When you start the mongos instance and specify the adresse of a config server, and this address is an IPV6, mongos can't resolve it because it parse it as a normal IP or hostname.

https://github.com/mongodb/mongo/blob/master/src/mongo/s/config.cpp#L984
to resolve this issue we can remplace:

 if ( name.find( ":" ) != string::npos ) {
            if ( withPort )
                return name;
            return name.substr( 0 , name.find( ":" ) );
        }

by:

 if ( name.find( ":" ) != string::npos ) {
            if ( withPort )
                return name;
            return name.substr( 0 , name.find_last_of( ":" ) );
        }

Example:

2001:0db8:0000:85a3:0000:0000:ac1f:8001:port

mongos will try to resolve "2001" as the host part of the adresse intead of 2001:0db8:0000:85a3:0000:0000:ac1f:8001