The D channel between the router and the ISDN switch is always enabled. The standard ISDN Q.921 describes the processes LAPD data link protocol operated as a Layer 2 in the OSI reference model. The D channel is used for call control functions such as setting, marking and cutting of the call. These functions are implemented according to the Q.931 protocol. The Q.931 specifies the functions of Layer 3 of OSI reference model.

The standard recommended Q.931 network layer connection between the terminal end and the local ISDN switch, but does not require a recommendation from end to end. Because some ISDN switches were developed before the standardization of Q.931, ISDN different providers and different types of switch can be used (do) various implementations of Q.931. Switch types are not standard, routers must have commands in your configuration that specify ISDN switch which are connected.

When placing a call BRI or PRI the following sequence of events:

• 1. The D channel is used to send the dialed number to the local ISDN switch.
• 2. The local switch uses the SS7 signaling protocol to set up a route and send the dialed number to the remote ISDN switch.
• 3. The remote ISDN switch makes a signal to the destination using the D channel.
• 4. The ISDN NT-1 device target remote ISDN switch sends a message to connect the call.
• 5. The remote ISDN switch uses SS7 to send a message to connect the call to the local switch.
• 6. The local ISDN switch connects one B channel from end to end and let the other B channel available for a new conversation or data transfer. Both B channels can be used simultaneously.

ISDN – Benchmarks:

The ISDN standards define the functional groups such as hardware devices or components that allow the user to access the services of BRI or PRI. Manufacturers can create hardware that supports one or more functions. ISDN specifications define four reference points that connect with each other ISDN device. Each device on an ISDN network performs a specific task to facilitate end-to-end connectivity.

To connect devices that perform specific functions, the interface between the two devices must be well defined. These interfaces are called benchmarks. The reference points that affect the client side of the ISDN connection are:

• R: refers to a terminal device connection between type 2 (NT2) is not compatible with ISDN terminal adapter (TA), for example an RS-232 serial interface.
• S: refers to the connection points to a switching device Network Termination type 2 (NT2) and enables customer calls between different types of customer equipment.
• T: identical to the S from the electrical point of view, refers to the outgoing connection from the NT2 to the network device or to ISDN Network Termination Device type 1 (NT1).
• U: refers to connections between devices and the network NT1 ISDN telephone company property.

As S and T references are similar from the electrical point of view, some interfaces are specified as interfaces S / T. Though perform different functions, the port is the same, from electrical point of view and can be used for both functions.

The IPX version of RIP is quite similar to the IP version. Function essentially the same way, the routers periodically broadcast the contents of their routing tables and other routers are gathered listening and integrating the information they receive. Nodes only need to know your local network and make sure to send datagrams to other destinations through its local router. The router is responsible for collecting and redirects these datagrams to the next hop of the route.

In an IPX environment, we need to spread the net a second kind of information. Announcement Protocol (Service Advertisement Protocol, SAP) carries information about what services are available in which nodes in the network. For example, SAP is the protocol that allows users to obtain lists of file servers and network printing.

The SAP protocol works by nodes that provide services to periodically disseminate the list of services offered. The IPX network routers collect this information and propagate throughout the network with routing information of the network. To be a compatible IPX router, must be both propagate the RIP as the SAP information.

As well as IP, IPX on Linux support provides a daemon of routing called ipxd that performs tasks associated with the treatment of the routing. Again, as in the IP, is actually the kernel that manages the forwarding of datagrams between IPX network interfaces, but it takes place according to a set of rules contained in the IPX routing table. The devil ipxd kept updated set of rules that listening to all active network interfaces and analyzing when to change routing. Ipxd daemon also answers requests from the nodes of a network connected directly to request routing information.

No need to configure the daemon ipxd. When launched, it automatically manages the on-road IPX devices that have been configured. The key is to make sure that all IPX devices are configured correctly using the command ipx_interfaces before launching ipxd. Although the auto may work when making routing functions is better not to take chances, so manually configure the interfaces and save on-road problems annoying. Every 30 seconds, ipxd re-inspect all IPX networks and automatically manages hooked.

This provides a way to manage network interfaces that can not be active all the time, such as PPP interfaces. Normally ipxd is launched at boot time from an init rc script: # /usr/sbin/ipxd do not need a character & because ipxd is placed by default in the background.

Although the devil ipxd is especially useful on machines acting as IPX routers is also useful to nodes in segments where there are multiple routers. When you specify the argument, ipxd act passively, listening to the segment routing information and update routing tables, but it shall not transmit any routing information. Thus, a node can keep its routing tables without having to request routes each time you want to contact a remote node.

