BGP table route origin codes

[Kashish_Patel]

I am trying to understand bgp table and confused in what cases will a route appear as IGP,EGP or incomplete, basically a route origin code? Also when will a route appear as internal route? Can somebody help me understand this (with maybe an example)?

[Reza Sharifi]

Origin Attribute

The origin is a mandatory attribute that defines the origin of the path information. The origin attribute can assume three values:

• IGP—Network Layer Reachability Information (NLRI) is interior to the AS of origination. This normally happens when you issue the bgp network command . An i in the BGP table indicates IGP.

• EGP—NLRI is learned via exterior gateway protocol (EGP). An e in the BGP table indicates EGP.

• INCOMPLETE—NLRI is unknown or learned via some other means. INCOMPLETE usually occurs when you redistribute routes from other routing protocols into BGP and the origin of the route is incomplete. An ? in the BGP table indicates INCOMPLETE

More info:

http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a00800c95bb.shtml#origin

HTH

[Kashish_Patel]

Hi Reza,

I have read that, I was expecting an answer with some examples explaining in which scenario a particular origin code will be seen. Thanks for replying though!

Thanks.

[Bilal Nawaz]

Hello Kashish,

Here is a very basic explanation and example of this in case studies:

http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a00800c95bb.shtml#origin

and first section here:

http://www.informit.com/library/content.aspx?b=CCIE_Practical_Studies_II&seqNum=103

Hope this helps

Please rate useful posts and remember to mark any solved questions as answered. Thank you.

[Kashish_Patel]

I am still confused.

In my router, I see two routes in bgp table, one marked as i, other as ?

*> 10.147.41.2/32   10.219.65.210                          0 65000 64999 65156 i

*> 10.224.0.24/32   10.219.65.210                          0 65000 64999 ?

On the router, I don't see second route learnt in BGP via redistribution. Why is ? appearing in origin code then?

[cpembleton · Accepted solution]

*> 10.147.41.2/32   10.219.65.210                          0 65000 64999 65156 i

The router in AS 65156 learned this route via iBGP from another router in AS 65156.  iBGP being 2 routers in the same AS.   

*> 10.224.0.24/32   10.219.65.210                          0 65000 64999 ?

The router in AS 64999 learned the route via redistribution.  That router is runing and IGP like EIGRP/RIP/OSPF.  Your router is learning via eBGP. 

HTH

Chad

[Kashish_Patel]

Thanks Chad..That explains it..

[ankitnaik2992]

Hi Reza, from the ISP prespective, is it possible for ebgp ISP router to filter routes using regular expression to drop routes learnt via ibgp (our Ibgp network ). If yes, if i change origin type to ebgp, will it cause any routing conflicts ?