
Configuring IP Services
5-20
Best Route Calculation for Equal Routes
The following eight rules (tie breakers) are used to choose between two equal
BGP routes:
1. Choose the route with the lower route weight.
2. Choose the route with the higher Local Preference attribute.
3. Choose the route with the lower Inter-AS Metric attribute (if both routes
include this optional attribute).
4. Choose the route with the lower interior cost to the Next Hop.
5. Choose external BGP over IBGP.
6. Choose the route with the lower BGP identifier.
7. Choose the route with the lower BGP connection remote address.
8. Choose the route with the lower BGP connection local address.
OSPF/BGP Interaction
RFC 1403 defines the interaction between BGP and OSPF when OSPF is the IGP
within an autonomous system. For routers running both protocols, the OSPF
router ID and the BGP identifier must be an IP address and must be identical. A
route policy must be configured in order to allow BGP advertisement of OSPF
routes.
For more information, see “Using the External Route Tag in an ASE” on page 4-
16.
Interaction between BGP-4 and OSPF includes the ability to advertise supernets
to support classless interdomain routing (CIDR). BGP-4 allows interdomain
supernet advertisements. OSPF can carry supernet advertisements within a
routing domain.
Comentários a estes Manuais