JN0-363 Exam Dumps : Service Provider Routing and Switching, Specialist (JNCIS-SP)

Neighbors Stuck in Exstart/Exchange State The problem occurs most frequently when you attempt to run OSPF between a Cisco router and another vendor router. The problem occurs when the maximum transmission unit (MTU) settings for neighboring router interfaces do not match. If the router with the higher MTU sends a packet larger that the MTU set on the neighboring router, the neighbor router ignores the packet. When this problem occurs, the output of the show ip ospf neighbor command displays output similar to what is shown in this figure.

A mismatched Maximum Transmission Unit (MTU) setting on OSPF interfaces can cause routers to get stuck in the ExStart state. OSPF requires that both sides of a link have the same MTU to form a full adjacency.References:

• OSPF Troubleshooting, Juniper Networks Documentation
• MTU and OSPF, Juniper Networks Documentation

To verify the status of the tunnel from R1, you would issue a ping from the source address that is assigned to R1's end of the tunnel. In the exhibit, we can see that the tunnel interface (gre-0/0/0.0) has the IP address 198.51.100.1 on R1. Therefore, to test the tunnel's status, you should ping the IP address at the other end of the tunnel (which is likely the address on User B's interface or another interface on R2) from R1's tunnel source address.

References:

• Juniper Networks documentation on GRE: GRE Interface Configuration

The root bridge in a spanning-tree network is the bridge with the smallest or the lowest bridge ID.

In the absence of a manually configured priority, the Spanning Tree Protocol (STP) elects the root bridge based on the lowest bridge ID, which is a combination of the priority and the MAC address. The device with the lowest MAC address will have the lowest bridge ID and thus be elected as the root bridge.

References

• Juniper Networks Technical Documentation on STP