Preventing broadcast storms by setting too high or low values of threshold discards excessive broadcast MAC traffic, multicast or unicast. In addition, the configuration of securities to raise thresholds in a switch can disable the port.

STP problems include broadcast storms, loops, BPDU and dropped packets. The function of STP is to ensure that there are no logical loops in a network by designating a root bridge. The root bridge is the focal point of a spanning-tree configuration that controls the way the protocol operates.

The location of the root bridge in the extended network router and switch is necessary for effective diagnosis of faults. The show commands on the router and the switch can display root bridge information. Fixed parameter settings root bridge timers to delay shipment or maximum age for STP information. Manually configuring a device as the root bridge is another configuration option.

If the extended network router and switch goes through a period of instability, it is advisable to minimize the STP processes that occur between devices. If it becomes necessary to reduce BPDU traffic, set the maximum values for the timers on the root bridge. Specifically, set the delivery delay parameter in the maximum value of 30 seconds, and the parameter max_age in up to 40 seconds.

A physical port on a router or switch may be part of more than one spanning tree if it is a trunk. Spanning Tree Protocol (STP) is considered as one of the most important protocols in Layer 2 Catalyst switches. By avoiding the logical loops in bridged network, STP allows Layer 2 redundancy without generating broadcast storms. Minimize the spanning-tree problems actively developing a baseline study of the network.

By adding more nodes, increases the demand on the available bandwidth and imposes an additional burden on the media. When it increases the number of nodes in a single segment, it increases the likelihood of collisions, and this causes more retransmissions. One solution is to divide a large segment into parts and separate it into isolated collision domains.

To accomplish this, a bridge keeps a table of MAC addresses and their associated ports. The bridge then forwards or discards frames based on the entries in your table. The following steps illustrate the operation of a bridge mode:

• The bridge has just been turned, so the bridging table is empty. The bridge only expected traffic on that segment. When it detects traffic, the bridge is processed.





• Host A is doing ping to the Host B. Data is transmitted by the entire collision domain segment, both the bridge and Host B processed package.
• The bridge adds the source address of the frame to its bridging table. Since the address was in the source address field and received the frame on Port 1, the frame must be associated with port 1 of the table.




• The destination address of the frame compared to the bridging table. Since the address is not in the table, although it is in the same collision domain, the frame is sent to another segment. The address of Host B is not registered yet as it only records the source address of a frame.
• Host B ping processes the request and sends a ping response back to Host A. The data is transmitted over the entire collision domain. Both Host A and the bridge receive the frame and process.
• The bridge adds the source address of the frame to its bridging table. Because the source address was not in the bridging table and received on port 1, the source address of the frame must be associated with port 1 of the table. The destination address of the frame compared to the bridging table to see if your entry is there. Because the address is on the table, check the port assignment. The address of Host A is associated with the bridge by which the frame arrived, and then the frame is not sent.
• Host A will now ping Host C. Since data is transmitted across the segment the collision domain, both the bridge and Host B process the frame. Host B dismisses the plot because it was not set destination.
• The bridge adds the source address of the frame to its bridging table. Because the address was already registered in the bridging table, it is simply renewed.
• The destination address of the frame compared to the bridging table to see if your entry is there. Because the address is not in the table, it forwards the frame to another segment. The address of Host C not registered yet, as it only records the source address of a frame.
• Host C processes the ping request and sends a ping response back to Host A. The data is transmitted over the entire collision domain. Both the Host D as the bridge receives the frame and process. Host D discards the plot because it was the destination set.
• The bridge adds the source address of the frame to its bridging table. Since the address was in the source address field and the frame is received on Port 2, the frame must be associated with port 2 of the table.
• The destination address of the frame is compared to the bridging table see if your entry is there. The address is on the table but is associated with port 1, and then the frame is sent to another segment.
• When Host D transmits data, the MAC address is also recorded in the bridging table. This is the way the bridge controls the traffic between collision domains.

These are the steps we used the bridge to send and discard frames that are received in any of its ports.

There are two main standards:

• Simple Network Management Protocol (SNMP) – Community of IETF
• Common Management Information Protocol (CMIP) – Community of telecommunications.

SNMP actually refers to a set of standards for network management which includes a protocol, a specification of the structure of the database and a set of data objects. The SNMP was adopted as a standard for TCP/ IP in 1989 and became very popular. In 1993 it adopted an update known as the SNMP version 2c (SNMPv2c).

The SNMPv2c supports the distributed and centralized management strategies and included improvements in the structure of management information (SMI), protocol operations, management architecture and security. It was designed to operate in both OSI-based networks such as TCP/IP.

