3com 8807 참조 가이드

key: Authentication on the interface. keyid is from 1 to 255 and key is a string up 
to 16 characters. It must be consistent with the authentication of a Sham-link 
peer. When the display current-configuration command is executed, the 
system displays the 24-character MD5 authentication in cipher text. You can also 
input a 24-character authentication in cipher text.

dead seconds: Specifies the interval, in seconds, for the dead timer. This value 
ranges from 1 to 8192 and defaults 40. It must be consistent with the value of 
dead seconds for a Sham-link peer router.

hello seconds: Specifies the interval, in seconds, between Hello message 
transmission through the interface. This value ranges from 1 to 8192 and defaults 
to 10. It must be consistent with the value of hello seconds for a Sham-link peer 
router.

retransmit seconds: Specifies the internal, in seconds, for LSA packet 
retransmission through the interface. This value ranges from 1 to 8192 and 
defaults to 5.

trans-delay seconds: Specifies the delay period, in seconds, for LSA packet 
transmission through the interface. This value ranges from 1 to 8192 and defaults 
to 1.

Use the sham-link command to configure a Sham-link.

Use the undo sham-link command to 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. They are connected to different PE routers and 
there is an intra-domain OSPF link (Backdoor) between them. Though there may 
be other routes connecting the two sites via PE routers, these routes are 
intra-domain routes, and OSPF will first select those routes through the Backdoor 
link. Sometimes, users desire to first select the routes through VPN Backbone. 
Hence it is required to establish Sham-links between PE routers. In this case, the 
routes through VPN Backbone are of the highest priority within the OSPF area.

If a Backdoor link (an OSPF link that does not pass the MPLS backbone) exists 
between two PE routers and you want the data to be transported over the MPLS 
backbone, you need to configure a Sham-link between the two PE routers. The 
sham link between VPN PE routers is taken as a link within the OSPF area. When 
configuring the Sham-link command, the optional parameters are not mutually 
exclusive. You can only choose in the undo command those parameters which are 
selected in the corresponding sham-link command.

c 

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The source and destination addresses of a sham link are both Loopback 
interface addresses with a 32-bit mask, which must be bound to a VPN 
instance and imported into BGP through a direct-connect route.

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In an OSPF processes of VPN, the Loopback interface routes used by the 
Sham-link cannot be imported directly (so the import direct command cannot 
be used in the OSPF processes of VPN). OSPF can only advertise the route by 
importing a BGP route.