Yes — cdc.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 cdc.gov has 2 IPv6 addresses and answers on every one we tested. ✓ 2600:1408:c400:11::17cd:6b56 answers · 443✓ 2600:1408:c400:11::17cd:6b44 answers · 443	yes
www over IPv6 www.cdc.gov has 2 IPv6 addresses and answers on every one we tested. ✓ 2600:1408:c400:78c::2461 answers · 443✓ 2600:1408:c400:784::2461 answers · 443	yes
Mail servers (MX) have IPv6 None of the mail servers has an AAAA record. alt2.us.etp.fireeyegov.com ✗alt3.us.etp.fireeyegov.com ✗primary.us.etp.fireeyegov.com ✗alt1.us.etp.fireeyegov.com ✗	no
Nameservers have IPv6 6 of 6 nameservers checked have an AAAA record, so IPv6-only resolvers can look the domain up. a2-64.akam.net ✓a1-43.akam.net ✓a9-64.akam.net ✓a8-67.akam.net ✓a28-65.akam.net ✓a5-66.akam.net ✓	yes

HTTPS over IPv6 · not part of the grade yet
Loads over IPv6 with a valid certificate after 2 redirects: HTTP 200.

https://cdc.gov/ via 2600:1408:c400:11::17cd:6b56 → 301https://www.cdc.gov/ via 2600:1408:c400:78c::2461 → 301https://www.cdc.gov/index.html via 2600:1408:c400:78c::2461 → 200

works

What's keeping cdc.gov from an A

Mail servers without IPv6
alt2.us.etp.fireeyegov.com, alt3.us.etp.fireeyegov.com, primary.us.etp.fireeyegov.com, alt1.us.etp.fireeyegov.com 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

cdc.gov Has IPv6

A (IPv4)	23.205.107.68 23.205.107.86
AAAA (IPv6)	2600:1408:c400:11::17cd:6b56 2600:1408:c400:11::17cd:6b44

www.cdc.gov Has IPv6

A (IPv4)	23.49.180.79
AAAA (IPv6)	2600:1408:c400:78c::2461 2600:1408:c400:784::2461

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: cdc.gov
Measured 2026-10-31 08:05:19 UTC by aaaa.bot (one server on Fly.io, region iad)

A (IPv4):    23.205.107.68, 23.205.107.86
AAAA (IPv6): 2600:1408:c400:11::17cd:6b56, 2600:1408:c400:11::17cd:6b44
www AAAA:    2600:1408:c400:78c::2461, 2600:1408:c400:784::2461

Readiness grade B: Works over IPv6, with one gap: its mail servers lack IPv6.
- Website over IPv6: cdc.gov has 2 IPv6 addresses and answers on every one we tested.
    2600:1408:c400:11::17cd:6b56: answers (TCP 443)
    2600:1408:c400:11::17cd:6b44: answers (TCP 443)
- www over IPv6: www.cdc.gov has 2 IPv6 addresses and answers on every one we tested.
    2600:1408:c400:78c::2461: answers (TCP 443)
    2600:1408:c400:784::2461: answers (TCP 443)
- Mail servers (MX) have IPv6: None of the mail servers has an AAAA record.
- Nameservers have IPv6: 6 of 6 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 2 redirects: HTTP 200.
    https://cdc.gov/ via 2600:1408:c400:11::17cd:6b56 -> HTTP 301, certificate: valid
    https://www.cdc.gov/ via 2600:1408:c400:78c::2461 -> HTTP 301, certificate: valid
    https://www.cdc.gov/index.html via 2600:1408:c400:78c::2461 -> HTTP 200, certificate: valid
DNS answers via DNS-over-HTTPS (Cloudflare). Method: https://aaaa.bot/method
Permanent link: https://aaaa.bot/r/JSLPaxKx0F

Permanent link: aaaa.bot/r/JSLPaxKx0F · How we measure

Checked 2026-10-31 08:05:19 UTC. Full DNS report: dns.pizza/domain/cdc.gov · JSON: /api/v1/cdc.gov