ip`	Command may be rejected (group doesn't exist yet)
Skipping preempt on SW1	SW1 never reclaims AVG after recovery
Skipping delay on SW1	SW1 preempts before convergence -> traffic drops
Not configuring SW2's virtual IP	SW2 never joins the GLBP group
Not saving	Config lost on reboot

Memory Tip

Think of it as "IP -> Priority -> Preempt" - you always establish the group identity first (virtual IP), then assert dominance (priority), then define recovery behavior (preempt + delay). Same order on both devices, but only the designated primary (SW1) gets priority and the delay.

AVG = the "manager" that assigns virtual MACs to group members. Even the non-AVG router (SW2) actively forwards packets - that's GLBP's advantage over HSRP.

Topics

#GLBP#FHRP#High Availability#Layer 3 Switching

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