Moving Layer 3 routing closer to the network edge can reduce dependence on large Layer 2 domains and enable more scalable, deterministic network designs. This white paper explores how routed edge architectures can improve convergence, simplify troubleshooting, increase resilience and help network teams manage growing Ethernet environments more efficiently.
Key Takeaways
- Layer 3 routing forwards traffic between different IP networks or subnets, extending routing intelligence beyond traditional Layer 2 switching.
- Moving Layer 3 functionality closer to the network edge can reduce the size and complexity of Layer 2 broadcast and failure domains.
- Routed edge designs can improve network convergence, resilience and scalability while reducing reliance on Spanning Tree Protocol for uplink redundancy.
- Layer 3 switches can support high-speed routing between VLANs and subnets inside the LAN, while dedicated routers remain important for many WAN and perimeter functions.
- The right Layer 2/Layer 3 boundary depends on network size, redundancy requirements, routing protocol support and operational complexity.
Implementing Layer 3 at the edge of a LAN can have many benefits, including increased network security, greater availability and improved network utilization, but it’s not always clear where Layer 3 routing should be used in the LAN. Our white paper discusses when to employ a Layer 3 switch at the edge of a network and gives definitions and applications for several widely used routing protocols, including RIP, DVMRP, PIM and OSPF.
What Is Layer 3 Routing at the Network Edge?
Traditionally, Layer 3 routers were at the core of the networks and acted as gateways to the Wide Area Network. As technology, pricing and availability have changed, Layer 3 routing has moved closer to the edge of the network. In an edge-routing design, Layer 3 switches route traffic between local IP networks or VLANs closer to connected users and devices, instead of sending all inter-network traffic back to the core.
This does not mean every access-layer switch must perform routing. Where Layer 3 functions belong in your Layer 3 network depends on the size and needs of the LAN, and routing at the edge is one option within a broader Ethernet network architecture.
The physical and logical design should be planned together, beginning with a clear understanding of LAN and premise architecture.
Layer 2 Switching vs Layer 3 Routing
In a Layer 2 vs Layer 3 comparison, the main difference is what each layer forwards and where. Layer 2 switching forwards Ethernet frames within the same broadcast domain, while Layer 3 routing forwards packets between different IP networks. A Layer 3 switch combines both functions in one device.
| Factor | Layer 2 Switching | Layer 3 Routing |
|---|---|---|
| Forwarding function | Forwards Ethernet frames | Forwards IP packets |
| Addressing | MAC addresses | IP addresses |
| Broadcast domains | Traffic stays within one broadcast domain | Separates broadcast domains; routes between IP networks |
| Typical network role | Connecting devices within a LAN segment or VLAN | Connecting subnets, VLANs and networks |
Benefits of Moving Layer 3 Routing to the Network Edge
Depending on the design, moving Layer 3 routing toward the edge can offer benefits such as:
- Smaller Layer 2 domains, which can reduce the size of broadcast and failure domains.
- Improved fault isolation, since problems in one segment are less likely to spread across the LAN.
- More direct traffic paths between local networks.
- Greater control of routing policy.
- Reduced dependence on Spanning Tree Protocol for uplink redundancy.
These are design-dependent benefits, not guaranteed outcomes. Results vary with network size, topology, equipment and how the network is configured and managed.
The placement of routing services should also reflect the broader relationship between edge, enterprise and cloud infrastructure.
Common Layer 3 Routing Applications
The white paper covers several principal use cases for Layer 3 routing and Layer 3 switch deployments, summarized below along with the routing protocols that support them.
Inter-VLAN Routing
Inter VLAN routing allows devices on different VLANs to communicate. A Layer 3 switch routes traffic between VLAN interfaces while maintaining logical network segmentation. The white paper also covers assigning static IP routes to VLANs and subnets.
Routed Uplinks to the Network Core
Routing on high-speed uplinks to the core can reduce the size of Layer 2 domains and provide clear Layer 3 boundaries between the access layer and the core or distribution layers. This is one way Layer 3 routing can shape a LAN’s Ethernet network architecture. OSPF can be used to route IP traffic through the LAN into the core router.
Multicast Routing at the Network Edge
IGMP and multicast routing protocols such as PIM do different jobs. IGMP manages which hosts have joined a multicast group, while PIM routes multicast traffic between networks. The technologies may work together in a Layer 3 network, but they do not perform the same role. The white paper covers IP multicast routing with IGMP and DVMRP, as well as PIM-DM and PIM-SM multicast routing in the LAN.
Default-Gateway Redundancy
VRRP provides first-hop gateway redundancy by assigning responsibility for a virtual router to participating routers. If the primary router fails, another participating router can take over, so devices keep a working default gateway. The white paper covers VRRP in the LAN.
Routing, Multicast and Redundancy Protocols
The protocols covered in the white paper serve different functions, so they are grouped here by role instead of under one label:
- Unicast routing: static routes, Routing Information Protocol (RIP) and Open Shortest Path First (OSPF).
- Multicast group membership: Internet Group Management Protocol (IGMP).
- Multicast routing: Protocol Independent Multicast (PIM-DM and PIM-SM) and the legacy Distance Vector Multicast Routing Protocol (DVMRP).
- Gateway redundancy: Virtual Router Redundancy Protocol (VRRP).
Together, these routing protocols are the building blocks of Layer 3 routing in a Layer 3 network. The white paper gives definitions and applications for each.
Layer 3 Switch vs Router: Which Should You Use?
Layer 3 switches are commonly used for high-speed LAN and inter-VLAN routing. Dedicated routers may provide broader WAN, security, tunneling and service capabilities. Modern product capabilities overlap, so choose based on the features you need rather than the device name alone.
When comparing Layer 2 vs Layer 3 devices, consider the routing protocols you need, the speed of your uplinks, your WAN and security requirements and how complex the network will be to manage.
Download the Layer 3 Routing at the Network Edge White Paper
Our white paper provides more detailed protocol definitions, diagrams and deployment examples for Layer 3 routing, routing protocols and Ethernet network architecture.
Download our Layer 3 Routing at the Network Edge white paper.
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Frequently Asked Questions
What Is Layer 3 Routing?
Layer 3 routing forwards packets between different IP networks or subnets, using IP addresses to decide where traffic goes.
What Does Layer 3 Routing at the Network Edge Mean?
It means routing traffic between local IP networks or VLANs closer to connected users and devices, instead of only at the network core.
What Is the Difference Between a Layer 2 and Layer 3 Switch?
A Layer 2 switch forwards Ethernet frames within a broadcast domain. A Layer 3 switch does this and can also route IP packets between networks or VLANs.
What Are the Benefits of a Routed Access Network?
Depending on the design, benefits can include smaller Layer 2 domains, better fault isolation and less reliance on Spanning Tree Protocol. Results depend on the network.
When Should You Use a Layer 3 Switch Instead of a Router?
Use a Layer 3 switch for high-speed LAN and inter-VLAN routing. Choose a router when you need broader WAN, security or tunneling features, and compare actual feature support.