Term
What forwarding decision does a switch (bridge) make on receiving a broadcast or multicast frame? |
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Definition
Flood on all ports except the one it was received on. |
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Term
| What forwarding decision does a switch (bridge) make on receiving a unicast frame? |
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Definition
If the destination is in the switch CAM table, then forward only to the associated port. If destination is not known, broadcast (flood) on all ports except the originating one. |
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Term
| What forwarding decision does a switch (bridge) make on receiving a unicast frame where the source and destination hosts are associated with the same port on the switch? |
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Definition
| Frame is filtered and not forwarded. |
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Term
| What are the differences/advantages of a switch (bridge) over a hub? |
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Definition
Hubs will flood all traffic on all ports in one large collision domain. Bridges/switches separate collision domains and will forward frames more intelligently/efficiently. Bridges/switches can also segment LANs using VLAN. |
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Term
| What are the differences between bridges and switches? |
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Definition
Switches switch in hardware; bridges in software
Switches can be full duplex; bridges are half duplex
Bridges can only use store and forward mode
Generally:
Switches have more ports/higher port density
Bridges are generally slower |
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Term
| What are the characteristics of the store and forward switching mode? |
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Definition
Only mode that bridges can also use. The entire frame is buffered and CRC/FCS is run to ensure validity. |
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Term
| What are the characteristics of the cut through switching mode? |
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Definition
High speed at cost of reliability:
Switch makes forwarding decision after receiving the first 6 bytes (destination MAC) after preamble of frame, and immediately begins to forward frame. CRC/FCS not checked; though switch can be set to fall back to Store & Forward mode if bad CRC/FCS threshold is hit.
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Term
| What are the characteristics of the fragement free switching mode? |
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Definition
Switch buffers the first 64 bytes of the frame, updates the source MAC/port if needed, then forwards the frame. Frames smaller than 64 bytes (runts) are discarded. Speed vs. reliability in between the store & forward and cut through modes.
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Term
| What is microsegmentation? |
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Definition
| When all connections to a switch are in full duplex mode, it creates a zero-collision environment, because every device has been segmented into its own collision domain. |
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Term
| What are the advantages of VLANs? (5) |
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Definition
- increase number of broadcast domains while reducing their size
- additional security
- increase flexibility of equipment
- allow logical grouping of users by function (not location)
- make adding/editing users easier |
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Term
What are the main steps to implementing a VLAN
and assigning a port to it? |
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Definition
1. Create the VLAN
switch(config)#vlan n
2. Name the VLAN
3. Assign switch ports to the VLAN
switch(config-if)#switchport access vlan n
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Term
| What does Dynamic VLAN Membership do and what service does it require? |
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Definition
Dynamic VLAN Membership automatically assigns switchports to a VLAN based on the MAC of the connected host Requires VMPS (VLAN Membership Policy Server) to run on the switch |
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Term
| What are the characteristics of a trunk port? |
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Definition
Trunk ports connect multiple VLANs with a single link between switches (by default, all VLANs are allowed over a trunk) |
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Term
What are the two supported VLAN frame tagging trunk encapsulations? What are their main characteristics and which is more common? |
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Definition
ISL - Cisco proprietary; adds 26 byte header & 4 byte trailer; re-encapsulates original frame 802.1Q - IEEE standard; inserts 4 byte tage into header; more common
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Term
What are the characteristics of the five switchport modes?
1. off
2. on
3. NoNegotiate
4. (Dynamic) Desirable
5. (Dynamic) Auto
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Definition
1. off - access port that does not trunk
2. on - trunks unconditionally if neighbor can trunk
3. NoNegotiate - trunks even if neighbor disagrees; does not respond to solicitations
4. Desirable - solicits trunk with neighbor
5. Auto - only trunks if solicited by neighbor
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Term
What switch port mode on the neighboring port is required to trunk for the following port modes: 1. On 2. NoNegotiate 3. Desirable 4. Auto
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Definition
1. On - On, Auto, Desirable, NoNegotiate 2. NoNegotiate - On, NoNegotiate 3. Desireable - On, Auto, Desirable 4. Auto - On, Desirable |
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Term
What are the commands to configure the following port modes: 1. off 2. on 3. NoNegotiate 4. (Dynamic) Desirable 5. (Dynamic) Auto
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Definition
1. switchport mode access 2. switchport mode trunk 3. switchport nonegotiate 4. switchport mode dynamic desirable
5. switchport mode dynamic auto
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Term
| What is the command to set the trunk encapsulation (to ISL or 802.1Q)? |
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Definition
switchport trunk encapsulation isl
switchport trunk encapsulation dot1q |
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Term
| What does VTP stand for and what does it do? |
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Definition
VLAN Trunking Protocol takes care of creating and naming VLANs on all switches in the system |
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Term
What are the three VTP switch modes?
