OSPF - Routing Protocols and Concepts - page 509

At this point, any host on the LAN attached to RTA will be able to access ISP and be able to ping the
Public Web Server at 209.165.202.129. However, RTB and RTC still cannot ping outside the
192.168.1.0/24 address space. Why?
Because neither router has a default route
Document the command that needs to be configured on RTA to fix this problem.
RTA(config-router)# default-information originate
Fine-Tuning OSPF Exercise
Modifying the Reference Bandwidth
Cisco OSPF cost uses accumulated bandwidth. The bandwidth value of each interface is calculated
using 100,000,000/bandwidth. The 100,000,000, or 10 8 , is known as the reference bandwidth.
As you know from previous studies, we now have link speeds that are much faster than 100,000,000
(the speed of Fast Ethernet), including Gigabit Ethernet and 10GigE. Therefore, 100,000,000 results in
interfaces with bandwidth values of 100 Mbps and higher having the same OSPF cost of 1.
For RTA, RTB, and RTC, document the commands to change the reference bandwidth to 10,000.
RTA(config-router)# auto-cost reference-bandwidth 10000
RTB(config-router)# auto-cost reference-bandwidth 10000
RTC(config-router)# auto-cost reference-bandwidth 10000
Make sure that you configure this command on all routers in the OSPF routing domain.
Modifying OSPF Intervals
OSPF routers must use matching Hello intervals and Dead intervals on the same link. The default
interval values result in efficient OSPF operation and seldom need to be modified. However, you can
change them.
Again, refer to Figure 11-10. Assuming that the current intervals are 10 and 40, document the com-
mands necessary to change these intervals on the link between RTB and RTC to a value four times
greater than the current value.
RTB(config)# interface serial 0/0/0
RTB(config-if)# ip ospf hello-interval 40
RTB(config-if)# ip ospf dead-interval 160
RTC(config)# interface serial 0/0/1
RTC(config-if)# ip ospf hello-interval 40
RTC(config-if)# ip ospf dead-interval 160
Note that it is not necessary to configure the Dead interval as long as the desired interval is four times
the Hello. The IOS will automatically increase the Dead interval to four times the configured Hello
interval.