ACL refers to a list IP addresses, both origin and destination, and ports where traffic is permitted to pass. The *router* does this? Access control lists can generally be configured to control both inbound and outbound traffic, and in this context they are similar to firewalls. How are they different from firewalls, is at all? Is the ACL just the "firewall settings"?

VLAN is a list of IP addresses that you control. This means that you can control access to those IP addresses. You can assign these addresses as you like. Traffic within a VLAN is encrypted (question) How?

Relevant tickets: #4128 /#4625/#3952

1. What do you want customers to know about AppNexus VLANs and VLAN requests and migrations?
2. How does it work to have a VLAN in NY and a VLAN in LA?
3. What do you do when you want a bigger VLAN?
4. What's the migration process?
5. Will migrating be available through the API in the future?
6. Can you add IPs to a VLAN or connect two VLANs?6. Multinetting?? Does it turn two VLANs into one?
7. OK so looks like multinetting is nixed by Peak. So how to two VLANs interact? How does that work? And what's the optimal solution here?
8. VPNs??? What are they exactly. Customer VPN question and answer:

What is the capacity of our VPN hardware?
Currently there is no customer-allocated VPN hardware. If you need VPN capabilities, please let us know and we may be able to provide them to you for a fee.

Stateful vs. non stateful inspection.

These questions are also answered on the wiki FAQ but may be helpful here.

1. Why do you use ACLs instead of a stateful firewall?

Stateful inspection is most useful for protecting outbound traffic, but with hosting, the servers tend to receive traffic instead of initiate it. Also, because we are dealing with an unknown amount of traffic, the ability to scale is very important. Stateful inspection is an expensive task for a device to perform and therefore subject to strict capacity limitations (we're talking sub Gigabit for most firewalls). On the other hand, Cisco routers perform ACL packet filtering at line rate with absolutely no performance hit. So, while stateful inspection is appropriate for small, stable amounts of outbound traffic or for protecting niche pieces of the network, (like e-commerce databases), ACLs are more scalable and efficient for protecting inbound traffic to servers. If a customer still desires a stateful firewall, we can add it for a fee.

2. What are the security implementations at each relevant layer of the OSI Reference Model?

3. How do you detect, prevent, and manage DDoS attacks and application-level attacks?

Preemptive protection against DDoS attacks is difficult, because we have no way of knowing when, where, or what type to expect. Also, please note that AppNexus does not manage nor monitor the customer's applications (even their OS). That said, in the event of an attack the use of Cisco ACLs allows us to apply deny statements for the source of the attack without affecting performance of the rest of the network. Also, we highly recommend that our customers utilize the F5 server load balancing technology for front-ending their web applications, as the F5s provide built-in DDoS protection when it performs full-proxy session offload.