Design Reference

• Minimize the number of OSPF areas for each switch to avoid excessive shortest path
calculations.
The switch executes the Djikstra algorithm for each area separately.
• Ensure that the OSPF dead interval is at least four times the OSPF hello interval
• Use MD5 authentication on untrusted OSPF links.
• Use stub or NSSA areas as much as possible to reduce CPU overhead.
OSPF and CPU utilization
After you create an OSPF area route summary on an area border router (ABR), the summary
route can attract traffic to the ABR for which the router does not have a specific destination
route. Enabling ICMP unreachable message generation on the switch can result in a high CPU
utilization rate.
To avoid high CPU utilization, Avaya recommends that you use a black hole static route
configuration. The black hole static route is a route (equal to the OSPF summary route) with
a next-hop of 255.255.255.255. This configuration ensures that all traffic that does not have a
specific next-hop destination route is dropped.
OSPF network design examples
You can use OSPF routing in the core of a network. For more information, see
Layer 1, 2, and
3 design examples on page 139.
The following figure describes a simple implementation of an OSPF network: enabling OSPF
on two switches (S1 and S2) that are in the same subnet in one OSPF area.
Figure 22: Example 1: OSPF on one subnet in one area
The routers in the preceding figure use the following configuration:
• S1 has an OSPF router ID of 1.1.1.1, and the OSPF port uses an IP address of
192.168.10.1.
• S2 has an OSPF router ID of 1.1.1.2, and the OSPF port uses an IP address of
192.168.10.2.
The general method to configure OSPF on each routing switch is:
1. Enable OSPF globally.
2. Enable IP forwarding on the switch.
Open Shortest Path First
Network Design Reference for Avaya VSP 4000 February 2014 63