BGP Origin Attribute

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In our previous blogs, we have discussed BGP local reference attribute, in this article, we will discuss the BGP originate attribute.

What is BGP Origin Attribute?

The purpose of the origin attribute in BGP is to keep track of the source of a prefix. This attribute can have one of three values: IGP, EGP, or Incomplete.

  • i (IGP) – Originated from an interior gateway protocol (such as EIGRP,RIP etc).This indicates the route was injected into BGP via the network command under the BGP process.
  • e (EGP) – Originated from an external gateway protocol.
  • ? (incomplete) – Unknown origin. This usually indicates the route was redistributed into BGP (from either connected, static, or IGP routes). An origin code of “?” is the least preferred.
  • From amongst the above 3 origin codes, “i”is the most preferred while “?” is the least preferred.

Related- iBGP vs eBGP

Scenario Example

Below is the scenario where 3 Routers R1, R2 and R3 are connected in serial. With each in different Autonomous system no i.e. 1, 2 and 3 respectively.

origin attribute in bgp

In the BGP routing table of R2 , the BGP origin code is listed at the end of each line in the table –

bgp-origin-attribute

The “i” at the end of the first routing entry indicates the 1.1.1.0/24 network was originated via an IGP, via the BGP network command. The 3.3.3.0/24 network was redistributed into BGP in AS 3, since it shows “?” at the end of that routing entry.

What is the significance of BGP Origin Attribute?

Origin Attribute is the crucial factor when BGP is employing algorithm to determine the best path to a destination network. This attribute is important in resolving conflicts between various alternative paths available in the network. This attribute comes under mandatory attribute hence receives significant attention in our updates.

Continue Reading:

BGP Community Attribute

BGP Confederation

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If you want to learn more about Linux, then check our e-book on BGP Interview Questions in easy to understand PDF Format explained with relevant Diagrams (where required) for better ease of understanding.

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