Testing Internet connection on same subnrt - Page 1
Forum section: electronics / testgear

author: BocaDev
author_rank: Contributor
timestamp: November 27, 2018, 09:51:53 pm
content: I hope this is the correct sub-forum to post this question.I received a communications controller in for repair. This controller is operated through its hardware Ethernet connector. My shop has a Comcast single IP address coming directly into my ATT router. I plugged in an Ethernet cable connecting it from the UUT to the back of my ATT router which has four Ethernet connectors, one of which is my computer plugged into. However, I am not able to establish a connection using my web browser. My web browser just times out. My computer is on IP address 192.168.1.100 and the UUT is at IP address 192.168.1.245.Question.. Should I be able to do this on the same sub-net or do I need another router in here somewhere?Thanks,Alan

author: capt bullshot
author_rank: Super Contributor
timestamp: November 27, 2018, 10:30:33 pm
content: Of course, there are many pitfalls in many details - like the four ports of your router aren't a ethernet switch like everyone would expect, or the router issues subnets smaller than /24 as everyone would expect, or your computer is configured wrong in a subtle way, or the UUT is simply defective ...But in general your setup looks like it should work, nothing else required.

author: cdev
author_rank: Super Contributor
timestamp: November 27, 2018, 10:51:36 pm
content: Try inserting Wireshark in there to see what exactly is being sent back and forth.Depending on how your network is set up youmayneed to do network sniffing using port mirroring on a managed switch, a hub or whatever.The Wireshark wiki has a good discussion of this.

author: retiredcaps
author_rank: Super Contributor
timestamp: November 27, 2018, 11:34:15 pm
content: Quote from: BocaDev on November 27, 2018, 09:51:53 pmFirst test is always to ping the device. On your computer, do you get a ping response from 192.168.1.245?

author: PaulAm
author_rank: Frequent Contributor
timestamp: November 27, 2018, 11:38:11 pm
content: This stuff can drive you nuts. Just today I had a voip box that would only allow initial configuration if plugged into a Windows box.Does the device expect to be plugged into a local network or directly into a PC? If you're using the cable that came with it, it might or might not be cross connected (if it's supposed to be directly connected to the PC and you're using the cable that came with it, it's probably a cross cable and might not work directly plugged into your router. Some routers will recognize cross cables and handle things accordingly to further confuse things; some won't.)You can get a cheap network hub, configure a static IP on your machine and plug the 2 devices into that and take ATT out of the equation entirely. The router might be providing DHCP addresses and the device might be picking that up. Are you sure it's got a static IP?You can also open a command window and use the ping command to see if your computer can see the device. You might get more diagnostics that way. You could also get nmap and use it to scan your network to see if the device is out there somewhere with an unexpected IP..

author: cdev
author_rank: Super Contributor
timestamp: November 28, 2018, 01:23:06 am
content: I don't know if anybody makes 'cheap networkhubs' any more. So if you have any, save em. Don't let anybody throw them out, as they represent the easiest way to diagnose some kinds of IP problems.

author: bson
author_rank: Unknown
timestamp: November 28, 2018, 07:02:29 pm
content: Quote from: cdev on November 28, 2018, 01:23:06 amIndeed, this is why I still have an old 10baseTX half duplex collision domain hub. This way when tracking down some bug like a bad checksum or truncated packet, I can simply look at the traffic in both directions with wireshark and see what is actually going on the wire. Managed switches will do it too (I have several), but they require work to set up while this old hub just requires plugging in. So unless I need 100M speed or VLAN, or some other feature I usually just reach for the slow old 10base HD hub!

author: Brumby
author_rank: Unknown
timestamp: November 29, 2018, 03:45:04 am
content: When I first delved into networking (on the small scale) I researched what hubs, switches and routers do - and I decided to go for switches instead of hubs.I hadn't really thought about it before, but having a hub on hand for diagnostic purposes does make a lot of sense. Pity I don't have one anywhere within my collection of stuff.

author: LapTop006
author_rank: Unknown
timestamp: November 29, 2018, 09:31:15 am
content: Quote from: Brumby on November 29, 2018, 03:45:04 amThey can still be picked up cheap on eBay.I have some taps which can be handy for debugging too.

author: grumpydoc
author_rank: Super Contributor
timestamp: November 29, 2018, 09:41:35 am
content: How do you know the IP address of the unit is 192.168.1.245 - if that was the address in some other network but the unit uses DHCP to acquire an address it will probably pick up a different one in your network.Unless the IP address is fixed, in which case it might help to know what subnet mask the unit is using - it should be 255.255.255.0 (but could be anything and certain combinations will prevent it chatting on your network).Otherwise wireshark on a laptop connected via a hub to sniff the network packets going to and from the unit is a good suggestion.

author: GeorgeOfTheJungle
author_rank: Super Contributor
timestamp: November 29, 2018, 11:53:48 am
content: If you're not sure of its address, the broadcast address for the network 192.168.1.0/24 is 192.168.1.255, ping that and everything in the network should respond. If you still can't see it, could also try with a ping to 255.255.255.255 although many/most things are configured to ignore pings to this address.

