Information Technology Reference
In-Depth Information
Modifying the Cost Metric Exercise
Assume that RTB and RTC are both Cisco 2800 series routers. The default bandwidth on serial inter-
faces for 2800 routers is 1544 kbps (T1). What command would you enter to verify the default or con-
figured bandwidth on an interface?
show interface
Referring to Figure 11-5, document the commands needed to configure the bandwidth correctly so
that OSPF uses an accurate cost metric.
RTB(config)#
interface serial 0/0/0
RTB(config-if)#
bandwidth 386
RTC(config)#
interface serial 0/0/1
RTC(config-if)#
bandwidth 386
Instead of configuring the bandwidth, you could configure the cost directly. Document the commands
for RTB and RTC that would configure the actual OSPF cost?
RTB(config)#
interface serial 0/0/0
RTB(config-if)#
ip ospf cost 259
RTC(config)#
interface serial 0/0/1
RTC(config-if)#
ip ospf cost 259
OSPF and Multiaccess Networks
A multiaccess network is a network with more than two devices on the same shared media. Examples
of multiaccess networks include Ethernet, Token Ring, and Frame Relay. Token Ring is LAN technol-
ogy that is for the most part obsolete. Frame Relay is a WAN technology that is discussed in a later
CCNA course. The following exercises cover the concepts of multiaccess networks in OSPF and the
DR/BDR election process.
OSPF and Multiaccess Networks Completion Exercise
Complete the missing words or phrases in the following paragraphs.
On multiaccess networks (networks supporting more than two routers), such as Ethernet and Frame
Relay networks, the Hello protocol elects a
designated router
(
DR
) and a
backup designated router
(
BDR
). Among other things, the
designated router
is responsible for generating LSAs for the entire
multiaccess network, which allows a reduction in routing update traffic.
The DR, BDR, and every other router in an OSPF network sends out Hellos using
224.0.0.5
as the
destination address. If a DRother (a router that is not the DR) needs to send an LSA, it will send it
using
224.0.0.6
as the destination address. The DR and the BDR will receive LSAs at this address.
The DR/BDR election is based on OSPF
priority
and OSPF router
ID
. By default, all OSPF routers
have a
priority
of
1
. If all OSPF routers have the same
priority
, the highest router
ID
determines the
DR and BDR.
Unless a loopback interface is configured, the
highest
IP address on an active interface at the moment
of OSPF process startup is used as the router
ID
.
In Figure 11-6, label each router with its router ID. Assume that all routers came up simultaneously
and that all interfaces are active.
