Multicast and Routing Guide K/KA/KB.15.15

OSPF global and interface settings
When first enabling OSPF, you may want to consider configuring ranges and restricting redistribution
(if an ASBR is used) to avoid unwanted advertisements of external routes. You may also want to
enable the OSPF trap and authentication features to enhance troubleshooting and security. However,
HP generally recommends that the remaining parameters with non-null default settings be left as-is
until you have the opportunity to assess OSPF operation and determine whether any adjustments
to non-default settings is warranted.
NOTE: Set global level parameters in the ospf context of the CLI. To access this context level,
ensure that routing is enabled, then execute router ospf at the global CONFIG level. For
example:
HP Switch (config)# router ospf
HP Switch (ospf)#
Use the VLAN interface context to set interface level OSPF parameters for the desired VLAN. To
access this context level, use vlan vid either to move to the VLAN context level or to specify that
context from the global config level. For example, both of the following command sets achieve the
same result:
HP Switch(config)# vlan 20
HP Switch(vlan-20)# cost 15
HP Switch(config)# vlan 20 cost 15
Changing the RFC 1583 OSPF compliance setting
In OSPF domains supporting multiple external routes from different areas to the same external
destination, multiple AS-external-LSAs advertising the same destination are likely to occur. This can
cause routing loops and the network problems that loops typically generate. On the routing switches,
if RFC 1583 compatibility is disabled, the preference rules affecting external routes are those stated
in RFC-2328, which minimize the possibility of routing loops when AS-external-LSAs for the same
destination originate from ASBRs in different areas. However, because all routers in an OSPF
domain must support the same routing-loop prevention measures, if the domain includes any routers
that support only RFC 1583 preference rules, all routers in the domain must be configured to
support RFC 1583.
NOTE: The routing switch is configured, by default, to be compliant with the RFC 1583 OSPF
V2 specification. (Use show ip ospf general to view the current RFC 1583 configuration
setting.)
All routes in an AS should be configured with the same compliance setting for preference rules
affecting external routes. Thus, if any routers in an OSPF domain support only RFC 1583, all routers
must be configured with 1583 compatibility. In the default OSPF configuration, RFC 1583 support
is enabled for the routing switches.
If all routers in the domain supportRFC 2178 or RFC 2328, you should disable RFC 1583
compatibility on all of the routers, because conformance to these later RFCs provides more robust
protection against routing loops on external routes.
Assigning the routing switch to OSPF areas
After you globally enable OSPF on the routing switch (see “Changing the RFC 1583 OSPF
compliance setting” (page 200)), use this command to assign one or more OSPF areas within your
200 Open Shortest Path First Protocol (OSPF)