Ethernet Switches & Routers

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Contributor
Posts: 22
Registered: ‎11-12-2012

Overlapping subnet... why

Hello All,

I have a no explanation for this. I have multiple subnets at new customers site as seen below. For whatever reason, when I enter in VE68 (10.35.68.1/21) it tells me it is overlapping with ve64 (10.35.64.1/23)... Can someone tell me what the deal is with this.. never seen it before as they are clearly not overlapping subnets. tried it on a cisco box and had same results.

interface ve 1

port-name MainData

ip address 10.35.48.2 255.255.248.0

!

interface ve 56

port-name TorontoWireless

ip address 10.35.56.1 255.255.248.0

!

interface ve 64

port-name VoIP

ip address 10.35.64.1 255.255.254.0

!

interface ve 67

port-name CCTV

ip address 10.35.67.1 255.255.255.0

!

interface ve 68

port-name TorontoPublic

ip address 10.35.68.1 255.255.248.0       <- this is the overlapping subnet?

!

interface ve 74

ip address 10.35.74.1 255.255.255.0

Joe Lentine BCNE
Frequent Contributor
Posts: 118
Registered: ‎06-15-2009

Re: Overlapping subnet... why

Which Brocade switch are you using here Dlentine?

thanks

deepti

Brocadian
Posts: 3
Registered: ‎04-30-2013

Re: Overlapping subnet... why

dlentine,

The subnets are overlapping, if you take the 10.35.68.0/21 subnet and break it down in the calculator, you will find that the root network address is 10.35.64.0/21 (range is 10.35.64.1  to 10.35.71.254 ), therefore your second subnet of 10.35.64.1/23 is part of the overall /21 subnet.

What you should do is choose the 10.35.72.0/23 for your second subnet.

Best.

Contributor
Posts: 22
Registered: ‎11-12-2012

Re: Overlapping subnet... why

Thanks for your response James. I see how it falls under a 10.35.64.0/21 subnet, but why can I make it a /22 and it dosent overlap? I have already moved the Subnets around, but I'm just not seeing this one right .

Just an FYI for first response the switch is an sx800

Joe Lentine BCNE
Brocadian
Posts: 3
Registered: ‎04-30-2013

Re: Overlapping subnet... why

dlentine,

That's correct, if you make it a /22 then your boundaries will be 10.35.64.0/22 and 10.35.68.0/22 and so on.

Think of it like this, you have a finite amount of numbers to use there, but you have to stick to the rules of subnetting. So it does depend on how you break up the IP blocks, but you cant break the bit boundaries. Best way to stay efficient is to use a IP subnetting calculator. It keeps me honest.

Occasional Contributor
Posts: 17
Registered: ‎08-09-2013

Re: Overlapping subnet... why

Hello dlentine,

  The following URLs might help ya out with CIDR notations & netmasking.

CIDR SUBNET MASK CHEATSHEET & ICMP TYPE CODES

CheatSheet/IPv4CIDRNotation - SamatsWiki

** An actual calculator **

Online IP Subnet Calculator

Cheers,

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