3Com CoreBuilder 3500, Implementation Manual

Page: 369 / 592

Key Guidelines for Implementing OSPF 369
Key Guidelines for
Implementing OSPF
Consider the following guidelines when you design a scalable and
dependable OSPF internetwork:
These parameters
must be consistent
across all routers
The following OSPF interface parameters must be consistent across all
routers on an attached network:
■
Hello interval
■
Dead interval
■
Password
Addressing scheme
The addressing structure that you implement can affect both the
scalability and the performance of your OSPF internetwork. Consider the
following guidelines when you define an addressing structure to use for
your OSPF internetwork:
■
Make the range of subnets that are assigned within each OSPF area
should be contiguous to allow optimal summarization by area border
routers (ABRs).
■
Define the address space so that you can easily add new areas,
restructure existing ones, or add additional routers as your network
grows.
Router placement
and participation
When you populate an area with OSPF routers, consider the following
guidelines:
■
Because OSPF uses a CPU-intensive algorithm, keep the maximum
number of routers participating in OSPF exchanges in any given area
to around 50. This number decreases the likelihood of performance
problems that may be associated with router recalculation. If the link is
of high quality and the number of routes is minimal, you can increase
the number of area routers.
■
Keep the maximum number of neighbors for any one router to around
60. Each time that a topological change occurs, a router exchanges
information only with those neighbors with which it has formed an
adjacency. On a multiaccess network, this neighbor count is only of
concern to the designated and backup-designated router of an area
because, on a multiaccess network, area routers do not exchange
link-state information with each other. Instead, they exchange
link-state information with only the designated and backup
designated routers.