Refer to the exhibit. Based on this command output,what can we conclude about R3?
R3#show ip ospf database
OSPF Router with ID (172.16.1.1) (process ID 123)
Router Link States (Area 0.0.0.0)
Link ID ADV Router Age Seq# Checksum
Link Count
172.16.1.1 172.16.1.1 128 0x800000020x00D748
1
192.168.0.4 192.168.0.4 128 0x8000000C0x000EA9
1
Net Link States (Area 0.0.0.0)
Link ID ADV Router Age Seq# Checksum
116.16.34.4 192.168.0.4 128 0x800000030x00CC36
Summary Net Link States (Area 0.0.0.0)
Link ID ADV Router Age Seq# Checksum
116.16.35.0 172.16.1.1 245 0x800000010x00E4C0
140.140.1.1 192.168.0.4 728 0x800000010x004013
140.140.2.1 192.168.0.4 728 0x800000010x00951D
140.140.3.1 192.168.0.4 728 0x800000010x008A27
192.168.0.4 192.168.0.4 728 0x800000010x0095cB
Router Link States (Area 2)
Link ID ADV Router Age Seq# Checksum
Link Count
172.16.1.1 172.16.1.1 127 0x800000020x00F725
1
192.168.0.5 192.168.0.5 128 0x8000000E0x00258B
1
Net Link States (Area 2)
Link ID ADV Router Age Seq# Checksum
116.16.35.5 192.168.0.5 128 0x800000030x00BB43
Summary Net Link States (Area 2)
116.16.34.0 172.16.1.1 245 0x800000010x00EFB6
140.140.1.1 172.16.1.1 124 0x800000010x00A77A
140.140.2.1 172.16.1.1 124 0x800000010x009C84
140.140.3.1 172.16.1.1 124 0x800000010x00918E
192.168.0.4 172.16.1.1 124 0x800000010x009C33
A.
R3 is an ABR.
B.
R3 is not connected to the backbone.
C.
R3 has four neighbors.
D.
R3 is the DR for area 2.
Explanation:
From the output we learned that this router is getting Type 3 LSAs (Summary Net Link
States) for both Area 0 and Area 3 -> It is an ABR between Area 0 & Area 3 .
From the LSA Type 1 we learn that R3 only has 1 neighbor, which is 192.168.0.4.
To find the DR for an area, we need to look at the LSA Type 2 of that area. In this case we
find out 116.16.35.5 is the DR for area 2, not R3.
To help you understand more clearly about the “showip ospf database” command, we want
to explain more about the fields in the output:
+ Link IDis the OSPF Router-ID of a router in the area for LSA Type 1 & 2 but it is can be
the Router-ID or the network address for LSA Type 3, 5 & 7.
+ The ADV Routeris the ID of the router that sent the LSA (Advertising Router) into the
area
+ Age: The max age of the link state
+ Seq# and Checksum: these fields are used to verify link-state integrity.
For example, from the Router Link States (Area 0.0.0.0):
The first “Link ID” 172.16.1.1 is the Router-ID of the local router R3 (because it is the same
as “OSPF Router with ID”). This “Link ID” is, of course, advertised by itself so the ADV
Router has the same value.
The second “Link ID” is the Router-ID of 192.168.0.4, which is advertised by 192.168.0.4 so
it is directly connected to R3.
Notice that these 2 routers belong to Area 0.
From the Net Link States:
We learn that the “Link ID” 116.16.34.4 is advertised from the neighbor 192.168.0.4, which
is directly connected to R3. This router (116.16.34.4) also belongs to Area 0 and it is the DR
of that segment.
The Summary Net Link States gives us information about LSA Type 3 (advertised by the
ABR of area 0. Recall that ABRs generate a Type 3 LSA for each subnet in one area, and
advertises each Type 3 LSA into the other areas)
From the output we learn that the subnet 116.16.35.0 is advertised via 172.16.1.1 and four
routers (in fact, interfaces) are advertised by 192.168.0.4. Notice that these routers
(interfaces) can belong to other areas.
