Yes — cancer.gov has IPv6.

Has both IPv4 (A) and IPv6 (AAAA) addresses.

IPv6 readiness

Works over IPv6, with one gap: its mail servers lack IPv6.

Website over IPv6 cancer.gov has an AAAA record and answers on it. ✓ 2607:f220:41d:21c1::812b:fe27 answers · 443	yes
www over IPv6 www.cancer.gov has 2 IPv6 addresses and answers on every one we tested. ✓ 2600:1408:5400:35::17ca:e6c8 answers · 443✓ 2600:1408:5400:35::17ca:e6e0 answers · 443	yes
Mail servers (MX) have IPv6 At least one mail server has no AAAA record (8 of 10 checked do). nihcesxway.hub.nih.gov ✗nihcesxway2.hub.nih.gov ✗nihcesxway3.hub.nih.gov ✓nihcesxway4.hub.nih.gov ✓nihcesxway5.hub.nih.gov ✓nihcesxwayst01.hub.nih.gov ✓nihcesxwayst02.hub.nih.gov ✓nihcesxwayst03.hub.nih.gov ✓nihcesxwayst04.hub.nih.gov ✓nihcesxwayst05.hub.nih.gov ✓	partly
Nameservers have IPv6 3 of 3 nameservers checked have an AAAA record, so IPv6-only resolvers can look the domain up. ns.nih.gov ✓ns2.nih.gov ✓ns3.nih.gov ✓	yes

First measured 2026-11-06; last confirmed 2026-11-06.

HTTPS over IPv6 · not part of the grade yet
Loads over IPv6 with a valid certificate after 1 redirect: HTTP 200.

https://cancer.gov/ via 2607:f220:41d:21c1::812b:fe27 → 301https://www.cancer.gov/ via 2600:1408:5400:35::17ca:e6c8 → 200

works

What's keeping cancer.gov from an A

Mail servers without IPv6
nihcesxway.hub.nih.gov, nihcesxway2.hub.nih.gov have no AAAA record, so mail from IPv6-only servers can't reach them directly. If a provider runs your mail, that's their setting; if you run it, add AAAA records for these hosts.

Check again

cancer.gov Has IPv6

A (IPv4)	129.43.254.39
AAAA (IPv6)	2607:f220:41d:21c1::812b:fe27

www.cancer.gov Has IPv6

Alias of	akamai-prod.cancer.gov.edgekey.net → e336944.dscb.akamaiedge.net
A (IPv4)	23.48.203.176 23.48.203.184
AAAA (IPv6)	2600:1408:5400:35::17ca:e6c8 2600:1408:5400:35::17ca:e6e0

Browsers on dual-stack networks will usually pick IPv6 here (the "Happy Eyeballs" algorithm races both and prefers v6).

Copy the evidence — a citation-ready record of this measurement

IPv6 measurement: cancer.gov
Measured 2026-11-15 17:08:32 UTC by aaaa.bot (one server on Fly.io, region iad)

A (IPv4):    129.43.254.39
AAAA (IPv6): 2607:f220:41d:21c1::812b:fe27
www AAAA:    2600:1408:5400:35::17ca:e6c8, 2600:1408:5400:35::17ca:e6e0

Readiness grade B: Works over IPv6, with one gap: its mail servers lack IPv6.
- Website over IPv6: cancer.gov has an AAAA record and answers on it.
    2607:f220:41d:21c1::812b:fe27: answers (TCP 443)
- www over IPv6: www.cancer.gov has 2 IPv6 addresses and answers on every one we tested.
    2600:1408:5400:35::17ca:e6c8: answers (TCP 443)
    2600:1408:5400:35::17ca:e6e0: answers (TCP 443)
- Mail servers (MX) have IPv6: At least one mail server has no AAAA record (8 of 10 checked do).
- Nameservers have IPv6: 3 of 3 nameservers checked have an AAAA record, so IPv6-only resolvers can look the domain up.

Reachability = a TCP connection opened on port 443 (or 80).

HTTPS over IPv6 (not graded): Loads over IPv6 with a valid certificate after 1 redirect: HTTP 200.
    https://cancer.gov/ via 2607:f220:41d:21c1::812b:fe27 -> HTTP 301, certificate: valid
    https://www.cancer.gov/ via 2600:1408:5400:35::17ca:e6c8 -> HTTP 200, certificate: valid
DNS answers via DNS-over-HTTPS (Cloudflare). Method: https://aaaa.bot/method
Permanent link: https://aaaa.bot/r/at5xYgs_g1

Permanent link: aaaa.bot/r/at5xYgs_g1 · How we measure

Checked 2026-11-15 17:08:32 UTC. Full DNS report: dns.pizza/domain/cancer.gov · Age, certificate and blocklists: how.is/cancer.gov · JSON: /api/v1/cancer.gov