Subnet mask

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Networking
Hi, On my network, my switch subnet is 255.255.255.224 (/27) and I have a VLAN with subnet 255.255.255.192 (/26). When I first connect 2 PCs to the switch with both with subnet /26 they could not ping each other, however, when I make the subnet /27 they can ping. After they ping each other, I returned the subnet for the PCs to /26 and they still ping each other. Why /26 does not ping from the first time? Regards, Rayan
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Subnet 1 = 255.255.255.224 with vlan 255.255.255.192

A – why is the vlan bigger than the subnet it is under?

B – they can ping after the first success be cause ‘windows’ retains routes. Do NBTSTAT -c to see the cached list of addresses.

C – subnet 255.255.255.0 gives and address space of 253, since 0 and 255 are already taken. subnet 255.255.254.0 would be 510. In your example 255.255.255.224 (254-224 = 30) is thirty addresses and 255.255.255.192 (254-192=62) is sixty-two addresses a bigger area.

D – sometimes subnetting can be very counter intuitive.
Good luck.

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  • Wickedstick
    I haven't given this a great deal of thought but initially, and without knowing more information, I would guess that: a) the switchports initially weren't in the same VLAN, or b) the first time you configured them to /26 you may have fat-fingered one of them. When changing to /27 you got the mask correct, as well as when you switched it back to /26. There's no reason why they would respond when on /27 as opposed to /26 as long as the mask was properly configured and the switchports were in the same VLAN.
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  • Snapper70
    You haven't given the actual addresses, so that leaves us guessing somewhat. If the subnet masks are different but the address range overlaps, then the broadcast address that ARP relies on may be changing. Once the switch/device have learned where each other are, you can switch back from /27 to /26; but it may be next time you shut down for power maintenance or failure, you may be in the same boat. Or, as previously mentionned, could just be the address was fat-fingered.
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