BGP on router

If a router run a BGP with neighbors, will it use the BGP Path attributes and Best-Path algoritm to determine the best route to particular network and then put it into routing table ?  Or, does the router only check its BGP routing table only and decide which path to go for a particular network ?

Who is Participating?
JustInCaseConnect With a Mentor Commented:
If question is:
"Can I say that a BGP router can use a BGP route only when it is both in BGP and routing table?"
Yes. BGP is relaying on support from IGP. From Wiki - BGP:
Route selection

The BGP standard specifies a number of decision factors, more than the ones that are used by any other common routing process, for selecting NLRI to go into the Loc-RIB. The first decision point for evaluating NLRI is that its next-hop attribute must be reachable (or resolvable). Another way of saying the next-hop must be reachable is that there must be an active route, already in the main routing table of the router, to the prefix in which the next-hop address is reachable.
Have in mind that BGP is not actually routing protocol, it is application.

And yes.
Route need to be present in both (routing table and BGP table), however, route present in routing table does not always have to be BGP route. For example, if static and directly connected routes are redistributed into BGP, routes will be present in BGP table and will be present in routing table... but routes in routing table will not be BGP routes. The reason why route need to be present in both tables is that BGP is in essence distance vector protocol and distance vector protocols can only "work with" routes that are present in routing table.

General rules for putting in route in routing table are:
- all routes there are not duplicated routes (prefix + subnet mask) will be placed into routing table (if routing protocol consider route valid)
- if there are multiple copies of the same route present - router will compare administrative distance (AD) choose one with the lowest AD
- if there are multiple copies of the same route with the same AD present, router will choose one with the lowest metric
AXISHKAuthor Commented:
Can I say that a BGP router can use a route only when it is both in BGP and routing table ? And BGP will select the route based on the BGP Path Attributes and Best-Path Algorithm ?

Question has a verified solution.

Are you are experiencing a similar issue? Get a personalized answer when you ask a related question.

Have a better answer? Share it in a comment.

All Courses

From novice to tech pro — start learning today.