For instance we have been having problems with our one CT scanner sending images through to our Conquest archive. Eventually we managed to get the technician on site and go into thier settings. It turns out they set the defualt gateway incorrectly. It is such a basic thing, but many people out there actually don't know what a default gateway does!
With this in mind I have compiled a list of links that I think are manditory for anyone who wishes to setup or troubleshoot network connections:
7 Layers of the OSI model
The 7 Layers of the OSI model define the basic levels of network communication. It is critical for a technician to have an understanding of the various layers of the OSI model and understand how information traverses these layers.
For instance DICOM is a layer 7 protocol that will have to traverse all the other layers for a connection to be estabished. This will mean that layer 1 - 7 all need to be operational before any images can be sent.
Command Line
The command line is a network admininstrators greatest friend! You can do a massive amount of troubleshooting and diagnostic work from command line. Here are a couple of basic commands to get you started:
ping
this command is used to test basic end to end connectivity. If you can ping a device then there is network connectivity between the two. If you cannot ping a device then you know that something is going wrong between the two computers.
Usage: ping [-t] [-a] [-n count] [-l size] [-f] [-i TTL] [-v TOS]
[-r count] [-s count] [[-j host-list] | [-k host-list]]
[-w timeout] [-R] [-S srcaddr] [-4] [-6] target_name
Options:
-t Ping the specified host until stopped.
To see statistics and continue - type Control-Break;
To stop - type Control-C.
-a Resolve addresses to hostnames.
-n count Number of echo requests to send.
-l size Send buffer size.
-f Set Don't Fragment flag in packet (IPv4-only).
-i TTL Time To Live.
-v TOS Type Of Service (IPv4-only).
-r count Record route for count hops (IPv4-only).
-s count Timestamp for count hops (IPv4-only).
-j host-list Loose source route along host-list (IPv4-only).
-k host-list Strict source route along host-list (IPv4-only).
-w timeout Timeout in milliseconds to wait for each reply.
-R Use routing header to test reverse route also (IPv6-only).
-S srcaddr Source address to use.
-4 Force using IPv4.
-6 Force using IPv6.
tracert
This command shows you the route a packet takes to get to its destination. Tracert is critical when you need to know if there are any routing problems on the network.
Usage: tracert [-d] [-h maximum_hops] [-j host-list] [-w timeout]
[-R] [-S srcaddr] [-4] [-6] target_name
Options:
-d Do not resolve addresses to hostnames.
-h maximum_hops Maximum number of hops to search for target.
-j host-list Loose source route along host-list (IPv4-only).
-w timeout Wait timeout milliseconds for each reply.
-R Trace round-trip path (IPv6-only).
-S srcaddr Source address to use (IPv6-only).
-4 Force using IPv4.
-6 Force using IPv6.
arp
ARP stands for address resolution protocol. You can use this command to get the mac address of a computer on the local network. Please note that if you use this command to try get the mac address of a computer that is not on the same subnet as you the command will return the local interface mac address of your router.
Displays and modifies the IP-to-Physical address translation tables used by
address resolution protocol (ARP).
ARP -s inet_addr eth_addr [if_addr]
ARP -d inet_addr [if_addr]
ARP -a [inet_addr] [-N if_addr] [-v]
-a Displays current ARP entries by interrogating the current
protocol data. If inet_addr is specified, the IP and Physical
addresses for only the specified computer are displayed. If
more than one network interface uses ARP, entries for each ARP
table are displayed.
-g Same as -a.
-v Displays current ARP entries in verbose mode. All invalid
entries and entries on the loop-back interface will be shown.
inet_addr Specifies an internet address.
-N if_addr Displays the ARP entries for the network interface specified
by if_addr.
-d Deletes the host specified by inet_addr. inet_addr may be
wildcarded with * to delete all hosts.
-s Adds the host and associates the Internet address inet_addr
with the Physical address eth_addr. The Physical address is
given as 6 hexadecimal bytes separated by hyphens. The entry
is permanent.
eth_addr Specifies a physical address.
if_addr If present, this specifies the Internet address of the
interface whose address translation table should be modified.
If not present, the first applicable interface will be used.
Example:
> arp -s 157.55.85.212 00-aa-00-62-c6-09 .... Adds a static entry.
> arp -a .... Displays the arp table.
IPConfig
This tool allows you to see all the networking information about your computer.
The most common usages of this command are:
ipconfig /all - this will give you all the information about your networking connections.
ipconfig /flushdns - This flushes the DNS cache. (i.e. clears your DNS tables)
ipconfig /renew - this gets a new DHCP address
USAGE:
ipconfig [/allcompartments] [/? | /all |
/renew [adapter] | /release [adapter] |
/renew6 [adapter] | /release6 [adapter] |
/flushdns | /displaydns | /registerdns |
/showclassid adapter |
/setclassid adapter [classid] ]
where
adapter Connection name
(wildcard characters * and ? allowed, see examples)
Options:
/? Display this help message
/all Display full configuration information.
/allcompartments Display information for all compartments.
/release Release the IPv4 address for the specified adapter.
/release6 Release the IPv6 address for the specified adapter.
/renew Renew the IPv4 address for the specified adapter.
/renew6 Renew the IPv6 address for the specified adapter.
/flushdns Purges the DNS Resolver cache.
/registerdns Refreshes all DHCP leases and re-registers DNS names
/displaydns Display the contents of the DNS Resolver Cache.
/showclassid Displays all the dhcp class IDs allowed for adapter.
/setclassid Modifies the dhcp class id.
The default is to display only the IP address, subnet mask and
default gateway for each adapter bound to TCP/IP.
For Release and Renew, if no adapter name is specified, then the IP address
leases for all adapters bound to TCP/IP will be released or renewed.
For Setclassid, if no ClassId is specified, then the ClassId is removed.
Examples:
> ipconfig ... Show information
> ipconfig /all ... Show detailed information
> ipconfig /renew ... renew all adapters
> ipconfig /renew EL* ... renew any connection that has its
name starting with EL
> ipconfig /release *Con* ... release all matching connections,
eg. "Local Area Connection 1" or
"Local Area Connection 2"
> ipconfig /allcompartments ... Show information about all
compartments
> ipconfig /allcompartments /all ... Show detailed information about all
compartments
Other Tools
There are a host of networking related tools on the internet. Here are a list of the ones that I use on a daily basis.
Superscan
Superscan is a port scanning program. It basically finds all the computers in a specific ip range. I find this too usefull when I need to find a computer on the network or when I need to find computers running specific services on the network.
I prefer version 3.0. The latest version irritates me a bit.
Ping a ding ding
This is a very basic tool that pings an IP address and makes a noise when it can or cannot see the remote device. I find this very useful when a machine has lost connectivity and I need to know as soon as it is available again.
UltaVNC
UltraVNC remote admin tool that allows you to take over the remote computer.
The Dude
I have written about the dude before. This is an awsome application for monitoring your network infrastructure. We use it to monitor all of our core networking devices and some of our servers including the serivces on those servers i.e. DICOM services.
