Sistema linfático y linfedema

In contention-based networks, such as Ethernet, all connected nodes share the media and its available bandwidth. Therefore, if there are 10 nodes on a network that has a 10 Mbps

bandwidth, it can be said that each node has an available bandwidth of a tenth of the total bandwidth, or 1 Mbps. If you add nodes to the network, the share each has of the total decreases in inverse proportion to the number of connected nodes. Therefore, when there are 20 nodes, each has a twentieth of the bandwidth. A significant problem of contention networks with many

connected nodes is that throughput degrades. A bigger issue is the collision that occurs on a link, which results in the further reduction of the available bandwidth. The simple solution is to reduce the number of nodes in each segment. You can do this by implementing MAC-level bridging.

A switch is like a hub. It acts as a wiring concentrator to which all network devices are connected. It performs the same isolation when a cable failure occurs while maintaining the integrity of the network.

However, there are some fundamental differences.

Characteristics of a Switch Layer 2 Switches

The significant difference between a hub and switch is that the switch can perform MAC-level bridging between ports. In other words, each node has exclusive use of the bandwidth of the segment during its transmission. So every device connected to the switch is exclusively talking with the switch. The switch has a table that shows which MACs are connected to which ports. This means that traffic is only sent to the wires that require the information.

You can configure each host to have a single port, or you can connect a hub to a switch port. When you connect a hub to a switch port, the nodes on the hub all share the bandwidth configured for the port on the switch to which the hub is connected. In this manner, you can determine how much bandwidth is

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4-18 Connecting Network Components

available to each port and nodes connected to the ports. Switches that provide this function are known as Layer 2 switches.

With modern switches, you can also program a group of ports to behave like a hub. For example, you could create a group of ports to enable network load balancing or to provide for network level analysis.

Layer 3 Switches

Some switches can provide protocol-specific routing functions at the protocol stack layer. For example, you can configure the switch to provide routing for IP packets, but not to perform MAC-level bridging for non-IP-based frames. Switches that provide this routing functionality are known as Layer 3 switches.

Note: Network protocols, such as IP, encapsulate instructions received from higher-level protocols, such as TCP, into a structure known as a packet.

Layer 3 switches route packets. The switch examines the packet and makes a routing decision based on the destination packet address. Layer 3 switches also perform additional routing functions. For example, Layer 3 switches can check packet integrity, respond to Simple Network Management Protocol (SNMP) management systems, and observe and decrement packet Time-to-Live (TTL) values.

In some ways, a Layer 3 switch can provide several improvements over more traditional routers. For example, Layer 3 switches:

• Divide networks into logical subnets by using the Layer 2 configuration instead of at the port level, such as a traditional router. This provides a more flexible configuration.

• Are generally less expensive than traditional routers.

• Provide faster forwarding performance than traditional routers.

Be aware that Layer 3 switches do not provide support for wide area networks (WANs).

Layer 4 Switches

Some more advanced switches are equipped with a firewall service module that enables the switch to make forwarding decisions based on the type of data in the segment. These kinds of advanced functionality switches are known as Layer 4 switches.

Also as discussed in Module 3, switches allow for creating a VLAN. A VLAN is a virtual implementation of a LAN that lets you control what nodes receive what traffic and then group the nodes accordingly. For example, nodes in a different physical or geographical location can behave as if they were on the same logical network.

Note: Transport protocols, such as TCP, encapsulate instructions received from applications into a structure known as a segment.

Switches with a firewall service module examine the content of segments received and determine whether and how to route the segment based on the specific TCP port being used.

Note: TCP ports are examined in a later module of this course.

In addition to port switching, Layer 4 switches (and some Layer 3 switches) can make switching decisions based on the priority of network traffic. In this mode, lower-priority traffic is buffered at the switch, whereas higher-priority traffic is handled.

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Fundamentals of a Windows Server Infrastructure 4-19

Note: Quality of Service (QoS) values are a way to indicate the priority of traffic. Some network transport protocols implement QoS to support application prioritization needs. The switch can read and interpret these QoS values.

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4-20 Connecting Network Components

Lesson 4