Could you please explain the process of answering this question? Thank you. Cons

Question

Could you please explain the process of answering this question? Thank you.

Consider a router that interconnects three subnets: Subnet A, Subnet B, and Subnet C. Suppose all of the interfaces in each of these three subnets are required to have the prefix 172.16.2.192/26. Also suppose that Subnet A is required to support up to 29 interfaces, and Subnets B and C are each required to support up to 12 interfaces. Provide three network addresses (of the form a.b.c.d/x) that satisfy these constraints.

Explanation / Answer

This is possible. You either need a router with 4 actual routed/layer 3 ports (most are just 2 L3 ports with several switch (L2) ports) or you need a router that supports vlans.

If your router has 4 L3 ports you can just assign an IP from each network to each port and then tell the devices on that network to use that IP as the default gateway.

Eg:
- assign 172.16.2.192/29 to port 1 and plug the DDNS server into port 1 and assign the DDNS server 172.16.2.192/29 and make it's default gw 172.16.2.192
- assign 172.16.7.1/12 to port 2 and plug the web server into port 2 and assign the web server 192.168.7.10/24 and make it's default gw 172.16.7.1
- assign 172.16.12.1/12 to port 3 and plug the switch with the PCs into port 3 and hand out the gateway to the PCs of 172.16.12.1
- assign your internet IP(s) to port 4
- set the default route on the router out the internet


If you don't have 4 L3 ports but you have vlans you can probably replicate the above with switched virtual interfaces. Let's say you have a router with 1 wan port and 4 switched lan ports that supports vlans. You can plug the internet into the wan port, assign IPs on each network to a different vlan interface then set the physical switchports as corresponding access ports.

Eg:
- configure vlan 1 as 172.16.7.1/12, set switchport 1 on the router to be vlan 1 untagged (this is probably the default) and plug the switch with PCs into switchport 1 using a default gw of 172.16.7.1 on the PCs
- configure vlan 2 as 172.16.2.192/29 , set switchport 2 on the router to be vlan 2 untagged and plug the DDNS server into switchport 2 with the IP 192.168.5.10/24 and gw 172.16.2.192
- configure vlan 3 as 172.16.12.1/12 set switchport 3 on the router to be vlan 3 untagged and plug the web server into switchport 3 with the IP 172.16.12.1/12 and gw 172.16.12.1

Lastly, if your router only has 2 ports, WAN and LAN but supports vlans and you have a separate switch that also supports vlans you can replicate the above vlan setup. You'll need to connect the servers to access ports on the switches instead of the router and then configure the LAN port on the router and the physically connected switchport as a vlan trunk port to get all the applicable vlans across

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