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Greeting's, this is my first attempt at network connectivity and hence would truly appreciate if community at large can review and guide me through it.

We have one main office with 7 branch offices. We don't plan to expand over 12-15 branch offices (even if we do, I feel my following assumptions and design should stand).

We plan to have P2P VPN lines between offices. I have proposed that we use 172.16/12 subnet. With 172.16.x.x for HQ and 172.17.x.x and so on for each branch. We will never have over 500 PC's per branch.

There are as of now 6 departments and I have proposed 172.16.1.x and so on for each department which will stay consistent over the branches.

We have (for whatever) reason L3 switches all around and each switch may hold computers of 2 or more departments. Hence to segregate I've proposed VLANs which will be (VLAN IDs) consistent between switches (I am unsure of this part). Hence, if sales computers are in VLAN2 on switch 2. Other switches (switch 3 for example) will have VLAN2 holding subnet and PC dedicated to sales. I've attached a diagram for better explanation. I want to know if it's possible for inter VLAN communication based on the diagram I've attached and of course the changes recommend based on our needs.

I am certain of having made mistakes with trunking. Please do guide me through it. Will the firewall be able to see IP's of endpoint with trunking on uplinks and L3 switch. Also all the switches in the diagram are L3

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Thanking you all in anticipation!

Edit:

My requirements are for L3VPN as per one of the answers. Thank you again. Just to confirm and reiterate since this is critical and my job hangs on getting it right - As someone suggested - I am planning to shift to 10/8 subnet for better expendability. Hence: 1. HQ will have 10.1.0.0 subnet

  1. Branches will start with 10.2.0.0 series.

  2. There will be further subdivision of IP ranges using VLANs per department. This will be consistent throughout the organization A. Sales will be allocated 10.1.1.0 in HQ. B. 10.2.1.0 in branch 1 and 10.3.1.0 in branch 3 – so on and so forth. Network device topology will remain consistency throughout branches:

  3. ISP CPE - Firewall - L3 Core swtich - L3 (working in L2 mode) switches - Endpoints. Physical topology between branches will be -
  4. Endpoints - L2 Switches - L3 Core switch - firewall - ISP CPE - L3VPN - ISP CPE - Firewall - L3 Core swtich - L3 (working in L2 mode) switches - Endpoints. Topology with IP addresses for illustration will be: Endpoints (10.1.1.5) - L2 Switches (10.1.5.2) - L3 Core switch (10.1.1.1) - firewall (10.1.1.250 - question - should this be on same subnet or is it better to have firewall IP as 10.1.0.250) - ISP CPE - L3VPN - ISP CPE - Firewall (10.2.1.250) - L3 Core swtich (10.2.1.1)- L3 (working in L2 mode) switches (10.1.5.2) - Endpoints (10.2.1.5)

Questions: 1. Is this optimum with respect to security (VLAN segregation for each departments), manageability, bandwidth (broadcast domains and compromised endpoint quarantine)? 2. Will a machine on different VLAN and IP subnet (10.1.2.5) communicate with machine at HQ (10.1.1.5) and with 10.2.2.5 (at branch)? I reckon that within the same office (HQ/Branch) machines won't communicate. However, they will between branches of same department (10.1.1.5 with 10.2.1.5).

Thank you very very much to everyone who has reviewed and assisted me with this.

Second diagram machine to machine between branch and HQ with IPs

  • Does the firewall support multiple virtual interfaces(VLAN interfaces) basically router on a stick? – Anirudh Malhotra Nov 3 '16 at 8:39
  • It's a Cisco ASA 5525-X model. Here is a CIsco document stating base model gets 200 VLAN licenses. Is this what you're inquiring about? Thanks. – user31781 Nov 3 '16 at 9:56
  • I would recommend using 10/8 for your addressing scheme instead of 172.16/12. This way you have many more subnets to work with and it is more scalable. You can assign a 10.x/16 supernet for each site and further subnet it for your various vlans. – John K. Nov 3 '16 at 12:00
  • Did any answer help you? If so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you could provide and accept your own answer. – Ron Maupin Aug 15 '17 at 5:09
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There are many ways to do this. Here are a few observations:

  • It's generally a good idea to push layer 3 as close to the end users as possible. Since you have layer 3 switches everywhere, this is easy for you to do.
  • You should consider creating a routing hierarchy, with the branch switch terminating the local VLANs, and the core switch terminating the branch links.
  • While it's fine to put each department on a separate VLAN, unless you plan to restrict access between departments, there's no real value.
  • It's more important to insure that there are no layer 2 links connecting your branch offices. Everything should be L3. I don't see a need to use trunking anywhere.
  • Place your servers on their own VLAN for design consistency and also since that's the most likely place to enforce policy.
  • According to questioner there may be 500 users in a branch how do you plan to accommodate that without any L2 links? – Anirudh Malhotra Nov 3 '16 at 11:53
  • I don't see the problem. Create as many VLANs as needed at each branch.. – Ron Trunk Nov 3 '16 at 11:54
  • But all the hosts cannot connect to a single switch(for obvious reasons), Therefore more switches needed! How to connect multiple switches? I don't think you would want to configure point to point IPs between them, Would you? That too won't make sense for connecting same VLANs on different switches. – Anirudh Malhotra Nov 3 '16 at 11:58
  • As I said, unless the OP is trying to restrict inter department traffic, there's little value in VLAN per department. It's better to have VLAN per area (floor/bldg/site). More importantly, if you trunk VLANs all the way back to the FW, you create a failure domain across the entire network. A problem at one branch can take down everything. – Ron Trunk Nov 3 '16 at 12:02
  • Also, we don't know what the branch switches are. It could be a chassis or stackable switches. Not that that changes things. – Ron Trunk Nov 3 '16 at 12:04
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So here are a few points I would suggest:

