Cisco Aironet 1400 Series Specification Sheet - Page 13
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OSPF Sham-Link Support for MPLS VPN
area sham-link cost
To configure a sham-link interface on a provider edge (PE) router in a Multiprotocol Label Switching
(MPLS) Virtual Private Network (VPN) backbone, use the area sham-link cost command in global
configuration mode. To remove the sham-link, use the no form of this command.
Syntax Description
area-id
source-address
destination-address
number
Defaults
No default behavior or values.
Command Modes
Global configuration
Command History
Release
12.2(8)T
Usage Guidelines
In the MPLS VPN environment, several VPN client sites can be connected in the same OSPF area. If
these sites are connected over a backdoor link in addition to the VPN backbone, all traffic passes over
the backdoor link instead of over the VPN backbone. OSPF always selects intra-area routes over
interarea (external) routes.
To correct this default OSPF behavior in an MPLS VPN, use the area sham-link cost command to
configure a sham-link between two PEs to connect the sites through the MPLS VPN backbone. A
sham-link represents an intra-area (unnumbered point-to-point) connection between PEs. All other
routers in the area see the sham-link and use it to calculate intra-area shortest path first (SPF) routes to
the remote site.
Configure the source and destination addresses of the sham-link as a host route mask (255.255.255.255)
on the PE routers that serve as the endpoints of the sham-link. The source and destination IP addresses
must belong to the VRF and be advertised by Border Gateway Protocol (BGP) to remote PE routers. The
sham-link endpoint addresses should not be advertised by OSPF.
area area-id sham-link source-address destination-address cost number
no area area-id sham-link source-address destination-address cost number
ID number of the Open Shortest Path First (OSPF) area assigned to the
sham-link. Valid values: numeric value or valid IP address. There is no
default.
IP address of the source PE router in the format: ip-address [mask].
IP address of the destination PE route in the format: ip-address [mask].
OSPF cost to send IP packets over the sham-link interface.
Valid values are from 1 to 65535.
Modification
This command was introduced.
area sham-link cost
Cisco IOS Release 12.2(8)T
13