Our first lab
delving into the OSPF world of the CCIE lab exam will focus on some
fundamentals related to how OSPF works over broadcast media as well as
introduce some basic concepts and common problems associated with design issues
related to OSPF with some topologies.
-Using process ID 100 for the following two tasks
1-Configure OSPF area 13 on R1 and R3 without using the OSPF network command
2-Configure OSPF area 34 and area 24 on R3, R4, and R2 using the network command
only, using a seperate network command for each area without any overlap
3-Note any issues related to the current configuration
4-configure fa 0/0 on R1, R2, and R3 in area 0
5-Note any changes to the routing table
Topology
GNS3 Files: Link
Solution
To begin we should
establish our peering per the tasks defined by the lab. The tasks ask us to
establish peering with specific neighbors using different peering configuration
methods. Both methods have the same result and have no material difference in terms
of how OSPF establishes the peering.
It's important to
note that unlike RIP the network statement as well as the interface command to
enable OSPF only enable the process on the interfaces associated with the
commands. So with the network statement any interface that has an IP address
within the range of the network command would send and receive OSPF hello's.
This is also true with the interface command IP OSPF AS Area Area_number. Both
commands have the same result but the network command can apply to multiple
interfaces. The interface command would apply only to the interface on which it
is entered.
Begin configure
tasks 1 and 2:
R1(config)#int s1/0
R1(config-if)#ip
ospf 100 area 13
R2(config)#router
ospf 100
R2(config-router)#network
192.168.24.0 0.0.0.255 area 24
R3(config)#int s1/0
R3(config-if)#ip
ospf 100 area 13
R3(config-if)#int
s1/1
R3(config-if)#ip
ospf 100 area 34
R4(config-if)#router
ospf 100
R4(config-router)#network
192.168.34.0 0.0.0.255 area 34
R4(config-router)#network
192.168.24.0 0.0.0.255 area 24
At this point the
lab asks us to note any issues with the configuration, so let's take a look.
No summary LSAs:
R1#sh ip ospf
database
OSPF Router with ID
(199.198.197.196) (Process ID 100)
Router Link States (Area 13)
Link ID ADV Router Age Seq# Checksum Link count
199.198.197.196
199.198.197.196 1347 0x80000001
0x0086C3 1
R1#sh ip route | b
Gateway
Gateway of last
resort is not set
1.0.0.0/8 is variably subnetted, 2
subnets, 2 masks
C 1.1.1.0/24 is directly connected,
Loopback0
L 1.1.1.1/32 is directly connected,
Loopback0
192.168.13.0/24 is variably subnetted, 2
subnets, 2 masks
C 192.168.13.0/24 is directly connected,
Serial1/0
L 192.168.13.1/32 is directly connected,
Serial1/0
192.168.123.0/24 is variably subnetted, 2
subnets, 2 masks
C 192.168.123.0/24 is directly connected,
FastEthernet0/0
L 192.168.123.1/32 is directly connected,
FastEthernet0/0
199.198.197.0/24 is variably subnetted, 2
subnets, 2 masks
C 199.198.197.0/24 is directly connected,
Loopback99
L 199.198.197.196/32 is directly
connected, Loopback99
R2#sh ip ospf
database
OSPF Router with ID (2.2.2.2)
(Process ID 100)
Router Link States (Area 24)
Link ID ADV Router Age Seq# Checksum Link count
2.2.2.2 2.2.2.2 530 0x80000002 0x0062B6 1
192.168.34.4 192.168.34.4 535
0x80000002 0x00B255 1
Net Link States (Area 24)
Link ID ADV Router Age Seq# Checksum
192.168.24.4 192.168.34.4 535
0x80000001 0x00F399
R2#sh ip route | b
Gateway
Gateway of last
resort is not set
2.0.0.0/8 is variably subnetted, 2
subnets, 2 masks
C 2.2.2.0/24 is directly connected,
Loopback0
L 2.2.2.2/32 is directly connected,
Loopback0
192.168.24.0/24 is variably subnetted, 2
subnets, 2 masks
C 192.168.24.0/24 is directly connected,
FastEthernet0/1
L 192.168.24.2/32 is directly connected,
FastEthernet0/1
192.168.123.0/24 is variably subnetted, 2
subnets, 2 masks
C 192.168.123.0/24 is directly connected,
FastEthernet0/0
L 192.168.123.2/32 is directly connected,
FastEthernet0/0
R3#sh ip ospf
database
OSPF Router with ID
(199.198.197.196) (Process ID 100)
Router Link States (Area 13)
Link ID ADV Router Age Seq# Checksum Link count
199.198.197.196
199.198.197.196 168 0x80000001
0x0086C3 1
Router Link States (Area 34)
Link ID ADV Router Age Seq# Checksum Link count
199.198.197.196
199.198.197.196 168 0x80000001
0x0044F0 1
R3#
R3#sh ip route | b
Gateway
Gateway of last
resort is not set
3.0.0.0/8 is variably subnetted, 2
subnets, 2 masks
C 3.3.3.0/24 is directly connected,
Loopback0
L 3.3.3.3/32 is directly connected,
Loopback0
192.168.13.0/24 is variably subnetted, 2
subnets, 2 masks
C 192.168.13.0/24 is directly connected,
Serial1/0
L 192.168.13.3/32 is directly connected,
Serial1/0
192.168.34.0/24 is variably subnetted, 2
subnets, 2 masks
C 192.168.34.0/24 is directly connected,
Serial1/1
L 192.168.34.3/32 is directly connected,
Serial1/1
192.168.123.0/24 is variably subnetted, 2
subnets, 2 masks
C 192.168.123.0/24 is directly connected,
FastEthernet0/0
L 192.168.123.3/32 is directly connected,
FastEthernet0/0
R4#sh ip ospf
database
OSPF Router with ID
(199.198.197.196) (Process ID 100)
Router Link States (Area 24)
Link ID ADV Router Age Seq# Checksum Link count
2.2.2.2 2.2.2.2 101 0x80000002 0x0062B6 1
199.198.197.196
199.198.197.196 100 0x80000002
0x0030C4 1
Net Link States (Area 24)
Link ID ADV Router Age Seq# Checksum
192.168.24.4 199.198.197.196 100 0x80000001 0x00304A
Router Link States (Area 34)
Link ID ADV Router Age Seq# Checksum Link count
199.198.197.196
199.198.197.196 145 0x80000001
0x0044F0 1
R4#sh ip route | b
Gateway
Gateway of last
resort is not set
192.168.24.0/24 is variably subnetted, 2
subnets, 2 masks
C 192.168.24.0/24 is directly connected,
FastEthernet0/0
L 192.168.24.4/32 is directly connected,
FastEthernet0/0
192.168.34.0/24 is variably subnetted, 2
subnets, 2 masks
C 192.168.34.0/24 is directly connected,
Serial1/0
L 192.168.34.4/32 is directly connected,
Serial1/0
199.198.197.0/24 is variably subnetted, 2
subnets, 2 masks
C 199.198.197.0/24 is directly connected,
Loopback99
L 199.198.197.196/32 is directly
connected, Loopback99
So first thing to
note is the lack of any summary LSA's on any of the routers. There are two
kinds of summary LSA's type 3 and type 4. Type 3 Summary LSA's are a list of
all type 1 & 2 LSA's for a given area sent by an ABR to an adjacent area.
