by Matthew G. Naugle
Wiley Computer Publishing, John Wiley & Sons, Inc.
ISBN: 0471196568 Pub Date: 11/01/98
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Illustrated TCP/IP
by Matthew G. Naugle Wiley Computer Publishing, John Wiley & Sons, Inc. ISBN: 0471196568 Pub Date: 11/01/98 |
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A virtual link is shown in the slide. The backbone must be contiguous. This means that an ABR must connect directly to the backbone and not to another area. Area-to-area communication is not allowed directly, only through the backbone. However, there will be designs that force the creation of an area that will not have direct connectivity to the backbone. This makes the backbone is no longer contiguous. Backbone connectivity is restored through a virtual link.
Virtual links can be configured between any two ABR routers that have an common interface to a nonbackbone area. The virtual link is configured on each ABR and acts like a point-to-point link. Virtual links belong to the backbone. The routing protocol traffic that flows along the virtual link uses intra-area routing only.
As shown in the slide, the two endpoints of the link are ABRs and the link is configured in both routers. The two ABRs used in the virtual link also must belong to a common area, not the backbone area.
Simply stated, a virtual link is like a point-to-point link between two fully adjacent ABRs that allows an area to receive and transmit summary information (learn routes within the AS) when it is not directly connected to the backbone area. That’s simply stated?
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