Localhost refers to the loopback network interface of a device that is used to access resources (such as a website or a server) hosted on the same device. It is commonly used for development and testing purposes.
Hostname [name of the host machine] and IP address are used to identify computer devices.
This tutorial will provide you a brief overview of localhost. We will also address a few FAQs on What is Localhost.
What is Localhost?
When we call localhost, the machine will communicate with itself, since localhost is a hostname that designates the computer system on which the calling program is operating.
Even when network hardware malfunctions, it enables us to test network services on the machine. Network services are accessed when "localhost" is used through the loopback logical network interface. The IP address of the loopback interface is 127.0.0.1. Localhost resolves to 127.0.0.1 as a result of the name resolution.
What is a Loopback Address?
The loopback network interface is present in all operating systems. Packets sent over this interface are returned (looped) to the same interface on the same machine. As a result, the interface is known as a loopback.
The entire block of 127.0.0.0/8 is reserved for network loopback purposes, according to the IETF Standards for IPv4 addressing. A loopback interface is configured by default after each server installation.
Take a look at the snippet below.
ip a show lo
Output
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 76238871 bytes 6955286874 (6.9 GB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 76238871 bytes 6955286874 (6.9 GB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
sudo cat /etc/hosts
Output
127.0.0.1 localhost
127.0.1.1 sandbox1
# The following lines are desirable for IPv6 capable hosts
::1 ip6-localhost ip6-loopback
Loopback Packet Processing Internals
Loopback packets are generally distinguished from other IP packets by their addresses. The link layer of the TCP/IP Stack handles loopback packets with the loopback address. This data will be transmitted within the computer systems themselves. It will not be intercepted by the Hardware NIC Cards in the same way that other IP packets are. There is also a rule that routers should not route the loopback IP address.
For example, when we request the address 127.0.0.1. Because of the first octet, the request will not be forwarded to the internet (127). The TCP/IP stack recognizes the request and returns it to the same machine.
Below is a quick diagram of the packet flow walkthrough for localhost and other IP packets.
ping -c 4 localhost
Output
PING localhost (127.0.0.1) 56(84) bytes of data.
64 bytes from localhost (127.0.0.1): icmp_seq=1 ttl=64 time=0.035 ms
64 bytes from localhost (127.0.0.1): icmp_seq=2 ttl=64 time=0.043 ms
64 bytes from localhost (127.0.0.1): icmp_seq=3 ttl=64 time=0.041 ms
64 bytes from localhost (127.0.0.1): icmp_seq=4 ttl=64 time=0.040 ms
--- localhost ping statistics ---
4 packets transmitted, 4 received, 0% packet loss, time 3075ms
rtt min/avg/max/mdev = 0.035/0.039/0.043/0.008 ms
ping -c 4 google.com
Output
PING google.com (142.250.71.46) 56(84) bytes of data.
64 bytes from maa03s35-in-f14.1e100.net (142.250.71.46): icmp_seq=1 ttl=120 time=2.14 ms
64 bytes from maa03s35-in-f14.1e100.net (142.250.71.46): icmp_seq=2 ttl=120 time=2.18 ms
64 bytes from maa03s35-in-f14.1e100.net (142.250.71.46): icmp_seq=3 ttl=120 time=2.19 ms
64 bytes from maa03s35-in-f14.1e100.net (142.250.71.46): icmp_seq=4 ttl=120 time=2.20 ms
--- google.com ping statistics ---
4 packets transmitted, 4 received, 0% packet loss, time 3004ms
rtt min/avg/max/mdev = 2.147/2.180/2.203/0.051 ms
Application Testing Using Localhost
Application services can initially be accessed through the network interface. If the application service is mapped to a physical interface, it can be accessed externally. Similarly, if an application is mapped with a logical loopback interface, it can only be accessed from that particular computer system and not externally.
It's always easier to develop and test your code from a local server than from another remote host. To achieve this, map the production domain name to the new loopback address (127.0.1.100) in the /etc/hosts file. Entries in /etc/hosts take precedence over DNS.
The following snippet shows an organic ping response from a local server to a remote VegaStack web server. The domain mapping is shown in the second snippet. After mapping the 127-segment IP to the hosts file vegastack.com, a closer look at the output will direct the traffic to the loopback network interface.
ping -c 4 vegastack.com
Output
PING vegastack.com (172.67.74.167) 56(84) bytes of data.
64 bytes from 172.67.74.167 (172.67.74.167): icmp_seq=1 ttl=59 time=34.5 ms
64 bytes from 172.67.74.167 (172.67.74.167): icmp_seq=2 ttl=59 time=34.5 ms
64 bytes from 172.67.74.167 (172.67.74.167): icmp_seq=3 ttl=59 time=34.5 ms
64 bytes from 172.67.74.167 (172.67.74.167): icmp_seq=4 ttl=59 time=34.5 ms
--- vegastack.com ping statistics ---
4 packets transmitted, 4 received, 0% packet loss, time 3005ms
rtt min/avg/max/mdev = 34.521/34.529/34.541/0.227 ms
sudo cat /etc/hosts
Output
127.0.0.1 localhost
127.0.1.1 sandbox1
127.0.1.100 vegastack.com
# The following lines are desirable for IPv6 capable hosts
::1 ip6-localhost ip6-loopback
ping -c 4 vegastack.com
Output
PING vegastack.com (127.0.1.100) 56(84) bytes of data.
64 bytes from vegastack.com (127.0.1.100): icmp_seq=1 ttl=64 time=0.074 ms
64 bytes from vegastack.com (127.0.1.100): icmp_seq=2 ttl=64 time=0.094 ms
64 bytes from vegastack.com (127.0.1.100): icmp_seq=3 ttl=64 time=0.042 ms
64 bytes from vegastack.com (127.0.1.100): icmp_seq=4 ttl=64 time=0.055 ms
--- vegastack.com ping statistics ---
4 packets transmitted, 4 received, 0% packet loss, time 3062ms
rtt min/avg/max/mdev = 0.042/0.066/0.094/0.020 ms
FAQs on What is LocalHost ?
What is the IP address of localhost?
The IP address of localhost is typically 127.0.0.1. It is known as the loopback address and is used to access services running on the local machine.
Can localhost be accessed by other devices on the network?
No, localhost is used to refer to the current device only. Other devices on the network cannot access resources hosted on the localhost directly.
How is localhost different from an IP address?
An IP address is used to identify a specific device on a network, whereas localhost represents the same device that is making the request.
What are some common uses of localhost?
Localhost is commonly used for hosting local web servers, accessing databases, running local development environments, and testing websites or applications.
Can I access the internet using localhost?
No, localhost is used for internal communication within the device itself and does not provide access to the internet.
Why do developers use localhost for development and testing?
Developers use localhost to test applications or websites locally before making them available on the internet. It provides a safe and controlled environment for debugging and verifying functionality.
Can localhost be used with any operating system?
Yes, localhost can be used with any operating system that supports networking. It is not specific to any particular OS.
Conclusion
Localhost is the default name for the system running the program and is useful for testing applications and troubleshooting network issues. This is achieved using a local loop mechanism over the loopback network interface. This helps you to test your software independently of your network hardware configuration.
If you have any queries, please leave a comment below and we’ll be happy to respond to them.