In a network, the edge is typically the point where every customer and device connection come into and depart from a data center. Specialized edge routers are used here. These are designed to be able to deal with the many types of data packets (and the different routing protocols) coming in and out of the data center. High availability (a high percentage of uptime) and redundancy (duplicate devices kept in case of system failure) are crucial. And as a data center’s initial contact-point with the outside world, edge routers have a key role to play in a network’s security.
NSX-V Edge Services Gateway (ESG) is a multi-function, multi-use virtual machine appliance for network virtualization. It gives you access to the logical services that we’ll be looking at in the coming sections. Multiple ESG virtual appliances can be installed in a data center. NSX-T provides the same services through an NSX Edge appliance - not to be confused with an Edge Services Gateway!
ECMP (equal cost multi-path) can be used to increase bandwidth between physical and virtual networks. (Bandwidth is the amount of data that can be sent from one point to another in a set amount of time.) ECMP also provides faster convergence (the merging of data, telephone, and video networks into a single network).
If centralized services (such as NAT) need to run on the Edge appliance, the appliance will need to be in what’s known as an active-standby mode. In this mode, all stateful services (i.e., services that keep track of the network’s state - load balancing, for example) are available.
Dynamic routing uses protocols such as Open Shortest Path First (OSPF – an intra-domain protocol that prioritizes the shortest path based on the cost of available paths) in the case of NSX-V, and Border Gateway Protocol (BGP – an inter-domain protocol that prioritizes the best path as defined by a list of attributes) in the case of NSX-T Data Center.
As discussed in section 4.1, Network Address Translation (NAT), takes an IP address and translates it into another IP address. ESG supports both source NAT where a private IP address is translated into a public IP address, and destination NAT, a public IP address to private IP address translation. NAT is also an integral part of load balancing, which we’ll discuss next.