Splitting Subnet and Routing

[Jamie Joh]

Hi all,

I have a quick query regarding splitting our subnet down.

Basically we are a managed school and receive an IP range of 10.193.8.x/21 with a Cisco router located on site with an interface ip of 10.193.8.1 and can only get out to the internet if we use an IP within that range.

Now we want to split that subnet into smaller 24 bit subnets (10.193.8.x/24, 10.193.9.x/24 etc) which we will do on a HP layer 3 switch, clients will use the vlan ip as their gateway and the switch will have its default gateway as the cisco router.

We don't have access to the Cisco router but am I right in thinking that even though the interface on the cisco is 10.193.8.x/21 and the switch will now be /24 that because it is directly connected the router should still understand where to route these packets and won't require us to contact the managed service to add static routes for each vlan subnet?

Many thanks

Jamie

[milan.kulik]

Hi,

I guess you would need to enable proxy ARP feature on that HP switch as the router would send ARP requests to the LAN for all 10.193.8.x/21 destination IP addresses?

Best regards,

Milan

[Gregor Blaj]

Yes, that seems to work in my lab with the "HP" configured as below. No static routes on the Cisco and I was able to reach a loopback interface configured on it with 8.8.8.8/32.

HP

Fa0/1 (L3 to Cisco): 10.193.8.2/24

SVI VLAN 10: 10.193.9.1/24

SVI VLAN 20: 10.193.10.1/24

Default route: 10.193.8.1 or Fa0/1