What is an Autonomous System Number (ASN)?

What is an ASN? An autonomous system number (ASN) is a unique number, assigned by IANA that is available globally to identify an autonomous system and which enables that system to exchange exterior routing information with other neighboring autonomous systems. [1] Figure 1 : BGP/ASN Example ASN Types There are…

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A Look into BGP's LOCAL_PREF Attribute

What is the Local Preference? Local Preference (aka LOCAL_PREF) is a BGP well-known attribute that is used when there are multiple exit paths out from a single AS exist. Whereas the MED is used to tell routers outside of an AS which entrance path to take, the LOCAL_PREF…

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A Look into the BGP MED Attribute

What is the MED? The MED (Multi-Exit Discriminator) is an optional BGP attribute, that is used when there are multiple external points for a single AS. For example, you may want traffic coming into your AS destined for network A to take one path but traffic destined for network B…

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Cisco IOS - A Look into BGP Peer Groups

What is a BGP Peer Group? BGP peer groups are used to simplify configuration and to improve performance. This is achieved by assigning the same outbound policy to each of the neighbours. Because UPDATEs are generated only once per peer group rather multiple times for each neighbouring router, peer groups…

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What is a BGP Path Attribute?

A path attribute is an additional piece of information associated with a prefix, that is included within the UPDATE packet during the exchanging of routes. BGP provides various different path attributes. These path attributes are then used by BGP to pick the best path (also known as the path selection…

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