Avaya Configuring IP Exterior Gateway Protocols (BGP and EGP) Uživatelský manuál stáhnout pdf (Strana 267)

Converting Cisco to Nortel Networks Equivalents

308628-15.0 Rev 00

B-11

Comparing BGP Route Selection Processes

Table B-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 B-3. Route Selection Process Comparison

Cisco BGP Path Selection

Nortel Networks BGP Best-Route

Calculation for Equal Routes

1. If the path specifies an inaccessible next

hop, 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 originated by BGP

running on the router.

5. If no route was originated, prefer the

route with 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 lower route

weight.

2. Choose the route with the higher local

preference attribute. (If the BGP global

parameter local-pref-calculation is

disabled (nondefault), the LP of routes is

set to 100 unless a policy overrides this

value.)

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

multiexit 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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