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- The SSH client programs should be installed. In my case, it’s already installed. Installing SSH Server Software: If you want to connect to your CentOS 8 server using SSH, then, you must have SSH server software installed on your CentOS 8 machine.
- The SSH protocol. The SSH protocol uses encryption to secure the connection between a client and a server. All user authentication, commands, output, and file transfers are encrypted to protect against attacks in the network. For details of how the SSH protocol works, see the protocol page. To understand the SSH File Transfer Protocol, see the.
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The Secure Shell Protocol (SSH) is a protocol for secure remote login and other secure network services over an insecure network. This document describes the SSH authentication protocol framework and public key, password, and host-based client authentication methods. Additional authentication methods are described in separate documents. The SSH authentication protocol runs on top of the SSH. VSSH 1.11.1 - is advanced customizable SSH and Telnet client with iCloud connections, macros and keys sharing. VSSH 1.11.1 – SSH protocol connectivity tools. Developer Tools Mac AppStore vSSH. Developer Tools Mac AppStore vSSH. Sublime Text 4 build 4085 – Sophisticated text editor for code, markup, and prose.
SSH is a cryptographically protected remote login protocol that replaces insecure telnet and rlogin protocols. It provides strong protection against password sniffing and third party session monitoring, better protecting your authentication credentialsand privacy. In addition, SSH offers additional authentication methods that are considered more secure than passwords, such as public key authentication and extensiveprotection against spoofing.
The SSH employs a public key cryptography that uses two keys pairs, for host and user.
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SSH servers offer the client a selection of authenticationmethods. The server advertises what it supports, and the clientattempts to authenticate over each method that it can support.Generally, the client will choose methods that are the least intrusiveto the user, if they are available. In most cases, the client providesthe option to choose which methods can be used. In WinSCP, you can configure this on SSH > Authentication page of Advanced Site Settings dialog.
The actual order of authentication methods is as follows: GSSAPI (SSH-2 only), public key (using Pageant), public key (using configured file), keyboard-interactive (SSH-2 only), TIS or Cryptocard (SSH-1 only), password.
To prevent man-in-the-middle attacks, each SSH server has a unique identifying code, called a host key. These keys prevent a server from forging another server’s key. If you connect to a server for the first time or if the server presets a different key then previously, WinSCP will prompt you to verify the key.
SSH clients and servers can use a number of encryption methods. Most widely used encryption methods in SSH-2 are AES andBlowfish. By default, AES is used if supported by the server. While AES isconsidered to be highly secure, AES encryption requires substantial processor overhead. Blowfish is also consideredsecure, but with less computational overhead, it’s also theoreticallyeasier to perform a brute-force attack. Depending on your security andperformance requirements, you may wish to configure WinSCP to preferthe Blowfish algorithm. 3DES and DES are used with SSH-1 servers. DESis widely regarded as insecure, as the resources to perform anexhaustive brute-force attack have been well within the realm ofcommercial feasibility for some time.
Two major versions of the SSH protocol exist, SSH-2 and SSH-1. Most SSH servers nowadays allow modern and secure SSH-2 only.
WinSCP’s default setting is to use SSH-2. If you need to use deprecated and insecure SSH-1 at all, you can configure this in SSH preferences.
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SSH supports data stream compression between the clientand the server. On slow links, this may increase throughput, while in faster connections the added CPU overhead may actually result inslower transfers, particularly depending on the data type you’re transferring. Calendarique 2 0 1. Large text files may still benefit significantly, whilebinaries may transfer more slowly. You may want toexperiment to find what works best in your situation. Compression mayalso improve security slightly, in part by rendering known cyphertextattacks more difficult and by providing less data forcryptanalysis.
See list of supported SSH algorithms.
Linux provides many command-line tools to help sysadmins manage, configure, and troubleshoot network settings.
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Networking configuration and troubleshooting are crucial tasks that sysadmins need to perform regularly. Some of these tasks can be challenging. However, when dealing with connectivity issues, using the right tools will assist you in achieving the results in a faster and consistent way.
