Networking II Exam #2
Terms in this set (39)
What is a broadcast domain?
A group of devices receiving broadcast frames which are initiated from any device in the group
What is a collision domain?
A group of computers on the same Ethernet network that can be affected by a common collision.
What terminates a collision domain?
Routers, switches, bridges.
What terminates a broadcast domain?
What is the difference between a bridge and a switch
One is a single aspect of itself, while one is a multiple of the other. Bridges operate with software, and switches operate with hardware.
How can a switch make a network more secure?
What is spanning tree protocol (STP)?
This is used to stop loops. As frames are forwarded, this lowers or eliminates the risk of that frame being caught in a loop and degrading network performance.
What is IEEE 802.1d?
this was created by IEEE. It's a standard version of STP.
What are bridge protocol data units (BPDUs)?
This is how STP allows communication among switches. These are multicast frames that send data between switches and allow communications between them.
What are 4 stages used by STP (Spanning-tree protocol)?
Blocking state: frames are not forwarded. The switch will still listen to BPDUs.
Listening state: Listens to BPDUs to ensure that no loops occur on the network before passing frames on.
Learning state: Learns MAC address and builds a filter table but does not forward frames.
Forwarding state: Sends and receives all data on the port.
What is a root bridge?
This is all designated ports.
What is a non-root bridge?
This is either non-designated ports, or designated ports.
How is a root bridge determined?
by priority assigned to the switch. If switches have the same priority, then the switch with the lowest MAC address is designated as the root bridge.
What is a designated port?
operates in the forwarding state, thus it can send and receive traffic.
What is a non-designated port?
operates in the blocking state, thus it does not forward traffic.
What are the three basic switching modes?
Store and forward, cut-through (real time), and fragment free
Store and forward
The switch copies the entire frame to if buffers, calculates the CRC. If the CRCs do not match, the frame is discarded. Also the frame is discarded if the frame is too short(less than 64 bytes) or too long(greater than 1518 bytes).
Cut-through (real time)
The switch copies only the destination address in to its buffers, looks up the forwarding port in its filter tables, and forwards the frame to its destination. This provides a faster operation since the frame is forwarded as soon as its destination address is read. Some switches can be configured to perform cut-through until a threshold level is reached. It then changes to store-and-forward mode in order to stop forwarding corrupted frames. When the error rate falls below a predetermined error level, the port automatically changes back to cut-through
This is modified cut-through method. The switch checks the first 64 bytes of a frame for fragmentation. usually, when a collision occurs, it occurs at the start of a frame. This is the first 64 bytes appears to be in order, the switch will begin to forward the frame. This is the default method of the Cisco 1900 switch.
What are the security considerations for a VLAN?
In a broadcast domain, since all devices can see all other devices, there is nothing to stop any device from responding to a broadcast packet.
- Any device can interrogate any other device's security, such as a password.
- Users can join a workgroup just by plugging into the existing hub.
- A network analyzer could be plugged into an existing hub and thus all traffic on that workgroup could be seen.
Two basic methods of defining VLAN boundaries:
- End to end VLANs: span the entire switch fabric from end to end. All switches in the end-to-end understand all configured VLANs. VLANs are configured by function, project, department, not by physical location. The administrator defines the port that a user is connected to.
- Local VLANs: VLANs are configured by physical location and not by function, project, department. in a centralized server configuration, local VLANs are easier to manage.
What is the 80/20 rule
try to keep 80% of the traffic within the VLAN. Only 20% should extend outside the VLAN.
As a frame traverses a switch fabric, it is tagged with a VLAN ID, such that the network can keep track of which VLAN it belongs to. As the frame travels over a trunk link, it retains its VLAN ID. As it exits the trunk line onto an access link, the switch removes the VLAN ID. The end device receives the frame without having to process the VLAN ID.
What is ISL?
This is a Cisco proprietary protocol used only by Cisco. It tags VLAN information onto the Ethernet frame. The original frame is not altered but encapsulated into an new 26 byte header.
What is IEEE 802.1q
This protocol should be used on non Cisco equipment. This differs from ISL in that it uses an internal tagging process. This internal method changes the ethernet frame by adding the VLAN information to a field within the frame itself. Thus, the frame looks like a standard Ethernet frame and can travel on both access links and trunk links.
What is IEEE 802.3ac?
Because of added length of the Ethernet frames, this must be involved. This additional tag is 4 bytes and it is inserted between the Source field and Length field.
LAN emulation (LANE)
used to communicate multiple VLANs over ATM
IEEE 802.10 FDDI
Used to send VLAN info over FDDI
What is an access link?
each port can only be a member of 1 VLAN. Ports can be assigned both dynamically and statically.
What is a trunk link?
this must carry traffic to and from all VLANs.
What is the default VLAN?
What is FastEthernet?
What is Gigabit Ethernet lines?
Category 6 cable (cat 6)
Three functions of a switch
- Address learning: access the source MAC address of a frame, and enter it into a MAC filter table.
- Forward/Filter decisions: When a frame is received on a switch port, the switch looks up the correct port of the destination MAC address in the MAC filter table.
- Loop avoidance: If multiple switches and multiple links are used in the network, loops can occur.
4 methods of frame tagging
3. LAN emulation
4. 802.10 FDDI
only supported on fast Ethernet and gigabit Ethernet
Default mode of VTP (VLAN trunk protocol)
If a link connecting a switch and a workstation, or subnet is associated with only 1 VLAN, then it is called an access link
If the trunk link carries info from many VLANS, it is called a trunk link.
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