You have a DMVPN hub with the following configuration applied:

Last Updated on August 1, 2021 by Admin 1

You have a DMVPN hub with the following configuration applied:

300-410 Part 07 Q19 092
300-410 Part 07 Q19 092

What problem could occur if the bandwidth 1000 command were missing from the tunnel interface?

  • the tunnel interface will intermittently flap up and down
  • split horizon will prevent routing updates from traversing from spoke to spoke
  • congestion will develop in the tunnel interface
  • the IPsec association will fail
In the absence of a bandwidth command on the tunnel interface, the default bandwidth on a tunnel interface is 9 Kbps. EIGRP will use 50% of that (4.5K), which is too low. This will cause problems with the maintenance of EIGRP neighbor relationships. From time to time this will cause the tunnel to flap up and then down as the relationships go up and down. When you execute the bandwidth command it has no real effect on the bandwidth of the link but it will allow EIGRP to use 50% of 10k or 5k for its purposes, leaving 4k for data. This will have little impact on the data while maintaining the neighbor relationships.

The bandwidth command will have no effect on split horizon. There will be no problems with split horizon, even though the output shows that it has been disabled on the tunnel interface with the no ip split-horizon eigrp 1 command.

The bandwidth command will not cause congestion on the link. It will only lower the bandwidth available to data from 4.5K to 4K.

The bandwidth command will not cause the IPsec association to fail. There is sufficient bandwidth for this process.

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Describe DMVPN (single hub)

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