Demo eNSP Troubleshooting Lab Solutions

We see that on R1, OSPF peering remains in state "Exchange" and does not go to "Full".

There can be various reasons for this, including an MTU mismatch. If the ospf mtu-enable command is configured, the MTU is checked during the exchange of DD packets. The command ospf mtu-enable is configured on both the R1 interface G0/0/0 and R2 G0/0/0. The configured MTU can be checked on R1 and R2 with display interface g0/0/0.

<R1>display interface GigabitEthernet 0/0/0
GigabitEthernet0/0/0 current state : UP
Line protocol current state : UP
Last line protocol up time : 2026-01-11 06:52:51 UTC-08:00
Description:HUAWEI, AR Series, GigabitEthernet0/0/0 Interface
Route Port,The Maximum Transmit Unit is 1503
Internet Address is 10.0.12.1/24
IP Sending Frames' Format is PKTFMT_ETHNT_2, Hardware address is 00e0-fc98-0546
Last physical up time : 2026-01-11 06:52:51 UTC-08:00
Last physical down time : 2026-01-11 06:52:32 UTC-08:00
Current system time: 2026-01-11 07:16:52-08:00
Port Mode: FORCE COPPER
Speed : 1000, Loopback: NONE
Duplex: FULL, Negotiation: ENABLE
Mdi : AUTO
Last 300 seconds input rate 176 bits/sec, 0 packets/sec
Last 300 seconds output rate 208 bits/sec, 0 packets/sec
Input peak rate 368 bits/sec,Record time: 2026-01-11 06:53:37
Output peak rate 400 bits/sec,Record time: 2026-01-11 06:58:07

(output omitted)

<R2>display interface g0/0/0
GigabitEthernet0/0/0 current state : UP
Line protocol current state : UP
Last line protocol up time : 2026-01-11 06:52:52 UTC-08:00
Description:HUAWEI, AR Series, GigabitEthernet0/0/0 Interface
Route Port,The Maximum Transmit Unit is 1500
Internet Address is 10.0.12.2/24
IP Sending Frames' Format is PKTFMT_ETHNT_2, Hardware address is 00e0-fc48-6b90
Last physical up time : 2026-01-11 06:52:52 UTC-08:00
Last physical down time : 2026-01-11 06:52:43 UTC-08:00
Current system time: 2026-01-11 07:18:57-08:00
Port Mode: FORCE COPPER
Speed : 1000, Loopback: NONE
Duplex: FULL, Negotiation: ENABLE
Mdi : AUTO
Last 300 seconds input rate 208 bits/sec, 0 packets/sec
Last 300 seconds output rate 176 bits/sec, 0 packets/sec
Input peak rate 400 bits/sec,Record time: 2026-01-11 06:56:18
Output peak rate 368 bits/sec,Record time: 2026-01-11 06:53:38

(output omitted)

As we can see, the MTU is configured differently on the interfaces. We therefore change the MTU on R1 to the standard value of 1500 bytes.

[R1]interface GigabitEthernet 0/0/0
[R1-GigabitEthernet0/0/0]undo mtu

After that, OSPF peering between R1 and R2 comes up and is in "Full" state.

We do not have OSPF peering between R2 and R3. First, we check the R2 interface G0/0/1 configuration. Here we see that an inbound ACL is configured.

<R2>display current-configuration interface g0/0/1
#
interface GigabitEthernet0/0/1
ip address 10.0.23.2 255.255.255.0
traffic-filter inbound acl 2000
#

We see that the ACL only has one rule, which discards everything.

<R2>display acl 2000
Basic ACL 2000, 1 rule
Acl's step is 5
rule 10 deny

Since we are not allowed to delete or remove any ACLs from the interface according to the General Rules of the Troubleshooting Lab, we must add a permit entry before the deny entry.

[R2]acl 2000
[R2-acl-basic-2000]rule 5 permit

Since OSPF peering still does not come up after this adjustment, let's take a look at the configuration on R3.

On R3, we also first check the configuration on interface G0/0/0.

What we see here is that the subnet mask is incorrect according to the layout (/23 instead of /24). For the OSPF peering, the subnet mask must be the same on both side, which is why we correct it on R3.

[R3]interface GigabitEthernet 0/0/0
[R3-GigabitEthernet0/0/0]ip address 10.0.23.3 24

After that, OSPF peering to R2 comes up and is in “Full” state.

Now all OSPF peerings are in place. However, if we check the routing table on R1, we still see that the Loopback0 network from R3 is missing and therefore the ping is not working.

On R3, we can see with display ip interface brief that the Loopback0 interface is “up” and that both the IP address and the subnet mask are correct.
With display current-configuration configuration ospf (or display c c ospf for short), we take a closer look at the OSPF configuration.

Here we see that the network statement for the Loopback0 network does not match. We can correct this in two ways.

1) We change the network and leave the wildcard mask the same

ospf 1
area 0.0.0.0
network 10.0.3.3 0.0.0.0
#

2) We leave the network and change the wildcard mask

ospf 1
area 0.0.0.0
network 10.0.3.0 0.0.0.255
#

Both variants lead to the same result, in that the Loopback0 network of R3 is now propagated.

Now we can ping from the R1 Loopback0 network to the Loopback0 network of R3, which is required as a final test.

• The process ID does not have to be the same on all routers. It makes no difference if routers R1 and R3 have process ID 1 and router R2 has process ID 42.
• The ACL on interface G0/0/1 on R2 no longer has any function and would not be needed. However, according to the general rules of the troubleshooting lab, we are not allowed to delete or remove any ACLs from the interface, which is why we are leaving it as it is.
• It does not matter whether the wildcard mask for the loopback0 network is 0.0.0.0 or 0.0.0.255, as long as the network part matches (see description of Solution 4).