BGP: Difference between revisions
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Routing Table List of Best Routes |
Routing Table List of Best Routes |
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= Attributes<ref>www.accenture.com</ref>= |
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Mnemonics: [[Mnemonics|N-WLLA-OMNI]] |
Mnemonics: [[Mnemonics|N-WLLA-OMNI]] |
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*It uses the BGP Best Path Selection Algorithm to do this. |
*It uses the BGP Best Path Selection Algorithm to do this. |
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*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. |
*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. |
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Well known BGP attribute types: |
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Well-known mandatory: Attributes of this type must be understood by all BGP implementations and must EXIST in the BGP update messages. |
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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. |
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Optional BGP attribute types: |
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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. |
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Optional non-transitive: Attributes of this type are also optional as the name implies and will not be passed to other neighbors. |
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<center> |
<center> |
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! Attribute !! Which is better |
! Attribute !! Which is better |
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|Next Hop reachable || Route cannot be used if next hop is unreachable |
|Next Hop reachable || Route cannot be used if next hop is unreachable || Well-known Mandatory |
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|Weight || Bigger |
|Weight || Bigger |
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|Local Preference || Bigger |
|Local Preference || Bigger || Well-known discretionary |
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|Locally Injected || Locally injected is better than iBGP/eBGP learned |
|Locally Injected || Locally injected is better than iBGP/eBGP learned |
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|AS Path Length || Smaller |
|AS Path Length || Smaller || Well-known mandatory |
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|Origin || Prefer IGP(network cmd) > EGP > ?(reditributed) |
|Origin || Prefer IGP(network cmd) > EGP > ?(reditributed) || Well-known Mandatory |
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|MED(Metric) || Smaller |
|MED(Metric) || Smaller || Optional non-transitive |
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|Neighbor Type || Prefer eBGP over iBGP |
|Neighbor Type || Prefer eBGP over iBGP |
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