author: LapTop006
author_rank: Unknown
timestamp: November 29, 2018, 12:05:39 pm
content: Quote from: GeorgeOfTheJungle on November 29, 2018, 11:53:48 amOr use nmap to scan the subnet.If it's dynamic and you have DHCP server logs, look at those.

author: kaderud
author_rank: Newbie
timestamp: November 29, 2018, 12:06:45 pm
content: One thing I would do is try to set the IP with the ARP-command from your computer, if you know the MAC-address of the device.From a "cmd"-window:arp -aDisplays the arp table.arp -s 192.168.1.55 00-01-de-ad-be-efAdds a static entry to the arp table. Choose an IP in your IP-range, and replace the MAC-address (00-01..) with the device's address

author: BocaDev
author_rank: Contributor
timestamp: November 29, 2018, 07:19:56 pm
content: Quote from: grumpydoc on November 29, 2018, 09:41:35 amHi grumpy,There is a hardware switch on the unit to place everything in default values. After doing so, that defaulted the IP to 192.168.1.245 with the mask at 255.255.255.1.I have an old Netgear DS104 hub I can dig out from the closet (yes I have kept old hardware network stuff) and will hook up one of the ports with a cable between the output of my ATT router and the hub. Another port with a cable between the Hub and the UUT. Then another port connected to my laptop. I'll load Wireshark onto the laptop and exam what I see. Should turn out to be an interesting afternoon of network troubleshooting.And a special thanks to everyone else with their suggestions and things to try. I will try every one.Thanks,Alan

author: GeorgeOfTheJungle
author_rank: Super Contributor
timestamp: November 29, 2018, 07:38:30 pm
content: Quote from: BocaDev on November 29, 2018, 07:19:56 pmAnd what's your IP? With that (funny) mask it can only communicate withevenodd hosts: 192.168.1.1, 192.168.1.3, 192.168.1.5 etc etc. If I were you I would try to setup the IP of the PC manually to one of those (odd) IPs, with the funny mask (255.255.255.1) too, in network settings, then try to ping it.

author: grumpydoc
author_rank: Super Contributor
timestamp: November 29, 2018, 08:39:46 pm
content: Quote from: BocaDev on November 29, 2018, 07:19:56 pmThat's an invalid mask.Masks have to be all '1's followed by all '0's so 255.255.255.0 is valid (11111111111111111111111100000000) as is 255.255.255.128 (11111111111111111111111110000000), 255.255.255.192 (11111111111111111111111111000000) and so-on.Quote from: GeorgeOfTheJungle on November 29, 2018, 07:38:30 pmI don't think it will even do that, if that really is the mask, it's just invalid - so might not want to talk to anything.

author: GeorgeOfTheJungle
author_rank: Super Contributor
timestamp: November 29, 2018, 08:52:28 pm
content: https://tools.ietf.org/html/rfc1219Quote

author: JDubU
author_rank: Frequent Contributor
timestamp: November 29, 2018, 09:32:18 pm
content: Here is an easy to use, freeware, network scanner that works well (Windows only):http://www.advanced-ip-scanner.com/

author: grumpydoc
author_rank: Super Contributor
timestamp: November 29, 2018, 10:08:04 pm
content: Quote from: GeorgeOfTheJungle on November 29, 2018, 08:52:28 pmOK, well, you learn something new every dayHowever seehttps://tools.ietf.org/html/rfc1519QuoteThe odds that someone writing embedded firmware knew the bits don't have to be contiguous per 950 but not about the change in 1519 when CIDR was introducedandfound a way to use that mask usefully do not seem high compared with the mask of 255.255.255.1 being misreported or plain wrong in the default settings.

author: GeorgeOfTheJungle
author_rank: Super Contributor
timestamp: November 29, 2018, 10:35:51 pm
content: Yeah, that mask is either wrong or silly if you ask me :-) But sometimes they do these things (obscure, weird setups) on purpose.

author: BocaDev
author_rank: Contributor
timestamp: November 30, 2018, 01:47:10 am
content: Sorry everyone, the mask is set to 255.255.255.0My mistake. Too many numbers for my brain to keep track of.Alan

author: BocaDev
author_rank: Contributor
timestamp: November 30, 2018, 02:11:34 am
content: QuoteThanks JDubU,I just downloaded the advance IP scanner. Nice tool, even found attached network stuff I didn't know I had on my network. Anyway it did not find the UUT so I do have a problem. This unit has an internet activity LED on the front which is almost blinking continuously. Could be internet activity is coming in but nothing is being transmitted out.Tomorrow I'll connect the hub and laptop as grumpy suggested. Will post my findings.Thanks to everyone.Alan

author: BocaDev
author_rank: Contributor
timestamp: December 01, 2018, 01:24:33 am
content: I connected everything up today and have Wireshark on my laptop sniffing traffic. I can see several ARP request going out (who is 192.168.1.245) but no response from the UUT in response to the query's.After doing some visual inspection, I discovered the Ethernet connector has some burn carbon deposits on a few of the gold wire connections within the RJ45. It possible a lightning strike within the area of the building had made its way onto the Ethernet cable. I'll change out the connector and hold my breath that the processor didn't get hit.Thanks to all for your help,Alan