DNS (Domain Name System) fundamentally doesn't support port specification in records. A common misconception is that you can append ports to hostnames like example.com:8080 in DNS records - this simply doesn't work at the protocol level.

Reverse Proxy Solution

The most robust approach is using a reverse proxy like Nginx:

server {
    listen 80;
    server_name www.example.com;
    
    location / {
        proxy_pass http://localhost:87;
        proxy_set_header Host $host;
    }
}

SRV Records (Application-Specific)

Some protocols (like SIP, XMPP) support SRV records:

_service._proto.name. TTL class SRV priority weight port target
_http._tcp.example.com. 86400 IN SRV 10 5 87 server.example.com.

HTTP Host Header Routing

Modern web servers can route based on Host header:

// Node.js express example
const app = require('express')();

app.listen(87, () => {
  console.log('App listening on port 87');
});

app.get('/', (req, res) => {
  if(req.hostname === 'www.example.com') {
    res.send('Port 87 content');
  }
});

Port Forwarding at OS Level

Using iptables on Linux:

iptables -t nat -A PREROUTING -p tcp --dport 80 -j REDIRECT --to-port 87

Client-Side Configuration

For non-web services, implement client configuration:

# Python client example
import socket

def connect_service():
    host = 'example.com'
    port = 87 if host == 'www.example.com' else 80
    s = socket.socket()
    s.connect((host, port))

---

When dealing with multiple services running on a single server, traditional DNS records (A, AAAA, CNAME) only resolve to IP addresses without port information. This creates a fundamental limitation since port specification is crucial for service differentiation.

SRV Records (Service Records): The proper DNS solution for port specification:

_http._tcp.example.com. 300 IN SRV 10 5 87 webserver.example.com.
_http._tcp.www.example.com. 300 IN SRV 10 5 80 webserver.example.com.

Limitations:

• Requires client-side SRV record support (most browsers don't support HTTP SRV lookups)
• Widely supported by protocols like SIP, XMPP, LDAP

Reverse Proxy Configuration (Nginx example):

server {
    listen 80;
    server_name www.example.com;
    location / {
        proxy_pass http://localhost:87;
    }
}

server {
    listen 80;
    server_name api.example.com;
    location / {
        proxy_pass http://localhost:3000;
    }
}

HTTP/HTTPS: Use Host headers for virtual hosting

Database Protocols:

// MongoDB connection string with port
mongodb://myDBReader:D1fficultP%40ssw0rd@mongodb0.example.com:27017/?authSource=admin

CNAME Weighting: For load balancing across ports

service1.example.com. 300 IN CNAME server-a:8080.example.com.
service1.example.com. 300 IN CNAME server-b:8081.example.com.

• Consul service registry
• Kubernetes Services and Ingress
• Docker Swarm load balancing

URL Redirection:

HTTP/1.1 301 Moved Permanently
Location: http://example.com:8080/newpath

Client-Side Configuration:

# SSH config example
Host myserver
    HostName example.com
    Port 2222