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BGP Attributes: Local Preference Attribute

The local preference attribute is a well-know discretionary attribute. This means local preference must be recognized by all BGP implementations, but will not exist in all BGP update messages; specifically it will not exist in E-BGP update messages. BGP local preference attribute is one of the most used attributes in BGP real world to influence traffic. Local preference attribute is a four octet field of information that is used to inform internal peers about the autonomous system internal preference for an advertised route.

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BGP Attributes: Atomic Aggregate Atribute

Atomic aggregate is a Well-known Discretionary attribute; it must be recognized by all BGP implementations and does not have to exist in all BGP updates. The purpose of the attribute is to alert BGP speakers along the path that some information have been lost due to the route aggregation process and that the aggregate path might not be the best path to the destination. When some routes are aggregated by an aggregator, the aggregator does attache its Router-ID to the aggregated route into the AGGREGATOR_ID attribute and it sets the ATOMIC_AGGREGATE attribute or not; based on whether the AS_PATH information …

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BGP Attribute Types and Flags

BGP attributes is an interesting subject of study.  BGP is a very flexible and extensible protocol and I like that, let’s see how flexible is that protocol when it comes to attributes handling. We all know that BGP has four types of attributes as listed: Well-known mandatory. Well-known discretionary. Optional transitive. Optional non-transitive. I am not going to explain them in this post, they are explained everywhere over the internet. However, in short well-known attributes must be recognized by all BGP implementations, some of them are mandatory and must be included in all update messages, others are discretionary and may …

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The Role of BGP in MPLS networks

In almost every book you will read about MPLS, the author will state that one of the MPLS benefits is having a BGP free core network; sometimes they explain it sometimes not. However, to really understand this statement I encourage you to imagine removing MPLS from your core network and see what adjustments you need to do in order to get the transit traffic to its destination. Do this  just in your mind’s eye please If you are not willing to do this I will try in this post to bring the picture closer to you.

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BGP Route Refresh Capability

Service Providers or Large enterprises commonly change routing policies from time to time, specially when adding new links or peering relationships with other entities. When you change the inbound policy of your BGP speaker you need to reprocess the updates you received from that peer. BGP4 has no mechanism of requesting a re-advertisements from one of its peers. One solution to this problem is to store the received information local on the router and reprocess them without the need to refer to the peer who sent these updates. This option consumes a lot of resources on the router when you …

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BGP 4-Byte ASN

The internet growth is awesome, day by day people recognizes how  internet is important in their daily personal  and business life and even for their culture, so the internet has a good bit of newbie everyday which depleted some internet resources such as IPv4 address space and the BGP AS numbers (IPv4 exhaustion dilemma is more severe than the BGP ASN dilemma). The BGP AS number space is a finite amount of address space. It is defined as a 16 bit integer and hence limited to 65535 unique AS numbers. Not all can be used!! Out of the AS number …

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