Need some advice on learning networking

[n25an]

Re: Need some advice on learning networking

A couple of problems. If for some reason the subnet get changed, the IP address you enter into the host file may no longer be valid. If the target device is on DHCP it will have been changed or the computer and the target device may no longer be within the same subnet mask range.

An entry in the host or hosts file depending on OS actually takes precedence over DNS results. If an entry is found in the hosts file your browser goes directly to that address. It can be used to resolve frequently used web pages more quickly. More frequently it is used to block unwanted websites. Example 127.0.0.1 known.unwanted.site will block that site. Instead your browser will connect to the blank local host 127.0.0.1 By blocking certain adware sites can actually speed up the loading of many websites and unlike ad blockers is totally invisible to the website you are loading. How To Block Websites On Windows Using The Hosts File

this explains how some viruses and malware can redirect traffic away from malware removal resources online... interesting... all IT knowledge intersects sooner or later...

that being said... 15 years in the field... never seen or heard of it before... I have heard of netbios name issues once in 15 years... but thats about it...

doesn't mean it does not occur... just never had any issues with it...

good info to know though

[n25an]

Re: Need some advice on learning networking

The only real problem I ever really had with DHCP was when the DHCP function on a server shut itself down over night. Things that were on fixed IP addresses or had been on all night worked fine. Computers that had been shut off over night could not access the internet or any of the servers or printers. I got called out because in the stock yard office some people could not print. I took me all of 5 minutes to determine that DHCP wasn't working. I called the receptionist and asked her to have their IT call me. She called me back and told me the IT was too busy trying to determine which router was down. 5 minutes their IT supervisor in Seattle called me, the receptionist had called him when the local IT wouldn't take time to talk to me. I told him the problem and 10 minutes later the DHCP was back up.

correction... if dhcp is down just do an ipconfig from command line and see if you get a 169.xxx.xxx.xxx address if you do its down... thanks for the correction all...

and below is some command prompt wizardry to check if dns and dhcp servers are up...

to check if dns is working is to ping host name of copier from command line in windows... if all things are connected and settings are good you should get a response... and it should respond with the ip address if it responds with the gibberish thats ipv6 you can force it to do ipv4

below is an example with google.com

ping google.com

Pinging google.com [2607:f8b0:4000:801::200e] with 32 b
Reply from 2607:f8b0:4000:801::200e: time=34ms
Reply from 2607:f8b0:4000:801::200e: time=34ms
Reply from 2607:f8b0:4000:801::200e: time=34ms
Reply from 2607:f8b0:4000:801::200e: time=34ms

Ping statistics for 2607:f8b0:4000:801::200e:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss)
Approximate round trip times in milli-seconds:
Minimum = 34ms, Maximum = 34ms, Average = 34ms

ping google.com -4

Pinging google.com [172.217.2.238] with 32 bytes of dat
Reply from 172.217.2.238: bytes=32 time=55ms TTL=112
Reply from 172.217.2.238: bytes=32 time=37ms TTL=112
Reply from 172.217.2.238: bytes=32 time=36ms TTL=112
Reply from 172.217.2.238: bytes=32 time=37ms TTL=112

Ping statistics for 172.217.2.238:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss)
Approximate round trip times in milli-seconds:
Minimum = 36ms, Maximum = 55ms, Average = 41ms


How to find dhcp server from command prompt in windows...

ipconfig /all | find /i "DHCP Server"
DHCP Server . . . . . . . . . . . : 192.168.1.254

How to check from command prompt that dhcp server is working

ping 192.168.1.254

Pinging 192.168.1.254 with 32 bytes of data:
Reply from 192.168.1.254: bytes=32 time=74ms TTL=64
Reply from 192.168.1.254: bytes=32 time=6ms TTL=64
Reply from 192.168.1.254: bytes=32 time=6ms TTL=64
Reply from 192.168.1.254: bytes=32 time=6ms TTL=64

Ping statistics for 192.168.1.254:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 6ms, Maximum = 74ms, Average = 23ms

How to see what servers are running in windows or at the least are configured for the nic card either automatically or hard wired as a setting

ipconfig /all | find /i "Server"
DHCP Server . . . . . . . . . . . : 192.168.1.254
DNS Servers . . . . . . . . . . . : 192.168.1.254

[BillyCarpenter]

Re: Need some advice on learning networking

below is one method... may not be what slimslob used but its valid...
He probably figured it out from the copier screens...

never-the-less its listed below...

a way to check this from command prompt is listed below...

to check if dhcp is working is to ping host name of copier from command line in windows... if all things are connected and settings are good you should get a response... and it should respond with the ip address if it responds with the gibberish thats ipv6 you can force it to do ipv4

below is an example with google.com

ping google.com

Pinging google.com [2607:f8b0:4000:801::200e] with 32 b
Reply from 2607:f8b0:4000:801::200e: time=34ms
Reply from 2607:f8b0:4000:801::200e: time=34ms
Reply from 2607:f8b0:4000:801::200e: time=34ms
Reply from 2607:f8b0:4000:801::200e: time=34ms

Ping statistics for 2607:f8b0:4000:801::200e:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss)
Approximate round trip times in milli-seconds:
Minimum = 34ms, Maximum = 34ms, Average = 34ms

ping google.com -4

Pinging google.com [172.217.2.238] with 32 bytes of dat
Reply from 172.217.2.238: bytes=32 time=55ms TTL=112
Reply from 172.217.2.238: bytes=32 time=37ms TTL=112
Reply from 172.217.2.238: bytes=32 time=36ms TTL=112
Reply from 172.217.2.238: bytes=32 time=37ms TTL=112

Ping statistics for 172.217.2.238:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss)
Approximate round trip times in milli-seconds:
Minimum = 36ms, Maximum = 55ms, Average = 41ms


