BGP Routing Policies - Configuring BGP Policies

10 important questions on BGP Routing Policies - Configuring BGP Policies

What is the description and BGP PA type of PA Weight? 3

-Cisco Proprietary setting
-Not advertised to peers
-Bigger is better

NO BGP PA type

What is the description and BGP PA type of PA LOCAL_PREF? 3

-Communicated inside a single AS
-Bigger is better
-Range 0 t/m 2 -32

BGP PA type Well-known discretionary

What is the default weight of a route locally injected into BGP?

32.768
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How does the feature Confedetarions the total number ASs in the AS_PATH length calculation?

Do NOT count in calculation

How does the feature aggregate-address the total number ASs in the AS_PATH length calculation? 3

-If component have different AS_PATHs, the summary route has only the local AS in the AS_SEQ
-If component have the same AS_PATHs, the summary route has the same AS_SEQ as the components
-IF AS-set command is set; it counts as one

What is the command to change the origin of a route?

route-map set-origin
match as-path 10
Set origin IGP/incomplete

What are the BGP rules for picking lowest router ID of advertising router? (step 10 of BGP process)

1. Examine only eBGP lowest RID
2. If only iBGP, lowest RID

1. Examine the eBGP routes only, picking the route advertised by the router with the lowest RID
2.If only iBGP routes exist, pick the router advertised by the router with lowest RID.

What does the command bgp bestpath compare-routerid and for what protocol is it used?

The lowest RID is always used.
Only applies for eBGP routes

For an iBGP route, the decision is simply based on the lowest advertising router's RID

What are the rules when a router add multiple eBGP routes to the routing table for a single NLRI?

1. BGP must have had to use a tiebreaker (step 10/11) to determine best route
2. Maximum-paths number must be configured lager than 1 (maximum-path number)
3. Only eBGP routes whose adjacent ASNs are the same ASN as the best route are considered as candidates
4. If more candidates exist than called with maximum-paths, tiebreakers steps 10/11 determine the ones to use

What are the BGP maximum-paths command options

-maximum-paths number    eBGP routes only
-maximum-paths ibgp number    iBGP routes only
-maximum-paths eibgp number    Both type, but mpls only

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