Introduction:

Data Center Interconnect (DCI) technologies are used to link geographically dispersed data centers, enabling workload mobility, resource sharing, and business continuity. Cisco’s Overlay Transport Virtualization (OTV) is one such DCI technology that extends Layer 2 connectivity across Layer 3 networks. This report describes a scenario in which I had to troubleshoot and resolve an issue with OTV in a data center interconnect environment.

Scenario and Issue:

In our organization, we had two data centers connected using OTV. We began experiencing intermittent connectivity issues between virtual machines (VMs) located in different data centers. This affected business-critical applications and raised concerns about potential data loss and downtime.

Troubleshooting Steps and Resolution:

To identify the root cause and resolve the issue, I took the following steps:

1. Reviewed the network topology and OTV configuration on both data center Nexus switches, including the OTV edge devices, join interfaces, and VLAN mappings.
2. Used network troubleshooting tools like ping, traceroute, and show commands to verify the OTV control plane, data plane, and MAC address reachability.
3. Identified that one of the OTV edge devices had an incorrect join interface configuration, causing OTV adjacency and MAC address learning issues between data centers.
4. Corrected the join interface configuration on the affected OTV edge device and verified that the OTV adjacency was established and MAC addresses were learned correctly. Configuration example:

switch(config)# interface [JOIN_INTERFACE]
switch(config-if)# ip address [IP_ADDRESS] [SUBNET_MASK]
switch(config-if)# no shutdown

switch(config)# otv site bridge-domain [VLAN_NUMBER]
switch(config)# otv site-identifier [SITE_ID]

switch(config)# interface overlay1
switch(config-if)# otv control-group [MULTICAST_GROUP]
switch(config-if)# otv data-group [DATA_MULTICAST_GROUP_RANGE]
switch(config-if)# otv join-interface [JOIN_INTERFACE]
switch(config-if)# otv extend-vlan [VLAN_RANGE]
switch(config-if)# no shutdown

5. Monitored the OTV connection and tested VM-to-VM connectivity across data centers to ensure the issue was resolved.
6. Documented the changes and shared the findings with the team to prevent future OTV configuration issues.

Conclusion:

By identifying and correcting the join interface configuration issue on the OTV edge device, we were able to restore stable Layer 2 connectivity between the data centers and ensure seamless operation of business-critical applications. This experience emphasizes the importance of accurate configuration, thorough troubleshooting, and effective communication within the team to maintain reliable and efficient data center interconnect operations.