The SNMPv3 came later. To address the limitations of SNMPv1 and SNMPv2c, SNMPv3 provides secure access on the MIB through authentication and encryption of packets traveling over the network. The CMIP is an OSI protocol network management created and standardized by the ISO for the monitoring and control of heterogeneous networks.

A hub is an older type of aggregation device that also has multiple ports. However, the hubs are lower than those switches as all devices connected to a hub share the bandwidth and have the same collision domain.

Another disadvantage is that only hubs operating in half-duplex mode. In half-duplex mode, the hubs can only send or receive data at some point but can not do both simultaneously. The switches can operate in full duplex mode, which means they can send and receive data simultaneously.

Switches are multiport bridges. The switches belong to the current standard technology of Ethernet LAN using a star topology. A switch provides multiple virtual circuits dedicated point to point between the networks devices connected, so it is unlikely those collisions.

Given the dominant role of the switches in modern networks, the ability to understand and configure switches is essential for the technical assistance network.

The new switches are preset with default values. This configuration rarely meets the needs of network administrators. The switches can be configured and managed from a command line interface (CLI). Network devices can also be configured and managed via a browser interface and web based.

Network administrators should be familiar with all tasks related to the administration of networks with switches. Some of these tasks include maintenance of the switch and its IOS. Other tasks include managing interfaces and tables to achieve optimum operation, reliable and secure. The basic configuration of the switch, IOS upgrades and password recovery are essential skills network administrator.

The same SIP, then handles the message from the server side, ie the IP PBX, Cisco. The router in fact, the CME configuration, you can use two main VoIP protocols: a Cisco proprietary protocol called Skinny Protocol (SCCP), which is precisely the SIP. For an introduction to the protocol from the point of view, Cisco, see the documents listed on the site.

For an overview “presentation” of the Tech-invite SIP see the portal to the use of SIP in the IP PBX, you must configure both the same as SIP proxy server as a SIP registration. There are two main IOS commands that must be used for this purpose: the voice register pool command to define the device and its associated number, and the voice command register globals used to determine the parameters of the proxy server.

!
voice register global
mode cme
source-address 10.15.0.1 port 5060
max-dn 10
max-pool 12
!

You can see that this configuration going to spell out the IP address of the proxy and the port on which the service can be used (port 5060 is the standard UDP port for SIP signaling). The IP address of the proxy is nothing but the default gateway of the VLAN associated with voice service. In the case of the Cisco IP phone, the device configuration is implemented through the following commands:
!
voice register dn 1
number 1035
!
voice register pool 1
id mac 0018.DE12.977F
number 1 dn 1
codec g711ulaw
! appear where the MAC address the device itself (required to allow the association MAC - extension number required for proper registration of the device at the switchboard).

For security reasons, the router has two levels of access to commands:

• User EXEC mode: Typical tasks include checking the status of the router. Changes to the configuration of the router are not allowed in this mode.
• Privileged EXEC mode: Typical tasks include changes to the configuration of the router. The request for entry of user EXEC mode is displayed at login to the router. The commands available at the user level are a subset of available commands at the Privileged EXEC mode. For the most part, these commands allow the user to view information without changing the configuration of the router.

To access the complete set of commands, you must enter privileged EXEC mode. The request for the entry “>” write enable (enable). At the prompt password: (password), type the password you set with the enable secret command. You can use two commands to set a password to access privileged EXEC mode: enable password and enable secret.

If you use both commands, the enable secret command takes precedence. Once you have completed the steps to start the session, the prompt changes to “#”, to indicate that it has entered privileged EXEC mode. You can only enter global configuration mode from privileged EXEC mode.

The following are specific ways that you can also enter from global configuration mode:

• Interfaces
• Subinterfaces
• Line
• Router
• Maps routing

To return to user EXEC mode from privileged EXEC mode, you can execute commands disable or exit. To return to privileged EXEC mode from global configuration mode, run exit or Ctrl-Z. Control-Z can also be used to return directly to privileged EXEC mode from any secondary global configuration mode.

Help using the keyboard on the command line interface when typing a question mark (?). In the prompt user mode or privileged mode, appears a useful list of available commands. Notice the “-More-” (More) that appears at the bottom of the screen shows. The screen displays several lines at once. The request for entry “-More-” listed at the bottom of the screen indicates that there are more screens available. Whenever you see a request for input “-More-”, the next available screen can be displayed by pressing the spacebar. To display only the next line, press the Return or Enter. Press any key to return to the prompt.