What do they do? |
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Definition
1. server mode - the switch in charge of VLAN info for the VTP domain, which is stored in vlan.dat in NVRAM
2. client mode - these switches get VLAN info from the server, which are not saved to NVRAM; commands to add/edit VLAN are disabled
3. transparent mode - these switches forward VTP traffic but does not accept changes from the server; VLAN commands take effect locally |
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Term
| What are the four elements required for a switch to properly communicate with VTP? |
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Definition
1. All switches connected by working trunk links
2. Unique domain name configured identically on all switches in the VTP system (vtp domain [name])
3. One server mode switch
4. Same encapsulation / tagging ID (ISL, dot1q) |
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Term
What is the purpose of inter-VLAN routing?
What devices are required?
How does it work? |
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Definition
Route traffic from one VLAN to another
Requires a L3 device to route (router)
Trunk link connecting router to the switch. Then subinterfaces are configured on the router interface for each VLAN. |
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Term
What kind of physical connections can be used for trunking?
What is not required? |
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Definition
Physical links used for trunking:
10 Mbps Ethernet
100 Mbps Ethernet (FastEthernet)
1 Gigabit Ethernet
10 Gigabit Ethernet
Not required:
Full duplex, point to point connectivity |
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Term
| What does portfast do and where is it typically used? |
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Definition
Immediately brings up access or trunk link from blocked to forwarding state. Normally used on ports connecting to an end host, or to trunks. |
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Term
| Aside from the IP address, what needs to be configured on the router subinterfaces for inter-VLAN routing? |
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Definition
For each subinterface:
Router(config-sub-if)#encapsulation dot1q 1 native
or
Router(config-sub-if)#encapsulation dot1q [vlan#] |
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Term
| What kind of interfaces are displayed in the "show vlan" output? |
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Definition
| access mode (non-trunk) ports |
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Term
| What does setting a port to 'switchport trunk native...' do? |
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Definition
| Desginates a VLAN for all untagged (default) traffic? |
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Term
| What is the purpose of the VTP revision number? |
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Definition
| Indicates how current the update is. VTP client will only copy changes from a higher revision update. |
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Term
| What is the difference between configuring a VLAN and a VLAN interface? |
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Definition
VLAN divides a switch at L2 to separate broadcast domains, and have switchports assigned. VLAN interface is a virtual interface that is the only place on a L2 switch that will accept an IP address/mask. VLAN 1 interface is default and used for managing switch remotely. |
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Term
What are the 3 different types of secure MAC addresses in port security?
What are their characteristics? |
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Definition
Static secure: manually configured in the running config & loaded to the mac address table
Dynamic secure: dynamically learned; stored only in the mac address table & does not persist on reboot
Sticky secure: dynamically learned in the mac table; also stored in running config when sticky learning is enabled (which also retroactively adds all dynamically learned entries to config) |
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Term
| What are extended-range VLANs and their restrictions when configured on switches? |
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Definition
VLAN 1025-4096 as defined by 802.1q
Stored in running-config and not vlan.dat
Not supported by VTP (off or transparent mode)
STP extended system ID feature (aka MAC address reduction) must be enabled |
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Term
| What are the conditions where a port security violation occurs? |
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Definition
1. When the maximum number of secure MAC addresses is reached on a secure port a new source MAC tries to connect
2. If a secure MAC address that is configured or learned on one secure port attempts to access another secure port in the same VLAN |
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Term
| What are the characteristics of PVST? |
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Definition
Per-VLAN Spanning Tree
Maintains a separate STP instance for each VLAN configured in the network. (Including separate root bridge, forwarding/disabled ports, etc., per VLAN)
If designed correctly, it can optimize the network traffic. |
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Term
| What are the syntax for configuring the three modes for VTP? |
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Definition
| vtp mode [server | client | transparent] |
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Term
| How can VTP information be cleared on a VTP server? |
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Definition
| delete vlan.dat and reboot |
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