In the OSI model, layer 4 is where TCP and UDP ports live, also called the transport layer. Network rules in Azure Firewall, and the mitigations in DDoS Protection, both act at layers 3 and 4.
Also called Layer 4.
Read more: Microsoft Learn
In the Ultra Transcenders books
Each book explains L4 in context, with comparison tables and the common traps.
Terms in this definition
- WHERE
Limits a SELECT, UPDATE or DELETE to just the rows meeting a condition. Omit it, and the statement hits every row.
- TCP
A transport protocol that is connection-oriented.
- UDP
A transport protocol that sends data without establishing a connection.
- Azure Firewall
Stateful network firewall run by Azure as a managed service; it can be placed in Virtual WAN hubs and administered through Firewall Manager.
- DDoS
Short for distributed denial of service: flooding an application with so much traffic that it can no longer serve anyone. Within Azure, the DDoS Protection service shields public IP addresses from this kind of attack.
Related terms
- L7
The OSI application layer. Flow Virtual Networking's network load balancer stops at Layer 4, so it offers no balancing at this level.
- Network Load Balancer
Balances traffic arriving at a VPC or travelling between its VMs, using native layer 4 sessions. Flow Virtual Networking provides it, and each session is made up of targets and a listener.
- Public load balancer
Load balancer handling internet-facing traffic at Layer 4 through a public frontend IP. With the Standard SKU, its public IPs must be Standard SKU too.