internal/output/stats.go

@@ -144,6 +144,8 @@ func summaryTypeLabel(respType string) string {
 		return "query type not implemented by server"
 	case "cname_loop":
 		return "resulted in a CNAME loop"
+	case "ns_error":
+		return "nameserver lookup failed"
 	case "error":
 		return "resulted in an error"
 	case "referral":

internal/output/stats_test.go

@@ -88,6 +88,7 @@ func TestSummaryTypeLabelAllTypes(t *testing.T) {
 		"refused":    "query refused by server",
 		"notimp":     "query type not implemented by server",
 		"cname_loop": "resulted in a CNAME loop",
+		"ns_error":   "nameserver lookup failed",
 		"error":      "resulted in an error",
 		"referral":   "resulted in a referral",
 		"unknown_type": "unknown_type",

internal/output/text.go

@@ -220,6 +220,12 @@ func (f *textFormatter) formatResultLine(result traverse.TraversalResult) string
 			msg = result.Response.ErrorMessage
 		}
 		return f.colorize(fmt.Sprintf("%s %s", prob, msg), colorRed)
+	case traverse.RespNSResolutionFailed:
+		msg := "nameserver lookup failed"
+		if result.Response.ErrorMessage != "" {
+			msg = result.Response.ErrorMessage
+		}
+		return f.colorize(fmt.Sprintf("%s %s", prob, msg), colorYellow)
 	case traverse.RespError:
 		msg := "resulted in an error"
 		if result.Response.ErrorMessage != "" {

internal/output/text_test.go

@@ -121,6 +121,7 @@ Answers: []miekgdns.RR{
 {"refused", traverse.RespREFUSED, nil, ""},
 {"notimp", traverse.RespNOTIMPL, nil, ""},
 {"cname_loop", traverse.RespCNAMELoop, nil, "loop detected"},
+{"ns_error", traverse.RespNSResolutionFailed, nil, "nameserver ns1.example.com could not be resolved"},
 {"error", traverse.RespError, nil, "something went wrong"},
 }
 

internal/traverse/response.go

@@ -20,6 +20,11 @@ const (
 	RespNOTIMPL
 	RespCNAMELoop
 	RespError
+	// RespNSResolutionFailed indicates that the traversal could not resolve the
+	// IP address of an in-bailiwick nameserver.  The domain may still be
+	// reachable in practice (e.g. via glue records held by the registry), but
+	// the iterative traversal could not complete that path.
+	RespNSResolutionFailed
 )
 
 func (rt ResponseType) String() string {
@@ -44,6 +49,8 @@ func (rt ResponseType) String() string {
 		return "cname_loop"
 	case RespError:
 		return "error"
+	case RespNSResolutionFailed:
+		return "ns_error"
 	default:
 		return "unknown"
 	}
@@ -231,7 +238,7 @@ func (r *Response) resolveGlue(child *Referral) {
 
 func (r *Response) IsTerminal() bool {
 	switch r.Type {
-	case RespAnswer, RespNODATA, RespNXDOMAIN, RespSERVFAIL, RespREFUSED, RespNOTIMPL, RespCNAMELoop, RespError:
+	case RespAnswer, RespNODATA, RespNXDOMAIN, RespSERVFAIL, RespREFUSED, RespNOTIMPL, RespCNAMELoop, RespError, RespNSResolutionFailed:
 		return true
 	default:
 		return false

internal/traverse/response_test.go

@@ -246,6 +246,7 @@ func TestResponseIsTerminal(t *testing.T) {
 		{RespNXDOMAIN, true},
 		{RespSERVFAIL, true},
 		{RespError, true},
+		{RespNSResolutionFailed, true},
 		{RespReferral, false},
 		{RespCNAMEFollow, false},
 	}
@@ -272,6 +273,7 @@ func TestResponseTypeString(t *testing.T) {
 		{RespNXDOMAIN, "nxdomain"},
 		{RespSERVFAIL, "servfail"},
 		{RespError, "error"},
+		{RespNSResolutionFailed, "ns_error"},
 	}
 
 	for _, tt := range tests {

internal/traverse/traverser.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"fmt"
 	"net"
+	"strings"
 	"sync"
 	"time"
 
@@ -232,18 +233,28 @@ func (t *Traverser) processReferral(ctx context.Context, ref *Referral, cache *I
 		} else {
 			addrs, err := t.ResolveNS(ctx, ref.Name, cache, visitedCopy, t.depth)
 			if err != nil {
+				nsName := strings.TrimSuffix(ref.Bailiwick, ".")
+				if nsName == "" || nsName == "." {
+					nsName = strings.TrimSuffix(ref.Name, ".")
+				}
 				return &Response{
-					Referral: ref,
-					Type:     RespError,
+					Referral:     ref,
+					Type:         RespNSResolutionFailed,
+					ErrorMessage: fmt.Sprintf("nameserver %s could not be resolved", nsName),
 				}
 			}
 			if len(addrs) > 0 {
 				ref.Addresses = addrs
 				ref.State = StateResolved
 			} else {
+				nsName := strings.TrimSuffix(ref.Bailiwick, ".")
+				if nsName == "" || nsName == "." {
+					nsName = strings.TrimSuffix(ref.Name, ".")
+				}
 				return &Response{
-					Referral: ref,
-					Type:     RespError,
+					Referral:     ref,
+					Type:         RespNSResolutionFailed,
+					ErrorMessage: fmt.Sprintf("nameserver %s could not be resolved", nsName),
 				}
 			}
 		}