Avaya Configuring IP Exterior Gateway Protocols (BGP and EGP) Manual de usuario descargar pdf (Pagina 299)

Translating Cisco to Nortel Networks Equivalents

308628-14.00 Rev 00

C-11

Comparing BGP Route Selection Processes

Table C-3 compares the Cisco and Nortel Networks path or "best route" selection

processes. In this table, the most preferable criteria are higher in the table.

Table C-3. Route Selection Process Comparison

Cisco BGP Path Selection

Nortel Networks BGP Best Route

Calculation for Equal Routes

1. If the path specifies a next hop that is

inaccessible, drop the update.

2. Prefer the path with the largest weight

3. If the weights are the same, prefer the

path with the largest local preference.

4. If the local preferences are the same,

prefer the path that was originated by

BGP running on this router.

5. If no route was originated, prefer the

route that has the shortest AS_path.

6. If all paths have the same AS_path

length, prefer the path with the lowest

origin type (where IGP is lower than

EGP, and EGP is lower than

Incomplete).

7. If the origin codes are the same, prefer

the path with the lowest MED attribute.

8. If the paths have the same MED, prefer

the external path over the internal path.

9. If the paths are still the same, prefer the

path through the closest IGP neighbor.

10. Prefer the path with the lowest IP

address, as specified by the BGP router

ID.

1. Choose the route with the higher BGP-4

route preference.

2. Choose the route with the higher Local

Preference attribute (if the BGP Global

parameter "local-pref-calculation" is

DISABLED (non-default), the LP of

routes will be set to 100 unless a policy

overrides this).

3. Choose the route with the shortest AS

path.

4. Choose the route with the smallest

ORIGIN (IGP < EGP < INCOMPLETE)

5. Choose the route with the lower

Multi-Exit-Discriminator attribute (routes

without a MED are assumed to have a

max MED).

6. Choose the route with the lower interior

cost to the Next Hop.

7. Choose external BGP over IBGP.

8. Choose the route with the lower BGP

identifier.

9. Choose the route with the lower BGP

connection remote address.

10. Choose the route with the lower BGP

connection local address.

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