User manual
Chapter 4 - Layer 3 Command Set - IP Networking OSPFv2 (Dynamic Routing Protocol Module)
Alvarion BreezeNET B130/B300 GigE 154 Operational User Manual
1 cisco - a router will be considered as ABR if it has several configured links to
the networks in different areas one of which is a backbone area. Moreover, the
link to the backbone area should be active (working).
2 ibm - identical to cisco model but in this case a backbone area link may not be
active
3 standard - a router has several active links to different areas
4 shortcut - identical to standard but in this model a router is allowed to use a
topology of connected areas without involving a backbone area for inter-area
connections
Details on cisco and ibm models differences can be found in RFC3509. A shortcut
model allows ABR to create routes between areas based on the topology of the
areas connected to this router but not using a backbone area in case if
non-backbone route will be "cheaper"
ABR model is selected using the following command in config-router mode:
abr-type (cisco|ibm|shortcut|standard)
If you want to use "shortcut" routes (non-backbone) for inter-area routes, you can
use the following command in config-router mode:
area (A.B.C.D|<0-4294967295>) shortcut
(default|enable|disable)
Three models define a usage of a specified area for routes shortcutting in shortcut
mode:
Default - this area will be used for shortcutting only if ABR does not have a
link to the backbone area or this link was lost
Enable - the area will be used for shortcutting every time the route that goes
through it is cheaper
Disable - this area is never used by ABR for routes shortcutting
4.7.8.2 Stub areas
Some of the areas may be defined as stub areas. It is used for the area which has
either a single ABR or several ABR but route selection does not depend on
external destination address. The information about external link (to OSPF
system) is not sent to stub areas by ABR. Instead, ABR advertises a default
gateway to the stub area with a route coming through this ABR.