Question 1

What's the core difference between HTTP/2 and HTTP/3?

Accepted Answer

HTTP/2 multiplexes streams over a single TCP connection, but TCP still enforces sequential packet delivery, if one packet is lost, all streams stall (head-of-line blocking). HTTP/3 uses QUIC (UDP-based), where lost packets affect only individual streams, not the entire connection. Result: HTTP/3 is ~15-30% faster on mobile, especially on 4G/5G with packet loss. Desktop performance is similar (both fast), but HTTP/3 wins on high-latency or lossy networks.

Question 2

When should I use HTTP/3 vs HTTP/2?

Accepted Answer

HTTP/2 is the safe default in 2026, 98% of modern servers support it, browsers are mature. Use HTTP/2 everywhere your CDN supports it. Enable HTTP/3 alongside HTTP/2 (no downside) if your CDN supports QUIC (Cloudflare, Fastly, AWS CloudFront all do). HTTP/3 shines for mobile users on 4G, video streaming, and gaming. Desktop/broadband users won't notice much difference.

Question 3

How do QUIC and head-of-line blocking relate?

Accepted Answer

In TCP, if packet 5 is lost, the OS buffers packets 6+ until packet 5 arrives, all streams freeze. QUIC streams are independent: if stream A loses a packet, stream B continues unaffected. This is why HTTP/3 over QUIC is faster on unreliable networks. Modern LTE/5G drop ~1-2% of packets; QUIC's stream isolation matters more than older protocols assumed.

Question 4

Is TLS 1.3 required for HTTP/3?

Accepted Answer

Yes. HTTP/3 and QUIC mandate TLS 1.3 (released 2018), which is faster and safer than TLS 1.2. The entire QUIC handshake includes TLS 1.3 encryption from the start (0-RTT resumption available for repeat connections). TLS 1.2 is NOT compatible with HTTP/3. All modern clients support TLS 1.3; older IE 11 (end-of-life 2022) does not. Not a concern.

Question 5

Should I enable HTTP/2 server push? Is it still relevant?

Accepted Answer

Avoid aggressive server push. Initial enthusiasm faded because: (1) push ignores browser cache (wastes bandwidth if client already has the resource), (2) CDN/browser caching typically outperforms it, (3) HTTP/3 preload headers are preferred. Selective push (small critical assets on first visit only, behind feature flags) can help. Better approach: optimize images, lazy-load non-critical JS, use resource hints (`<link rel=preload>`). Push is deprecated in HTTP/3.

Question 6

What's browser support for HTTP/3 in 2026?

Accepted Answer

Chrome/Edge 90+, Firefox 88+, Safari 16.4+ all support HTTP/3. Combined, they cover ~92% of desktop users and ~88% of mobile. Mobile browsers are nearly universal (iOS 15.1+, all Android browsers). Legacy IE 11 (0.5% share) doesn't support it, but it doesn't support HTTP/2 server push either. Safe to enable HTTP/3 on all public sites.

Question 7

How do I debug QUIC and HTTP/3 issues?

Accepted Answer

Wireshark with QUIC dissector (GnuTLS or OpenSSL support required) captures QUIC packets. Chrome DevTools Network panel shows HTTP/3 protocol in the 'Protocol' column. `h2load` (Apache HTTP/2 load test tool) supports HTTP/3 with `--npn h3` flag. For production, check CDN dashboards (Cloudflare Analytics shows HTTP/3 %). ngtcp2 command-line client: `ngtcp2 -d 1000 example.com`. tcpdump + Wireshark is the heavyweight option.

प्रदेश	ज्युनियर	मध्यम	सीनियर
USA	$100k	$135k	$180k
UK	£58k	£78k	£115k
EU	€62k	€85k	€125k
CANADA	C$105k	C$142k	C$190k

HTTP/2 and HTTP/3

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