The network infrastructure is the underlying foundation of the system. It forms the services that create the operating makeup of your network. In a Communications Services deployment, determining your network infrastructure from the project goals ensures that you will have an architecture that can scale and grow.
The Existing Network
We need to understand our existing network infrastructure to determine how well it can meet the needs of our deployment goals. By examining our existing infrastructure, we identify if we need to upgrade existing network components or purchase new network components. We should build up a complete map of the existing network by covering these areas:
After completing this inventory, you need to review that information in conjunction with your project goals to determine what changes are required so that you can successfully deliver the deployment.
Network Infrastructure Components
The following common network infrastructure components have a direct impact upon the success of your deployment:
Routers and Switches
Routers connect networks of your infrastructure, enabling systems to communicate.
You need to ensure that the routers have spare capacity after the deployment to cope with projected growth and usage.
In a similar vein, switches connect systems within a network. Routers or switches running at capacity tend to induce escalating bottlenecks, which result in significantly longer times for clients to submit messages to servers on different networks. In such cases, the lack of foresight or expenditure to upgrade the router or switch could have a personnel productivity impact far greater than the cost.
Firewalls sit between a router and application servers to provide access control.
Firewalls were originally used to protect a trusted network (yours) from the untrusted network (the Internet). These days, it is becoming more common to protect application servers on their own (trusted, isolated) network from the untrusted networks (your network and the Internet).
Router configurations add to the collective firewall capability by screening the data presented to the firewall. Router configurations can potentially block undesired services (such as NFS, NIS, and so forth) and use packet-level filtering to block traffic from untrusted hosts or networks.
In addition, when installing a Sun server in an environment that is exposed to the Internet, or any untrusted network, reduce the Solaris software installation to the minimum number of packages necessary to support the applications to be hosted. Achieving minimization in services, libraries, and applications helps increase security by reducing the number of subsystems that must be maintained. The Solaris™ Security Toolkit provides a flexible and extensible mechanism to minimize, harden, and secure Solaris systems.
Use load balancers to distribute overall load on your Web or application servers, or to distribute demand according to the kind of task to be performed. If, for example, you have a variety of dedicated applications and hence different application servers, you might use load balancers according to the kind of application the user requests. If you have multiple data centers, you should consider geographic load balancing.
Geographic load balancing distributes load according to demand, site capacity, and closest location to the user. If one center should go down, the geographic load balancer provides failover ability.
For load balancers on Web farms, place the hardware load balancers in front of the servers and behind routers because they direct routed traffic to appropriate servers. Software load balancing solutions reside on the Web servers themselves. With software solutions, one of the servers typically acts a traffic scheduler.
A load balancing solution is able to read headers and contents of incoming packets. This enables you to balance load by the kind of information within the packet, including the user and the type of request. A load balancing solution that reads packet headers enables you to identify privileged users and to direct requests to servers handling specific tasks.
Storage Area Networks (SANs)
Understanding the data requirements of the storage system is necessary for a successful deployment. Increasingly, SANs are being deployed so that the storage is independent of the servers used in conjunction with it. Deploying SANs can represent a decrease in the time to recover from a non-functional server as the machine can be replaced without having to relocate the storage drives.
Use these questions to evaluate if your deployment storage requirements would be best served through a SAN:
Domain Name System (DNS)
Servers which make heavy usage of DNS queries should be equipped with a local caching DNS server to reduce lookup latency as well as network traffic.
When determining your requirements, consider allocating host names for functions such as mailstore, mail-relay-in, mail-relay-out, and so forth. You should consider this policy even if the host names all are currently hosted on one machine. With services configured in such a way, relocation of the services to alternate hardware significantly reduces the impacts of the change.
Planning Your Network Infrastructure Layout
In deriving your infrastructure topology, you need to consider the following topics:
Demilitarized Zone (DMZ)
These days, most company networks are configured for a DMZ. The DMZ separates the corporate network from the Internet. The DMZ is a tightly secured area into which you place servers providing Internet services and facilities (for example, web servers). These machines are hardened to withstand the attacks they might face. To limit exposure in case of a security breach from such attacks, these servers typically contain no information about the internal network. For example, the name server facilities only include the server and the routers to the Internet.
