configured AWS Cli on Linux system.
While running any command like "aws ec2 describe-instances" it is showing error "Invalid IPv6 URL"
Ran into the same error. 
Running this command fixed the error for me:
export AWS_DEFAULT_REGION=us-east-1
You might also try specifying the region when running any command:
aws s3 ls --region us-east-1
Hope this helps!
or run aws configure and enter valid region for default region name
Invalid IPv6 URL while running commands using AWS CLI