Review Questions

1.	Which of the following is one of the three components of MLS? MFSC PCF MLS-P MLSP
2.	Which of the following is one of the three components of MLS? MLS MLS-SW MLS-ES MLS-SE
3.	Which of the following is one of the three components of MLS? RP RSP MLS-RP MLS-MSFC
4.	Which of the following describes the router-on-a-stick topology? (Choose all that apply.) A router connected to a switch with coax A single external router connected to a single switch A single internal router (MSFC) installed in a switch A switch with an MSFC connected to an external router
5.	Which of the following elements are not used to create a flow or shortcut cache entry? (Choose all that apply.) ToS Protocol CRC Payload Source MAC Destination MAC Destination IP
6.	Which answer best describes the MLSP discovery process? The MLS-SE sends hello packets to the multicast address 01-00-0C-DD-DD-DD. MLS- RPs then respond to these hello packets. The MLS-RP sends hello packets to the multicast address 01-00-0C-DD-DD-DD. MLS- SEs then respond to these hello packets. The MLS-RP sends hello packets to the multicast address 01-00-0C-DD-DD-DD. MLS- SEs then record the hello packet information. The MLS-SE sends hello packets to the multicast address 01-00-0C-DD-DD-DD. MLS- RPs then record the hello packet information.
7.	What is the XTAG used for, and what is its significance? XTAG is a numerical value assigned by the MLS-SE to identify an MLS-RP. It must be unique throughout the VTP domain. XTAG is a numerical value assigned by the MLS-SE to identify an MLS-RP. It is locally significant. The XTAG is the MLS-RP router ID and is used to uniquely identify the MLS-RP to the MLS-SE. It is a unique value throughout the layer 2 network. The XTAG is the MLS-SE ID and is used to identify each MLS-SE in the layer 2 network. Therefore, it must be unique across all switches.
8.	What must you do on a 3550 switch before enabling CEF? Enable IP routing. Disable layer 2 switching. Nothing, the box is ready to run CEF. Nothing, CEF is enabled by default.
9.	What are the two prerequisites before a complete shortcut entry can be entered into cache? Identification of the MLS-SE Identification of the candidate packet Identification of the MLS topology Identification of the enable packet
10.	Which of the following criteria qualify a packet as a candidate packet? Any incoming packet that is destined for a MAC address associated with the MLS-RP Incoming packets sourcing from 224.0.0.1 and destined for the MAC address of the MLS-SE Incoming packets sourcing a MAC address associated with the MLS-RP Outbound packets destined for a remote host
11.	Which of the following criteria qualify a packet as an enable packet? (Choose all that apply.) The packet is sourced from an MLS-RP MAC address. The XTAG value matches the candidate packet XTAG value. The destination MAC address is the same as the corresponding candidate packet’s source MAC address. The destination IP address matches the destination IP of the corresponding candidate packet.
12.	Which component or device performs the frame rewrite? PFC MLSRP MSFC DCAM
13.	Which of the following fields can be rewritten by the MLS-SE? (Choose all that apply.) ISL header DEST MAC Source MAC Destination IP address
14.	Which of the following fields can be rewritten by the MLS-SE? (Choose all that apply.) Source IP address ToS CRC Payload
15.	At what MLS cache size does the probability of involving the router increase dramatically? 8KB 64KB 32KB 128KB 256KB
16.	What command can inadvertently disable MLS on a router or interface? (Choose all that apply.) no ip routing ip security ip access-group access-list-number [in|out] no tcp-small-servers
17.	What command can inadvertently disable MLS on a router or an MLS-configured interface? clear ip route ip tcp header-compression route-map ip router rip
18.	Which of the following caches does CEF consider when forwarding a packet? (Choose all that apply.) The CEF table The adjacency table The forwarding table The optimum route cache
19.	Which of the following commands enables MLS on an external router? set mls ip enable set mls enable mls rp ip mls ip
20.	When must you configure the VTP domain on an interface of an external router? Always When it uses ISL encapsulation When it doesn’t use ISL or 802.1Q encapsulation When it is connected to a VTP server or client

Answers

1.	D MLSP is the proper acronym for Multilayer Switching Protocol. MFSC should be MSFC; PCF should be PFC.
2.	D Multilayer Switching Switch Engine is the name of the component. The proper acronym is provided in the last answer.
3.	C MLS-RP represents the broad spectrum of route processors. RP, RSP, and MSFC are all types of route processors.
4.	B, C The topology name comes from the original look of an external router connected to a switch. With the implementation of MSFC, the same functional topology is achieved in the same chassis. The media connection type does not define the topology.
5.	C, D CRC can vary from packet to packet and is used for error checking. The payload is also unique for each packet. Flows are established by using packet similarities.
6.	C The key to this question is twofold. The MLS-RP is the only device that sends hello packets. Because the packets are sent to a multicast address, the MLS-RP doesn’t require a response from the switch. The MLS-RP doesn’t need to establish an actual connection with the switch.
7.	B XTAGs are used by the MLS-SE to identify each MLS-RP connected to the layer 2 network. Each switch can utilize the same XTAG values; they are used only locally.
8.	A The 3550 is a multilayer switch, but only layer 2 switching is enabled by default. You must specifically enable IP routing.
9.	B, D Both packets must be identified to complete the shortcut entry.
10.	A Incoming packets must be destined for a MAC address that is associated with the MLS-RP via the XTAG value. If the packet is not destined for this address, the packet is not tagged as a candidate packet.
11.	A, B, D Enable packets have more criteria to match than do candidate packets. Because the destination MAC address is different for every hop, there is no way that a packet could match using the destination MAC address and still use MLS.
12.	A MSFCs are layer 3 devices that are used in Catalyst switches. Pattern matching and frame rewrites are done by the PFC.
13.	A, B, C Although the rewrite engine can modify some fields in the IP header, it does not change the IP addresses.
14.	B, C The MLS-SE has to rewrite the CRC because it changes the values for the source MAC and destination MAC addresses. It calculates a new CRC for the new frame.
15.	C After the MLS cache size exceeds 32KB, chances are that the MLS-SE will not be able to shortcut-switch all flows, and packets will be sent to the router.
16.	A, B Other commands also can inadvertently disable MLS, but access control lists no longer do. They can cause the cache to be cleared, but since IOS 12.0(2), inbound as well as outbound access control lists are supported and do not disable MLS.
17.	B Using header compression disables MLS on the configured interface. clear ip route is not a correct answer because it temporarily clears the cache but it doesn’t disable MLS.
18.	B, C CEF looks at the route forwarding table and then the adjacency table.
19.	C The command set mls enable is used to enable MLS on a 6500 series switch, and the command mls rp ip is used to enable MLS on an external router.
20.	D Internal routers such as MSFCs don’t require a VTP domain configuration because they are physically connected to a single switch. However, external routers that have connections to VTP servers or clients must configure the interface for the VTP domain.