Operation Manual – IPv4 Routing
H3C S3610&S5510 Series Ethernet Switches
Chapter 3 OSPF Configuration
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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.
VII. Route types
OSPF prioritize routes into four levels:
z
Intra-area route
z
Inter-area route
z
Type-1 external route
z
Type-2 external route
The intra-area and inter-area routes describe the network topology of the AS, while
external routes describe routes to destinations outside the AS.
OSPF classifies external routes into two types: Type-1 and Type-2. A Type-1 external
route is an IGP route, such as a RIP or static route, which has high credibility and
whose cost is comparable with the cost of an OSPF internal route. The cost from a
router to the destination of the Type-1 external route= the cost from the router to the
corresponding ASBR+ the cost from the ASBR to the destination of the external route.
A Type-2 external route is an EGP route, which has low credibility, so OSPF considers
the cost from the ASBR to the destination of the Type-2 external route is much bigger
than the cost from the ASBR to an OSPF internal router. Therefore, the cost from the
internal router to the destination of the Type-2 external route= the cost from the ASBR
to the destination of the Type-2 external route. If two routes to the same destination
have the same cost, then take the cost from the router to the ASBR into consideration.
3.1.3 Classification of OSPF Networks
I. OSPF network types
OSPF classifies networks into four types upon the link layer protocol:
z
Broadcast: When the link layer protocol is Ethernet or FDDI, OSPF considers the
network type broadcast by default. On Broadcast networks, packets are sent to
multicast addresses (such as 224.0.0.5 and 224.0.0.6).
z
NBMA (Non-Broadcast Multi-Access): When the link layer protocol is Frame Relay,
ATM or X.25, OSPF considers the network type as NBMA by default. Packets on
these networks are sent to unicast addresses.
