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Beginner

CIDR IP addressing

Hi experts,

     I have a scenario whereby I need to confirm my findings. I am given a Class A IP addressing range in the form of 10.21.28.0/24. I want to subnet this further and am safe to use the /27 subnet in this case. Results would be:

  

Usable10.21.28.1 -10.21.28.30
Host10.21.28.0
Broadcast10.21.28.31
Subnet Mask255.255.255.224
Usable10.21.28.33 -10.21.28.62
Host10.21.28.32
Broadcast10.21.28.63
Subnet Mask255.255.255.224
Usable10.21.28.65 -10.21.28.94
Host10.21.28.64
Broadcast10.21.28.95
Subnet Mask255.255.255.224
Usable10.21.28.97 -10.21.28.126
Host10.21.28.96
Broadcast10.21.28.127
Subnet Mask255.255.255.224
Usable10.21.28.129 -10.21.28.158
Host10.21.28.128
Broadcast10.21.28.159
Subnet Mask255.255.255.224
Usable10.21.28.161 -10.21.28.190
Host10.21.28.160
Broadcast10.21.28.191
Subnet Mask255.255.255.224
Usable10.21.28.193 -10.21.28.222
Host10.21.28.192
Broadcast10.21.28.223
Subnet Mask255.255.255.224
Usable10.21.28.225 -10.21.28.254
Host10.21.28.224
Broadcast10.21.28.255
Subnet Mask255.255.255.224

EAch of these will be assigned a VLAN and the GW for each is 10.21.28.0 or each host address? If this is in a switch connected to an edge firewall for internet, would the ip-default-gateway be the FW? IF there is an OSPF, can I just add 10.21.28.0/24 route in it? Thank you!                 

1 ACCEPTED SOLUTION

Accepted Solutions
Rising star

CIDR IP addressing

Hi,

One VLAN = One subnet. So in your case for each VLAN there will be different subnet /27 with own GW(e.g 10.21.28.1, 10.21.28.33 etc).

If it is L3 switch connected to FW you can assign IP address from other subnet /30 mask or create one more VLAN, assign IP address for VLAN then make access port connected to FW. And yes, it will be default GW. About OSPF the answer is yes, just put summarized subnet and it should be ok.

Hope it will help.

Best regards,
Abzal

Hope it will help. Best regards, Abzal
2 REPLIES 2
Rising star

CIDR IP addressing

Hi,

One VLAN = One subnet. So in your case for each VLAN there will be different subnet /27 with own GW(e.g 10.21.28.1, 10.21.28.33 etc).

If it is L3 switch connected to FW you can assign IP address from other subnet /30 mask or create one more VLAN, assign IP address for VLAN then make access port connected to FW. And yes, it will be default GW. About OSPF the answer is yes, just put summarized subnet and it should be ok.

Hope it will help.

Best regards,
Abzal

Hope it will help. Best regards, Abzal
Beginner

CIDR IP addressing

Hi Abzal,

Thanks mate! The switch in question is a L3 switch.

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