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52 Cards in this Set
- Front
- Back
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What is a CAM Table?
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Content-Addressable Memory Table: A Layer 2 table that maps MAC addresses to ports.
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What three items are in the CAM table?
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Arriving switch port, source MAC address, & VLAN
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What is the CAM tables default aging timer?
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300 seconds (5 minutes)
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What is the Layer 2 forwarding table called?
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CAM Table
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What happens in the CAM table when a MAC is seen on a new port?
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Original entry is deleted and a new entry is created.
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What is the TCAM?
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Ternary Content-Addressable Memory table. It is a switching table used to evaluate packet forwarding decisions based on policies or ACLs.
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What are the three parts to the TCAM Structure?
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Value , Mask, & Result (VMR)
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What is the length of the TCAM Value field?
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134 bits
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What is the length of the TCAM Mask field?
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134 bits
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List some examples of the TCAM Results field.
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Permit, Deny, QoS Policy Index, Next-hop
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What does the TCAM use to store entries with ports?
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LOU (Logical Operation Unit)
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Are the TCAM tables accessed simultanously?
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Yes
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True or False: There is a single TCAM table per switch.
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FALSE (multiple TCAMs exists)
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What two components are part of TCAM operation?
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Feature Manager (FM)
Switching Database Manager (SDM) |
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What does the TCAM Feature Manager (FM) do?
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Complies, or merges, ACEs into entries in the TCAM
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What does the TCAM Switching Databse Manager (SDM) do?
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Configures and tunes the TCAM partitions if needed. Not availible on all switches.
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Where are security ACLs stored?
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TCAM
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Where are QoS ACLs stored?
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TCAM
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What three things are accessed simultanously to make switching decisions?
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CAM Table
Security ACLs QoS ACLs |
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What are the two types of Multilayer Switching?
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Route caching
Topology-based (CEF) |
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What MLS type is considered legacy?
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Route caching
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What type of MLS requires an RP and a SE (switch engine)?
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Route caching
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What is NetFlow Switching?
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Another name for route caching MLS
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What MLS type is Cisco Express Forwarding (CEF)?
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Topology-based
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What does CEF download into the FIB?
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The current routing table database.
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What is the FIB?
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Forwarding Information Base: Dynamically updated from the routing table and reformatted into an ordered list with the most specific routes first
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What are the four main parts of the FIB?
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IP Address
Next-Hop Address Next-Hop MAC Address Egress Port |
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What is the Layer 3 forwarding table called?
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FIB Table
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What is the root command for the CAM table?
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mac address-table
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Does CEF run by default on most switches?
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Yes
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What are the two main parts of CEF?
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FIB (Forwarding Information Base) & AT (Adjacency Table)
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True or False: The FIB and Layer 3 Engine are the same thing.
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FALSE
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What happens to packets that can not be handled by the FIB?
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They are sent to the Layer 3 engine for processing, know as "CEF Punt".
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List some examples of CEF punting.
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FIB is full
Entry not found in the FIB MTU exceeded ICMP redirect Encapsulation not supported NAT Tunneling |
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What is Accelerate CEF (aCEF)?
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CEF is distributed accoss multiple Layer 3 forwarding engines. FIB is partial, not full on all devices.
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What is Distributed CEF (dCEF)?
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CEF is distributed completely among multiple engines for imporved performance.
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What is the Adjacency Table (AT)?
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Portion of the FIB that consists of MAC addressess of nodes that can be reached in a single Layer 2 hop.
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What is kept in the Adjancency Table?
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IP Address & MAC Address of hosts on the same network.
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What is used to build the Adjancency Table?
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ARP table
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What is the CEF Glean State?
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A FIB entry is in the Glean State when the MAC is missing. While in this state (waiting for the Layer 3 Engine to handle the ARP) packets are dropped until ARP is replied to.
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What are some possible adjacency types found in the AT?
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Null (sent to null interface)
Drop (unsupported/bad packet) Discard (ACL) Punt (send to Layer 3 engine) |
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What is the root command for the FIB and CEF?
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ip cef
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List some packets that can not be handled by CEF.
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ARPs
IP-Helper Routing protocol updates CDP IPX Encryption NAT |
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What are the four basic MLS order of operations?
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1. Packet arrives on port
2. Packet place in ingress queue 3. Simultaneous table lookups 4. Packet placed in egress queue then sent |
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What four tables are accessed to make MLS decisions?
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CAM table
FIB table Security ACLs (TCAM) QoS ACLs (QoS TCAM) |
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What must a MLS rewrite for a packet?
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- Layer 2 destination address: change to next-hop MAC
- Layer 2 source address: changed to outbound Layer 3 switch MAC - Layer 3 IP TTL: decremented by one - Layer 3 IP Checksum: Recalculated - Layer 2 Frame Checksum: Recalculated |
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What is Store-and-forward switching?
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A switching technology where packets are received, stored for inspection, and then forwarded.
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What is unknown unicast flooding?
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When a switch does not have a MAC in its CAM table, the frame is forwarded out all ports assigned to the source VLAN.
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What are the four DHCP packets?
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1. DHCP Discover: Client broadcast to find DHCP server
2. DHCP Offer: Server broadcast in reply to Discover; includes address 3. DHCP Request: Client broadcast to requests use of offered address 4. DHCP ACK: Server broadcast to confirm use of address |
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What is DHCP relay?
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A switch can relay DHCP messages to central server or servers
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What command configures DHCP realy?
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ip helper-address
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What are the steps to configure a DHCP server?
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1. Set an excluded address range
2. Create an IP pool 3. Set the network 4. Set the default router 5. Set the Lease time |
