Section VIII. New Questions – Test online

Hint

The Internet Control Message Protocol (ICMP) Echo operation measures the end-to-end response time between two devices that use IPv4. The response time is computed by measuring the time taken between sending an ICMP Echo request message to the destination and receiving an ICMP Echo reply. An IP SLA can be used to performs network performance monitoring, including measure the latency, packet loss, jitter and response time in the network. The example below shows how to configure an IP SLA ICMP Echo (send an ICMP request to 192.168.1.254 every 300 second with a timeout of 500ms):

Device(config)#ip sla 1

Device(config-ip-sla)#icmp-echo 192.168.1.254
Device(config-ip-sla-echo)#frequency 300 //send an ICMP
Device(config-ip-sla-echo)#timeout 500
Device(config-ip-sla-echo)#exit
Device(config)#ip sla schedule 1 start-time now

Hint

Directly connected routes: In directly attached static routes, only the output interface is specified. The destination is assumed to be directly attached to this interface, so the packet destination is used as the next-hop address. This example shows such a definition: ipv6 route 2001:DB8::/32 gigabitethernet1/0/0 The example specifies that all destinations with address prefix 2001:DB8::/32 are directly reachable through interface GigabitEthernet1/0/0. Recursive Static Routes: In a recursive static route, only the next hop is specified. The output interface is derived from the next hop. This example shows such a definition: ipv6 route 2001:DB8::/32 2001:DB8:3000:1 This example specifies that all destinations with address prefix 2001:DB8::/32 are reachable via the host with address 2001:DB8:3000:1. Fully Specified Static Routes: In a fully specified static route, both the output interface and the next hop are specified. This form of static route is used when the output interface is a multi-access one and it is necessary to explicitly identify the next hop. The next hop must be directly attached to the specified output interface. The following example shows a definition of a fully specified static route: ipv6 route 2001:DB8:/32 gigabitethernet1/0/0 2001:DB8:3000:1 A fully specified route is valid (that is, a candidate for insertion into the IPv6 routing table) when the specified IPv6 interface is IPv6-enabled and up. Besides three of the static IPv routes, there is one more type of IPv6 static route, that is Floating Static Routes (static route with a higher administrative distance than the dynamic routing protocol it is backing up) For more information about these IPv6 routes, please read: http://www.cisco.com/c/en/us/td/docs/ios-xml/ios/ipv6/configuration/xe-3s/ipv6-xe-36s-book/ip6-stat-routes.html

Hint

The Dynamic Trunking Protocol (DTP) is a proprietary networking protocol developed by Cisco Systems for the purpose of negotiating trunking on a link between two VLAN-aware switches, and for negotiating the type of trunking encapsulation to be used. It is a Layer 2 protocol and it is enabled by default on Cisco switches (so the interfaces of your switches will be in “dynamic auto” or “dynamic desirable” mode). If you want to turn it off, use the “switchport nonegotiate” under interface mode.

Hint

There are only three port states left in RSTP that correspond to the three possible operational states. The 802.1D blocking, and listening states are merged into the 802.1w discarding state. * Discarding – the port does not forward frames, process received frames, or learn MAC addresses – but it does listen for BPDUs (like the STP blocking state) * Learning – receives and transmits BPDUs and learns MAC addresses but does not yet forward frames (same as STP). * Forwarding – receives and sends data, normal operation, learns MAC address, receives and transmits BPDUs (same as STP). Although the learning state is also used in RSTP but it only takes place for a short time as compared to STP. RSTP converges with all ports either in forwarding state or discarding state.

Hint

A Oct 5 23:29:16: %CDP-4-NATIVE_VLAN_MISMATCH: Native VLAN mismatch discovered on GigabitEthernet11/43 (512), with WS-C2950-12 FastEthernet0/6 (1) D http://blog.ine.com/2008/07/17/pvst-explained/ Case 1: Change the native VLAN on SW1 connection to R3: SW1: interface FastEthernet 1/3 switchport trunk native vlan 2 Rack1SW2# %SPANTREE-2-RECV_PVID_ERR: Received BPDU with inconsistent peer vlan id 2 on FastEthernet1/3 VLAN1. %SPANTREE-2-BLOCK_PVID_PEER: Blocking FastEthernet1/3 on VLAN2. Inconsistent peer vlan.PVST+: restarted the forward delay timer for FastEthernet1/3 %SPANTREE-2-BLOCK_PVID_LOCAL: Blocking FastEthernet1/3 on VLAN1. Inconsistent local vlan.PVST+: restarted the forward delay timer for FastEthernet1/3 Note that SW2 detects untagged packet with VLAN ID 2, Which does not correspond to the locally configured default native VLAN 1. The corresponding port is put in «inconsistent» state. The reason SW2 detects this condition (and not SW1) is because SW1 sending SSTP BPDUs and SW2 is not (it receives superios BPDUs). As soon as native VLAN is converted back to «1» on SW1, consistency is restored:

Hint

This question wants to ask how to use the router as the SSH client to connect into other routers. The table below shows the parameters used with SSH: For example the command “ssh -v 2 -l admin 10.1.1.1” means “use SSH version 2 to connect to a router at 10.1.1.1 with username “admin”. Answer C is not correct because it is missing the version needed to use.

