Physical Network Implementations

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The next step involves constructing a real network based on the logical network architecture. You can use several approaches to realize the network that functionally satisfies the logical architectural requirements.

The multi-tier data center is vendor independent, and you can use the network equipment that best suits your environment. We briefly describe the original multi-tier data center implementation (secure multi-tier architectures), then we describe the multiswitch approach, and finally we describe the collapsed approach.

Secure Multi-Tier

FIGURE 7-13 shows the overall structure of a classic multi-tier design.

Figure 7-13. Secure Multi-Tier


The advantages of this approach are simplicity and security. Clearly the only way to access the Data tier is through the application servers. There are no other possible network paths to access the Data tier. The drawbacks are limited flexibility and manageability. If an application running on the Web server needs to connect to an LDAP server or a database through a JDBC connection, a fundamental change to the architecture will be needed. As the number of tiers increases, so does the number of switches, which becomes a management issue.

Multi-Level Architecture Using Many Small Switches

FIGURE 7-14 shows the overall structure of a multi-level architecture that is composed of many small port density switches.

Figure 7-14. Multi-Tier Data Center Architecture Using Many Small Switches


This approach has few advantages and many disadvantages. One advantage is that the entry cost is low. One can start from a very small deployment, procuring small eight-port multilayer switches and Layer 2 switches and increasing the tiers and servers to the point where the ingress links become a bottleneck or the port density of the small multilayer switches becomes an issue. Actual tested configurations leveraged Alteon 180 switches as the multilayer switches and Extreme Networks Summit 48i for the Layer 2 switches, which had gigabit uplinks and 10/100 ports for connections to the server. This architecture has the following disadvantages:

  • Lower Availability Because of the number of links and devices, more things can go wrong. In particular, the serial connections drastically reduce the MBTF. The links are often prone to accidents and should be kept to a minimum. Due to the architecture, the link failure detection time and recovery is much slower because of the number of layers.

  • Waste In any network architecture, stateless functionality should be deployed towards the center of the network and complex processing should be deployed at the outermost edge. Having two layers of multilayer switches is a tremendous waste in terms of packet processing and equipment cost. When a packet undergoes Layer 7 processing, especially by software, it is extremely slow. The cost of a multilayer switch is much more than that of a plain Layer 2 or Layer 3 device.

  • Manageability As the number of switches increases, so does the manageability workload.

Flat Architecture Using Collapsed Large Chassis Switches

The flat network architecture using collapsed large chassis switches was found to be the best design for large-scale multi-tier deployments in availability, performance, and manageability.

In the lab, we built two different network configurations. One configuration used Extreme Networks equipment (FIGURE 7-15), and the other used Foundry Networks equipment (FIGURE 7-16).

Figure 7-15. Network Configuration with Extreme Networks Equipment


Figure 7-16. Sun ONE Network Configuration with Foundry Networks Equipment


The Extreme Networks switch that we used has built-in load balancing, so there was no need for an external load-balancing device.

The Foundry Networks products required use of a separate load-balancing switch.

Physical Network Connectivity

The physical wiring of the architecture is shown in FIGURE 7-17 and described in TABLE 7-3

Figure 7-17. Physical Network Connections and Addressing


Table 7-3. Physical Network Connections and Addressing

Switch

Description

Port

PHY Speed

Base Address

Netmask

edge

Client network to external network router

1,2,3,4

ge

172.16.0.1

255.255.255.0

edge

External network - mls1

5,6

ge

192.168.10.1

255.255.255.0

mls1

External network

1

ge

192.168.10.2

255.255.255.0

mls1

Web/app service router

3,4,5,6

ge

10.10.0.1

255.255.255.0

mls1

Directory service router

7,8

ge

10.20.0.1

255.255.255.0

mls1

Database services router

9,10

ge

10.30.0.1

255.255.255.0

mls2

External network

1

ge

192.168.10.2

255.255.255.0

mls2

Web/app service router

3,4,5,6

ge

10.10.0.1

255.255.255.0

mls2

Directory services router

7,8

ge

10.20.0.1

255.255.255.0

mls2

Database services router

9,10

ge

10.30.0.1

255.255.255.0


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    Networking Concepts and Technology. A Designer's Resource
    Networking Concepts and Technology: A Designers Resource
    ISBN: 0131482076
    EAN: 2147483647
    Year: 2003
    Pages: 116

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