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Removing Private AS Numbers in BGP

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. …

by ShahedJuly 10, 2011October 22, 20150

BGP Weight Attribute Configure BGP Weight Attribute is a Cisco Proprietary attribute that influences a router how to reach a certain prefix. The difference between Local Preference and Weight is that the former is propagated within an AS and the latter is router locally significant. Weight can be used if there is one router connected to two or more AS’s or just to just one with two or more eBGP peers. Now, lets configure weight and later use a route-map for more complex use of weight. [boxads] Weight is a Cisco Proprietary attribute for BGP that is “locally significant.” Local …