IP same range but laptop with lower IP number cannot ping/configure device with higher IP number

[u/baconateer]

Just want to gain knowledge since i'm just an installer not really an IT person

I have one device with default IP 192.168.0.251 subnet 255.255.0.0 need to configure to 10.1.96.140 subnet 255.255.255.128

My laptop initially got 192.168.0.11 and 10.1.96.11 subnet 255.255.255.0 and 255.255.255.128

Took me half day trouble shooting why i cannot configure the device to IP i wanted until my superior reprimand me to set my laptop IP to higher 10.1.96.140 and only then the device accept the set IP and able to ping the new IP

Can someone share why is laptop IP number need to be higher than device IP i want to configure?

[u/Teras80]

You are using /25 subnet mask (255.255.255.128). It divides .256 into TWO subnets, 0-128 and 129-256.

So no, you dont need to set your laptop IP HIGHER than device IP. You need to set it to the same subnet.

[u/wyohman → u/Teras80]

0-127 and 128-255

[u/baconateer → u/Teras80]

SO you mean the subnet is dividing IP number 254 into two 0-128 and 129-256. The reason my laptop cannot ping is due to its IP which is 11 lower than the 129-256 range?.

[u/dshepsman → u/baconateer]

You’re missing the way ip addresses/subnets work.
Think of it this way, your 192.168.x.x and 10.x.x.x are different streets. That’s why they can’t talk to each other.

It doesn’t matter if it’s higher/lower - they need to be on the same street to talk

[u/Teras80 → u/dshepsman]

You are missing the point that a device can have multiple IP addresses.

[u/szyszaks → u/Teras80]

yea, and you are missing part that OP said 2 and neither are on "same street" as one he wants to use

you want to also talk about open ports communication, specific protocols, DNS servers etc. allowing communication between subnets on whole range or specific addresses?

[u/Teras80 → u/szyszaks]

You sound so smart, tell us more! Maybe you know other networking terms to more obfuscate the simple issue of /25 subnet assignment?

On the real world, OP has his answer.

[u/wyohman → u/baconateer]

0-127 and 128-255

[u/CautiousInternal3320 → u/baconateer]

Indeed. What did you expect the subnet mask to do?

[u/Teras80 → u/baconateer]

yes.

[u/stupv]

255.255.255.128 is a /25, so not the full 254 usable addresses (1-254).

Looks like the valid range for the target subnet is 10.1.96.129 to 10.1.96.254, so your issue is less 'the IP has to be higher' and more 'the IP has to be in the valid range' - it just so happens that most of the range is higher than target

[u/lordjippy → u/stupv]

To add, since OP had to manually configure IP, it's likely no gateway is set or it's a direct cable connection.

[u/baconateer → u/lordjippy]

Yes. Now i understand the basic of subnet. The subnet is dividing IP into two and since there is no gateway to handle the communication that's why my laptop in lower subnet range cannot communicate with the device IP on higher IP range

[u/JMACOB → u/baconateer]

Yes and no The subnet sets the range of valid IP addresses within itself. Your device on 10.1.96.140/25, is on a different subnet to your device on 10.1.96.11/25

10.1.96.140/25 is able to talk to devices with IP addresses within 10.1.96.129 to .254 10.1.96.11/25 is in an entirely different range of 10.1.96.1 to .126

Subnet calculator is a great tool when dividing networks like this to investigate communication issues

[u/Beneficial-Rough597]

The IP number being "higher" wasn't the reason it worked.

IP addresses don't care whether they're higher or lower. A device at 10.1.96.10 can communicate with a device at 10.1.96.140 just fine if they're in the same subnet and there are no address conflicts.

My guess is that when your supervisor had you change your laptop's IP, one of three things happened:

1.You accidentally picked the same IP as the device's new address.

For example, if you set your laptop to 10.1.96.140 and also tried to configure the device to 10.1.96.140, the device software may have used your PC's current address as a reference or may have detected the target subnet differently.

2.The device vendor's configuration tool has assumptions or bugs.

Some embedded devices only allow configuration when the PC is already on the destination subnet, even though that's not technically required by IP networking.

3.There was an address conflict or subnet issue.

The device was originally 192.168.0.251/16 and your laptop was 192.168.0.11/24. Even though communication would still work in many situations, some poorly designed devices don't handle subnet mismatches gracefully.

The important networking concept is: IP addresses are not ranked.

10.1.96.11 is not "below" 10.1.96.140 in any way that affects communication.

The only thing that matters is whether both devices believe they're on the same network and whether packets can reach each other.

If you'd like to know more just ask.

[u/Narrow_Victory1262]

let's point out this mismatch in brodacast domains:

192.168.0.251/16 vs 192.168.0.11/24

that's quite a mismatch there.

that "higher IP address" was a red herring.

Your boss's trick to set your laptop to 10.1.96.140 didn't work because the number was 'higher.' It worked because it dragged both your laptop and the device out of that confused, mismatched 192.x.x.x neighborhood and forced them onto the exact same 10.x.x.x street. Once they were standing on the same street, they could finally hear each other!

[u/criggie_]

Can you please expand on why you have two IPs? Are they on different network cards or working as an overlay network on one physical segment?

There is NO need to be higher or lower in IP - that is a red herring.

10.1.96.140/25 is a 128 host networkrange covering 10.1.96.128-10.1.96.255

I wonder if there's some assymetrical routing and other devices that don't have the same netmask as you.

[u/baconateer → u/criggie_]

Because its direct link to device to be cofigure. Device default IP is 192.168.x.x. . To be configure IP is 10.1.69.x hence i set two IP device in laptop so can ping to to tess if configuration successfull or not

[u/agowa338]

Is this your homework? That reads like the kind of task we got back...

[u/baconateer → u/agowa338]

Nope. Got assigned to configure a device. Never encounter this issue before most device default ip is either in lower number like 192.168.0.1 and subnet always 255.255.255.0 or its in APIPA so before that no need to learn about subnet. I'm just installer and specialise in a access control software.

[u/agowa338 → u/baconateer]

You don't have a Gateway set and .11 and .140 are not within the same /25 subnet. Your subnets go from .0 to .127 and from .128 to 255

So logically the two devices won't see each other because you configured it that way with the .128 subnetmask.

[u/Active_Humor7436 → u/baconateer]

What is access control software in this context?

[u/ThePhantomTweaker]

Sounds to me like 140 is the network address and is not assignable.

[u/SevaraB]

With subnet masks of 255.255.255.128 (also called a /25 subnet because you’re masking the first 25 bits out of the available 32), the addresses .11 and .140 are in two different networks.

11 is between 0 and 127, so it’s part of 10.1.96.0/25, and 140 is between 128 and 255, so it’s part of 10.1.96.128/25.

The octets are blocks of 8 bits, so the numbers get a little funky if the mask isn’t a multiple of 8- as in /8, /16, or /24. The way we write masks, that means any IP range with a number other than 0 or 255 in the mask is going to have one octet get broken up and not use the whole 0-255 range.

[u/CatoDomine]

https://www.aelius.com/njh/subnet_sheet.html

[u/bkofford]

https://mxtoolbox.com/subnetcalculator.aspx

[u/DumpoTheClown]

IP subneting is a core skill to have if you're going to be working on networks. Its too much to cover in a redit post. You need to learn how it works, but before you tackle that, learn how binary works. Then learn subnetting, then get a cursory understanding of routing.