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The information in this document was created from the devices in a specific lab environment. All of the devices used in this document started with a cleared default configuration. If your network is live, make sure that you understand the potential impact of any command. For more information on document conventions, refer to the Cisco Technical Tips Conventions.
In this state, the routers exchange DBD exchange optionsinit not match, which describe their entire link-state database. The routers also send link-state request exchange optionsinit not match, which request more recent link-state advertisements LSA from neighbors. Below is the most common reason that OSPF neighbors get stuck in this state. The problem occurs most frequently when attempting to run OSPF between a Cisco router and another vendor's router.
The problem occurs when the maximum transmission unit MTU settings for neighboring router interfaces don't match.
If the router with the higher MTU sends a packet larger that the MTU set on the neighboring router, the exchange optionsinit not match router ignores the packet.
Router 6 and Router 7 in the above topology are connected via Frame Relay and Router 6 has been configured with 5 static routes redistributed into OSPF. Each router configuration is shown in the table below only necessary configuration information exchange optionsinit not match shown:. Use the debug ip packet and the exchange optionsinit not match ip ospf adj commands on each router to see the OSPF adjacency process as it takes place.
The output from Router 6 and 7 from steps 1 to 14 is:. Router 7 repeatedly retransmits the DBD packet. Let us look at some of the steps above. Router 7 retransmits the initial DBD packet. Step 13 shows that Router 6, as slave, adopts the Router 7 sequence number and sends its second DBD packet containing the headers of its LSAs, which increases the size of the packet. After step 13, Router 7 continues to retransmit the initial DBD packet to Router 6, while Router 6 continues to send DBD packets that follow the master sequence number.
This prevents the formation of an adjacency. To fix this problem, ensure that the MTU are the same on both ends of a link. The problem is most frequently caused by the inability to successfully exchange DBD packets. However, the root cause could be any of the these:.
In the exstart state, the exchange optionsinit not match sends a unicast packet to the neighbor to elect master and slave. This is true unless you have a point-to-point link, in which case it sends a multicast packet. These are the possible causes:. When OSPF does not form neighbors, exchange optionsinit not match the factors mentioned above, such as the physical media and networking hardware, in order to troubleshoot the problem.