From b2f269d5b7bb04c226cf509c3794481ef4395519 Mon Sep 17 00:00:00 2001
From: Maisem Ali <maisem@tailscale.com>
Date: Thu, 24 Mar 2022 22:21:41 -0700
Subject: [PATCH] net/dnsfallback: do not attempt lookups of IPs.

Currently if the passed in host is an IP, Lookup still attempts to
resolve it with a dns server. This makes it just return the IP directly.

Updates tailscale/corp#4475

Signed-off-by: Maisem Ali <maisem@tailscale.com>
---
 net/dnsfallback/dnsfallback.go | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/net/dnsfallback/dnsfallback.go b/net/dnsfallback/dnsfallback.go
index 0e09861eb..20dc3be8c 100644
--- a/net/dnsfallback/dnsfallback.go
+++ b/net/dnsfallback/dnsfallback.go
@@ -27,6 +27,10 @@ import (
 )
 
 func Lookup(ctx context.Context, host string) ([]netaddr.IP, error) {
+	if ip, err := netaddr.ParseIP(host); err == nil && !ip.IsZero() {
+		return []netaddr.IP{ip}, nil
+	}
+
 	type nameIP struct {
 		dnsName string
 		ip      netaddr.IP