Internet access is becoming more and more critical for handling everyday business. To ensure Internet redundancy and optimum performance, organizations may want to consider implementing BGP multihoming to different ISPs. Configuring a redundant link to the Internet has given my company improved service and has reduced outages and related costs. This strategy also offers network administrators peace of mind as a bonus.

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In the last article , we discussed and configured one of the technologies that can be used to reduce the requirement of fully meshed IBGP peers within an AS. In this article, we will be discussing the second method which is by making use of Confederations.

Two articles ago, we described how Confederations work: an AS is broken down into smaller member ASs. There are a couple of terms we need to be familiar with when configuring confederations. The second terminology is the Member AS which represents an AS that is contained within the confederation. To avoid clashing with real AS numbers assigned on the Internet, member AS numbers are usually taken from the private use AS numbers, between and The configuration of confederations is fairly similar to how we configure normal BGP sessions.

We will also use the bgp confederation peers command to specify the member ASs that are part of the confederation. R2 and R4. The configuration on the routers R2 and R4 are similar because they both have the confederation ID and the confederation peers are configured as follows:.

Also, the configuration of the internal peers in the member ASs i. R1, R3 and R5 are also similar. The only thing they have configured is the confederation ID. However, notice that the neighbor configuration for R2 on R6 specifies the remote-as 1 and not Likewise, the neighbor configuration for R4 on R7 specifies the remote-a 1 and not This is because member ASs are not visible outside the local confederation; they are represented as a single entity by the confederation ID.

We will now see how these segment types are used when routing information is exchanged. This is like in normal IBGP advertisement. Therefore, when R2 advertises the 6. Therefore, when R2 advertises the 1. The packet capture for the 1.

Since member ASs should only be visible within a confederation, route advertisements to external peers must be stripped of any member ASs numbers. Therefore, when R2 advertises the 5. What happens with locally-originated route advertisement is fairly easy to infer. For example, when R2 advertises its locally-originated 2. For example, when R2 is advertising the 2. For example, look at prefix 6. One of the issues with using Confederations is that it is quite intrusive because we will need to reconfigure all the BGP speakers within an AS to use Confederations.

Also, all the BGP speakers within a Confederation must support the Confederation feature unlike in the case of route reflectors. InfoSec institute respects your privacy and will never use your personal information for anything other than to notify you of your requested course pricing. We will never sell your information to third parties. You will not be spammed. Author Adeolu Owokade. Adeolu Owokade is a technology lover who has always been intrigued by Security.

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How to use BGP to achieve Internet redundancy

However, this attribute can vary depending on the type of BGP session that has been formed between the BGP peers and whether the destination network is within the AS or outside it. We will now consider these different case studies. We will look at two different scenarios to explain this. The first scenario is a destination 1. The second scenario we will consider under this section is where the destination network is not directly connected to the advertising BGP speaker as shown in the network diagram below:. The configuration changes on R2 are as follows:.


On-line BGP Resources and Information

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