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BGP Origin Code Attribute explained

The BGP Origin Code is one of the attributes that is used for path selection. There are three origin codes that the BGP table can show:

  • IGP (shows up as i)
  • EGP (shows up as e)
  • Incomplete (shows up as ?)

You will see IGP when you use the network command for BGP. It means you advertised the network yourself in BGP. EGP is historical, and you won’t see it in the BGP table anymore. EGP is an old routing protocol. We don’t use it anymore. Incomplete means you have redistributed something into BGP.

Don’t confuse origin with originate, as explained in the locally originated lesson.

Configuration

Here’s a demonstration:

bgp as path prepend lab
Above, you can see the topology that I will use. R1 and R3 are in AS1 and connected to R2 in AS2. Both routers have a loopback0 interface with network 1.1.1.0/24 configured on it. Let’s configure BGP:

R1(config)#router bgp 1
R1(config-router)#neighbor 192.168.12.2 remote-as 2
R3(config)#router bgp 1
R3(config-router)#neighbor 192.168.23.2 remote-as 2
R2(config)#router bgp 2
R2(config-router)#neighbor 192.168.12.1 remote-as 1
R2(config-router)#neighbor 192.168.23.3 remote-as 1

The next step is to get network 1.1.1.0/24 in the BGP table:

R1(config)#router bgp 1
R1(config-router)#network 1.1.1.0 mask 255.255.255.0
R3(config)#router bgp 1
R3(config-router)#redistribute connected

On R1, I’ll advertise network 1.1.1.0/24 in BGP with the network command. On R3, we’ll redistribute it. Let’s see what R2 thinks of this…

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Forum Replies

  1. Hi Molenaar… Thanks a lot of this tutorial…its very helpful to who are intersted in bgp. I was facing the problem with this originate attribute when i was not read this… Now i am very happy. I never forget this concept. Once again thaks…God Bless You…

  3. Nice. I had doubt about this, now is crystal clear.

  4. Rene,

    It means Jack will reach 1.1.1.0/24 network through Jim because of this output
    *> 192.168.12.1 0 0 1 i
    However, it still learns from John but it will not install in the BGP table because of this
    * 1.1.1.0/24 192.168.23.3 0 0 1 ?
    Question is both Jim and John are advertizing 1.1.1.0/24 but why it is incomplete in Jack’s table from John’s standpoint.
    Please confirm this to me.
    Thanks
    Hamood

  5. Hi Hamood,

    It shows with the ‘?’ as incomplete because this route had been redistributed. If a route is advertised with the network command then it will show up with an ‘i’.

    Rene

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