Networking at the Command Line
Focus on some network utilities used for troubleshooting, testing and diagnosing network connectivity issues.
Commands
ping
ping- send one ore more ICMP ECHO_REQUEST packages to network hosts.it is part of the
iputilspackage
ping google.com
PING google.com (142.251.209.14) 56(84) bytes of data.
64 bytes from mil04s50-in-f14.1e100.net (142.251.209.14): icmp_seq=1 ttl=128 time=37.6 ms
64 bytes from mil04s50-in-f14.1e100.net (142.251.209.14): icmp_seq=2 ttl=128 time=33.2 ms
64 bytes from mil04s50-in-f14.1e100.net (142.251.209.14): icmp_seq=3 ttl=128 time=32.9 ms
64 bytes from mil04s50-in-f14.1e100.net (142.251.209.14): icmp_seq=4 ttl=128 time=33.6 ms
# It continuee the ping until stop (Ctrl+C)
# Ping a certain number of times
ping -c 2 google.com
PING google.com (142.251.209.46) 56(84) bytes of data.
64 bytes from mil04s51-in-f14.1e100.net (142.251.209.46): icmp_seq=1 ttl=128 time=34.5 ms
64 bytes from mil04s51-in-f14.1e100.net (142.251.209.46): icmp_seq=2 ttl=128 time=34.7 ms
--- google.com ping statistics ---
2 packets transmitted, 2 received, 0% packet loss, time 1002ms
rtt min/avg/max/mdev = 34.493/34.606/34.719/0.113 msifconfig
ifconfig- configure a network interfaceit is part of the
net-toolspackage
sudo apt install net-tools -y
ifconfig
ens33: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 192.168.31.133 netmask 255.255.255.0 broadcast 192.168.31.255
inet6 fe80::4d26:4984:fcf7:6061 prefixlen 64 scopeid 0x20<link>
ether 00:0c:29:c9:89:de txqueuelen 1000 (Ethernet)
RX packets 37168 bytes 54380681 (54.3 MB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 20049 bytes 1330857 (1.3 MB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
lo: flags=73<UP,LOOPBACK,RUNNING> mtu 65536
inet 127.0.0.1 netmask 255.0.0.0
inet6 ::1 prefixlen 128 scopeid 0x10<host>
loop txqueuelen 1000 (Local Loopback)
RX packets 657 bytes 70806 (70.8 KB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 657 bytes 70806 (70.8 KB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
# Two network interfaces listed: ens33 (lan interfaces) and lo (loop-back interface)
iwconfig
# for wireless adaptersip
ip- powerful tool for configuring network interfaces
ip a
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
inet 127.0.0.1/8 scope host lo
valid_lft forever preferred_lft forever
inet6 ::1/128 scope host
valid_lft forever preferred_lft forever
2: ens33: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000
link/ether 00:0c:29:c9:89:de brd ff:ff:ff:ff:ff:ff
altname enp2s1
inet 192.168.31.133/24 brd 192.168.31.255 scope global dynamic noprefixroute ens33
valid_lft 1186sec preferred_lft 1186sec
inet6 fe80::4d26:4984:fcf7:6061/64 scope link noprefixroute
valid_lft forever preferred_lft forever
# Print statistics
ip -s link
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT group default qlen 1000
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
RX: bytes packets errors dropped missed mcast
71259 661 0 0 0 0
TX: bytes packets errors dropped carrier collsns
71259 661 0 0 0 0
2: ens33: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP mode DEFAULT group default qlen 1000
link/ether 00:0c:29:c9:89:de brd ff:ff:ff:ff:ff:ff
RX: bytes packets errors dropped missed mcast
219198302 146066 0 0 0 0
TX: bytes packets errors dropped carrier collsns
4575119 74085 0 0 0 0
altname enp2s1
# Print basic info in color
ip -br -c a
# -br = brief basic information
# -c = colored output
# For more help on an option use help
ip a help
# Check the ip link option. Temporary disable/enable a device
sudo ip link set dev ens33 down
# Display routing table
sudo ip route listroute
route- show and manipulate the IP routing table
route
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
default _gateway 0.0.0.0 UG 100 0 0 ens33
link-local 0.0.0.0 255.255.0.0 U 1000 0 0 ens33
192.168.31.0 0.0.0.0 255.255.255.0 U 100 0 0 ens33
# Add a route
sudo ip route add 192.168.1.0/24 via 192.168.31.1
sudo ip route delete 192.168.1.0/24 via 192.168.31.1nslookup / dig
nslookup- query Internet name servers interactivelydig- DNS lookup utility. More information thannslookup
nslookup google.com
Server: 127.0.0.53
Address: 127.0.0.53#53
Non-authoritative answer:
Name: google.com
Address: 142.251.209.14
Name: google.com
Address: 2a00:1450:4002:410::200edig google.com
; <<>> DiG 9.18.1-1ubuntu1.2-Ubuntu <<>> google.com
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 42021
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1
;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 65494
;; QUESTION SECTION:
;google.com. IN A
;; ANSWER SECTION:
google.com. 5 IN A 142.251.209.14
;; Query time: 31 msec
;; SERVER: 127.0.0.53#53(127.0.0.53) (UDP)
;; WHEN: Wed Oct 26 19:29:30 CEST 2022
;; MSG SIZE rcvd: 55
# Perform a reverse lookup
dig -x 8.8.8.8
; <<>> DiG 9.18.1-1ubuntu1.2-Ubuntu <<>> -x 8.8.8.8
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 15982
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1
;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 65494
;; QUESTION SECTION:
;8.8.8.8.in-addr.arpa. IN PTR
;; ANSWER SECTION:
8.8.8.8.in-addr.arpa. 5 IN PTR dns.google.
;; Query time: 36 msec
;; SERVER: 127.0.0.53#53(127.0.0.53) (UDP)
;; WHEN: Wed Oct 26 19:31:02 CEST 2022
;; MSG SIZE rcvd: 73netstat
netstat- print network connections, routing tables, interface statistics, masquerade connections, and multicast member‐ships
# Show all the open TCP connections
netstat -at
# Show all the listening TCP ports
netstat -lt
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address Foreign Address State
tcp 0 0 localhost:ipp 0.0.0.0:* LISTEN
tcp 0 0 localhost:domain 0.0.0.0:* LISTEN
tcp6 0 0 ip6-localhost:ipp [::]:* LISTENss
ss- it replaces the netstat command
ss -tunlp
Netid State Recv-Q Send-Q Local Address:Port Peer Address:Port Process
udp UNCONN 0 0 0.0.0.0:5353 0.0.0.0:*
udp UNCONN 0 0 127.0.0.53%lo:53 0.0.0.0:*
udp UNCONN 0 0 0.0.0.0:631 0.0.0.0:*
udp UNCONN 0 0 0.0.0.0:35782 0.0.0.0:*
udp UNCONN 0 0 [::]:5353 [::]:*
udp UNCONN 0 0 [::]:50159 [::]:*
tcp LISTEN 0 4096 127.0.0.53%lo:53 0.0.0.0:*
tcp LISTEN 0 128 127.0.0.1:631 0.0.0.0:*
tcp LISTEN 0 128 [::1]:631 [::]:*📌 More on checking for listening ports here.
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