/// <reference types="node" />
import * as dns from 'dns';
export declare type DnsLookupFunction = Omit<typeof dns.lookup, '__promisify__'>;
export declare class CachedDns {
    private cacheDurationMs;
    private cache;
    constructor(cacheDurationMs: number);
    private cacheKey;
    lookup: DnsLookupFunction;
}
export declare function dnsLookup(lookupFn: typeof dns.lookup | DnsLookupFunction, hostname: string): Promise<string>;
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