Subnetting help

jmorris92

Hi everybody, I've been set a university cisco ccna assignment where we have to configure a network that has multiple VLANs, basic security configure, intervlan routing, use of ACL's , PPP and NAT and PAT etc. I can do most of this however the IP addressing I am having trouble with, if any could give me a hand i'd greatly appreciate it
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I'm thinking for the interconnecting router connections I could use on the left 10.1.1.1 and 10.1.1.2 and for the right hand side of the diagram I could use 10.2.2.1 and 10.2.2.2.
For the branch one, I can see need to use some VLSM. I would start this by looking at branch one first and tackling it from largest to smallest VLAN11 needs 1850 users, VLAN 21 needs 1650 and VLAN 31 needs 850. Would an 172.16.0.0 network be appropriate for these needs? 1 2 4 8 16 32 64 128 256 512 1024 2048 < going up in powers I can see VLAN 11 would need 11 bits 11111111.11100000.00000000.00000000 which corresponds to 255.224.0.0 and a block size of 32, VLAN 21 also needs the same amount and then VLAN 31 needs 850 so is covered by 1024 so it would go up in a block size of 64 afterwards? Is that correct ?

What my my main confusion is is if I do that IP addressing, what addresses do I give to the other devices on the other branch?

Thanks a lot! Best of luck with everyone's cert exams.

Jon_Cisco

If no information is given about which address to use then I would probably do as you suggest and use class B addresses.
Be careful with how you are reading your powers I think you are counting from the wrong side. It looks like you have 11 network bits not host bits.
/21 255.255.248.0 https://kb.wisc.edu/ns/page.php?id=3493

Most challenges like this want to see you effectively use a single address space so I am thinking you pick one Class B address and use that to create all of your subnets. If you try this I would put the connecting blocks of 4 at the end of your network range but I have no idea if that's how your instructor wants it done.

I hope this helps. I did not want to give you to much information as this is all part of the learning process.

Good Luck

xnx

I'd use 172.16.10.0/24 - 172.16.16.0/24

jmorris92

Thanks for the help guys, I'll have a look again and hopefully come up with a working addressing scheme. Has anyone got any good online guides or anything for this sort of thing? I can do the basic subnetting but find this question quite challenging.

Alex90

Chris Bryant has a good book on subnetting...

http://www.amazon.co.uk/CCNA-Success-Mastering-Binary-Subnetting-ebook/dp/B00G6L06VU

Jon_Cisco

I'm doing this quick in my head so double check the logic.
He is what I see for side 1.

Vlan 11 172.16.0.0/21 (allows 2046 users)
Vlan 21 172.16.8.0/21 (allows 2046 users)
Vlan 31 172.16.16.0/22 (allows 1022 users)
Connection to border router 172.16.20.0/30
(I'm not sure how you instructor wants you to place address for the border router. I listed the next subnet however this will break up usable address space)

or maybe if you wanted them all to be summarized into one route you could do something like this.


Vlan 11 172.16.0.0/21 (allows 2046 users)
Vlan 12 172.16.8.0/21 (allows 2046 users)
Vlan 21 172.16.16.0/21 (allows 2046 users)
Vlan 22 172.16.24.0/21 (allows 2046 users)
Vlan 31 172.16.32.0/22 (allows 1022 users)
Vlan 32 172.16.36.0/22 (allows 1022 users)
Connection to border router 172.16.40.0/30
Connection to border router 172.16.40.4/30

jmorris92

Hi thanks for the help much appreciated, I came up with a very similar scheme starting from 8.0 rather than using the zero subnet not that it'd matter I'd imagine. For the links i've chosen to use 172.16.48.1 and 172.16.48.2 for the branch 1 interconnections and 172.16.49.1 and 172.16.49.2 for branch 2 which seems to work, do you think this is okay? I also realised for the Fa 0/0 interfaces of each router branch 1 branch 2 I had to give addreses, so I'm using 172.16.1.1 and 172.16.2.1. I
managed to also get the PC's pinging to each other across the whole network but as soon as I introduced DHCP I started having problems, most of the PC's were fine receiving IP's, however, some would be able to ping across the whole network and some wouldn't which didn't seem to make much sense. Any ideas what I could be doing wrong? Are there any known bugs relating to DHCP in packet tracer? This is what I've managed to do so far (packet tracer file) https://onedrive.live.com/redir?resid=81FB7C5866F46812!1373&authkey=!AMRB8EWhKcjH_ZU&ithint=file%2c.pkt
Really appreciate the help guys

Jon_Cisco

Sorry I do not have packet tracer on my work machine so I can't look at your setup today.
As for some pings working and other not try watching them in simulation mode. This should show you where they fail and if you read the frame information at the spot it fails it should give you an idea of why it dropped it.

Possible a bad routing table at one spot. Or ACL configured wrong.
If you suspect dhcp try to locate the point of failure. Possibly you need to set up a helper address to cross a router to the dhcp server?

Please keep us updated. This is a great site for talking out problems and helping others.

Good Luck.

jmorris92

Okay I haven't tried simulation mode yet I don't think so I'll be sure to check that out. I've managed to get all but one PC getting appropriate ips through dhcp, the one works but has a 0.0.0.0 gateway which is annoying and I've configured its default router under its specific pool so it should pick up the right gateway not sure why that is.
I get a constant internet connection fitted today so i should be able to make some more progress, its been difficult diagnosing problems as I'm on holiday in rural France lol.
I don't get why 2/3 of the network works but that section on the right can't ping across, theres no acls, routing is in place, dhcp helper address is applied, the router can ping to the router next to it but the PC can't get that far? Very frustrating! Thanks again for the help

Jon_Cisco

I looked at what you posted very quickly. I don't know why vlan 22 is getting 0.0.0.0 for the default gateway.
Maybe redo the configs just to refresh it. (Possibly remove the other connections just to watch the dhcp work on this machine) It won't attempt to get an address in simulation mode until you go into the network settings from the desktop. So turn int off in realtime mode switch to simulation turn it back on and open the network settings window. Then your DHCP frame will appear.

I saw some messages for duplicate ip addresses. I think it's the vlan and sub interfaces.

I think vlans 11 and 12 were communicating ok so my guess is something is off in the vlan configs of the other ones. I didn't get to try and figure it out.