Hint

MDI stands for “Medium Dependent Interface”. MDI is a type of Ethernet port found on network devices. When connecting two devices with MDI ports (two hosts, for example) an Ethernet crossover cable is required. The crossover cable switches the send and receive ports on the two connectors, allowing data to flow correctly between two MDI ports.

Hint

http://www.cisco.com/c/en/us/support/docs/ip/routing-information-protocol-rip/13730-ext-pingtrace.html#ext_troute “This table lists the traceroute command field descriptions: Source address: The interface or IP address of the router to use as a source address for the probes. The router normally picks the IP address of the outbound interface to use. Minimum Time to Live [1]: The TTL value for the first probes. The default is 1, but it can be set to a higher value to suppress the display of known hops. Maximum Time to Live [30]: The largest TTL value that can be used. The default is 30. The traceroute command terminates when the destination is reached or when this value is reached.

Hint

To switch frames between LAN ports efficiently, the switch maintains an address table. When the switch receives a frame, it associates the media access control (MAC) address of the sending network device with the LAN port on Which it was received. The switch dynamically builds the address table by using the MAC source address of the frames received. When the switch receives a frame for a MAC destination address not listed in its address table, it floods the frame to all LAN ports of the same VLAN except the port that received the frame. When the destination station replies, the switch adds its relevant MAC source address and port ID to the address table. The switch then forwards subsequent frames to a single LAN port without flooding all LAN ports. Reference: http://www.cisco.com/c/en/us/td/docs/switches/datacenter/nexus5000/sw/configuration/guide/cli/CLIConfigurationGuide/MACAddress.html When the switch dynamically builds the MAC address table, it also specifies the time before an entry ages out and is discarded from the MAC address table. The default is 300 seconds.

Hint

The split-horizon rule states that “a router never sends information about a route back in same direction Which is original information came”. This rule is used in distance vector protocol (like RIP or EIGRP) to prevent Layer 3 routing loop.

Hint

VTP server usually has the same revision number with other switches (when they are synchronized) so answer C is not correct. To run VTP, the VTP domain names and VTP version must be matched among the devices running VTP.

Hint

NTP redundancy http://sflanders.net/2015/02/09/time-hard-proper-ntp-configuration/

Hint

At the end of each frame there is a Frame Check Sequence (FCS) field. FCS can be analyzed to determine if errors have occurred. FCS uses cyclic redundancy check (CRC) algorithm to detect errors in the transmitted frames. Before sending data, the sending host generates a CRC based on the header and data of that frame. When this frame arrives, the receiving host uses the same algorithm to generate its own CRC and compare them. If they do not match then a CRC error will occur. The “Type/Length” field is used to indicate the “Type”of the payload (Layer 3 protocol) Which is indicated as a Hexadecimal value. Note: Ethernet II uses “Type” while the old Ethernet version use “Length”

Hint

Single-mode fiber allows only one mode of light to propagate. Because of this, the number of light reflections created as the light passes through the core decreases, lowering attenuation and creating the ability for the signal to travel further. This application is typically used in long distance, higher bandwidth. Because of the high dispersion and attenuation rate with multimode fiber cable, the quality of the signal is reduced over long distances. Reference: https://www.multicominc.com/training/technical-resources/single-mode-vs-multi-mode-fiber-optic-cable/ In fact it is difficult to say what the maximum distance of single-mode or multimode fiber but according to this link (table 1): https://www.cisco.com/c/en/us/products/collateral/interfaces-modules/gigabit-ethernet-gbic-sfp-modules/product_data_sheet0900aecd8033f885.html Single-mode cable is good for installations longer than 10km. At present, there are four kinds of multi-mode fibers: OM1, OM2, OM3 and OM4. The letters “OM” stand for optical multi-mode. OM3 and OM4 fibers will support upcoming 40 and 100 Gb/s speeds.

