virtualbox.org

run the command:" Vboxmanage showvminfo <vmname>
The various Nics will be in the list.

The developers decided that folks needed to only see four NICs in the guest settings. I suggested showing all the possible NICs, or at least putting in a setting that would open up the number of NIC tabs in the main window to a higher limit than four, but it was negated on the forum and still dangles on the vine in the Bugtracker.

Moureg wrote:

scottgus1 wrote:I have never tried entering these commands, maybe you jus need to run them all again?

it's the same for me as I always used to work with 4 adapters not more.

I noticed it , it's because of none word it should be null.

VBoxManage modifyvm com.cisco.ios-xrv_1 --nic5 null

As my stalled work with gns3 is restored because I managed to get in done with virtualbox ,
I'd like to Thank scottgus1 for his great support here .

Much Thanks for you man and for all people here who responded and contributed here.