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41 Cards in this Set
- Front
- Back
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What is a major difference between voice and video traffic compared to data traffic?
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Voice traffic is highly latency-sensitive and drop-sensitive. Therefore, when a network experiences congestion due to lack of b/w, some of the problems you can experience are Delay (time for packet to travel src to dst), Jitter (uneven arrival of packets) and Drops (occurs when links congested and buffer overflows).
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What is used to inform an IP Phone of the phones VLAN?
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Cisco Discovery Protocol (CDP). The Data VLAN is often referred to as the Native VLAN, and the Voice VLAN as the Auxiliary VLAN. IP phone ports aren't trunk ports, they are known as Multi-VLAN access port, since carry just the Voice VLAN frames (tagged) and the Data frames (untagged).
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What is a Call Agent and what does it do?
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It provides call control, Call Admission Control (CAC), B/W control, management and address translation for IP phones. An IP phone must successfully register with its call agent to be able to place and receive calls. Can either be a UCM server or a UCME router.
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What are the processes of a Cisco IP phone bootup?
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1. Phone receives power (PoE or mains). 2. Loads its firmware from its Flash. 3. The switch informs the phone of its VLAN via CDP. 4. Phone requests ipconfig (including IP of TFTP server) info via DHCP. 5. Requests and receives a portion of its config info (including IP of call agent) from its TFTP server. 6. Phone registers with call agent.
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What is the protocol that carries voice calls between two IP phones?
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Real-time Transport Protocol (RTP).
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What are the prerequisites that should be considered before enabling AutoQoS on a router interface?
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CEF must be enabled because AutoQoS uses NBAR to recognize traffic types, and NBAR requires CEF to be enabled. No QoS policy must be currently attached to the interface. Correct b/w should be configured on the interface since AutoQos references it to determine which QoS policies should be enabled on an interface. An IP address must be configured on an interface if its speed is equal to or less than 768 kbps.
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What are the 3 steps to QoS configuration using Modular Quality of Service Command Line Interface (MQC)?
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1. Create a Class Map and Classify traffic with Match statements. 2. Create Policy map and assign polices to the different traffic classes. 3. Assign the Service policy (policy map) to an interface.
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What happens to all traffic that's not classified by one of the configured class maps?
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Cisco creates Class Map named Class-default, which categorizes any traffic not matched by one of the defined Class Maps. This class map has a policy of "fail-queue", which means traffic classified as "class-default" will be assigned to a queue that gets the rest of the available b/w.
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Where does Cisco recommend marking traffic for QoS?
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As close to the source as possible, but don`t want end users setting own priority markings so use switches to create a Trust Boundary. The exception are IP phones, since they perform priority markings for voice traffic, so can extend the trust boundary to the phone.
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What is the default Differential Services code point (DSCP) value and Per-Hop Behaviors (PHB) name that an IP phone marks voice packets leaving the phone with?
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DSCP 46, which is PHB Expedited Forwarding (EF). DSCP markings use the 6 left bits of the Type of Service (ToS) byte in IPv4 header, and are called PHB names because DSCP values can influence how traffic is treated at each hop along the path.
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Multicast packets are sent via UDP using class D addresses. What are these address ranges?
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The first 4 bits in first octet are always 1110. Reserved Link Local Addresses = 224.0.0.0 - 224.0.0.255, Globally Scoped Addresses = 224.0.1.0 - 238.255.255.255, Source-Specific Multicast (SSM) Addresses = 232.0.0.0 - 232.255.255.255, GLOP Addresses = 233.0.0.0 - 233.255.255.255, Limited Scope Addresses = 239.0.0.0 - 239.255.255.255
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What are the Multicast address ranges used for Network protocols?
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They are called Reserved Link Local Addresses. Multicast all hosts = 224.0.0.1, Multicast all routers = 224.0.0.2, OSPF = 224.0.0.5 & 224.0.0.6, RIPv2 224.0.0.9, EIGRP 224.0.0.10
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How is a 48 bit L2 multicast address constructed from the 32 bit L3 multicast IP address?
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The first 24 bits are always 01:00:5e, the 25 bit is always 0, and the remaining 23 bits are taken from the last 23 bits of the L3 address.
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What is the Internet Group Management Protocol (IGMP)?
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It is used between clients and routers to let routers know which of their interfaces have multicast receivers attached. Clients send report messages to join a group, and routers send Query messages (every 60 secs) to determine if clients want to remain members of a group.
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What's the main differences between IGMP v1 and v2?
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V1 is similar to v2 except it can send queries to specific groups and a leave message is supported so a receiver can proactively leave a group. They are interoperable, but V2 receivers would have to send a v1 report message to a v1 router. If a v2 router has v1 and v2 receivers, all leave messages must be ignored while there are v1 receivers present.
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How does PIM-SM differ in comparison to PIM-DM?
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PIM-SM offers all the benefits of PIM-DM (that is, optimal pathing by using Shortest Path Tree (SPT) switchover (cutting over from path via RP to the direct path) without PIM-DMs flood-and-prune behavior. Also this flood-and-prune behavior repeats every 3 minutes, therefore PIM-DM doesn't scale well.
