External address detection does not work in small sw... | libp2p/go-libp2p

I'm operating a small private IPFS (+ other things making use of the IPFS DHT) swarm (~16 nodes, give or take) and I'm playing around with DCUtR. I've discovered that none of the nodes behind NAT seem to be aware of their own public IP address (not present in node.Addrs()). This happens on Kubo (v0.16.0) nodes as well as on nodes running the libp2p program I'm working on. Here's a debug log from one of the custom nodes:

2022-11-12T01:02:00.672+0100	DEBUG	net/identify	identify/obsaddr.go:397	added own observed listen addr	{"observed": "/ip4/my.public.ip.addr/tcp/8001"}
2022-11-12T01:02:00.672+0100	DEBUG	net/identify	identify/obsaddr.go:397	added own observed listen addr	{"observed": "/ip4/my.public.ip.addr/tcp/8001"}
2022-11-12T01:02:00.851+0100	DEBUG	net/identify	identify/obsaddr.go:397	added own observed listen addr	{"observed": "/ip4/my.public.ip.addr/tcp/8001"}
2022-11-12T01:02:00.851+0100	DEBUG	net/identify	identify/obsaddr.go:397	added own observed listen addr	{"observed": "/ip4/my.public.ip.addr/tcp/8001"}
2022-11-12T01:02:00.857+0100	DEBUG	net/identify	identify/obsaddr.go:397	added own observed listen addr	{"observed": "/ip4/my.public.ip.addr/tcp/8001"}
2022-11-12T01:02:00.857+0100	DEBUG	net/identify	identify/obsaddr.go:397	added own observed listen addr	{"observed": "/ip4/my.public.ip.addr/tcp/8001"}
2022-11-12T01:02:00.888+0100	DEBUG	net/identify	identify/obsaddr.go:397	added own observed listen addr	{"observed": "/ip4/my.public.ip.addr/tcp/8001"}
2022-11-12T01:02:00.888+0100	DEBUG	net/identify	identify/obsaddr.go:397	added own observed listen addr	{"observed": "/ip4/my.public.ip.addr/tcp/8001"}
2022-11-12T01:02:00.896+0100	DEBUG	net/identify	identify/obsaddr.go:397	added own observed listen addr	{"observed": "/ip4/my.public.ip.addr/tcp/8001"}
2022-11-12T01:02:00.896+0100	DEBUG	net/identify	identify/obsaddr.go:397	added own observed listen addr	{"observed": "/ip4/my.public.ip.addr/tcp/8001"}
2022-11-12T01:02:00.932+0100	DEBUG	net/identify	identify/obsaddr.go:397	added own observed listen addr	{"observed": "/ip4/my.public.ip.addr/tcp/8001"}
2022-11-12T01:02:00.932+0100	DEBUG	net/identify	identify/obsaddr.go:397	added own observed listen addr	{"observed": "/ip4/my.public.ip.addr/tcp/8001"}
2022-11-12T01:02:01.647+0100	DEBUG	autonat	autonat/autonat.go:312	NAT status is private
2022-11-12T01:02:01.647+0100	DEBUG	autonat	autonat/autonat.go:312	NAT status is private
2022-11-12T01:02:15.827+0100	DEBUG	autonat	autonat/autonat.go:312	NAT status is private
2022-11-12T01:02:15.827+0100	DEBUG	autonat	autonat/autonat.go:312	NAT status is private
2022-11-12T01:02:15.901+0100	DEBUG	autonat	autonat/autonat.go:312	NAT status is private
2022-11-12T01:02:15.901+0100	DEBUG	autonat	autonat/autonat.go:312	NAT status is private
2022-11-12T01:02:15.901+0100	DEBUG	autonat	autonat/autonat.go:312	NAT status is private
2022-11-12T01:02:15.901+0100	DEBUG	autonat	autonat/autonat.go:312	NAT status is private
2022-11-12T01:02:15.943+0100	DEBUG	autonat	autonat/autonat.go:312	NAT status is private
2022-11-12T01:02:15.943+0100	DEBUG	autonat	autonat/autonat.go:312	NAT status is private
2022-11-12T01:02:15.943+0100	DEBUG	autonat	autonat/autonat.go:312	NAT status is private
2022-11-12T01:02:15.943+0100	DEBUG	autonat	autonat/autonat.go:312	NAT status is private
2022-11-12T01:02:15.970+0100	DEBUG	autonat	autonat/autonat.go:312	NAT status is private
2022-11-12T01:02:15.970+0100	DEBUG	autonat	autonat/autonat.go:312	NAT status is private

I have two guesses as to why that might be happening, either or:

As you can see in the log, AutoNAT finishes after the obsaddr events have stopped. I'm assuming this code prevents the observation from actually doing anything before the node knows it's behind a NAT: https://github.com/libp2p/go-libp2p/blob/1ad0a50be62b1e00388b9d85fc997d66e8910c9d/p2p/protocol/identify/obsaddr.go#L405-L407
I also did the same test in the regular IPFS swarm. The most notable observation is that obsaddr messages are also coming in after the AutoNAT messages.
There's a threshold on how many times the public address needs to be observed before it's accepted that I'm unaware of, and my swarm is too small to cross that threshold.

