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How to subnet with Inter-VLAN routing?

By rds41 ·
I have a practice skills exam I need some help with. It is implementing Inter-VLAN routing as well as subnetting. We are given the IP add of 192.168.50.0. We are then given VLAN 10 (30 host ips), VLAN 20 (6 host ips), VLAN 30 (60 host ips) and VLAN 99 (10 host ips/VLAN trunks). She wants us to subnet based on the hosts required for each VLAN. We must address for each of the following: S1 Vlan 99, S2 Vlan 99, R1 loopback, R1 Fa0/1.1, R1 Fa0/1.10, R1 Fa0/1.20 and R1 Fa0/1.99, then 3 host PC's. The way she wants is it that I would subnet VLAN 30 then 10 then 99 then 10. If I need to subnet the VLANs first, how do I come about the S1 and S2 VLAN 99 addresses, as with the R1 loopback and R1 Fa0/1.99? Any help would be greatly appreciated! Thank you and I look forward to being a member on these boards.

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All Answers

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google it because theres millions of pages on subnetting

by CG IT In reply to How to subnet with Inter- ...
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Reponse To Answer

by rds41 In reply to google it because theres ...

I know how to subnet, I am just confused in which order to do so. Do I subnet vlans then S1 and S2 vlan 99's, then host PCs?

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Subnet order

by NetMan1958 In reply to How to subnet with Inter- ...

My take on it is that it appears that she wants you to calculate the subnets starting with the one that requires the most hosts (VLAN 30) then the one that requires the 2nd most hosts (VLAN 10) and so on down the line. Once you have the subnets calculated, the IP Addresses on the R1 sub-interfaces will be an address out of the subnet you calculated for the respective VLAN. Take VLAN 20 for example, R1 interface Fa0/1.20 will get one of the IPs from the subnet you calculated for VLAN 20 and it will be the default gateway for hosts in that VLAN.

Did she mention which VLAN(s) she wants the PCs to be in? Start with your subnets and go from there and if you run into trouble, post what you have done so far and I'm sure someone will help you.

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Reponse To Answer

by rds41 In reply to Subnet order

Thanks netman. She did not post which PC goes to which VLAN, but we've been doing it so that VLAN 10 goes to PC1, VLAN 20 goes to PC2, etc.
VLAN 30 (60 hosts) - 192.168.50.1 - 192.168.50.62 /26 prefix = usable range
VLAN 10 (30 hosts) - 192.168.50.65 - 192.168.50.94 /27 = usable range
VLAN 99 (10 hosts) - 192.168.50.97 - 192.168.50.110 /28 = usable range
VLAN 20 (6 hosts) - 192.168.50.113 - 192.168.50.118 /29 = usable range

Now this is where I get confused. I still have to configure:
S1 VLAN 99 IP add -
S2 VLAN 99 IP add -
R1 Fa0/0 IP add -
and PC1, PC2, and PC3

I'm pretty sure I have it correct up to here. Any more help guys I'd appreciate it. Thanks

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IP Addresses

by NetMan1958 In reply to How to subnet with Inter- ...

S1 and S2 VLAN 99 IPs will be any of the usable IPs in the subnet you calculated for VLAN 99 (192.168.50.97 - 192.168.50.110) - just be sure to assign each IP to only one device.

Each PC will get an IP from the subnet you calculated for the VLAN that PC is in. Example, PC1 is in VLAN 10, it gets one of the IPs from 192.168.50.65 - 192.168.50.94.

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Reponse To Answer

by rds41 In reply to IP Addresses

Awesome explanation, man. I was looking at it at a more complex approach, I guess. Thank you for your time netman!

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you can assign whatever address within the subnet, that you want

by CG IT In reply to How to subnet with Inter- ...

You said the instructor's instructions are : We must address for each of the following: S1 Vlan 99, S2 Vlan 99, R1 loopback, R1 Fa0/1.1, R1 Fa0/1.10, R1 Fa0/1.20 and R1 Fa0/1.99, then 3 host PC's"

you can use any address within the subnet address space. Most start with the first and work up to the last.

these are subinterfaces for roas: R1 Fa0/1.1, R1 Fa0/1.10, R1 Fa0/1.20 and R1 Fa0/1.99

typically, best practice is to make the subinterface the same as the vlan #. so
R1 Fa0/1.1 is subinterface # 1 and would correspond to Vlan1 the administrative vlan
R1Fa0/1.10 is subinterface # 10 and would correspond to Vlan 10. you give that subinterface and address from the 192.168.50.65-94/27 address space [first address]

so on and so forth.... for hosts [PCs might as well give them the next addresses... so for R1Fa0/1.10 subinterface address would be 192.168.50.65 255.255.255.224
PCs would be 192.168.50.66 255.255.255.224

you really don't have to address the vlan...simply create it on the switch and assign switchports to the vlan. then make sure all the pcs that belong in the vlan are plugged in to the correct ports...assuming your using 48 port switches [96 total ports but you have 106 hosts so your short a switch]
Switch 1 Vlan 1 [administrative vlan] ports 0
Switch 1 Vlan 20 [6 hosts] switchports 1-6
Switch 1 Vlan 10 [30 hosts] switchports 7--37
Switch 1 Vlan 99 [5 hosts] switchports 38-43 [you could give the VLAN an address]
Switch 2 Vlan 99 [5 hosts] switchports 1-5 [same here but why waste it]
Switch 2 Vlan 30 [60 hosts] switchports 6-48 [which is 42 hosts sooo..this is where you need another switch for the extra 18 hosts that don't have a switchport..you could use the unused 5 on switch 1 but...still short switchports.]
so on and so forth

remember you need a trunk port between switches and switchports on Cisco switches will try to negotiate trunk if it can by default [older 2950s ] so you need either gigabit uplink ports or 1 of the regular switchports for a trunk port.

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Reponse To Answer

by rds41 In reply to you can assign whatever a ...

Here is what I have, so far:
S1 VLAN 99 - 192.168.50.97 /28
S2 VLAN 99 - 192.168.50.98 /28
R1 Fa0/0 loopback - 192.168.50.0 /24
R1 Fa0/1.1 - 192.168.50.? I don't know how you get this
R1 Fa0/1.10 - 192.168.50.64 /27
R1 Fa0/1.20 - 192.168.50.112 /29
R1 Fa0/1.30 - 192.168.50.1 /26
R1 Fa0/1.99 - 192.168.50.96 /28
PC1 - 192.168.50.65 /27
PC2 - 192.168.50.113 /29
PC3 - 192.168.50.2 /26
Anything I did wrong and how do I come up with the R1 Fa0/1.1 ip? Thanks!

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A couple of things

by NetMan1958 In reply to How to subnet with Inter- ...

R1 Fa0/1.99 - 192.168.50.96 /28 won't work as 192.168.50.96 is the subnet address. I would use .97 for this interface and use .99 for S1 VLAN 99.

I'm a little confused about R1 Fa0/0 loopback - 192.168.50.0 /24 - is the address supposed to go on interface Fa0/0 or on a loopback interface, for example interface loopback1 ?

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Reponse To Answer

by rds41 In reply to A couple of things

Thanks. It just says R1 Fa0/0 OR (Loopback). Does everything else look okay though?

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