By

Contents
  1. 1. Multiplexers
    1. 1.1. mosh
    2. 1.2. ss
    3. 1.3. mtr
    4. 1.4. iftop
    5. 1.5. iperf
    6. 1.6. Troubleshooting layer 1 problems
    7. 1.7. HTTP core protocol
      1. 1.7.1. Request
      2. 1.7.2. Response
    8. 1.8. cURL
    9. 1.9. netcat
      1. 1.9.1. Basic client/server

Table of Contents

Multiplexers

mosh

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mosh jdoe@10.10.10.101
mosh username@remoteserver.org --ssh="ssh -i ~/.ssh/identity_file -p 1234"

ss

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user@opsschool ~$ ss -tuln
Netid  State      Recv-Q Send-Q         Local Address:Port         Peer Address:Port
tcp    LISTEN     0      128                        *:80                      *:*
tcp    LISTEN     0      50                         *:4242                    *:*
tcp    LISTEN     0      50                        :::4242                   :::*
tcp    LISTEN     0      50                         *:2003                    *:*
tcp    LISTEN     0      50                         *:2004                    *:*
tcp    LISTEN     0      128                       :::22                     :::*
tcp    LISTEN     0      128                        *:22                      *:*
tcp    LISTEN     0      100                        *:3000                    *:*
tcp    LISTEN     0      100                      ::1:25                     :::*
tcp    LISTEN     0      100                127.0.0.1:25                      *:*
tcp    LISTEN     0      50                         *:7002                    *:*
  • means the deamon is listening on all IP addresses the server might have.

127.0.0.1 means the daemon is listening only to the loopback interface

::: is the same thing as *, but for IPv6

::1 is the same as 127.0.0.1, but for IPv6

mtr

is a program that combines the functionality of ping and traceroute into one utility

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 mtr -r uow.edu.au
Start: 2020-08-09T15:14:55+1000
HOST: stan-OptiPlex-380           Loss%   Snt   Last   Avg  Best  Wrst StDev
  1.|-- router.lan                 0.0%    10    0.4   0.4   0.3   0.4   0.0
  2.|-- 58.162.27.77               0.0%    10    8.6  12.7   8.0  17.5   3.4
  3.|-- 10.2.2.150                 0.0%    10    8.6  13.7   8.3  29.7   6.6
  4.|-- 10.2.1.149                 0.0%    10   15.2  13.6  10.2  16.1   2.0
  5.|-- Bundle-Ether77.chw-edge90  0.0%    10   12.2  14.0  10.1  23.7   3.9
  6.|-- bundle-ether2.ken-edge903  0.0%    10   12.1  13.3   9.2  26.3   4.8
  7.|-- aar3533567.lnk.telstra.ne  0.0%    10   14.3  14.1  10.4  31.7   6.5
  8.|-- xe-0-2-1.pe1.rsby.nsw.aar  0.0%    10   12.7  12.0   8.9  14.8   2.2
  9.|-- 138.44.5.111               0.0%    10   10.2  14.5  10.2  17.5   2.5
 10.|-- 203.10.91.20               0.0%    10   11.8  16.6   9.9  27.2   6.1
 11.|-- www.uow.edu.au             0.0%    10   11.8  13.7  11.8  16.4   1.5

iftop

Displays bandwith usage on a specific interface, broken down by remote host

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sudo iftop -i eth0

iperf

a bandwidth testing utility. It consists of a daemon and client, running on separate machines.

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sudo iperf3 -c remote-host

Troubleshooting layer 1 problems

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ip -s link show eth0
sudo ethtool eth0
## -S, which shows all the same metrics as the ip command, plus many, many more
sudo ethtool -S eth0

HTTP core protocol

Request

Method Description
GET Tranfers a current representation of the target resource.
HEAD Same as GET, but only transfer the status line and header section.
POST Perform resource-specific processing on the request payload.
PUT Replace all current representations of the target resource with the requested payload.
DELETE Remove all current representations of the target resource.
CONNECT Establish a tunnel to the server identified by the target resource.
OPTIONS Describe the communication options for the target resource.
TRACE Perform a message loop-back test along the path to the target resource.

Response

Code Reason Description
200 OK The request has succeeded.
301 Moved Permenantly The target has moved to a new location and future references should use a new location. The server should mention the new location in the Location header in the response.
302 Found The target resources been temporarily moved. As the move is temporarily, future references should still use the same location.
400 Bad Request The server cannot process the request as it is perceived as invalid.
401 Unauthorized The request to the target resource is not allowed due to missing or incorrect authentication credentials.
403 Forbidden The request to the target resource is not allowed for reasons unrelated to authentication.
404 Not Found The target resource was not found.
500 Internal Server Error The server encountered an unexpected error.
502 Bad Gateway The server is acting as a gateway/proxy and received an invalid response from a server it contacted to fulfill the request.
503 Service Unavailable The server is currently unable to fulfill the request.

cURL

is a tool and library for transferring data with URL syntax, capable of handling various protocols.

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curl http://foobar/index.html
With the --request or -X parameter, the method can be specified. To include the the headers in the output.
curl -I --request GET  http://www.opsschool.org/en/latest/http_101.html
The -O switch makes cURL write output to a local file named like the remote file.
$ curl -O http://localhost/bigfile

By default cURL does not follow HTTP redirects, and instead a 3xx redirection message is given.
The -L switch makes cURL automatically follow redirects and issue another request to the given localtion till it finds the targeted resource.

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curl -IL foobar.org

netcat

a networking tool capable of reading and writing data across a network connection.

Basic client/server

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$ nc -l 192.168.0.1 1234 > output.log
### then in another terminal, pipe some data to netcat that is connected to the destination ip and port
$ echo "I'm connected as client"| nc 192.168.0.1 1234
## Then again in the first (server) terminal, the data is displayed:
$ cat output.log
I'm connected as client
Contents
  1. 1. Multiplexers
    1. 1.1. mosh
    2. 1.2. ss
    3. 1.3. mtr
    4. 1.4. iftop
    5. 1.5. iperf
    6. 1.6. Troubleshooting layer 1 problems
    7. 1.7. HTTP core protocol
      1. 1.7.1. Request
      2. 1.7.2. Response
    8. 1.8. cURL
    9. 1.9. netcat
      1. 1.9.1. Basic client/server