User guide

Displaying OSPF Settings
ExtremeWare 7.2e Installation and User Guide 243
problems. For example, when a router has a memory shortage, it might be that the Link State database
is not complete, resulting in an incomplete or inaccurate routing table. By setting the overload bit in its
LSPs, other routers can ignore the unreliable router in their SPF calculations until the router has
recovered from its problems.
Set the overload bit when you want to prevent traffic flow.
Default Routes to Nearest Level 1/2 Switch for Level 1 Only Switches
When one router is a level 1 switch, the route to the nearest level 1/2 switch which attaches to a level 2
backbone network may be installed in the kernel routing table of the level 1 switch.
There are three kinds of level 1 only switches:
• a switch that does not attach to any level 1/2 switch; it is part of a level 1 only network
• a switch that attaches to at least one level 1/2 switch, but none of the level 1/2 switches are attached
to a level 2 backbone network. Here the level 1 non-pseudo node LSP of the level 1/2 switches
should set the attach bit to 0. A level 1 only switch will not install the default routes based on the
unattached level 1/2 switch’s LSP information.
• a switch that attaches to at least one level 1/2 switch, and at least one of the level 1/2 switches is
attached to the level2 backbone network. Here the level1 non-pseudo node LSP of the level1/2
switch should set the attach bit to 1. A level 1 only switch will install the default routes based on the
attached level 1/2 switch’s LSP information.
The level 1/2 switch that is attached to the level 2 backbone network when at least one of area
addresses of level2 LSP received from other level2 or level 1/2 switches is not in the list of the level1
union area address set.