How to find dhcp server from command prompt in windows...

ipconfig /all | find /i "DHCP Server"
DHCP Server . . . . . . . . . . . : 192.168.1.254

How to check from command prompt that dhcp server is working

ping 192.168.1.254

Pinging 192.168.1.254 with 32 bytes of data:
Reply from 192.168.1.254: bytes=32 time=74ms TTL=64
Reply from 192.168.1.254: bytes=32 time=6ms TTL=64
Reply from 192.168.1.254: bytes=32 time=6ms TTL=64
Reply from 192.168.1.254: bytes=32 time=6ms TTL=64

Ping statistics for 192.168.1.254:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 6ms, Maximum = 74ms, Average = 23ms

How to see what servers are running in windows or at the least are configured for the nic card either automatically or hard wired as a setting

ipconfig /all | find /i "Server"
DHCP Server . . . . . . . . . . . : 192.168.1.254
DNS Servers . . . . . . . . . . . : 192.168.1.254

That's good stuff to know and it works. See below:

dhcp server.JPG

[BillyCarpenter]

Re: Need some advice on learning networking

below is one method... may not be what slimslob used but its valid...


to check if dhcp is working is to ping host name of copier from command line in windows... if all things are connected and settings are good you should get a response... and it should respond with the ip address if it responds with the gibberish thats ipv6 you can force it to do ipv4

I pinged the host name of the copier and it did respond like you said, but I'm unsure how this proves that DHCP is working. I understand how it proves DNS is working but not DHCP. Can you explain further? Thanks.

[bsm2]

Re: Need some advice on learning networking

The only way it can resolve a hostname is through DNS not DHCP.

[BillyCarpenter]

Re: Need some advice on learning networking

The only way it can resolve a hostname is through DNS not DHCP.

So, I'm correct that pinging the hostname of the copier only proves that DNS is working? It does not prove that DHCP is working?

[bsm2]

Re: Need some advice on learning networking

So, I'm correct that pinging the hostname of the copier only proves that DNS is working? It does not prove that DHCP is working?

Yes if DHCP is not working you could run an ipconfig and the the pc address would 169. something same as if you connect a copier with DHCP address would be 169. something.

You would have no internet no printing etc.......

[n25an]

Re: Need some advice on learning networking

The only way it can resolve a hostname is through DNS not DHCP.

the things that happen when a man is sleepy... well you guys get the idea... the point being... you can tell if the host name is connecting to the ip address... or not...

and yes its dns not dhcp... my appologies for mixing my terms...

also yep... if you get a 169.xxx.xxx.xxx address that usually means dhcp is down...
sorry about that...
just got up...
and reread my junk...

made the correction in the original post...
let me know if all is well...
I am never a man averse to learning or correction...

[n25an]

Re: Need some advice on learning networking

I pinged the host name of the copier and it did respond like you said, but I'm unsure how this proves that DHCP is working. I understand how it proves DNS is working but not DHCP. Can you explain further? Thanks.

my thinking was if you can't pull the dhcp server up using ipconfig in the way instructed above from the command line... or even ping it... then its probably down...

atleast that was my thought...

its a roundabout way of doing it...
but that was my thinking...

[BillyCarpenter]

Re: Need some advice on learning networking

my thinking was if you can't pull the dhcp server up using ipconfig in the way instructed above from the command line... or even ping it... then its probably down...

atleast that was my thought...

its a roundabout way of doing it...
but that was my thinking...

Don't worry about it. You, along with others, have taught me so much. A few weeks ago I wouldn't have even caught that mistake. This is no longer about only networking a copier for me. I want to know much more and I want to know how to troubleshoot DHCP and DNS. At the heart of IT it's about solving problems and you have to have a deep understanding of this stuff to find and correct the problem. Right?

[bsm2]

Re: Need some advice on learning networking

Don't worry about it. You, along with others, have taught me so much. A few weeks ago I wouldn't have even caught that mistake. This is no longer about only networking a copier for me. I want to know much more and I want to know how to troubleshoot DHCP and DNS. At the heart of IT it's about solving problems and you have to have a deep understanding of this stuff to find and correct the problem. Right?

Ping is your friend
ping the copier
ping the gateway
ping google.com

Now some network works are locked down IE enterprise where IT will give you and address you can't ping it but it works.

[BillyCarpenter]

Re: Need some advice on learning networking

Here's a question for the IT experts on here:

Lets say I suspect that a virus (or something else) is assigning rouge IP address and I want to find out if there's a duplicate IP address. What's the best way to see if there's a duplicate IP address. I know one way is to use a scan tool. I used NetScan Tools Pro and ran an ARP request for the copier IP address. It sent out an ARP request and showed every MAC addresses that's on that IP address. So that's one way. But that's an invasive method and I would need to get permission to run something like that on a customer's network.

Are there any less invasive ways to do this?

[bsm2]

Re: Need some advice on learning networking

Here's a question for the IT experts on here:

Lets say I suspect that a virus (or something else) is assigning rouge IP address and I want to find out if there's a duplicate IP address. What's the best way to see if there's a duplicate IP address. I know one way is to use a scan tool. I used NetScan Tools Pro and ran an ARP request for the copier IP address. It sent out an ARP request and showed every MAC addresses that's on that IP address. So that's one way. But that's an invasive method and I would need to get permission to run something like that on a customer's network.

Are there any less invasive ways to do this?

Unplug the copier and if you get a ping Bingo

[BillyCarpenter]

Re: Need some advice on learning networking

Unplug the copier and if you get a ping Bingo

Duh. Now I'm feeling really dumb. lol

[tsbservice]

Re: Need some advice on learning networking

Unplug the copier and if you get a ping Bingo

Yepp, that's the way