The ip command
The
ip
command is an all-around utility to show and manipulate network objects on your Linux system, including IP addresses, routes, and ARP tables. It's a useful tool to configure the network, as well as to troubleshoot network connectivity issues.The
ip
command replaces the functionality of many commands provided with the old net-tools
package such as ifconfig
, route
, and arp
, but it adds many other features.In its most basic form, you can just run
ip
and provide a network object to manipulate, such as an address, link, or route, and a subcommand to perform an action. If you do not give a subcommand, many objects default to the show
subcommand to display information related to that object.Here is the basic syntax:
For example, to see the link status on all network devices, run
ip link show
:Because
show
is the default subcommand, you can also obtain the same result by running ip link
or even ip l
(many objects recognize an abbreviation).The
ip
command manages many objects. The main ones are:link
orl
- controls the status of network devicesaddress
ora
- manipulates IP addresses on devicesroute
orr
- handles routing table entriesneighbor
orn
- controls ARP table entries
You can see a full list of objects and commands by running
ip help
.Some useful examples of the ip command
Show network statistics
-s
in human readable format -h
for a specific network interface:Show the IP addresses of all interfaces:
Show the IP address of a single interface e.g., enp1s0:
Add another IP address to an interface (requires
sudo
or root
user):Display the routing table:
Add a route (default gateway):
The
ip
command is a lower-level interface to configure network options on your Linux system. While it's useful as a troubleshooting tool, it may be harder to set the network with it. For this reason, many distributions provide a higher-level interface to accomplish the same task. Next, let's take a look at the Network Manager configuration tool nmcli
, which provides an integrated way to configure the network.The nmcli tool
Network Manager is a network configuration application available by default with many Linux distributions, including RHEL and Fedora. Network Manager runs as a daemon, and its goal is to provide a higher-level interface to make network configuration easier and more automated.
It's common for users of desktop Linux or servers with a graphical interface to use Network Manager GUI clients to configure the network. For cases where you work with headless servers or if you want to automate configuration via shell scripts, the
nmcli
tool comes in handy.Network Manager and
nmcli
are a versatile combination that allow you to verify and configure many network options. The basic syntax for nmcli
is:The most common objects are:
general
- shows Network Manager status and permissionsnetworking
- shows, enables, and disables networkingradio
- shows, enables, and disables WiFi and WWANdevice
- shows and manipulates the status of network devicesconnection
- manages Network Manager connection profiles
It's impossible to cover all the options on a single blog post. Let's check some examples of how to use
nmcli
for common network configurations tasks. For more examples, consult the official nmcli-examples page or the man pages with man nmcli-examples
.Check the status of network devices:
Show all connection profiles:
Show details about a specific connection (e.g., enp1s0):
Retrieve specific parameters from a connection (e.g., IP address and DNS):
Modify connection parameters, e.g., switch from DHCP to manual connection:
Restart the connection to enable new options:
Add a new connection profile:
nmcli
also allows you to edit a connection profile interactively. This interface provides help and auto-completion via the Tab key, which guides you through the many options available. Activate the editor using nmcli connection edit CONNECTION-NAME
:In the editor, you can define specific parameters with the
set
command. Use the Tab key auto-completion to see all available options:Then you can
print
the current values:When you finish your changes,
save
them to the connection and quit
to complete the operation:Finally, restart the connection to make the changes effective.
Network Manager and
nmcli
are a complete solution for network configuration. If you have never used it before, start with some of the basic commands and gradually move to more complex settings. Consult the man pages and examples to execute specific tasks.Next, let's review some commands that help you with network troubleshooting, starting with name resolution.
The nslookup command
When managing connectivity issues, DNS name resolution is often a source of headaches. The
nslookup
utility helps you check and troubleshoot DNS name resolution.This command is available with the
bind-utils
package on RHEL8 and Fedora systems. Install it with dnf
:To quickly check the name resolution for a particular host, use
nslookup
with the hostname as an argument. The command uses the default DNS configuration for the name resolution:If the name resolution fails, you can use an alternative name server for the resolution by providing its address as the third argument:
This information is useful for troubleshooting as it helps to identify whether the issue is local due to a specific server, or something more extensive.
