V2ray Slow Dns Server «99% FULL»

This review is intriguing because it highlights a counter-intuitive issue. DNS is usually the fastest part of a connection, so when a user complains about a "slow DNS server" specifically in the context of v2ray, it usually points to a misconfiguration or a misunderstood feature rather than an actual slow DNS provider.

Here is a breakdown of why this review is interesting and the technical realities behind it:

Solution B: The "DOH" Bypass (Fix UDP Throttling)

If your ISP or VPS provider throttles UDP DNS, switch to DNS-over-HTTPS (DoH). V2Ray natively supports DoH.

Configuration:

"dns": 
  "servers": [
    "https://dns.cloudflare.com/dns-query",
    "https://dns.google/dns-query"
  ]

Why this works: DoH uses TCP port 443 (same as HTTPS). Your V2Ray server treats it like normal web traffic, bypassing UDP shaping completely.

4) Avoid DNS leaks and slow upstreams

Use upstream DNS servers that are geographically/responsively close.
If using V2Ray’s DNS over the tunnel (remote DNS), ensure remote resolver isn’t overloaded.

Part 3: Diagnosis – Measuring the Real Bottleneck

Before changing anything, collect data.

4.5. Force TCP for DNS (if UDP is throttled)

Add "tcp" flag to DNS server definition: v2ray slow dns server

"dns": 
  "servers": [
"address": "1.1.1.1",
      "port": 53,
      "domains": ["geosite:geolocation-!cn"],
      "expectIPs": ["geoip:!cn"]
]

Better yet, use DoH (TCP-based) as shown earlier.

Query time (look at "Query time: XX msec")

If Query time > 100ms consistently, your upstream is slow. This review is intriguing because it highlights a

Technical Analysis: V2Ray Throughput Degradation Induced by Slow DNS Servers

Solution A: The "Trusted Local" Caching Server (Best for Privacy)

Instead of relying on public resolvers, run a local DNS cache on your VPS using dnsmasq or unbound. This reduces latency to near zero after the first query.

Step 1: Install Dnsmasq

apt install dnsmasq -y

Step 2: Configure Dnsmasq (/etc/dnsmasq.conf) Why this works: DoH uses TCP port 443 (same as HTTPS)

port=5353
listen-address=127.0.0.1
cache-size=10000
server=1.1.1.1
server=8.8.8.8

Step 3: Point V2Ray to Localhost In your V2Ray config:

"dns": 
  "servers": [
    "127.0.0.1:5353",
    "1.1.1.1",
    "8.8.8.8"
  ]

Why this works: The first query to google.com hits 127.0.0.1:5353. Dnsmasq fetches it (slow once), caches it. Subsequent queries take ~1ms.