Command Reference Guide

3Com Router 3000 Ethernet Family
Command Reference Guide
Chapter 2 BGP/MPLS VPN Configuration
Commands
3Com Corporation
2-23
key: Specifies authentication string at the interface, 16 characters at most. It must be
consistent with the authentication string of sham link peer. When the display
current-configuration command is executed, the system displays the 24-character
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 to 8192 seconds. By
default, it is 40 seconds. It must be consistent with the value of dead seconds for sham
link peer.
hello seconds: Specifies interval between Hello message transmissions at the
interface, in range of 1 to 8192 seconds. By default, it is 10 seconds. It must be
consistent with the value of hello seconds for sham link peer.
retransmit seconds: Specifies internal for LSA message retransmission at the
interface, in range of 1 to 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 to 8192 seconds. By default, it is 1 second.
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
belonging 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 inter-area routes, and OSPF
will first select those routes through the backdoor link. Sometimes, users desire to
select the routes first 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.
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, which must be bound to 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.