BGP: CONCEPT: WHAT IS MULTIHOMING ?


” TOPICS “

WHERE BGP IS REQUIRED?

WHAT IS  MULTIHOMING?

WHERE BGP IS REQUIRED?

BGP is Exterior Gateway Protocol. As name suggests, Its most common scenarios is while connecting a network to some other new network or outside network or unknown network

 

Example, where BGP is required ? 

Case 1: We have a Datacentre and we want to get connected to the Internet. To get the Internet connection or to learn routes from a new or different network, we have to get connected to some ISP(Internet Service Provider). So,while connecting our network with the ISP network, BGP comes into the picture

Case 2: Data center and Remote sites wants to have communication or simply get connected to each other. Then, ISP is required in between, which is a new network. So, BGP comes into picture 

 

BGP Multihoming

WHAT IS MULTIHOMING?

As discussed so far, connecting one network some other new or unknown network(we don’t have administrative control over this), BGP is required

 

Next Question is …

 How BGP is running or in which kind of scenario or how many routers are connected to ISP through how many links, all comes under Multihoming scenarios

As in above figure, Datacentre is connecting to two routers in ISP through two links

 

So, let’s discuss, Multihoming Cases

1. Single Homed

2. Dual Homed

3. Single Multihomed

4. Dual Multihomed

 

In BGP, whole network is divided into number of AS(Autonomous System)

Here details for above terminology,

Single represents single link

Dual represents more than one link

Homed means single AS

Multihomed means more than one AS

 

So, let’s make out the combinations ….

Single Homed Cases:

Means we have one AS and single connection from Datacentre to the ISP

 

Dual Homed Cases:

Means we have single AS in ISP and more than one connection from Datacentre to the ISP

 

Single Multihomed Cases:

Means we have more than one AS at ISP and single connection from Datacentre to the ISP

 

Dual Multihomed Cases:

Means we have more than one AS at ISP and more than one connection from Datacentre to ISP

 

Now, You are ready to put your hands into the configuration part in different Multihoming scenarios

In below link, you will get diagrams of different Multihoming scenarios along with BGP configuration required

Reference Link:

http://www.cisco.com/c/en/us/support/docs/ip/border-gateway-protocol-bgp/13762-40.html#conf1

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