How To Check - Connected IPs To Server | IPv4 And IPv6 Information | Kernel IP Routing | Network Interface Transactions

How To List Connected IPs To Server?

List Kernel IP Routing

List Network Interface Transactions

Check IPv4 & IPv6 Information

Usage of netstat Command

netstat is a command-line utility to list network connections, routing tables, interface statistics multicast memberships and masquerade connections.

# List all ports and IPs (tcp and upd)

netstat -a | more

Active Internet connections (servers and established)
Proto Recv-Q Send-Q Local Address               Foreign Address             State
tcp        0      0 *:sunrpc                    *:*                         LISTEN
tcp        0     52 192.168.0.2:ssh             192.168.0.1:egs             ESTABLISHED
tcp        1      0 192.168.0.2:59292           www.gov.com:http            CLOSE_WAIT
tcp        0      0 localhost:smtp              *:*                         LISTEN
tcp        0      0 *:59482                     *:*                         LISTEN
udp        0      0 *:35036                     *:*
udp        0      0 *:npmp-local                *:*
Active UNIX domain sockets (servers and established)
Proto RefCnt Flags       Type       State         I-Node Path
unix  2      [ ACC ]     STREAM     LISTENING     16972  /tmp/orbit-root/linc-76b-0-6fa08790553d6
unix  2      [ ACC ]     STREAM     LISTENING     17149  /tmp/orbit-root/linc-794-0-7058d584166d2

# List Only IPs

netstat -tn 2>/dev/null | grep :80 | awk '{print $5}' | cut -d: -f1 | sort | uniq -c | sort -nr | head

• Here -t is for tcp connections
• 2>/dev/null redirects all unwanted output to /dev/null
• grep :80 displays results only for IPs connected on port 80
• awk '{print $5}' displays fifth column only
• cut -d : -f1 is used to extract only IPs excluding port with delimeter ":"
• sort command sort the result
• uniq command groups the result
• sort -nr again sort it in reverse order
• head will display top 10 results

# Display kernel IP routing

netstat -r
Kernel IP routing table
Destination     Gateway         Genmask         Flags   MSS Window  irtt Iface
192.168.0.0     *               255.255.255.0   U         0 0          0 eth0
link-local      *               255.255.0.0     U         0 0          0 eth0
default         192.168.0.1     0.0.0.0         UG        0 0          0 eth0

# List Network Interface Transactions

netstat -i
Kernel Interface table
Iface       MTU Met    RX-OK RX-ERR RX-DRP RX-OVR    TX-OK TX-ERR TX-DRP TX-OVR Flg
eth0       1500   0     4459      0      0      0     4057      0      0      0 BMRU
lo        16436   0        8      0      0      0        8      0      0      0 LRU

# Check IPv4 & IPv6 Information

netstat -g
IPv6/IPv4 Group Memberships
Interface       RefCnt Group
--------------- ------ ---------------------
lo              1      all-systems.mcast.net
eth0            1      224.0.0.251
eth0            1      all-systems.mcast.net
lo              1      ff02::1
eth0            1      ff02::202
eth0            1      ff02::1:ffb4:da21
eth0            1      ff02::1