3Com 3031 Command Reference Manual page 801

MD5 authentication string in cipher text. You can also input 24-character
authentication string in cipher text.
dead seconds: Specifies interval for the dead timer, in range of 1~8192 seconds.
By default, it is 40 seconds. It must be consistent with the dead seconds value for
sham link peer.
hello seconds: Specifies interval between Hello message transmission at the
interface, in range of 1~8192 seconds. By default, it is 10 seconds. It must be
consistent with the hello seconds value for sham link peer.
retransmit seconds: Specifies internal for LSA message retransmission at the
interface, in range of 1~8192 seconds. By default, it is 5 seconds.
trans-delay seconds: Specifies delay period for LSA message transmission at the
interface, in range of 1~8192 seconds. By default, it is 1 second.
Description
Using the sham-link command, you can configure a sham link. Using the undo
sham-link command, you can delete a sham link.
In the OSPF PE-CE connection, suppose that in an OSPF area there are two sites
which belong to the same VPN, with each connected to different PE router and an
intra-domain link (backdoor) established between them. Though there may be
other routes connecting the two sites via the PE router, these routes are just
intra-domain routes, so OSPF will select those routes through the backdoor first.
Sometimes, the routes through VPN backbone are desired to be selected first, then
it is required to establish sham link between PE routers. In this case, the routes
through VPN backbone are of the highest priority within the OSPF area.
The sham link between VPN PE routers is taken as a link within the OSPF area. Its
source and destination addresses are both loopback interface addresses with
32-bit mask. This loopback interface must be bound with a VPN instance and
imported into BGP through a direct-connect route. The optional parameters can
be appended in the sham link command and only those appended in the sham
link command can be selected in the undo command.
CAUTION:
The source and destination addresses of a sham link are both loopback
interface addresses with 32-bit mask. This loopback interface must be bound
with a VPN instance and imported into BGP through a direct-connect route.
The source and destination addresses of a sham link cannot be the same.
The same sham link cannot be configured in the different OSPF procedures.
A maximum of 50 sham link can be configured in an OSPF procedure.
Example
Configure a sham link, with source address 1.1.1.1 and destination address
2.2.2.2.
[3Com-ospf-100-area-0.0.0.1] sham-link 1.1.1.1 2.2.2.2 cost 100
BGP/MPLS VPN Configuration Commands 801