3Com Switch 8807, Command Reference Manual

Page: 757 / 1099

LDP Configuration Commands 755
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.
Description
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
CAUTION:
■
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.
■
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.