  • Create virtual interface of each VLAN on the firewall itself, and use it as gateway for each host in the VLAN.
  • Try to get redundancy on the core switch, If stacking available please choose that.
  • Use different VLAN for servers and again put its virtual interface on firewall itself(use that interface IP as gateway for servers), In this way you will have a DMZ for servers.
  • Have a switch placed in the servers area as well, Do not connect them directly to the core switch.

We will never have over 500 PC's per branch.

  • never is a very strong word(avoid it) companies grow, networks grow. You never know when you will need new hardware for growing user base.
  • You will have to trunk the ports between switches({department and core} and {server switch and core}) and also between the L3 core and firewall.
  • Ports connected to hosts/servers are to be put in access vlan mode unless needed otherwise.
  • Yes inter-vlan traffic will go through firewall(you can apply policies what to allow and what not) in this topology.
  • Yes firewall will be directly able to see MACs of end hosts in this topology.

UPDATE You can also have L3 as the gateway of each VLAN rather than firewall, I am writing some cons and pros of having firewall as gateway(and vice versa):

Cons

  • Each host arp will come to firewall, you will have to see arp-cache size on firewall.
  • For inter-vlan routing you have to make policy on firewall(blessing in disguise).
  • SLAAC might not be available for IPv6 in firewall.
  • If firewall goes down, Inter-vlan traffic will also stop.

Pros

  • Lesser configuration overhead.

  • You can have DMZs configured(allow/disallow different traffic from internet/intranet).

  • More control over inter-vlan traffic.

  • Switching faster than routing, Packets will be switched to firewall.

  • Firewall will see all the hosts.

UPDATE 2(after question was updated):

Your diagram shows something else(than what you have explained). Anyways.

From Diagram: Do not use the management IP of switches from same VLAN as that clients! Use a separate network.

L2 Switches (10.1.5.2)

L2 switches at both ends have same management IP, don't do that. Assign different management IP range(I take this is a typo).

firewall (10.1.1.250 - question - should this be on same subnet or is it better to have firewall IP as 10.1.0.250)

Do not use the same network, its of no use. Use a point to point network(a /30) between L3 and firewall, Since in any case gateway of your VLANs will be the L3 so why complicate things(if you are going to use this topology i.e.)

  1. Is this optimum with respect to security (VLAN segregation for each departments), manageability, bandwidth (broadcast domains and compromised endpoint quarantine)?

Yes seems like so till now(will update if something comes in my mind).

  1. Will a machine on different VLAN and IP subnet (10.1.2.5) communicate with machine at HQ (10.1.1.5) and with 10.2.2.5 (at branch)?

As you said you are using L3VPN(routes are advertised via bgp mostly from one end router to another), So for example 10.1.0.0/8 from HQ is advertised to all the other branches via L3VPN and 10.2.0.0/8 from a branch to HQ, they will be able to communicate. So in essence, depending on how much routes your ISP lets you advertise. You can achieve this easily if the HQ office has routes of branch office and vice versa.

I reckon that within the same office (HQ/Branch) machines won't communicate. However, they will between branches of same department (10.1.1.5 with 10.2.1.5).

Is this something you think, or something you want. Because this won't happen by default. Its rather reverse of what you think(presuming) The local VLANs will be able to talk via inter-vlan(via L3) routing(since you have configured GWs of each VLAN on L3 itself). Also for different offices(HQ/branch) departments to talk you will need L3VPN routes transported(as explained above, job of ISP), though you can also achieve this with NAT(config overhead).

Hope this helps!

  • I think it would be simpler if the OP uses the L3 switch as the core instead of using the fw as the gateway for all VLANs. – Ron Trunk Nov 3 '16 at 11:26
  • Yes you may, But this topology was suggested for various reasons( easier manageability in inter-vlan routing, DMZs, Firewall will be able to see each end host) On top of all this there will be one less routing hop! – Anirudh Malhotra Nov 3 '16 at 11:51
  • Thank you all of you. While I'm trying to assimilate the information provided. I had a question about using L3 core switch as gateway or firewall. Will the hosts be able to access internet if the gateway is L3 core switch. If so do i require a rule or a route for internet access? – user31781 Nov 3 '16 at 12:11
  • Yes you will need a default route towards firewall and static routes of each of your LAN segments on your firewall towards your L3, Plus NAT each of your LAN segment with public IPs, as the private IPs are not routable! – Anirudh Malhotra Nov 3 '16 at 12:16
  • @user31781 updated answer with some pros and cons of having firewall as gateway of VLANs/ – Anirudh Malhotra Nov 3 '16 at 13:20

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