Huawei ARG3 Router How To - Troubleshooting OSPF: Netmask mismatch

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HUAWEI
ROUTER ARG3
Troubleshooting
OSPF - Lesson 3:
Netmask mismatch

1. General infos and application environment
01
OSPF is a routing protocol with some useful means of troubleshooting. Using the simple network scenario shown in the
picture, we will describe how it is possible to detect and solve some common OSPF configuration error.
This third lesson about OSPF troubleshooting will be focused on “Netmask mismatch”.
We will isolate the problem and we will correct the configuration.
Troubleshooting OSPF - Lesson 3: Netmask mismatch
HUAWEI ARG3 ROUTER

2. Checking IP connectivity between RouterC and RouterD
Ping RouterD
02
RouterD is
unreachable from
RouterC, so we
have to chek
RouterC routing
table.
Ping RouterD from RouterC
<RouterC> ping 10.1.3.2
PING 10.1.3.2: 56 data bytes, press CTRL_C to break
Request time out
Request time out
Request time out
Request time out
Request time out
--- 10.1.3.2 ping statistics ---
5 packet(s) transmitted
0 packet(s) received
100.00% packet loss
HUAWEI ARG3 ROUTER

3. Checking RouterC routing table
Display the
routing table
03
There is something
strange in the routing
table: only tne network
10.1.2.0/24 in Area 0
is known via OSPF,
there is no information
about network
10.1.3.0/24 in Area 2.
Anayway the OSPF
neighborship with
RouterA seems to be
OK, otherwise also
network 10.1.2.0/24
would be not known to
RouterC. So we can
go on checking
RouterA.
Check RouterC routing table
<RouterC> display ip routing-table
Route Flags: R - relay, D - download to fib
------------------------------------------------------------------------------
Routing Tables: Public
Destinations : 5 Routes : 5
Destination/Mask Proto Pre Cost Flags NextHop Interface
10.1.1.0/24 Direct 0 0 D 10.1.1.2 GigabitEthernet0/0/0
10.1.2.0/24 OSPF 10 2 D 10.1.1.1 GigabitEthernet0/0/0
27.0.0.0/8 Direct 0 0 D 127.0.0.1 InLoopBack0
HUAWEI ARG3 ROUTER

4. Checking RouterA routing table
Display the
routing table
04
There is something
strange in the routing
table: no networks are
known to RouterA via
OSPF. There is no
information about
network 10.1.3.0/24 in
Area 2. So next step
will be to check the
neighborship status of
RouterA with RouterB.
Check RouterA routing table
<RouterA> display ip routing-table
------------------------------------------------------------------------------
HUAWEI ARG3 ROUTER

5. Checking OSPF neighborship on RouterA
Display OSPF
neighbors
05
RouteA has only one
peer OSPF that is
RouterC (Router ID:
3.3.3.3) in Area 1; there
is no information about
RouterB in Area 0.
So we have to check if
there is some
configuration error in
OSPF on RouterA.
Check OSPF neighborship on RouterA
<RouterA> display ospf peer
OSPF Process 1 with Router ID 1.1.1.1
Neighbors
Area 0.0.0.1 interface 10.1.1.1(GigabitEthernet0/0/0)'s neighbors
Router ID: 3.3.3.3 Address: 10.1.1.2
State: Full Mode:Nbr is Master Priority: 1
DR: 10.1.1.2 BDR: 10.1.1.1 MTU: 0
Dead timer due in 33 sec
Retrans timer interval: 5
Neighbor is up for 00:17:58
Authentication Sequence: [ 0 ]
HUAWEI ARG3 ROUTER

6. Checking OSPF configuration errors on RouterA
Display errors in
OSPF
06
There are 14 Netmask
mismatch; so let’s
check the RouterA
configuration.
Check OSPF errors
<RouterA> display ospf error
OSPF Process 1 with Router ID 1.1.1.1
OSPF error statistics
HELLO packet errors:
14 : Netmask mismatch 0 : Hello timer mismatch
0 : Dead timer mismatch 0 : Virtual neighbor unknown
0 : NBMA neighbor unknown 0 : Invalid Source Address
HUAWEI ARG3 ROUTER

6. Checking OSPF configuration errors on RouterA
Display RouterA
configuration
07
So now we can
understand that the
problem is with the
netmask of GE0/0/1
that shoud be
255.255.255.0. This
causes the missing
neighbour.
Check RouterA configuration
<RouterA> display current-configuration
…………………………
#
interface GigabitEthernet0/0/1
ip address 10.1.2.1 255.255.255.252
#
…………………………
HUAWEI ARG3 ROUTER

7. Correcting OSPF configuration on RouterA
Enter the
configuration view
08
Enter the GE0/0/1 view
Correct netmask of interface GE0/0/1
<RouterA> system-view
[RouterA] interface GigabitEthernet 0/0/1
[RouterA-GigabitEthernet0/0/1] ip address 10.1.2.1 24
[RouterA-GigabitEthernet0/0/1] quit
[RouterA] Correct the Netmask
of GE0/0/1
(255.255.255.0)
Exit the GE0/0/1 view
HUAWEI ARG3 ROUTER

8. Checking the routing table on RouterC
Check the routing
table on RouterC
to verify the
OSPF routes
09
Now we can see that
RouterC has learned
the route to network
10.1.3.0/24 via OSPF.
Correct Router ID, save configuration and reboot the system
[RouterC] disp ip routing-table
------------------------------------------------------------------------------
[RouterC]
HUAWEI ARG3 ROUTER

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Huawei ARG3 Router How To - Troubleshooting OSPF: Netmask mismatch

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Huawei ARG3 Router How To - Troubleshooting OSPF: Netmask mismatch