diff --git a/cmd/utils/flags.go b/cmd/utils/flags.go
index a50fdd968a35..a81188342f60 100644
--- a/cmd/utils/flags.go
+++ b/cmd/utils/flags.go
@@ -1690,11 +1690,7 @@ func SetDNSDiscoveryDefaults(cfg *ethconfig.Config, genesis common.Hash) {
 	}
 	if url := params.KnownDNSNetwork(genesis, protocol); url != "" {
 		cfg.EthDiscoveryURLs = []string{url}
-	}
-	if cfg.SyncMode == downloader.SnapSync {
-		if url := params.KnownDNSNetwork(genesis, "snap"); url != "" {
-			cfg.SnapDiscoveryURLs = []string{url}
-		}
+		cfg.SnapDiscoveryURLs = cfg.EthDiscoveryURLs
 	}
 }
 
diff --git a/eth/backend.go b/eth/backend.go
index 7aac17eeb329..7d8b0c52c6a4 100644
--- a/eth/backend.go
+++ b/eth/backend.go
@@ -50,6 +50,7 @@ import (
 	"github.com/ethereum/go-ethereum/miner"
 	"github.com/ethereum/go-ethereum/node"
 	"github.com/ethereum/go-ethereum/p2p"
+	"github.com/ethereum/go-ethereum/p2p/dnsdisc"
 	"github.com/ethereum/go-ethereum/p2p/enode"
 	"github.com/ethereum/go-ethereum/params"
 	"github.com/ethereum/go-ethereum/rlp"
@@ -239,14 +240,17 @@ func New(stack *node.Node, config *ethconfig.Config) (*Ethereum, error) {
 	}
 	eth.APIBackend.gpo = gasprice.NewOracle(eth.APIBackend, gpoParams)
 
-	eth.ethDialCandidates, err = setupDiscovery(eth.config.EthDiscoveryURLs)
+	// Setup DNS discovery iterators.
+	dnsclient := dnsdisc.NewClient(dnsdisc.Config{})
+	eth.ethDialCandidates, err = dnsclient.NewIterator(eth.config.EthDiscoveryURLs...)
 	if err != nil {
 		return nil, err
 	}
-	eth.snapDialCandidates, err = setupDiscovery(eth.config.SnapDiscoveryURLs)
+	eth.snapDialCandidates, err = dnsclient.NewIterator(eth.config.SnapDiscoveryURLs...)
 	if err != nil {
 		return nil, err
 	}
+
 	// Start the RPC service
 	eth.netRPCService = ethapi.NewPublicNetAPI(eth.p2pServer, config.NetworkId)
 
@@ -544,6 +548,8 @@ func (s *Ethereum) Start() error {
 // Ethereum protocol.
 func (s *Ethereum) Stop() error {
 	// Stop all the peer-related stuff first.
+	s.ethDialCandidates.Close()
+	s.snapDialCandidates.Close()
 	s.handler.Stop()
 
 	// Then stop everything else.
diff --git a/eth/discovery.go b/eth/discovery.go
index 855ce3b0e1f4..70668b2b70bf 100644
--- a/eth/discovery.go
+++ b/eth/discovery.go
@@ -19,7 +19,6 @@ package eth
 import (
 	"github.com/ethereum/go-ethereum/core"
 	"github.com/ethereum/go-ethereum/core/forkid"
-	"github.com/ethereum/go-ethereum/p2p/dnsdisc"
 	"github.com/ethereum/go-ethereum/p2p/enode"
 	"github.com/ethereum/go-ethereum/rlp"
 )
@@ -62,13 +61,3 @@ func (eth *Ethereum) currentEthEntry() *ethEntry {
 	return &ethEntry{ForkID: forkid.NewID(eth.blockchain.Config(), eth.blockchain.Genesis().Hash(),
 		eth.blockchain.CurrentHeader().Number.Uint64())}
 }
-
-// setupDiscovery creates the node discovery source for the `eth` and `snap`
-// protocols.
-func setupDiscovery(urls []string) (enode.Iterator, error) {
-	if len(urls) == 0 {
-		return nil, nil
-	}
-	client := dnsdisc.NewClient(dnsdisc.Config{})
-	return client.NewIterator(urls...)
-}
diff --git a/eth/protocols/snap/handler.go b/eth/protocols/snap/handler.go
index 9bfac6f03ff7..3d668a2ebb6f 100644
--- a/eth/protocols/snap/handler.go
+++ b/eth/protocols/snap/handler.go
@@ -84,6 +84,12 @@ type Backend interface {
 
