CASE STUDY : Uninterrupted Connectivity With High Redundancy

DQC Bureau
New Update

The Internet has become one of the primary needs of the present generation.

And a Chennai-based financial company realized this all the more since all its

transactions were done online across its three offices in the city. What made

connectivity an issue for it was that three different ISPs were servicing the

three offices and uptime needed to be maintained at all costs.


Into the picture came a solution providing company from the same city-Fourth

Dimension Technologies (FourD). “The company was just sharing their requirements

with us on the need to have uninterrupted connec­tivity with high uptime. We

suggested a good solution for their requirements, which would have provided them

an uninter­rupted connectivity with high redundancy and clinched the deal,” said

N Jagannathan, CEO, Fourth Dimension Technologies.

And the project begins

The project started as a cut and dried one. FourD studied the client's

infrastructure and devised a meticulous plan to offer interconnectivity and

bandwidth management with least down­time. Then it connected all the three

locations using the metro Ethernet links. A metro Ethernet is a computer

network-based on the Ethernet standard, which covers a metropolitan area.

After that, FourD took care of high Internet availability which was provided

by using BGP Protocol across three locations within Chennai and each having

connectivity from different ISPs. The BGP Protocol or Border Gateway Protocol is

an inter-autonomous system routing protocol.


An autonomous system is a network or group of networks under a common

administration with common routing policies. BGP is used to exchange routing

information for the Internet and is the protocol used between Internet service

providers (ISP).

Customer networks, such as universities and corporations, usually employ an

Interior Gateway Protocol (IGP) such as RIP or OSPF for the exchange of routing

information within their networks. Customers connect to ISPs, and ISPs use BGP

to exchange customer and ISP routes. When BGP is used between autonomous systems

(AS), the protocol is referred to as External BGP (EBGP).

If a service provider is using BGP to exchange routes within an AS, then the

protocol is referred to as Interior BGP. The FourD mainly used this protocol to

bring in more redundancy between the links. Using this solution, the company

made sure that there is no downtime even if there was any failure in Internet

connectivity in any of the locations, as the location would seamlessly use the

available link at the other locations.


“All the three locations were interconnected by metro Ethernet links which is

used to carry the Internet traffic across locations. Each of the locations will

use their own ISP link for all Internet applications including VPNs. Our

solution ensures that, in case of any link failure, the respective location will

seamlessly use the available link at the other location,” Jagannathan informed.

Router redundancy

The deployment was based completely on the Cisco platform. Besides using BGP,

the company also used HSRP, which was used for bringing in redundancy between

the routers.

Hot Standby Router Protocol (HSRP) is a Cisco proprietary redundancy protocol

for establishing a fault-tolerant default gateway. The protocol establishes a

framework between network routers in order to achieve default gateway failover

if the primary gateway should become inaccessible, in close association with a

rapid-converging routing protocol like EIGRP or OSPF.


By multicasting packets, HSRP sends its hello messages to the multicast

address (all routers) using UDP port 1985, to other HSRP-enabled

routers, defining priority between the routers. The primary router with the

highest configured priority will act as a virtual router with a pre-defined

gateway IP and will respond to the ARP request from machines connected to the

LAN with the mac address 0000.0c07.acXX where XX is the group ID. If the primary

router fails, the router with the next-highest priority would take over the

gateway IP and answer ARP requests with the same mac address, thus achieving

transparent default gateway fail-over.

FourD used three engineers for the whole project and was executed in 45 days.

The project was worth Rs 75 lakh. “The internal audit conducted by the company

was so impressive and they have reported a good growth in terms of

productivity,” Jagannathan asserted.

NR Sethuraman