this post was submitted on 07 Apr 2025
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Basic networking/subnetting question. (lemmy.dbzer0.com)
submitted 2 weeks ago by marauding_gibberish142@lemmy.dbzer0.com to c/selfhosted@lemmy.world
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Sorry for being such a noob. My networking is not very strong, thought I'd ask the fine folks here.

Let's say I have a Linux box working as a router and a dumb switch (I.e. L2 only). I have 2 PCs that I would like to keep separated and not let them talk to each other.

Can I plug these two PCs into the switch, configure their interfaces with IPs from different subnets, and configure the relevant sub-interfaces and ACLs (to prevent inter-subnet communication through the router) on the Linux router?

What I'm asking is; do I really need VLANs? I do need to segregate networks but I do not trust the operating systems running on these switches which can do L3 routing.

If you have a better solution than what I described which can scale with the number of computers, please let me know. Unfortunately, networking below L3 is still fuzzy in my head.

Thanks!

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[–] possiblylinux127@lemmy.zip 2 points 2 weeks ago (1 children)

Subnets are on layer 3 not layer 2. You can easy access other devices on layer 3 by finding the right subnet on layer 2. ARP is used to resolve IP addresses into MAC addresses and vis versa.

[–] marauding_gibberish142@lemmy.dbzer0.com 1 points 2 weeks ago (2 children)

Thanks, but isn't ARP contained inside a subnet? I guess you could find everything if you inspected the MAC table of the main switch

[–] possiblylinux127@lemmy.zip 1 points 2 weeks ago (1 children)

ARP is in the broadcast domain (otherwise known as a lan)

Vlans create multiple lans

[–] nottelling@lemmy.world 1 points 2 weeks ago (2 children)

no. Arp bridges layer 1 and 2. It's switch local. With a VLAN, it becomes VLAN local, in the sense that 802.1q creates a "virtual" switch.

[–] marauding_gibberish142@lemmy.dbzer0.com 2 points 2 weeks ago

Sorry, I'm not sure what you mean by "ARP bridges L1 and L2". I'll have to read more about this. Other than that, I understand what you said.

[–] possiblylinux127@lemmy.zip 1 points 2 weeks ago

ARP is in a single broadcast domain which can span multiple switches.