route 020 - ospf virtual links
TRANSCRIPT
Instructor: Ali Shariaty
www.alishariaty.ir
www.rayka-co.ir
OSPF
OSPF Virtual Links
In this video
• Virtual Link Concepts
• Virtual Link Configuration (No Authentication)
• Virtual Link Configuration (With Authentication)
OSPF Virtual Links
www.alishariaty.irwww.rayka-co.ir
Ali Shariaty
Virtual Link Concepts
• OSPF area design rules
• However, in some cases:
• Two backbone areas exist.
• A non-backbone area may not have a connection to the backbone area.
• Virtual link allows two ABRs that connect to the same non-backbone area to
form a neighbor relationship through that non-backbone area, even when
separated by many other routers and subnets.
• Acts like a virtual point-to-point connection between the two routers, with
that link inside area 0.
OSPF Virtual Links
www.alishariaty.irwww.rayka-co.ir
Ali Shariaty
Virtual Link Concepts
OSPF Virtual Links
www.alishariaty.irwww.rayka-co.ir
Ali Shariaty
Two backbone areas now exist, and
OSPF requires that the backbone
area be contiguous.
A virtual link between
ABRs C1 and C2 solves
this problem.
The virtual link exists
inside area 0, making
area 0 contiguous.
Virtual Link Concepts
The ABRs connected over a virtual link act mostly like any other ABR , but:
• ABRs send all OSPF messages as unicast to the IP address of the router on
the other end of the link.
• The routers also mark the Do Not Age (DNA) bit in the LSAs, meaning that
all routers on the other side of the virtual link will not expect the LSAs to be
re-flooded over the virtual link on the usual 30-minute refresh interval.
OSPF Virtual Links
www.alishariaty.irwww.rayka-co.ir
Ali Shariaty
Virtual Link Configuration
No Authentication
Router(config-router)# area <area-number> virtual-link <remote-RID>
Router# show ip ospf virtual-link
• The “remote-RID” refers to the other router’s RID.
• The “area-num” refers to the transit area over which the packets flow
between the two routers.
• The transit area must not be a stubby area.
• OSPF does not require that the RID IP address range be advertised as a
route in OSPF. As a result, the RID listed in the area virtual-link command
may not be pingable, but the virtual link still work.
OSPF Virtual Links
www.alishariaty.irwww.rayka-co.ir
Ali Shariaty
Virtual Link Configuration
LAB Scenario
OSPF Virtual Links
www.alishariaty.irwww.rayka-co.ir
Ali Shariaty
OSPF Virtual Links
www.alishariaty.irwww.rayka-co.ir
Ali Shariaty
Virtual Link Configuration
LAB Scenario
OSPF Virtual Links
www.alishariaty.irwww.rayka-co.ir
Ali Shariaty
Virtual Link Configuration
LAB Scenario
Virtual Link Configuration
With Authentication
OSPF Virtual Links
www.alishariaty.irwww.rayka-co.ir
Ali Shariaty
Virtual Link Configuration
With Authentication Example
OSPF Virtual Links
www.alishariaty.irwww.rayka-co.ir
Ali Shariaty
Review
• Virtual Link Concepts
• Virtual Link Configuration (No Authentication)
• Virtual Link Configuration (With Authentication)
OSPF Virtual Links
www.alishariaty.irwww.rayka-co.ir
Ali Shariaty