云南龙网

  1. 首页 > 云知道 > >

RFC1586 - Guidelines for Running OSPF Over Frame Relay Networks( 二 )

云知道


require any changes to the OSPF protocol.
2. Summary of Recommendations
We propose expanding the general view of an OSPF interface to account
for its functional type (point-to-point, broadcast, NBMA) rather than
its physical type. In most instances, the physical network can only
serve one function and can only be defined as one type of OSPF
interface. For multiplexed interfaces such as FR however, logical
connections between routers can serve different functions. Hence one
VC on a FR interface can be viewed distintly from other VCs on the
same physical interface. The solution requires that OSPF be able to
support logical interfaces (networks) as well as physical interfaces.
Each logical network can be either point-to-point, that is, a single
VC, or NBMA, that is, a collection of VCs. It is not necessary to
define new interface types for logical networks, since the operation
of the protocol over logical point-to-point networks and logical NBMA
networks remains the same as for the corresponding physical networks.
For instance, logical point-to-point links could be numbered or
unnumbered. It is only necessary for implementations to provide the
hooks that give users the ability to configure an individual VC as a
logical point-to-point network or a collection of VCs as a logical
NBMA network.
The NBMA model does provide some economy in OSPF protocol processing
and overhead and is the recommended mode of operation for small
homogeneous networks. Other than the Designated Router (DR) and the
backup Designated Router (BDR), each router maintains only two
adjacencies, one each with the DR and BDR, regardless of the size of
the NBMA network. When FR VCs are configured as point-to-point
links, a router would have many more adjacencies to maintain,
resulting in increased protocol overhead. If all VCs were to have
comparable performance characteristics as well, there may not be
compelling reasons to assign a different link metric to each VC.
3. Implementing OSPF over FR
We recommend that OSPF router implementations be built so that
administrators can configure network layer interfaces that consist of
one or more FR VCs within a single physical interface. Each logical
network interface could then be configured as the appropriate type of
OSPF interface, that is, point-to-point for a single VC, or NBMA for
a collection of VCs. This capability would allow a router to belong
to one or more distinct IP subnets on a single physical FR interface.
Thus, it is necessary that the router be able to support multiple IP
addresses on a single physical FR interface. As with physical NBMA
networks, logical NBMA networks must be full-mesh connected. While
logical point-to-point links can be either numbered or unnumbered, we
show that it is easier to implement routers to handle numbered
logical point-to-point links.
3.1 Numbered Logical Interfaces
The router administrator should be able to configure numbered logical
interfaces over FR as follows:
STEP 1: Configure the physical interface specifying relevant
parameters such as the slot, connector, and port numbers,
physical frame format, encoding, and clock mode. In its
internal interface MIB [3], the router should create a new
ifEntry in the ifTable, assign the physical interface an
ifIndex, and increment the ifNumber by one.
STEP 2: Configure the data-link layer over the interface,
specifying frame relay as the encapsulation method.
Parameters such as the DLCI encoding type and length,
maximum frame size, management interface (Annex D, LMI),
and address resolution procedure (manual, inverse ARP). If
a management interface is not supported, FR VCs must be

推荐阅读


上一篇：如何理解西方媒体与政治的关系

下一篇：戊子时是几点 戊子时是几点钟