I passed the “Implementing Cisco IP Switched Network”exam successfully couple of days back.  Now I am one step closer to achieving mp CCNP. My approach was simple and straight forward, I read the Cisco Press title CCNP SWITCH 642-813 Official Certification Guide. Thanks to Cisco Press and Jamie Adams for providing me a copy of CCNP Study guides. The exam was pretty easy but be careful there are few ambiguous questions which really needs your experience and expert knowledge on the topic.

I have following piece of advice for the CCNP aspirers

• 1) Set the date for exam before starting your preparations (Goal Setting).
• 2) Read Cisco Press title CCNP SWITCH 642-813 Official Certification Guide.
• 3) Practice the Boson questions came with the title CCNP SWITCH 642-813 Official Certification Guide.
• 4) Watch CBT nuggets if needed as they are really cool videos to watch.
• 5) Practice labs, (create your own scenarios on STP, HRSP, VTP, VRRP, GLBP etc.) If you can afford get three Cisco 3550 Series Switches from eBay.
• 6) A week before exam review all the topics and practice few labs and boson practice test.

(My CCNP Switch Lab)

If you follow the above with dedication and determination nothing can stop you from achieving CCNP.

In my previous post I was discussing about Gateway Load Balancing Protocol (GLBP), now let’s see how Gateway Load Balancing Protocol (GLBP) does load balancing?  Basically there are three different types of Load balancing algorithms applied

Round Robin:

• This method is the default method used by Gateway Load Balancing Protocol (GLBP).
• In this method the when the client sends ARP requests to resolve the MAC- address of the default gateway , the reply contains the MAC address of the next possible router in round-robin fashion

 Weighted:

•  Gateway Load Balancing Protocol (GLBP) places a weight on each device to calculate the amount of load sharing that will occur through MAC assignment
• The routers participating in GLBP will advertise its weight and AVG will act based on that value
• For example if we have two routers named ITKE-Router A and ITKE-Router B. If the ITKE-Router A has double the bandwidth capacity then the ITKE-Router B. ITKE-Router A will be configured with the double weighting value of ITKE-Router B

Host-Dependent

• Each Client will always get the same Virtual MAC address.

• The Mac-address of the host is used to determine which AVF’s mac the host is directed towards.

• This method is used when the client needs a consistent gateway MAC -address.

• Host dependent GLBP is not recommended in situation where there are small number of hosts, for example, less than 20

In upcoming posts let’s see how to configure Gateway Load Balancing Protocol (GLBP) in Cisco devices.

GLBP better known as Gateway Load Balancing Protocol (GBLP) is a Cisco proprietary protocol especially designed overcome the limitations of Hot Standby Routing Protocol (HSRP) and Virtual Router Redundancy Protocol (VRRP). The added feature to Gateway Load Balancing Protocol (GLBP) is it can load balance between the gateways where as in HSRP and VRRP, the standby routers are configured for redundancy and act as standby only and become active only when the active router fails.

The Gateway Load Balancing Protocol (GLBP) provides load balancing over multiple routers (gateways) using a single virtual IP address and multiple virtual MAC addresses. The forwarding load is shared among all routers in a GLBP group rather than being handled by a single router while the other routers stand idle. Each host is configured with the same virtual IP address, and all routers in the virtual router group participate in forwarding packets. GLBP members communicate between each other through hello messages sent every 3 seconds to the multicast address 224.0.0.102, User Datagram Protocol (UDP) port 3222 (source and destination).

The Gateway Load Balancing Protocol (GLBP) elects one router as active virtual gateway (AVG) based on highest priority value or highest IP address in the group, if there is no highest priority.  The active virtual gateway (AVG) to respond to ARP requests sent to the virtual gateway IP address replying different virtual MAC addresses depends on which load-balancing algorithm is configured.

All routers participating in GLBP group gets the necessary virtual MAC addresses from the active virtual gateway (AVG). Up to four virtual MAC addresses can be used in any group. Each of these routers is referred to as an active virtual forwarder (AVF), forwarding traffic received on its virtual MAC address. Other routers in the group serve as backup or secondary virtual forwarders, in case the AVF fails. The AVG also assigns secondary roles.

The Gateway Load Balancing Protocol (GLBP) is part of CCNP 642-813 Exam curriculum and you must master this protocol as you can expect few questions.

In upcoming posts I will try to highlight on load balancing techniques used and how to configure Gateway Load Balancing Protocol (GLBP) in Cisco Routers and Cisco Catalyst Switches .When it comes to Catalyst Switches GLBP is currently available with Catalyst 6500 Supervisor 2 with IOS Release 12.2(14) SY4 or later and Supervisor 720 with IOS Release 12.2(17a) SX4 switch platforms.