Networking Commands

DNS:

DNS on Ubuntu

# Show statistics
sudo systemd-resolve --statistics

# Clear stats
sudo systemd-resolve --flush-caches

$ sudo systemd-resolve --statistics
DNSSEC supported by current servers: no

Transactions
Current Transactions: 0
  Total Transactions: 1157

Cache
  Current Cache Size: 32
          Cache Hits: 417
        Cache Misses: 156

DNSSEC Verdicts
              Secure: 0
            Insecure: 0
               Bogus: 0
       Indeterminate: 0

$ sudo systemd-resolve --flush-caches

$ sudo systemd-resolve --statistics
DNSSEC supported by current servers: no

Transactions
Current Transactions: 0
  Total Transactions: 1157

Cache
  Current Cache Size: 0
          Cache Hits: 417
        Cache Misses: 156

DNSSEC Verdicts
              Secure: 0
            Insecure: 0
               Bogus: 0
       Indeterminate: 0

 

Network Statistics:

Show number of connections per IP

netstat -ntu | tail -n +3| awk '{ print $5}' | cut -d : -f 1 | sort | uniq -c| sort -n -r
or
netstat -ntu | awk '{ print $5}' | cut -d : -f 1 | sort | uniq -c| sort -n -r

 

Show all connected IPs

netstat -nat | awk '{ print $5}' | cut -d: -f1 | sed -e '/^$/d' | uniq

 

Show number of connections by state

netstat -nat | tail -n +3 | awk '{print $6}' | sort | uniq -c | sort -n
or
netstat -nat | awk '{print $6}' | sort | uniq -c | sort -n

Show number of connections

netstat -an | grep ESTABLISHED | wc -l
or
sudo ss -s

 

Show ports and programs associated with the open ports

netstat -A inet -p
netstat -lnpute

sudo ss -utap
sudo ss -utlp

sudo lsof -i -n -P

Filter ports and programs

ss -anp 'dport = :443'
ss -npet 'sport = :22'

Show details for existing TCP connection:

ss -nti 'dport = :5201'

 

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