BGP: Difference between revisions
→BGP Route selection criteriawww.accenture.com
Line 81:
Routing Table List of Best Routes
=
Mnemonics: [[Mnemonics|N-WLLA-OMNI]]
Line 87:
*It uses the BGP Best Path Selection Algorithm to do this.
*Routes installed by different BGP instances are compared by the general algorithm, i.e. route distances are compared and the route with lower distance is preferred.
Well known BGP attribute types:
Well-known mandatory: Attributes of this type must be understood by all BGP implementations and must EXIST in the BGP update messages.
Well-known discretionary: Attributes of this type must be understood by all BGP implementations but they don’t have to exist in all BGP updates to all neighbors.
Optional BGP attribute types:
Optional transitive: optional BGP attributes as the name implies don’t need to be understood by all BGP implementations, but since the transitive flag is set they will be passed to other neighbors.
Optional non-transitive: Attributes of this type are also optional as the name implies and will not be passed to other neighbors.
<center>
Line 93 ⟶ 102:
! Attribute !! Which is better
|-
|Next Hop reachable || Route cannot be used if next hop is unreachable || Well-known Mandatory
|-
|Weight || Bigger
|-
|Local Preference || Bigger || Well-known discretionary
|-
|Locally Injected || Locally injected is better than iBGP/eBGP learned
|-
|AS Path Length || Smaller || Well-known mandatory
|-
|Origin || Prefer IGP(network cmd) > EGP > ?(reditributed) || Well-known Mandatory
|-
|MED(Metric) || Smaller || Optional non-transitive
|-
|Neighbor Type || Prefer eBGP over iBGP
| |||