Ospf Network Types - H3C S7500 Series Operation Manual

Operation Manual – Routing Protocol
H3C S7500 Series Ethernet Switches
aggregated into one route 19.1.0.0/16, and only one corresponding LSA, which
describes the route after summary, is generated on RTA.
ABR
Figure 4-1 Area partition and route aggregation

4.1.4 OSPF Network Types

I. Four OSPF network types
OSPF divides networks into four types by link layer protocols:
Broadcast: If Ethernet or FDDI is adopted, OSPF defaults the network type to
broadcast. In a broadcast network, protocol packets are sent in multicast
(224.0.0.5 and 224.0.0.6) by default.
Non-broadcast multi-access (NBMA): If Frame Relay, ATM, or X.25 is adopted,
OSPF defaults the network type to NBMA. In an NBMA network, protocol
packets are sent in unicast.
Point-to-multipoint (P2MP): OSPF will not default the network type of any link
layer protocol to P2MP. A P2MP network must be compulsorily changed from
another network type. The common practice is to change an NBMA network into
a P2MP network. In a P2MP network, protocol packets are sent in multicast
(224.0.0.5).
Point-to-point (P2P): If PPP or HDLC is adopted, OSPF defaults the network
type to P2P. In a P2P network, protocol packets are sent in multicast (224.0.0.5).
II. Principles for configuring an NBMA network
An NBMA network is a non-broadcast and multi-accessible network. ATM and frame
relay networks are typical NBMA networks.
Some special configurations need to be done on an NBMA network. In an NBMA
network, an OSPF router cannot discover an adjacent router by broadcasting Hello
packets. Therefore, you must manually specify an IP address for the adjacent router
and specify whether the adjacent router can vote for a DR.
An NBMA network must be fully connected. That is, any two routers in the network
must be directly reachable to each other through a virtual circuit. If two routers in the
network are not directly reachable to each other, you must configure the
corresponding interface type to P2MP. If a router in the network has only one peer,
you can change the corresponding interface type to P2P.
The differences between NBMA and P2MP are as follows:
Router A
19.1.0.0/16
Area 0
ABR
19.1.1.0/24
19.1.2.0/24
Router B
19.1.3.0/24
......
Area 1
4-4
Chapter 4 OSPF Configuration