In short type 3 LSA's provide a complete list of networks outside a given area.
Type 3 LSA's are sent between the backbone area and adjacent areas. Type 4
LSA's are generated by ABR for an area with an ASBR and provide path
information to build a shortest path tree to an ASBR.
Since inter-area LSA
exchange must be done through the backbone area none of the non-backbone areas
have received any summary LSA leaving them with an incomplete few of the
network.
The second and a
little more obvious issue is the following error messages on R1 and R3.
Duplicate Router ID
issue:
%OSPF-4-DUP_RTRID_NBR:
OSPF detected duplicate router-id 199.198.197.196 from 192.168.13.1 on
interface Serial1/0
%OSPF-4-DUP_RTRID_NBR:
OSPF detected duplicate router-id 199.198.197.196 from 192.168.13.3 on
interface Serial1/0
The message
indicates a potential configuration or design issue. Specifically the error
message indicates duplicate router ID's on the devices where the messages are
displayed. The problem creates problems due to the fact that LSA's origination
is based on router-id. The routers see duplicate LSA ID's causing continual
recalculation of SPF indicated by the log message.
The solution to this
problem is simple either change the loopback address IP on one router and then
clear the OSPF process or use the router-id command to specify a new router-id
on one of the devices. Each option will cause the router to recalculate SPF and
flood updated LSA's out.
So I will use the
router-id option on both R1 and R3. Issueing this command brings the neighbor
state down momentarily to allow SPF recalculation.
R1(config)#router
ospf 100
R1(config-router)#router-id
1.1.1.1
*Aug 4 19:16:02.799: %OSPF-5-ADJCHG: Process 100,
Nbr 199.198.197.196 on Serial1/0 from LOADING to FULL, Loading Done
R3(config)#router
ospf 100
R3(config-router)#router-id
3.3.3.3
% OSPF: Reload or
use "clear ip ospf process" command, for this to take effect
The OSPF process
must be restarted to use the new router-id.
Finally we configure
our backbone interfaces.
R1(config)#int fa
0/0
R1(config-if)#ip
ospf 100 area 0
R1(config)#int fa
0/0
R1(config-if)#ip
ospf 100 area 0
R1(config)#int fa
0/0
R1(config-if)#ip
ospf 100 area 0
And with that
configuration in place we see all our LSA's.
R1#sh ip ospf
database
OSPF Router with ID (1.1.1.1)
(Process ID 100)
Router Link States (Area 0)
Link ID ADV Router Age Seq# Checksum Link count
1.1.1.1 1.1.1.1 19 0x80000002 0x002437 1
2.2.2.2 2.2.2.2 20 0x80000002 0x00E56C 1
3.3.3.3 3.3.3.3 20 0x80000002 0x00A7A1 1
Net Link States (Area 0)
Link ID ADV Router Age Seq# Checksum
192.168.123.3 3.3.3.3 20 0x80000001 0x004CDD
Summary Net Link States (Area
0)
Link ID ADV Router Age Seq# Checksum
192.168.13.0 1.1.1.1 99 0x80000001 0x00ACD5
192.168.13.0 3.3.3.3 60 0x80000001 0x00700A
192.168.24.0 2.2.2.2 74 0x80000001 0x009C16
192.168.34.0 3.3.3.3 60 0x80000001 0x0088DC
Router Link States (Area 13)
Link ID ADV Router Age Seq# Checksum Link count
1.1.1.1 1.1.1.1 99 0x80000003 0x00D4CA 2
3.3.3.3 3.3.3.3 60 0x80000002 0x001680 2
Summary Net Link States (Area
13)
Link ID ADV Router Age Seq# Checksum
192.168.24.0 1.1.1.1 9 0x80000001 0x00C4F0
192.168.24.0 3.3.3.3 15 0x80000001 0x008825
192.168.34.0 1.1.1.1 14 0x80000001 0x00CE9D
192.168.34.0 3.3.3.3 60 0x80000001 0x0088DC
192.168.123.0 1.1.1.1 89 0x80000001 0x0075DD
192.168.123.0 3.3.3.3 50 0x80000001 0x003912
Sources
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