Hint

With Priority Queueing (PQ), traffic is classified into high, medium, normal, and low priority queues. The high priority traffic is serviced first, then medium priority traffic, followed by normal and low priority traffic. -> Therefore we can assign higher priority for voice traffic. Also with PQ, higher priority traffic can starve the lower priority queues of bandwidth. No bandwidth guarantees are possible -> It is still good because this network is mostly used for data traffic so voice traffic amount is small. With First In First Out (FIFO) or Weighted Fair Queueing (WFQ), there is no priority servicing so they are not suitable here. Reference: https://www.cisco.com/c/en/us/td/docs/ios/solutions_docs/qos_solutions/QoSVoIP/QoSVoIP.html Weighted Random Early Detection (WRED) is just a congestion avoidance mechanism. WRED measures the size of the queues depending on the Precedence value and starts dropping packets when the queue is between the minimum threshold and the maximum threshold -> It does not have priority servicing either.

Hint

The Internet authorities have reserved the multicast address range of 01:00:5E:00:00:00 to 01:00:5E:7F:FF:FF for Ethernet and Fiber Distributed Data Interface (FDDI) media access control (MAC) addresses.

Hint

The “!” is a special character Which is not allowed in the hostname of Cisco device.

Hint

First by comparing their MAC addresses we learn that switch B will be root bridge as it has lowest MAC. Therefore all of its ports are designated ports -> C & D are correct. On the link between switch A & switch C there must have one designated port and one non-designated (blocked) port. We can figure out Which port is designated port by comparing their MAC address again. A has lower MAC so Fa0/1 of switch A will be designated port while Fa0/1 of switch C will be blocked -> B is correct.

Hint

PortFast BPDU guard prevents loops by moving a nontrunking port into an errdisable state when a BPDU is received on that port. When you enable BPDU guard on the switch, spanning tree shuts down PortFast-configured interfaces that receive BPDUs instead of putting them into the spanning tree blocking state. In a valid configuration, PortFast-configured interfaces do not receive BPDUs. If a PortFast-configured interface receives a BPDU, an invalid configuration exists. BPDU guard provides a secure response to invalid configurations because the administrator must manually put the interface back in service. Reference: https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst4000/8-2glx/configuration/guide/stp_enha.html

Hint

In Cisco switches there are two encapsulations: 802.1q and ISL so we can set two ends to ISL instead -> A is not correct. The ports between two switches must be set to trunk ports so that they can exchange VLAN information through VTP -> C is not correct. To connect two switches we can use cross-over cable or straight-through cable (because modern Cisco switches can “auto-sense”) but not rollover cable -> E is not correct. To forward traffic in the same VLAN (between two or more switches) we can use switches only. If we want to forward VTP traffic between different VLANs we can use either a router or a Layer 3 switch -> F is not correct. Two switches can only communicate when they are set to the same VTP domain name (and the same VTP password) -> B is correct. One of the two switches must be set to VTP Server so that it can create VTP updates and advertise its VLAN information.

Hint

Floating static routes are static routes that have an administrative distance greater than the administrative distance (AD) of another static route or dynamic routes. By default a static route has an AD of 1 then floating static route must have the AD greater than 1 -> Answer A is correct as it has the AD of 201.

Hint

The ping command first sends an echo request packet to an address, then waits for an echo reply. The ping is successful only if: + The echo request gets to the destination, and + The destination is able to get an echo reply back to the source within a predetermined time called a timeout. The default value of this timeout is two seconds on Cisco routers. Reference: http://www.cisco.com/c/en/us/support/docs/ios-nx-os-software/ios-software-releases-121-mainline/12778-ping-traceroute.html

Hint

Reference: https://www.cisco.com/c/en/us/support/docs/ip/hot-standby-router-protocol-hsrp/9281-3.html#q17

Hint

Reference: https://www.cisco.com/c/en/us/td/docs/switches/blades/3030/software/release/12-2_37_se/configuration_/guide/swlldp.html

Hint

Reference: https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst3560/software/release/12-2_46_se/command/reference/cr1/intro.pdf

Hint

Reference: https://www.cisco.com/c/en/us/support/docs/switches/catalyst-6500-series-switches/12027-53.html

Hint

Reference: https://www.cisco.com/en/US/docs/switches/lan/catalyst3850/software/release/3.2_0_se/multibook/configuration_guide/b_consolidated_config_guide_3850_chapter_011111.html

Hint

Reference: https://www.cisco.com/c/en/us/td/docs/cloud-systems-management/application-policyinfrastructure-controller-enterprise-module/1-6-x/path_trace/user-guide/ b_Cisco_Path_Trace_User_Guide_1_6_0_x/b_Cisco_Path_Trace_User_Guide_1_6_0_x_chapter_0111.html