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DES-7200 Configuration Guide Chapter 2 Configuring BGP IP VPN
2-71
Note
This command is only applicable to OSPF instance associated with VRF.
If the domain-tag of VRF is not configured manually, then the default value
is the AS number of local BGP protocol.
In L3VPN, if one VPN site is connected with multiple PEs, then the VPN
route learned by PE through MP-BGP will be advertised to VPN site in
type-5 or type-7 LSA. Such route may also be learned by other PEs
connecting to this VPN site and then advertised, hence causing loop. To
avoid such loop, the same VPN route tag must be configured on PE for
VRF OSPF instances connecting to the same VPN site. When VRF OSPF
instance sends type-4 or type-7 LSAs to the VPN site, this LSA will also
carry the VPN route tag. When other PEs receive such type-5 or type-7
LSA containing the VPN route tag, if such route tag is the same as the
route tag of corresponding OSPF instance, this LSA won't participate in
OSPF computation.
Generally, OSPF instances associated with the same VPN must be
configured with the same VPN route tag.
# Configure the domain-tag of VRF OSPF protocol to 10.
DES-7200# configure terminal
DES-7200(config)# router ospf 10 vrf vrf1
DES-7200(config-router)# domain-tag 10
2.3.5.5 Configure sham-link (optional)
Sham-link is mainly used in the scenario where there is a backdoor link between VPN sites. If
you still expect to transmit VPN data via the MPLS backbone network, then you can establish
sham-link between the VRF OSPF instances of two PEs. Both instances can establish OSPF
neighbor through this sham-link and distribute LSA packets over the sham-link.
Command Function
DES-7200# configure terminal
Enter global configuration mode
DES-7200(config)# router ospf
ospf-id vrf vrf-name
Create OSPF instance and enter OSPF
configuration mode
DES-7200(config-router)# area
area-id sham-link source-address
destination-address
(Optional) Configure the area ID, source address
and destination address of sham-link