 // MakeProtocols constructs the P2P protocol definitions for `snap`.
 func MakeProtocols(backend Backend, dnsdisc enode.Iterator) []p2p.Protocol {
+	// Filter the discovery iterator for nodes advertising snap support.
+	dnsdisc = enode.Filter(dnsdisc, func(n *enode.Node) bool {
+		var snap enrEntry
+		return n.Load(&snap) == nil
+	})
+
 	protocols := make([]p2p.Protocol, len(ProtocolVersions))
 	for i, version := range ProtocolVersions {
 		version := version // Closure
diff --git a/go.mod b/go.mod
index 63636caae130..079d40ae6fed 100644
--- a/go.mod
+++ b/go.mod
@@ -60,6 +60,7 @@ require (
 	github.com/tklauser/go-sysconf v0.3.5 // indirect
 	github.com/tyler-smith/go-bip39 v1.0.1-0.20181017060643-dbb3b84ba2ef
 	golang.org/x/crypto v0.0.0-20210322153248-0c34fe9e7dc2
+	golang.org/x/sync v0.0.0-20210220032951-036812b2e83c // indirect
 	golang.org/x/sys v0.0.0-20210420205809-ac73e9fd8988
 	golang.org/x/text v0.3.4
 	golang.org/x/time v0.0.0-20201208040808-7e3f01d25324
diff --git a/go.sum b/go.sum
index cadcd1de95cf..3ae80f7b9c65 100644
--- a/go.sum
+++ b/go.sum
@@ -455,6 +455,8 @@ golang.org/x/sync v0.0.0-20190911185100-cd5d95a43a6e/go.mod h1:RxMgew5VJxzue5/jJ
 golang.org/x/sync v0.0.0-20200317015054-43a5402ce75a/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sync v0.0.0-20201020160332-67f06af15bc9 h1:SQFwaSi55rU7vdNs9Yr0Z324VNlrF+0wMqRXT4St8ck=
 golang.org/x/sync v0.0.0-20201020160332-67f06af15bc9/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
+golang.org/x/sync v0.0.0-20210220032951-036812b2e83c h1:5KslGYwFpkhGh+Q16bwMP3cOontH8FOep7tGV86Y7SQ=
+golang.org/x/sync v0.0.0-20210220032951-036812b2e83c/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sys v0.0.0-20180830151530-49385e6e1522/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20180905080454-ebe1bf3edb33/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20180909124046-d0be0721c37e/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
diff --git a/p2p/dnsdisc/client.go b/p2p/dnsdisc/client.go
index 3e4b50aaddb0..f2a4bed4c6e4 100644
--- a/p2p/dnsdisc/client.go
+++ b/p2p/dnsdisc/client.go
@@ -32,15 +32,17 @@ import (
 	"github.com/ethereum/go-ethereum/p2p/enode"
 	"github.com/ethereum/go-ethereum/p2p/enr"
 	lru "github.com/hashicorp/golang-lru"
+	"golang.org/x/sync/singleflight"
 	"golang.org/x/time/rate"
 )
 
 // Client discovers nodes by querying DNS servers.
 type Client struct {
-	cfg       Config
-	clock     mclock.Clock
-	entries   *lru.Cache
-	ratelimit *rate.Limiter
+	cfg          Config
+	clock        mclock.Clock
+	entries      *lru.Cache
+	ratelimit    *rate.Limiter
+	singleflight singleflight.Group
 }
 
 // Config holds configuration options for the client.
@@ -135,17 +137,20 @@ func (c *Client) NewIterator(urls ...string) (enode.Iterator, error) {
 
 // resolveRoot retrieves a root entry via DNS.
 func (c *Client) resolveRoot(ctx context.Context, loc *linkEntry) (rootEntry, error) {
-	txts, err := c.cfg.Resolver.LookupTXT(ctx, loc.domain)
-	c.cfg.Logger.Trace("Updating DNS discovery root", "tree", loc.domain, "err", err)
-	if err != nil {
-		return rootEntry{}, err
-	}
-	for _, txt := range txts {
-		if strings.HasPrefix(txt, rootPrefix) {
-			return parseAndVerifyRoot(txt, loc)
+	e, err, _ := c.singleflight.Do(loc.str, func() (interface{}, error) {
+		txts, err := c.cfg.Resolver.LookupTXT(ctx, loc.domain)
+		c.cfg.Logger.Trace("Updating DNS discovery root", "tree", loc.domain, "err", err)
+		if err != nil {
+			return rootEntry{}, err
 		}
-	}
-	return rootEntry{}, nameError{loc.domain, errNoRoot}
+		for _, txt := range txts {
+			if strings.HasPrefix(txt, rootPrefix) {
+				return parseAndVerifyRoot(txt, loc)
+			}
+		}
+		return rootEntry{}, nameError{loc.domain, errNoRoot}
+	})
+	return e.(rootEntry), err
 }
 
 func parseAndVerifyRoot(txt string, loc *linkEntry) (rootEntry, error) {
@@ -168,17 +173,21 @@ func (c *Client) resolveEntry(ctx context.Context, domain, hash string) (entry,
 	if err := c.ratelimit.Wait(ctx); err != nil {
 		return nil, err
 	}
-
 	cacheKey := truncateHash(hash)
 	if e, ok := c.entries.Get(cacheKey); ok {
 		return e.(entry), nil
 	}
-	e, err := c.doResolveEntry(ctx, domain, hash)
-	if err != nil {
-		return nil, err
-	}
-	c.entries.Add(cacheKey, e)
-	return e, nil
+
+	ei, err, _ := c.singleflight.Do(cacheKey, func() (interface{}, error) {
+		e, err := c.doResolveEntry(ctx, domain, hash)
+		if err != nil {
+			return nil, err
+		}
+		c.entries.Add(cacheKey, e)
+		return e, nil
+	})
+	e, _ := ei.(entry)
+	return e, err
 }
 
 // doResolveEntry fetches an entry via DNS.