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Network: 10.0.0.0/24

I decided to divide it into 4 sub-networks:

  • 10.0.0.0/26
  • 10.0.0.64/26
  • 10.0.0.128/26
  • 10.0.0.192/26

If I have to configure static routing on an external router, can I use the network 10.0.0.0/24 in destination or I have to put all the sub-networks? I heard about route aggregation but I'm not sure that's what it is.

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If all of the /26 networks are hosted on the same device, yes you can summarize with a single /24 route on your edge device.

For example, if all of the /26 networks are on a switch at 192.168.254.254 and you have a valid path from the router to the switch on that network, you could use a route on your edge router such as:

10.0.0.0 255.255.255.0 192.168.254.254

In this example, the switch would then figure out which /26 the traffic belongs to for further processing.

What you do with the traffic once it hits the switch would be irrelevant. You could even have 2 of the /26 networks on the switch directly connected to the edge router and then the other 2 /26 networks on a switch connected to the first switch, for example. The edge router would send the traffic to the switch it’s attached to and traffic for the 2 /26 network on the switch would stay there while traffic for the other 2 /26 networks would be sent to the other switch by a route statement you’d have on the 1st switch.

There are many other possible scenarios you might have. Now, if you had 2 of the /26 networks on one switch and the other 2 /26 networks on another switch and BOTH of them were directly connected to the edge router, you would NOT be able to summarize the route as a /24 because traffic would then be sent to the wrong switch in some cases. So, you’d have to instead either use a route for each /26 or you could summarize into 2 /25 routes (1 pointing to each switch).

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    OK thank you, I understand. If I use different VLANs (for each subnetwork) with interVLAN routing, it works too? – nopapus Jun 13 at 13:58
  • @nopapus Yes. I edited my answer with some more examples for you to help clarify. – Jesse P. Jun 13 at 14:11

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