Skip to content

Networking & Security

Debug APIs, manage SSH, inspect certificates, probe networks.

curl — Modern Patterns

POST JSON (the --json flag sets Content-Type and method automatically):

curl --json '{"name":"test"}' https://api.example.com/users

Measure request timing:

curl -o /dev/null -s -w "DNS: %{time_namelookup}s\nConnect: %{time_connect}s\nTLS: %{time_appconnect}s\nTotal: %{time_total}s\n" https://example.com

Follow redirects and show response headers:

curl -sSL -D - https://example.com -o /dev/null

Download with retry and resume:

curl -LC - --retry 3 -o file.zip https://example.com/file.zip

httpie — Human-Friendly HTTP

GET request with automatic formatting:

http https://api.example.com/users

POST with JSON body:

http POST https://api.example.com/users name=test email=test@example.com

Send with a bearer token:

http https://api.example.com/me Authorization:"Bearer $TOKEN"

Install: brew install httpie · pip install httpie

SSH

Config File (~/.ssh/config)

Host myserver
    HostName 192.168.1.100
    User deploy
    IdentityFile ~/.ssh/id_ed25519
    Port 22

Host jump
    HostName bastion.example.com
    User admin

Host internal
    HostName 10.0.0.5
    ProxyJump jump

Generate an Ed25519 key:

ssh-keygen -t ed25519 -C "you@example.com"

Start the agent and add your key:

eval "$(ssh-agent -s)"
ssh-add ~/.ssh/id_ed25519

Copy public key to a server:

ssh-copy-id myserver

Port forwarding (local):

Access remote port 5432 at localhost:5432:

ssh -L 5432:localhost:5432 myserver

Tunnel through a jump host:

ssh -J jump internal

OpenSSL — Certificate Inspection

View a remote server's TLS certificate:

echo | openssl s_client -connect example.com:443 -servername example.com 2>/dev/null | openssl x509 -noout -text

Check certificate expiration:

echo | openssl s_client -connect example.com:443 2>/dev/null | openssl x509 -noout -dates

Inspect a local certificate file:

openssl x509 -in cert.pem -noout -text

Verify a certificate chain:

openssl verify -CAfile ca-bundle.crt cert.pem

DNS

Lookup DNS records with dig:

dig example.com A +short
dig example.com MX +short
dig example.com TXT +short

Trace DNS resolution path:

dig +trace example.com

dog (modern DNS client)

dog example.com A AAAA MX

Install: brew install dog

Network Debugging

Which process is using a port:

lsof -i :3000

ss -tlnp | grep :3000

Test TCP connectivity:

nc -zv example.com 443

Scan open ports on a host:

nmap -sT -p 1-1000 192.168.1.1

Note

Only scan hosts you own or have explicit permission to test.