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To create Class Maps (and enter class map config mode), which are each used to classify the different traffic types. By default all match statements must be met before a packet is classified.
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R1(config)# class-map [match-any | match-all] [class name]
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To specify the different match statements, with all traffic that meets the "match" statement classified under the Class Map. Can choose to match any or all the match statements before the packet is classified.
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R1(config-cmap)# match protocol [protocol name]
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To create a Policy map (enter policy map config mode) that defines how the classified traffic (in class maps) is to be treated.
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R1(config)# policy-map [policy name]
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From policy map config mode, to enter policy map class config mode to assign policies to the different traffic classes.
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R1(config-pmap)# class [class name]
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From within policy map class config mode, to assign QoS policies to traffic classified by each class map. Bandwidth = At least the specified b/w and more, Police = Max b/w utilization limit, Priority = Gets priority and has b/w up to specified limit. Can use "percent" and % value instead of b/w.
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R1(config-pmap-c)# [bandwidth [value] | police [value] | priority [value]]
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To assign a Service Policy (Policy Map) to an interface.
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R1(config-if)# service-policy [input | output] [policy map name]
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To list each class map showing which "match" statements are under each.
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R1# show class-map
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To show how each class of traffic is to be treated within a policy map. So what QoS polices have been applied to each class.
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R1# show policy-map
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To view Policy map statistics for packets crossing a specific interface. Shows the different Class maps and statistics for them.
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R1# show policy-map interface [type] [mod/num] [input | output]
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To configure AutoQoS on a router interface. The "Trust" keyword indicates that it should classify voice traffic using DSCP markings rather than NBAR.
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R1(config-if)# auto qos voip [trust] [fr-atm]
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To verify the AutoQoS configuration either globally or for a specified interface. It shows all the access lists, class maps and policy maps AutoQoS has created.
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R1# show auto qos voip [interface [type] [mod/num]]
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To enable AutoQoS on a switch interface. It configures the interface to trust Class of Service (CoS) markings (L2 QoS priority markings on an Ethernet connection) for classifying VoIP traffic.
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SW1(config-if)# auto qos voip trust
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To configure a switch interface to trust CoS markings only if those markings came from an attached IP phone. CDP is used to detect an attached phone.
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SW1(config-if)# auto qos voip cisco-phone
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To configure a switch to instruct an interface to trust DSCP markings on packets entering the interface. To preserve priority markings on wireless traffic as it enters a wired network you could issue this cmd on a switch port that connects to a WLC.
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SW1(config-if)# auto qos voip cisco-phone
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To start the AutoQoS Discovery phase to dynamically learn all the applications and protocols seen on an interface (recommended for 2 to 3 days). "Trust" keyword instructs the router to classify traffic based on existing DSCP markings as apposed to using NBAR.
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R1(config-if)# auto discovery qos [trust]
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To see the results of AutoQoS Discovery Phase It shows what traffic has been classified and what behavior is specified in its recommended policy. It can recognize traffic in as many as 10 different classes.
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R1# show auto discovery qos
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To enable AutoQoS Enterprise ( only for routers) after you have already done the discovery phase. Similar to AutoQoS VoIP, but targets all known applications on an enterprise network.
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R1(config-if)# auto qos
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To globally enable IGMP snooping, and then needs enabling per VLAN. It allows a switch determine which interfaces are connected to receivers for specific multicast groups, preventing the need to flood multicast frames.
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SW1(config)# ip igmp snooping
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After globally enabling IGMP snooping, to enable it for individual VLANs.
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SW1(config)# ip igmp snooping vlan [vlan id]
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To enable a router for multicast routing. Once enabled, individual interfaces need to be configured for PIM support.
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R1(config)# ip multicast-routing
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To configure an interface to participate in an IP multicast network using PIM. Dense uses a Src Dist Tree (more memory usage), Sparse uses a Shared Dist Tree (less memory required) and sparse-dense uses dense until it detects (learns location of) an RP, and their after uses sparse.
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R1(config-if)# ip pim [dense-mode | sparse-mode |sparse-dense mode]
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To configure non-RP routers to point to a statically defined RP router. However, in larger topologies is recommended that the RP is automatically discovered using either AutoRP (Cisco Proprietary) or Bootstrap Router (BSR) (standards based).
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R1(config)# ip pim rp-address [ip add]
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To see who is multicast IGMP Designated Querier. Used in bcast network (e.g. Ethernet) where more than 1 Multicast router exists on it. The Designated Querier is the router with lowest unicast IP address.
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R1# show ip igmp interface [type] [mod/num]
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To display the multicast groups of whom the router is aware.
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R1# show ip igmp group
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To view the Multicast routing table. (S,G = src dist tree, (*,G) = shared dist tree. Other valuable info shown in this cmd are the identities of incoming and outgoing interfaces.
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R1# show ip mroute
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