BGP Path Attributes: Origin

bgp-path-attribute-origin-ipcisco

BGP Path Attributes – Origin

The Origin attribute informs the Autonomous Systems (AS) about the originator of that route. It is a Well-Known Mandatory BGP Path attribute. It is supported in all BGP implementations and in all update packets it must exist.

There are three different Origin type. These are :


• i (IGP)
• e (EGP)
• ? (Incomplete)

i (IGP) routes are the routes which are originated from a routing protocol, like RIP, OSPF, EIGRP etc. Generally this is done via network command under the BGP process.

e (EGP) routers are the routes which are originated from External Gateway Protocol (EGP). Now the only EGP is BGP, so this is the routes originatd from BGP.

? (Incomplete) routes are the routes which are Redistributed from static, IGP etc. into the BGP.

You can see any BGP route’s origin with “show ip bgp” command. At the end of the output table, the origin code ( i, e or ?) is shown.

Let’s check the bgp routes of the below topology.

bgp path attribute, origin
 

BGP Path Attribute, Origin
In the output of “show ip bgp” command, you can see the origin code values of the routes. As you can see, in the bgp route table above, there are two routes and two of these routes are i (IGP) routes.
Lesson tags: BGP, origin, path attributes, routing
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