![]() In larger networks where you have multiple switches and routers chained together, they all follow the same principle of 'if you don’t know where it is, send it to the default gateway'. The devices now know that if they need to send traffic to an IP that is not on the local network, it should be sent to the router. For the devices connected to Switch B you specify 10.0.2.1 as the default gateway. ![]() For the devices connected to Switch A you specify 10.0.1.1 as the default gateway. On Switch A it has an ip address of 10.0.1.1, while on switch B it has an IP address of 10.0.2.1. The router is connected to both switches. The Switch A network can be on 10.0.1.0/24 and the Switch B network can be on 10.0.2.0/24 or even have a completely different network mask like 10.2.0.0/16.įor machines to be able to communicate with another network it needs a gateway. In contrast, if you are using a router that is aware of IP addresses, they can be on different subnets. All of the machines on Switch A and Switch B would have to share the same 10.0.1.0/24 subnet. The key difference here is that if you are using a bridge to connect the two networks they have to be on the same IP network. It looks at the traffic and decides where to send the traffic based on the information in its routing table. The router operates at layer 3 which means it knows about IP addresses. It will then receive the traffic on one interface and pass it onto the other. If you want to stay on layer 2 you need to use a bridge, the bridge will simply build up it’s own ARP table of MAC addresses so that it knows where the MAC addresses are.You will need something that can forward the traffic when switch A and switch B don’t know where to send the traffic. Now imagine you have two of these networks and you need to connect them together. The layer 2 switch does not care which IP addresses are used, it simply knows were the MAC addresses are and forwards all the traffic for it to that physical port. This means they all have an IP address between 10.0.0.1- 10.0.0.254 and a subnet of 255.255.255.0.Īt this level you don't even need to specify a default gateway. The machines can communicate with each other because the switch knows all of the MAC addresses attached to it based on the ARP table it builds up while listening to all the devices. All of them have IP addresses in the 10.0.1.0/24 range. Imagine a small network where there are just a few machines connected with a basic Layer 2 switch. Network devices that operate here are Layer 7 firewalls. The application we are referring to is not necessarily the application such as Internet Explorer or Chrome, but rather any process that uses the application layer protocol such as HTTP, DNS, FTP etc. Now we skip ahead to the Application Layer. ![]() Network devices that work up to layer 3 are routers. The Network layer provides the means for transferring data from one node to another. Network devices that operate up to layer two are switches and bridges This is where the MAC (Media Access Control) address resides. The Data link layer is the lowest level where communication occurs. Network devices that operate only at layer one are hubs and repeaters. ![]() The Physical layer pertains to the actual connectivity medium and device such as the physical cables and network cards. So lets first recap on some basic networking theory.Īlmost all network theory and understanding references the OSI model (Open Systems Interconnection.) The OSI model defines 7 logical layers, each addressing more complex functionality and each layer supporting the one above it. The differences between Sophos UTM's operational modes are best understood if you understand where they differ from an OSI layer perspective. In this article we’ll investigate how they work to help you decide which mode(s) to use for your network. Sophos UTM can be configured to act in different operation modes, each with its own potential advantages and drawbacks.
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