Progressively, DMZ implementations have moved the segment behind the firewall as firewall security and facilities have increased in robustness. However, the DMZ still remains segmented from the internal networks. You should continue to locate all machines hosting Web servers, FTP servers, mail servers, and external DNS on a DMZ segment. A simpler network design might only define separate DMZ segments for Internet services, VPN access, and remote access. However, security issues exist with VPN and remote access traffic. You need to separate appropriate connections of these types from the rest of the network.
The firewall providing the DMZ segmentation should allow only inbound packets destined to the corresponding service ports and hosts offering the services within the DMZ. Also, limit outbound initiated traffic to the Internet to those machines requiring access to the Internet to carry out the service they are providing (for example, DNS and mail). You might want to segment an inbound-only DMZ and an outbound-only DMZ, with respect to the type of connection requests. However, given the potential of a denial-of-service attack interrupting DNS or email, consider creating separate inbound and outbound servers to provide these services. Should an email-based Trojan horse or worm get out of control and overrun your outbound mail server, inbound email can still be received. Apply the same approach to DNS servers.
The DMZ provides a network segment for hosts that offer services to the Internet.
This design protects your internal hosts, as they do not reside on the same segment as hosts that could be compromised by an external attack. Internally, you also have similar services to offer (Web, mail, file serving, internal DNS, and so on) that are meant solely for internal users. Just as the Internet services are segmented, so too, are the internal services. Separation of services in this manner also permits tighter controls to be placed on the router filtering.
Just as you separate the Internet-facing services into the DMZ for security, your private internal services should reside in their own internal DMZ. In addition, just as multiple DMZs can be beneficial—depending on your services and your network’s size—multiple intranets might also be helpful.
The firewall rules providing the segmentation should be configured similarly to the rules used for the DMZ’s firewall. Inbound traffic should come solely from machines relaying information from the DMZ (such as inbound email being passed to internal mail servers) and machines residing on the internal network.
The segments that remain make up your internal network segments. These segments house users’ machines or departmental workstations. These machines request information from hosts residing on the intranet. Development, lab, and test network segments are also included in this list. Use a firewall between each internal network segment to filter traffic to provide additional security between departments. Identify the type of internal network traffic and services used on each of these segments to determine if an internal firewall would be beneficial.
Machines on internal networks should not communicate directly with machines on the Internet. Preferably, these machines avoid direct communication with machines in the DMZ. Ultimately, the services they require should reside on hosts in the intranet. A host on the intranet can in turn communicate with a host in the DMZ to complete a service (such as outbound email or DNS). This indirect communication is acceptable.
Only the machines directly communicating with machines on the Internet should reside in the DMZ. If users require Internet access, though, this creates a problem based on your previous topology decisions. In this situation, proxies become helpful. Place a proxy on an internal network segment, or, better yet, an intranet segment. A machine requiring access to the Internet can pass its request onto the proxy, which in turn makes the request on the machine’s behalf. This relay out to the Internet helps shield the machine from any potential danger it might encounter.
Because the proxy communicates directly with machines on the Internet, it should reside in the DMZ. However, this conflicts with the desire to prevent internal machines from directly communicating with DMZ machines. To keep this communication indirect, use a double proxy system. A second proxy residing in the intranet passes connection requests of the internal machines to the proxy in the DMZ, which in turn makes the actual connection out on the Internet.
In addition to the typical packet-filtering features, most firewalls provide features to prevent IP spoofing. Use IP-spoofing protection whenever possible.
For instance, if there is only one entry point into your network from the Internet and a packet is received from the Internet with a source address of one of your internal machines, it was likely spoofed. Based on your network’s topology, the only packets containing a source IP address from your internal machines should come from within the network itself, not from the Internet. By preventing IP spoofing, this possibility is eliminated, and the potential for bypassing IP address-based authorization and the other firewallfiltering rules is reduced. Use the same IP-spoofing protection on any internal firewall as well.
When you have remote or mobile users, pay attention to how you will provide them access to the facilities. Will there be any facilities they cannot access? What kind of security policies do you need to address? Will you require SSL for authentication? Also, examine whether your mobile user population is stable or is expected to increase over time.
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