Supported Platforms
Related Documentation
- MX Series, QFabric System, QFX Series standalone switches
- Understanding Storm Control
- QFabric System, QFX Series standalone switches
- Overview of Layer 2 Networking
- Understanding Bridging
- Understanding Bridging and VLANs
Understanding Layer 2 Broadcasting
In a Layer 2 network, broadcasting refers to sending traffic to all nodes on a network.
Layer 2 broadcast traffic stays within a local area network (LAN) boundary; known as the broadcast domain. Layer 2 broadcast traffic is sent to the broadcast domain using a MAC address of FF:FF:FF:FF:FF:FF. Every device in the broadcast domain recognizes this MAC address and passes the broadcast traffic on to other devices in the broadcast domain, if applicable. Broadcasting can be compared to unicasting (sending traffic to a single node) or multicasting (delivering traffic to a group of nodes simultaneously).
Layer 3 broadcast traffic, however, is sent to all devices in a network using a broadcast network address. For example, if your network address is 192.0.0.0, the broadcast network address is 192.255.255.255. In this case, only devices that belong to the 192.0.0.0 network receive the Layer 3 broadcast traffic. Devices that do not belong to this network drop the traffic.
Broadcasting is used in the following situations:
- Address Resolution Protocol (ARP) uses broadcasting to map MAC addresses to IP addresses. ARP dynamically binds the IP address (the logical address) to the correct MAC address. Before IP unicast packets can be sent, ARP discovers the MAC address used by the Ethernet interface where the IP address is configured.
- Dynamic Host Configuration Protocol (DHCP) uses broadcasting to dynamically assign IP addresses to hosts on a network segment or subnet.
- Routing protocols use broadcasting to advertise routes.
Excessive broadcast traffic can sometimes create a broadcast storm. A broadcast storm occurs when messages are broadcast on a network and each message prompts a receiving node to respond by broadcasting its own messages on the network. This, in turn, prompts further responses that create a snowball effect. The LAN is suddenly flooded with packets, creating unnecessary traffic that leads to poor network performance or even a complete loss of network service.
Related Documentation
- MX Series, QFabric System, QFX Series standalone switches
- Understanding Storm Control
- QFabric System, QFX Series standalone switches
- Overview of Layer 2 Networking
- Understanding Bridging
- Understanding Bridging and VLANs
Published: 2014-07-23
Supported Platforms
Related Documentation
- MX Series, QFabric System, QFX Series standalone switches
- Understanding Storm Control
- QFabric System, QFX Series standalone switches
- Overview of Layer 2 Networking
- Understanding Bridging
- Understanding Bridging and VLANs
