Recently I wish to split the network by VLANs. Mainly for two reasons

  1. Exclude management interfaces from the commonly accessible lan
  2. Separate WiFi traffic (security and broadcasts)

The current idea is to enable vlans and Layer 3 features of 2960s cisco switch. We have a Mikrotik router and it increases the lag in the network, even while forwarding packets between vlans. That is why I want to dedicate this work to cisco.

Here is the schema:

enter image description here

Switch(config)#ip route

  1. In Vlan 1 I have servers, printers and other things.
  2. In Vlan 2 I have PCs
  3. In Vlan 3 I have WiFi
  4. And one more Vlan, not shown on the figure.

Client PCs in Vlan 2 and 3 do receive IPs from DHCP (in Vlan 1). It is configured on the switch using ip helper-address

Fortunately the schema works perfect. But I have tested it only with few devices and do not know if there could be any problems in future.

Maybe any of you have any idea about this implementation. How reliable is it?

  1. For example, I am not sure how good is cisco 2960 working as DHCP relay.
  2. Or how does Mikrotik know the destination MAC of the host. (It is clear that now the switch replies to every request and in ARP table of Mikrotik everything is assigned to the Mac of Cisco, but let's assume we initialize the connection from another network and Mikrotik does not know the destination mac, it will send the arp to cisco, but how cisco will reply, if his arp is also empty?)

1 Answer 1

  1. For example, I am not sure how good is cisco 2960 working as DHCP relay.

The 2960 will work just fine as a DHCP relay. I assume you have created a DHCP scope for each VLAN.

  1. How does Mikrotik know the destination MAC of the host.

Because the 2960 is a layer 3 device, it will rewrite the MAC addresses when forwarding packets to the Mikrotik. So every packet the Mikrotik receives will have the source MAC of the 2960. Only the 2960 needs to know the MAC address of the host.

  • Yes, thank you, you assumed right. What you wrote about my second question I have also seen already. But I mean, what will Cisco do in case Mikrotik tries to make an ARP request for a host in vlan 2? Will it just for any ARP from Mikrotik answer with his MAC?
    – Dex
    Aug 30, 2015 at 15:20
  • I am just wondering, whether I need to configure static routes at Mikrotik, or just do a simple network on the interface connected to Cisco (btw, now it works with /24 network, but I assume that routes would be better)
    – Dex
    Aug 30, 2015 at 15:25
  • Yes, you should have static routes on the MikroTik. For each subnet (VLAN), you create a route with 2960 as the next hop address.
    – Ron Trunk
    Aug 30, 2015 at 19:18

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