3Com MSR 50 Series, Configuration Manual

Page: 937 / 2443

OSPF Configuration Task List 937
Configuring area IDs on PEs can differentiate VPNs. Sites in the same VPN are
considered as directly connected. PE routers then exchange OSPF routing
information like on a dedicated line, thus network management and OSPF
operation efficiency are improved.
n
For configuration of this feature, refer to “BGP Configuration” on page 825 and
“MPLS Basics Configuration” on page 1311 .
OSPF sham link
An OSPF sham link is a point-to-point link between two PE routers on the MPLS
VPN backbone.
In general, BGP peers exchange routing information on the MPLS VPN backbone
using the BGP extended community attribute. OSPF running on a PE at the other
end utilizes this information to originate a type3 summary LSA as an inter-area
route between the PE and CE.
If a router connects to a PE router in the same area and establishes an internal
route (backdoor route) for a special destination, in this case, since an OSPF
intra-area route has a higher priority than a backbone route, VPN traffic will
always travel on the backdoor route rather than the backbone route. To avoid this,
an unnumbered sham link can be configured between PE routers, connecting the
router to another PE router via an intra-area route with low cost.
n
For sham link configuration, refer to “BGP Configuration” on page 825 and “MPLS
Basics Configuration” on page 1311 .
Related RFCs
■
RFC 1765:OSPF Database Overflow
■
RFC 2328: OSPF Version 2
■
RFC 3101: OSPF Not-So-Stubby Area (NSSA) Option
■
RFC 3137: OSPF Stub Router Advertisement
■
RFC 3630: Traffic Engineering Extensions to OSPF Version 2
OSPF Configuration
Task List
Complete the following tasks to configure OSPF:
Task Description
“Configuring OSPF Basic Functions” on page 939 Required
“Configuring OSPF Area Parameters” on page 940 Optional
“Configuring OSPF Network
Types” on page 941 “Configuring the OSPF
Network Type for an
Interface” on page 941 Optional
“Configuring an NBMA
Neighbor” on page 942 Optional
“Configuring a Router Priority
for an OSPF Interface” on
page 942 Optional