What could be reason for OSPF neighbor being stuck in Exstart?

What could be reason for OSPF neighbor being stuck in Exstart?

The most common reason for the neighbors to be stuck in Exstart/Exchange state is due to MTU mismatch on the OSPF enabled interfaces between the two neighbors. The issue can be resolved by either configuring same MTU on both OSPF interfaces or enabling mtu-ignore on the OSPF interface.

What happens in OSPF Exstart?

Exstart State This state specifies that DR and BDR have been elected and master-slave relation is determined. An initial sequence number for adjacency formation is also selected. The router with the highest router ID becomes the master and begins to exchange Link State data.

What happens if MTU mismatch in OSPF?

Database Description packet is rejected. Basically this means that if a router tries to negotiate an adjacency on an interface in which the remote neighbor has a larger MTU, the adjacency will be denied.

What are the potential causes of OSPF Neighbour issues?

The most common possible causes of this problem are as follows :

• OSPF is not enabled on the interface.
• Layer 1/2 is down.
• The interface is defined as passive under OSPF.
• An access list is blocking OSPF Hellos on both sides.
• A subnet number/mask has been mismatched over a broadcast link.

How do I troubleshoot OSPF neighbor down?

Make sure that the interfaces at both ends are configured to support OSPF. There could be a mismatch in the OSPF Network Type. Verify that Hello and Dead timers match on each end of the link. Neighboring interfaces must be in the same OSPF Area.

What happens if OSPF stuck in Exstart exchange state?

If you see the the state is stuck in EXCHANGE or LOADING State. It means that either LSA Headers are not getting exchanged or LSA Updates are not getting exchanged. Things to Check: a) We should make sure MTU matches on the OSPF Peers and also on the device (switch/transparent firewall) in between.

How do I troubleshoot OSPF in Exstart?

Things to check:

1. Check if the layer3 connectivity between these two routers are working (ping source x host y).
2. Check if the devices are in the same OSPF area.
3. Check if the devices have the same authentication configuration (e.g., username, password, or authentication type).
4. Check if the devices are on the same subnet.

How do I troubleshoot OSPF flapping?

TROUBLESHOOTING STEPS

1. STEP 1: FAULTY SWITCH PORT.
2. STEP 2: FAULTY CABLE.
3. STEP 3: FAULTY ROUTER PORT.
4. STEP 4: SPEED / DUPLEX SETTINGS.
5. STEP 5: OSPF HELLO / DEAD TIMER.
6. STEP 6: CHECK CPU UTILIZATION.
7. STEP 1: FAULTY SWITCH PORT. There might be the case that switch port is faulty.
8. STEP 2: FAULTY CABLE.

How would you troubleshoot OSPF adjacency stuck in init or Exstart or exchange or loading states?

What are major issues in OSPF?

Ineffective Load Balancing. The SPF algorithm calculates a single ‘best’ path between two points in a network.

Lack Of Visibility. The operation of the OSPF algorithm is opaque, and it’s difficult to monitor the SPF algorithm status.

Poor Path Weighting.

Scaling.

Unreliable Self-Configuration.

Why do OSPF routers maintain neighbor adjacencies?

OSPF Operation Overview Establish neighbor adjacencies: OSPF-enabled routers must form adjacencies with their neighbor before they can share information with that neighbor. An OSPF-enabled router sends Hello packets out all OSPF-enabled interfaces to determine whether neighbors are present on those links.

How do I troubleshoot OSPF issues?

How do I reset my OSPF neighbor?

Description

1. Reconfigure the OSPF neighbors on the NBMA interface with the neighbor command.
2. Issue the clear ip ospf database command to clear and reset the OSPF adjacencies.
3. Issue the shutdown command followed by the no shutdown command on the interface.

What does OSPF use to avoid adjacencies?

OSPF Message Types Type 1: Hello packet: Hello packets are used to discover, build, and maintain OSPF neighbor adjacencies.

How do I clear my OSPF neighbor Juniper?