Cisco 350-401 Practice Test - Questions Answers, Page 36

Cisco Express Forwarding (CEF) switching is a proprietary form of scalable switching intended to tackle the problems associated with demand caching. With CEF switching, the information which is conventionally stored in a route cache is split up over several data structures. The CEF code is able to maintain these data structures in the Gigabit Route Processor (GRP), and also in slave processors such as the line cards in the 12000 routers. The data structures that provide optimized lookup for efficient packet forwarding include:

The Forwarding Information Base (FIB) table - CEF uses a FIB to make IP destination prefix-based switching decisions. The FIB is conceptually similar to a routing table or information base. It maintains a mirror image of the forwarding information contained in the IP routing table. When routing or topology changes occur in the network, the IP routing table is updated, and these changes are reflected in the FIB. The FIB maintains next-hop address information based on the information in the IP routing table.

Because there is a one-to-one correlation between FIB entries and routing table entries, the FIB contains all known routes and eliminates the need for route cache maintenance that is associated with switching paths such as fast switching and optimum switching.

Adjacency table - Nodes in the network are said to be adjacent if they can reach each other with a single hop across a link layer. In addition to the FIB, CEF uses adjacency tables to prepend Layer 2 addressing information. The adjacency table maintains Layer 2 next-hop addresses for all FIB entries.

CEF can be enabled in one of two modes:

Central CEF mode - When CEF mode is enabled, the CEF FIB and adjacency tables reside on the route processor, and the route processor performs the express forwarding. You can use CEF mode when line cards are not available for

CEF switching, or when you need to use features not compatible with distributed CEF switching.

Distributed CEF (dCEF) mode - When dCEF is enabled, line cards maintain identical copies of the FIB and adjacency tables. The line cards can perform the express forwarding by themselves, relieving the main processor - Gigabit Route

Processor (GRP) - of involvement in the switching operation. This is the only switching method available on the Cisco 12000 Series Router. dCEF uses an Inter-Process Communication (IPC) mechanism to ensure synchronization of FIBs and adjacency tables on the route processor and line cards.

For more information about CEF switching, see Cisco Express Forwarding (CEF) White Paper.

Mobility, or roaming, is a wireless LAN client's ability to maintain its association seamlessly from one access point to another securely and with as little latency as possible. Three popular types of client roaming are:

Intra-Controller Roaming: Each controller supports same-controller client roaming across access points managed by the same controller. This roaming is transparent to the client as the session is sustained, and the client continues using the same DHCP-assigned or client-assigned IP address.

Inter-Controller Roaming: Multiple-controller deployments support client roaming across access points managed by controllers in the same mobility group and on the same subnet. This roaming is also transparent to the client because the session is sustained and a tunnel between controllers allows the client to continue using the same DHCP- or client-assigned IP address as long as the session remains active.

Inter-Subnet Roaming: Multiple-controller deployments support client roaming across access points managed by controllers in the same mobility group on different subnets. This roaming is transparent to the client because the session is sustained and a tunnel between the controllers allows the client to continue using the same DHCP-assigned or client-assigned IP address as long as the session remains active.

Reference: https://www.cisco.com/c/en/us/td/docs/wireless/controller/7-4/configuration/guides/consolidated/b_cg74_CONSOLIDATED/b_cg74_CONSOLIDA TED_chapter_01100.htmlIn three types of client roaming above, only with Inter- Subnet Roaming thecontrollers are in different subnets.

Low latency queuing (LLQ) adds a priority queue to CBWFQ from which delay-sensitive traffic, such as voice traffic, can be transmitted ahead of packets in other queues.

By configuring the quality of service (QoS), you can provide preferential treatment to specific types of traffic at the expense of other traffic types. Without QoS, the device offers best-effort service for each packet, regardless of the packet contents or size. The device sends the packets without any assurance of reliability, delay bounds, or throughput.

The following are specific features provided by QoS:

Low latency

Bandwidth guarantee

Buffering capabilities and dropping disciplines

Traffic policing

Enables the changing of the attribute of the frame or packet header

Relative services

Modular QoS Command-Line Interface

Supported QoS Features for Wired Access

Hierarchical QoS

EIGRP is based on DUAL (Diffusing Update Algorithm) while OSPF uses Dijkstra's Shortest Path Algorithm with the major difference in how they calculate the shortest routing path.

OSPF has capability to calculate the best shortest path to each reachable subnet/network using an algorithm called SFP (Shortest Path First) also known as Dijkstra algorithm. "Neighbor Table" that contain all discovered OSPF neighbour with whom routing information will be interchanged.

The Link Management Protocol (LMP) performs the following functions: + Verifies link integrity by establishing bidirectional traffic forwarding, and rejects any unidirectional links + Exchanges periodic hellos to monitor and maintain the health of the links + Negotiates the version of StackWise Virtual header between the switches StackWise Virtual link role resolution

Reference: https://www.cisco.com/c/en/us/products/collateral/switches/catalyst-9000/nb-06-cat-9k-stack-wp-cte-en.html