To enter privileged EXEC mode, type enable or its abbreviation ena. This can cause the router prompt the user for a password, which is quoted above. If you enter a “?” (sign of interrogation) when the prompt shows the privileged EXEC mode, the screen displays a list of commands longer than that obtained when the prompt shows the user EXEC mode.
The result displayed varies depending on the level of Cisco IOS software and configuration of the router.

If a user wants to set the clock on the router but do not know the appropriate command, you can use the help function to know what the correct command. The following exercise illustrates one of the many uses of the help function. The task is to configure the router clock. Consider that knows no corresponding command, and do the following:

• Step 1: Use to find the appropriate command to set the clock. The result indicates that aid is needed the command clock (clock).
• Step 2: Check the syntax to make changes on the hour.
• Step 3: Enter the current time in hours, minutes and seconds, as shown in Fig. The system indicates that you must supply additional information to complete the command.
• Step 4: Press Ctrl-P (or the up-arrow key) to repeat the above command automatically. Then add a space and a question mark (?), to display additional arguments. Now you can complete the command.
• Step 5: The circumflex (^) and the aid response indicates an error. The location of the accent ^ shows the place where the possible problem is located. To re-enter the correct syntax, re-enter the command to the location of the caret, and then type a sign of question (?).
• Step 6: Enter the year, following the correct syntax and press Return or Enter to execute the command.

Reliability increases due to redundancy. A network based on switches or bridges present redundant links between those switches or bridges to overcome the failure of a single link. These connections introduce physical loops in the network. These bridging loops are created so that if one link fails, another link may take over the function of sending traffic.

When an unknown switch targeted traffic floods the traffic from all ports except the port that received the traffic. The broadcast and multicast frames are also sent flood out all ports except the port that received the traffic. This traffic can be caught in a loop. In the Layer 2 header, there is no life time value (TTL). If a frame is sent to a loop topology with Layer 2 switches, you can move around the loop indefinitely. This wastes bandwidth and network unusable.

At Layer 3, the TTL decreases and the packet is discarded when the TTL reaches 0. This creates a dilemma. A physical topology that contains switching or bridging loops is necessary for purposes of reliability; however, a switched network can not have loops.

The solution is to allow physical loops, but create a loop free logical topology. For this logical topology, traffic destined to the central server connected to Cat 5 from any workstation connected to Cat 4 travel through Cat 1 and Cat 2. This occurs even if there is a direct physical connection between Cat 5 and Cat 4.

The loop free logical topology that is created is called a tree. The resulting topology is a logical topology star or extended star. This topology is the spanning tree (spanning tree) network. It is considered as a spanning tree since all network devices can reach or grasp.

The algorithm used to create this loop free logical topology is the spanning-tree algorithm. This algorithm can take a fairly long time to converge. We developed a new algorithm called rapid spanning-tree algorithm to reduce the time it takes a network to compute a loop free logical topology.

A “network analyzer” is a device that allows you to “hear” the traffic of a network, i.e. to capture the information on them.

In fact, in a switched network, data is sent to all network terminals. However, with a normal exploitation of the terminals ignore packets that are not intended for them. Then, using the network interface in a particular mode (usually called promiscuous mode) you can hear the traffic passing through a network adapter (Ethernet card, a wireless network card, etc.).

Using the sniffer:

A sniffer is a powerful tool that allows studying the network traffic. Generally serves administrators to diagnose problems on their networks and to know that traffic circulates. So the intrusion detection systems (IDS) are based on a sniffer to capture textures, and use a database of rules to find the suspected plots.

Unfortunately, like all the instruments of administration, the sniffer can also be used for a malicious person who has physical access to the network to gather information. This risk is even more important since it is hard on the wireless radio waves in a limited scope is defined; making sure that people with bad intentions can simply listen to the traffic being around.

The vast majority of Internet protocols are passing the information in the clear, i.e. in a non- encrypted. So when a user consults its network messaging protocol through POP or IMAP, or surf the Internet on sites whose address does not begin with HTTPS, all information sent or received can be intercepted. So those specific sniffers have been developed by the pirates to recover passwords circulating flows in the network.

The protections:

There are several ways to guard against the inconveniences caused by use of a sniffer on your network:

• Use encrypted protocols for all communications whose content possess a high level of confidentiality.
• Segment the network to limit the dissemination of information. It is especially recommended to prefer the use of switches (switches) to the hubs (concentrators) as they switch communications, that information is delivered only to end recipients.
• Use a sniffer detector. This is a tool that probes the network looking for hardware mode using promiscuous.
• For wireless you should reduce the power of the hardware in such a way as to cover only the area needed. This does not prevent the pirates to listen to any network but reduces the geographical perimeter of the zone of action.