Version Information

cloud.google.com/go v0.65.0
cloud.google.com/go/bigquery v1.8.0
cloud.google.com/go/datastore v1.1.0
cloud.google.com/go/pubsub v1.3.1
cloud.google.com/go/storage v1.10.0
dmitri.shuralyov.com/app/changes v0.0.0-20180602232624-0a106ad413e3
dmitri.shuralyov.com/gpu/mtl v0.0.0-20190408044501-666a987793e9
dmitri.shuralyov.com/html/belt v0.0.0-20180602232347-f7d459c86be0
dmitri.shuralyov.com/service/change v0.0.0-20181023043359-a85b471d5412
dmitri.shuralyov.com/state v0.0.0-20180228185332-28bcc343414c
git.apache.org/thrift.git v0.0.0-20180902110319-2566ecd5d999
github.com/AndreasBriese/bbloom v0.0.0-20190825152654-46b345b51c96
github.com/BurntSushi/toml v0.3.1
github.com/BurntSushi/xgb v0.0.0-20160522181843-27f122750802
github.com/DataDrake/cli-ng/v2 v2.0.2
github.com/alecthomas/template v0.0.0-20190718012654-fb15b899a751
github.com/alecthomas/units v0.0.0-20190924025748-f65c72e2690d
github.com/anmitsu/go-shlex v0.0.0-20161002113705-648efa622239
github.com/benbjohnson/clock v1.3.0
github.com/beorn7/perks v1.0.1
github.com/bradfitz/go-smtpd v0.0.0-20170404230938-deb6d6237625
github.com/buger/jsonparser v0.0.0-20181115193947-bf1c66bbce23
github.com/census-instrumentation/opencensus-proto v0.2.1
github.com/cespare/xxhash v1.1.0
github.com/cespare/xxhash/v2 v2.1.2
github.com/cheekybits/genny v1.0.0
github.com/chzyer/logex v1.1.10
github.com/chzyer/readline v0.0.0-20180603132655-2972be24d48e
github.com/chzyer/test v0.0.0-20180213035817-a1ea475d72b1
github.com/cilium/ebpf v0.4.0
github.com/client9/misspell v0.3.4
github.com/cncf/udpa/go v0.0.0-20191209042840-269d4d468f6f
github.com/containerd/cgroups v1.0.4
github.com/coreos/go-systemd v0.0.0-20181012123002-c6f51f82210d
github.com/coreos/go-systemd/v22 v22.4.0
github.com/cpuguy83/go-md2man/v2 v2.0.0
github.com/davecgh/go-spew v1.1.1
github.com/davidlazar/go-crypto v0.0.0-20200604182044-b73af7476f6c
github.com/decred/dcrd/crypto/blake256 v1.0.0
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github.com/go-stack/stack v1.8.0
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github.com/google/gopacket v1.1.19
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github.com/google/pprof v0.0.0-20200708004538-1a94d8640e99
github.com/google/renameio v0.1.0
github.com/google/uuid v1.3.0
github.com/googleapis/gax-go v2.0.0+incompatible
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github.com/gopherjs/gopherjs v0.0.0-20181017120253-0766667cb4d1
github.com/gorilla/websocket v1.5.0
github.com/gregjones/httpcache v0.0.0-20180305231024-9cad4c3443a7
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github.com/ipfs/go-cid v0.3.2
github.com/ipfs/go-datastore v0.6.0
github.com/ipfs/go-detect-race v0.0.1
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github.com/ipfs/go-ipfs-util v0.0.2
github.com/ipfs/go-ipns v0.3.0
github.com/ipfs/go-log v1.0.5
github.com/ipfs/go-log/v2 v2.5.1
github.com/ipld/go-ipld-prime v0.18.0
github.com/jackpal/go-nat-pmp v1.0.2
github.com/jbenet/go-cienv v0.1.0
github.com/jbenet/go-temp-err-catcher v0.1.0
github.com/jbenet/goprocess v0.1.4
github.com/jellevandenhooff/dkim v0.0.0-20150330215556-f50fe3d243e1
github.com/jpillora/backoff v1.0.0
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github.com/jstemmer/go-junit-report v0.9.1
github.com/jtolds/gls v4.20.0+incompatible
github.com/julienschmidt/httprouter v1.3.0
github.com/kisielk/errcheck v1.5.0
github.com/kisielk/gotool v1.0.0
github.com/klauspost/compress v1.15.11
github.com/klauspost/cpuid/v2 v2.1.1
github.com/konsorten/go-windows-terminal-sequences v1.0.3
github.com/koron/go-ssdp v0.0.3
github.com/kr/logfmt v0.0.0-20140226030751-b84e30acd515
github.com/kr/pretty v0.3.0
github.com/kr/pty v1.1.3
