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IP Addressing

Just a questions on this. This seems simple but doesn't make sense to me. I have seen engineers who have an IP of for an SVI address. My question is if you are going to use a /26 why would you use .1 as your SVI IP? Shouldn't you use Doesn't this defeat the purpose of using a /26? Isn't on another network? Thanks for any response

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Joseph W. Doherty
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Unclear you confusion. is indeed in a different network from is the first IP in its /26 network, as is the first in the next /26 network.



Your question needs clarification. is the first address on the network and so is a valid address to use. is the first address on the network. so you can have the following configuration:

interface vlan 10

ip address

interface vlan 20

ip address

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Would that be the first address because the address is a class C and should be a /24 and since we are moving over the bits to a /26 the would be covered under this?

VLAN 10 is the SVI for VLAN10

Should I start my dhcp at or start at It seems I should start with the .65 since I am using a /26.


Hi, is in a different network to Since SVI for vlan 10 is your dhcp range would be from -

Have a look at the following doc that explains a little about subnets:



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The default subnet mask for a Class C address is /24 which will give you through as usable addresses.

If you choose not to use the default mask of /24, you can split that /24 subnet up into four /26 subnets. Exactly four /26 subnets make up a /24 subnet, although that may not be the best way of thinking about it if you are learning :)

If you want to use as your example and you wanted to use a /26 mask, you would end up with the following subnets: - for hosts is broadcast address - is broadcast address - is broadcast address - is broadcast address

If you choose to split the Class C network up into four smaller /26 networks, you would get the subnets above. Obviously you would not longer be able to use as a /24. 

/24 is just the 'default' subnet mask for Class C addresses but you can make a subnet smaller or bigger by changing the subnet mask. Using a /26 is making it smaller and allowing you to have four smaller subnets instead of one larger /24 subnet.

Hopefully that makes some sense...