129. Cisco 2950 Switch System LED:
The system LED shows whether the system is receiving power and functioning
LED Off: System is not powered up.
LED color is Green: System is operating normally.
LED color is Amber: System is receiving power but is not functioning properly. The amber color on a Cisco2950 series switch indicates that the system is malfunctioning.
130. The cable determines the DTE/DCE combination. The router with DCE cable needs to be configured with clock rate for proper functioning of the WAN link.
131. There are different types of cables:
Also, you can’t connect the Ethernet port on PC to another Ethernet port on a router using a straight through cable. You need crossover cable for this purpose. Also, the PC need to have a network card, and appropriate networking protocol stack properly installed and configured.
132. There are three ways a router learns how to forward a packet:
133. There are broadly three types of routing protocols:
Benefits of Link State protocols:
134. There may be times that you have lost the passwords for accessing the router and need to recover from the lost passwords. ROM Monitor (rommon), stored ROM is used for password recovery. By hitting special Break key within the first 60 seconds of the router power-on, it is possible to recover from lost passwords. Broadly, the sequence of operations is as below (For a 2501 router):
135. To change the enable password, you use "enable password password".
To change the enable secret, you use "enable secret password".
136. To configure your router to do look-up for domain name server, the correct syntax is:
Here the ipaddress_of_server is the ip address of the DNS server.
137. To enable the Cisco IOS to forward packets destined for obscure subnets of directly connected networks onto the best route, you use "ip classless" command.
138. Trace command has syntax, "trace ip <destination_address> ".
The trace command traces the path to the destination hop by hop. This is
achieved by setting the TTL (Time To Live) to 1 for the first packet to
send and increasing TTL in the intervals of 1. This causes the successive
next hop devices to send a time out message. This message is used for finding
out the route that the packet takes to reach the destination.
Important Trace responses are:
P ……The Protocol was Unreachable
N …… The Network was Unreachable
U …… The port was Unreachable
* …… The packet timed out
!H ….. Could not be forwarded due to access list violation
Tracert, Ping use ICMP as their base protocol.
Traditionally, the router interface on a serial link is a 60-pin D-shell connector. The CSU/DSU may have EIA/TIA 232 interface to the router. The CSEU/DSU interface to the service provider could be RJ-11, RJ-45 etc.
139. Transport Layer is responsible for multiplexing the packets received from upper layers. It also makes the network transparent to the upper layers (Session, Presentation, and Application layers)..
140. Typical WAN interfaces, that one come across frequently are:
EIA 232, EIA 449, EIA 530, V.35, and X.21. The Cisco router serial interface will be a 60-pin D-shell connector. This in turn is connected to service provider equipment, usually through a CSU/ DSU. Therefore, appropriate conversion cable need to be used when interfacing with a WAN device such a CSU/DSU. CSU/ DSU in turn is connected to the service provider through the cable supplied by the service provider.
141. UDP is known as unreliable protocol because there is no way for the source to know if any packets are lost during transit to the destination. Important fields that are available with TCP header, but not available with UDP header include sequence number, acknowledgement number, and window size.
Variable-Length Subnet Masking:
Variable-length subnet masking (VLSM) means implementing more than one mask on the same major class of a network. It allows for a more efficient use of IP address space both in terms of hosts and subnets, and can be essential on a network that does not have an abundance of IP address space.
The following routing protocols support VLSM:
1. RIP v2
142. VLAN port assignments can be configured either of two ways:
Static VLANs: The administrator statically configures VLAN port assignment.
VLAN memberships on the switch ports are assigned on a port-by-port basis.
Dynamic VLANs: A VMPS (VLAN Management Policy Server) can dynamically assign VLAN ports. The MAC address of the node is used to determine the VLAN assignment. A separate server or a Catalyst 5000 can function as a VMPS server. When a frame arrives on a dynamic port at the switch, it queries the VMPS for the VLAN assignment based on the source MAC address of the arriving frame.
143. WAN (Wide Area Network) devices extend the reach of LAN (Local Area Network) devices. WANT typically span over a wide area, such over multiple cities / countries. WANS are connected over serial lines that operate at lower speeds than LANs. Some of the WAN devices are:
144. When designing an ESS WLAN, APs with overlapping coverage areas should be configured to use non-overlapping channels. This is true whether the APs are using DSSS (Direct Sequence Spread Spectrum) or FHSS (Frequency Hopping Spread Spectrum) technology.
145. While a packet travels through an Internetwork, it usually involves multiple hops. It is important to know that the logical address (IP address) of source (that created the packet) and destination (final intended destination) remain constant, the hardware (Interface) addresses change with each hop.
146. Windowing, Buffering, and Congestion avoidance are three different types of flow controls used frequently.
147. Wired Equivalent Privacy (WEP) is a protocol used to secure IEEE 802.11 wireless networks. It is part of the IEEE 802.11 wireless networking standard. Wireless networks broadcast messages using radio, and therefore more susceptible to eavesdropping than wired networks. WEP was intended to provide confidentiality comparable to that of a traditional wired network.
148. Wi-Fi Protected Access (WPA and WPA2) is a class of systems to secure wireless (Wi-Fi) computer networks. WPA is forward compatible with the IEEE 802.11i standard, and was intended as an intermediate measure to take the place of WEP while 802.11i was prepared. 802.11i includes dynamic key exchange, stronger encryption, and user authentication. It is not backward compatible with WPA. The 802.11i standard is widely known as WPA2.
149. WPA stands for Wi-Fi Protected Access. The key features of the protocol are given below:
You can use "show controllers serial [port number]" to see if the interface detects a DCE or DTE cable.
150. You need to assign a different network number for each subnet. Also, you need to set aside one network number for each WAN connection.
151. Three important modes of a Cisco router are:
Global configuration mode allows you to perform tasks that affect the entire router, such as naming the router, configuration of banner messages, enabling routed protocols, and generally anything that affects the operation of the entire router.
152. When you first switch on a router, you enter Setup mode. Setup mode is different from configuration mode in that setup mode appears when there is no configuration file present. Upon entering setup mode, you can supply some basic configuration parameters to Cisco router.
153. You use show vlan or shor vlan vlan# command to see the configuration details of VLANs. The command "sh vlan" will display the configuration information for all VLANs, where as the command "sh vlan vlan#" shows only the configuration information pertaining to that vlan. For example, if you want to see the configuration information for vlan2, you give the command "sh vlan 2".
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