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BGP MED Attribute Configuration example

by ShahedJuly 27, 2011October 22, 20150

BGP MED Attribute Configuration example BGP MED Attribute Configuration example BGP MED is an optional non-transitive attribute meaning its not propagated throughout the whole internet but just to adjacent AS. The word “optional” means that this is not necessarily by default sent with the BGP updates. The purpose of MED is to influence how other autonomous systems enter your AS to reach a certain prefix. If the other attributes are set to default, MED will be the attribute used for path selection however, if Weight or Local preference is configured on the adjacent AS router, then MED will not be …

by ShahedJuly 24, 2011October 22, 20150

Removing Private AS Numbers in BGP Autonomous System (AS) is identified by a number in the range 1 to 65535. AS numbers in the range 1 to 64511 are assigned by InterNIC. These are reserved and globally unique AS numbers. AS numbers in the range 64512 to 65535 are known as private AS numbers, and like private IP addresses, these can be used to address ASs when a globally unique AS number is not necessary. It is important to ensure that the private AS numbers are not introduced into the global BGP table through the AS-Path attribute. To removing private …

by ShahedJuly 23, 2011October 24, 20150

BGP as-override and allowas-in: Today i will discuss basic difference between as-override and allowas-in command & which are configure which router. [boxads] These two functions are pretty similar, just with subtle differences. They can be used in an environment where a customer is using one AS number for many sites that are connected to an ISP. This is shown in the example below. You can see that AS 65001 connects to the ISP at two locations. So when R2 receives the prefix 99.99.99.99/32, he will see that the AS path is via 1, 65001. Because of the loop prevention mechanism, …

by ShahedJuly 20, 2011October 22, 20150

BGP AS path Prepending outbound routes BGP AS path Prepending outbound routes is rich in features that you can have more control than on what IGP’s offer however, you can only have control on how the traffic leaves your autonomous system and can’t really control how other autonomous systems reach you. Other AS’es might have BGP policies that route the traffic in a way you don’t intend it to go. You don’t have control over those because, its their autonomous systems after all. However, there are work arounds which allow, an autonomous system affect the other autonomous systems, one of …

by ShahedJuly 15, 2011October 22, 20150

BGP Local-Preference Attribute Cisco Router BGP Local-Preference Attribute Cisco is another BGP attribute that’s important in the decision process for multiple redundant paths. In fact, if you’re concerned about the order of things, you should know that on Cisco routers, the “weight” attribute is checked first, so that if a given neighbor has a higher weight, the local preference isn’t even checked. However, it’s still quite important because it is an important attribute on all routers, and it affects the BGP routing process in much the same way. [boxads] Local Preference is one of the ways to alter the path …

by ShahedJuly 14, 2011October 22, 20150

Change BGP Weight Attribute Cisco Router by Route Maps Change BGP Weight Attribute Cisco router by Route Maps. Weight attribute is used by BGP to break the tie when there are more routes to the same network. Route with the highest weight is preferred. Weight attribute is a Cisco feature, it has local meaning and it is not transmitted to other routers. [boxads] In this example we will discuss about how to change BGP weight attribute cisco router by Route Maps. In the picture you see that WEST router in AS 65520 receives the routes advertised by EAST router in AS 65523 (172.16.0.0/24 and 192.168.100.0/24) over ISP-1 and ISP-2 routers. …