KB.15.15

Modules operating in nonstop mode

When a switch is in standalone mode and OSPF routing is enabled, the "empty hello list" is

transmitted whenever the boot or reload commands are executed.

When the switch is operating in nonstop switching mode (redundant) and a single module is being

reloaded or booted, the standby module will notify neighboring switches of the management

module failover. If the failover fails, the "empty hello list" is transmitted before the switch is rebooted.

When a switch is operating with multiple management modules in warm standby mode, the "empty

hello list" is sent when a reload or boot command is executed. The standby management module

sends out OSPF hello packets after becoming the active management module.

OSPF equal-cost multipath (ECMP) for different subnets available through the same

next-hop routes

The switches support optional load-sharing across redundant links where the network offers two,

three, or four equal-cost next-hop routes for traffic to different subnets. (All traffic for different hosts

in the same subnet goes through the same next-hop router.)

For example, in the OSPF network shown in Figure 43 (page 204), IP load-sharing is enabled on

router "A". In this case, OSPF calculates three equal-cost next-hop routes for each of the subnets

and then distributes per-subnet route assignments across these three routes.

Figure 43 Example of load-sharing traffic to different subnets through equal-cost next-hop routers

Example of a routing table for the network in Figure 43 (page 204)

Router "A" next hopDestination subnet

Router "C"10.1.0.0/16

Router "D"10.2.0.0/16

Router "B"10.3.0.0/16

Router "B"10.32.0.0/16

Router "D"10.42.0.0/16

IP load-sharing does not affect routed traffic to different hosts on the same subnet. That is, all traffic

for different hosts on the same subnet will go through the same next-hop router. For example, if

subnet 10.32.0.0 includes two servers at 10.32.0.11 and 10.32.0.22, all traffic from router "A"

to these servers will go through router "B".

204 Open Shortest Path First Protocol (OSPF)