You can also use it to run reverse DNS queries by providing the IP address instead of a hostname:
The
nslookup
utility is a useful tool to help troubleshoot network issues related to DNS name resolution. Next, let's take a look at troubleshooting local network sockets.The ss utility
Another common task when troubleshooting network connectivity issues is determining whether a connection is established or a particular service is available on a server.
The
ss
command, short for socket statistics, is a convenient tool that displays network socket information. It's the modern replacement for netstat
that provides similar functionality, but includes a few extra features.Use
ss
with no options to see the complete list of all established network sockets for socket types TCP, UDP, and UNIX.Since the default command displays all established network connections, this list can be extensive on a busy machine, with over a thousand entries. To help you with troubleshooting,
ss
provides several filtering options.You can display socket information for specific socket types with the following command-line parameters:
-t
for TCP, -u
for UDP, and -x
for UNIX.For example, display TCP socket information with
ss -t
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You can also filter the list by source or destination hostname or IP address. For example, here is a list of established connections for destination IP address 192.168.122.1:
![Vssh 1 8 – ssh protocol connectivity tools tool Vssh 1 8 – ssh protocol connectivity tools tool](https://cdn.geckoandfly.com/wp-content/uploads/2018/11/hyper-ssh.jpg)
These commands are useful to troubleshoot network connectivity in general or between specific hosts in the network. Another practical application for
ss
is to verify whether network services are listening on the local machine with the correct address and port. To verify listening sockets, use the option -l
:You can use the same filtering options described above to filter specific socket types. For example, to list all listening TCP sockets enter:
Instead of displaying the service name, like
ssh
or hostmon
, ss
can display port numbers by using the -n
option:Finally, another useful option is
-p
to display process related information such as user name and process ID (PID). Some services may require elevated privileges via sudo
or as root
to list process information:The
ss
tool is an essential command in the sysadmin toolbox for network troubleshooting tasks. Next, let's take a look at tracepath
to trace network connectivity between hosts.The tracepath command
The
tracepath
command is a network troubleshooting tool that displays the network connectivity path between the local host and a remote host, identifying all routers used to route the traffic between them.In case you're unable to connect to a network service in a remote host,
tracepath
helps you determine where the issue is.tracepath
is a replacement for traceroute
, offering similar functionality. The main difference is that tracepath
uses random UDP ports instead of the ICMP protocol for the trace, thus not requiring elevated privileges to run.For the basic usage, provide the hostname or IP address of the destination host. You can also provide the option
-n
to display IP addresses for the routers instead of their names:If
tracepath
cannot connect to a network hop, it displays no reply. By default, the maximum number of hops it tries is 30, which is usually enough. You can change that with the option -m
.Suppose it receives no replies after a particular hop. That is a good indicator where to go next for your troubleshooting task.
tracepath
information is not definitive, as the traffic could be blocked for several reasons. However, it helps you narrow down the issue and focus on the resolution efforts.For security reasons, many routers on the Internet block traffic, so
tracepath
may not be as useful for tracing connectivity with Internet services. It's still useful for local network troubleshooting.What's next?
In this article, we explored five essential network configuration and troubleshooting tools for Linux systems. These tools are powerful and provide many options that are hard to cover in a single post. We encourage you to check them out and look at documentation and man pages to see how you can incorporate them into your workflow.
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There are other useful Linux network tools, such as
tcpdump
, nmap
, and firewall-cmd
. These tools are covered in other Enable Sysadmin articles.![Vssh 1 8 – ssh protocol connectivity tools tool Vssh 1 8 – ssh protocol connectivity tools tool](https://mac-cdn.softpedia.com/screenshots/SSH-Tunnel-Manager_9.png)
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