EDNS Size Estimator

Estimate DNS message size and UDP fragmentation risk with EDNS buffer recommendations

Size Estimation: Calculate total DNS message size including headers and record data.
Fragmentation Risk: Assess likelihood of UDP packet fragmentation and delivery issues.
EDNS Recommendations: Get buffer size recommendations for optimal DNS performance.

Response Examples

Query Configuration

Response Records

Size Analysis

Size Breakdown

DNS Header
12 bytes
Records Data
84 bytes
Total Size
96 bytes
UDP Safe (96 / 512 bytes)

Fragmentation Analysis

LOW RISK
≤ 512 bytes (Classic DNS)
≤ 1232 bytes (Safe for most networks)
≤ 4096 bytes (Common EDNS buffer)

UDP Limitations

Classic DNS over UDP is limited to 512 bytes. Larger responses require EDNS0 extension to advertise bigger buffer sizes. Without EDNS0, servers must truncate responses.

Fragmentation Issues

UDP packets larger than ~1232 bytes may be fragmented by network devices. Fragmented packets are more likely to be dropped, causing DNS resolution failures.

EDNS Buffer Sizes

Common EDNS buffer sizes are 1232, 4096, and 8192 bytes. Larger buffers allow bigger responses but increase fragmentation risk. Choose based on your network environment.

Optimization Strategies

Minimize record sizes with shorter names and values. Use separate queries for large responses. Consider TCP for consistently large responses like DNSSEC-signed zones.