Qtech QSW-3900-24-SFP-AC [100/245] Abr route summarization

QTECH Software Configuration Manual

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Like stub areas, virtual links cannot transit NSSA areas.

\ NSSA area

8.1.2.6 Route summarization

Route summarization : An ABR or ASBR summarizes routes with the same prefix with a single route and

distribute it to other areas.

Via route summarization, routing information across areas and the size of routing tables on routers will be

reduced, improving calculation speed of routers.

For example, as shown in the following figure, in Area 1 are three internal routes 19.1.1.0/24, 19.1.2.0/24,

and 19.1.3.0/24. By configuring route summarization on Router A, the three routes are summarized with the route

19.1.0.0/16 that is advertised into Area 0.

Route summarization

OSPF has two types of route summarization :

1) ABR route summarization

To distribute routing information to other areas, an ABR generates Type-3 LSAs on a per network segment

basis for an attached non-backbone area. If contiguous network segments are available in the area, you can

summarize them with a single network segment. The ABR in the area distributes only the summary LSA to reduce the

scale of LSDBs on routers in other areas.

2) ASBR route summarization

If summarization for redistributed routes is configured on an ASBR, it will summarize redistributed Type-5

LSAs that fall into the specified address range. If in an NSSA area, it also summarizes Type-7 LSAs that fall into the

specified address range.

If this feature is configured on an ABR, the ABR will summarize Type-5 LSAs translated from Type-7

LSAs.

8.1.2.7 Route types

OSPF prioritize routes into four levels :

· Intra-area route

· Inter-area route

· Type-1 external route

· Type-2 external route