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github.com/libp2p/go-buffer-pool v0.1.0
github.com/libp2p/go-cidranger v1.1.0
github.com/libp2p/go-flow-metrics v0.1.0
github.com/libp2p/go-libp2p v0.23.4
github.com/libp2p/go-libp2p-asn-util v0.2.0
github.com/libp2p/go-libp2p-core v0.20.0
github.com/libp2p/go-libp2p-kad-dht v0.18.0
github.com/libp2p/go-libp2p-kbucket v0.5.0
github.com/libp2p/go-libp2p-peerstore v0.8.0
github.com/libp2p/go-libp2p-record v0.2.0
github.com/libp2p/go-libp2p-routing-helpers v0.2.3
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github.com/libp2p/go-libp2p-xor v0.1.0
github.com/libp2p/go-mplex v0.7.0
github.com/libp2p/go-msgio v0.2.0
github.com/libp2p/go-nat v0.1.0
github.com/libp2p/go-netroute v0.2.0
github.com/libp2p/go-openssl v0.1.0
github.com/libp2p/go-reuseport v0.2.0
github.com/libp2p/go-sockaddr v0.0.2
github.com/libp2p/go-yamux/v3 v3.1.2
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github.com/libp2p/zeroconf/v2 v2.2.0
github.com/lucas-clemente/quic-go v0.29.1
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github.com/mailru/easyjson v0.0.0-20190312143242-1de009706dbe
github.com/marten-seemann/qpack v0.2.1
github.com/marten-seemann/qtls-go1-16 v0.1.5
github.com/marten-seemann/qtls-go1-17 v0.1.2
github.com/marten-seemann/qtls-go1-18 v0.1.2
github.com/marten-seemann/qtls-go1-19 v0.1.0
github.com/marten-seemann/tcp v0.0.0-20210406111302-dfbc87cc63fd
github.com/marten-seemann/webtransport-go v0.1.1
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github.com/microcosm-cc/bluemonday v1.0.1
github.com/miekg/dns v1.1.50
github.com/mikioh/tcp v0.0.0-20190314235350-803a9b46060c
github.com/mikioh/tcpinfo v0.0.0-20190314235526-30a79bb1804b
github.com/mikioh/tcpopt v0.0.0-20190314235656-172688c1accc
github.com/minio/blake2b-simd v0.0.0-20160723061019-3f5f724cb5b1
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github.com/multiformats/go-base32 v0.1.0
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github.com/multiformats/go-multiaddr v0.7.0
github.com/multiformats/go-multiaddr-dns v0.3.1
github.com/multiformats/go-multiaddr-fmt v0.1.0
github.com/multiformats/go-multibase v0.1.1
github.com/multiformats/go-multicodec v0.6.0
github.com/multiformats/go-multihash v0.2.1
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github.com/neelance/sourcemap v0.0.0-20151028013722-8c68805598ab
github.com/nxadm/tail v1.4.8
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golang.org/x/perf v0.0.0-20180704124530-6e6d33e29852
golang.org/x/sync v0.0.0-20220923202941-7f9b1623fab7
golang.org/x/sys v0.0.0-20220919091848-fb04ddd9f9c8
golang.org/x/term v0.0.0-20210927222741-03fcf44c2211
golang.org/x/text v0.3.7
golang.org/x/time v0.0.0-20191024005414-555d28b269f0
golang.org/x/tools v0.1.12
golang.org/x/xerrors v0.0.0-20200804184101-5ec99f83aff1
google.golang.org/api v0.30.0
google.golang.org/appengine v1.6.6
google.golang.org/genproto v0.0.0-20200825200019-8632dd797987
google.golang.org/grpc v1.33.2
google.golang.org/protobuf v1.28.1
gopkg.in/alecthomas/kingpin.v2 v2.2.6
gopkg.in/check.v1 v1.0.0-20201130134442-10cb98267c6c
gopkg.in/errgo.v2 v2.1.0
gopkg.in/fsnotify.v1 v1.4.7
gopkg.in/inf.v0 v0.9.1
gopkg.in/tomb.v1 v1.0.0-20141024135613-dd632973f1e7
gopkg.in/yaml.v2 v2.4.0
gopkg.in/yaml.v3 v3.0.1
grpc.go4.org v0.0.0-20170609214715-11d0a25b4919
honnef.co/go/tools v0.0.1-2020.1.4
lukechampine.com/blake3 v1.1.7
rsc.io/binaryregexp v0.2.0
rsc.io/quote/v3 v3.1.0
rsc.io/sampler v1.3.0
sourcegraph.com/sourcegraph/go-diff v0.5.0
sourcegraph.com/sqs/pbtypes v0.0.0-20180604144634-d3ebe8f20ae4

External address detection does not work in small swarms

Description

Contributor guide

First steps

Research direction

Assessment