Quick
Notes - VLANS
What are VLANs?
VLANs are broadcast domains in a Layer 2 network. Each broadcast domain is like a distinct virtual bridge within the switch. Each virtual bridge you create in a switch defines a broadcast domain. By default, traffic from one VLAN cannot pass to another VLAN. Each of the users in a VLAN is also in the same IP subnet, and each switch port can belong to only one VLAN.
What are the three characteristics of a typical VLAN setup?
The three characteristics of a typical VLAN setup are:
Each logical VLAN is like a separate physical bridge.
VLANs can span multiple switches.
Trunks carry traffic for multiple VLANs.
What are trunk links?
By default, each port on a switch can belong to only one VLAN. For devices that are in VLANs (that span multiple switches) to talk to other devices in the same VLAN, you must use trunking or have a dedicated port per VLAN. Trunk links allow the switch to carry multiple VLANs across a single link.
What are the two methods you can use to assign a port to a VLAN?
The two methods to assign a port to a VLAN are
Statically
Dynamically
What is Inter-Switch Link (ISL)?
ISL is a Cisco proprietary protocol used to interconnect switches that have multiple VLANs. It maintains VLAN information as traffic goes between switches, allowing the traffic to enter the correct VLAN. ISL operates in a point-to-point environment.
At which layer of the OSI model does ISL function?
ISL functions at Layer 2 of the OSI model. It encapsulates a data frame with a new ISL header and CRC. Because ISL operates at Layer 2 of the OSI model, it is protocol-independent.
What type of tagging method does ISL use?
Many network professions refer to the way ISL tags frames as an external tagging mechanism. This is because ISL encapsulates each frame and does not modify the original packet.
Many network professions refer to the way ISL tags frames as an external tagging mechanism. This is because ISL encapsulates each frame and does not modify the original packet.
How many extra bytes does ISL add to an existing Ethernet frame?
ISL adds a 26-byte ISL header and a 4-byte CRC to each frame, extending each Ethernet frame by 30 bytes. ISL tagging is implemented in ASICs, so tagging is done at wire speed.
What is VTP?
VLAN Trunking Protocol (VTP) is a Layer 2 messaging protocol that maintains VLAN configuration consistency throughout a common administrative domain by managing VLANs' additions, deletions, and name changes across multiple switches. Without VTP, you would have to add VLAN information in all switches in your network.
What is a VTP domain?
A VTP domain is one or more interconnected switches that share the same VTP environment. A switch can be in only one VTP domain, and all VLAN information is propagated to all switches in the same VTP domain.
What are the three VTP modes?
The three VTP modes are
Server
Client
Transparent
What is VTP server mode?
A switch in VTP server mode can add, delete, and modify VLANs and other configuration parameters for the entire VTP domain. This is the default mode for all Catalyst switches. VLAN configurations are saved in NVRAM. When you change VLAN configuration in server mode, the change is dynamically propagated to all switches in the VTP domain.
What is VTP client mode?
In VTP client mode, a switch cannot create, delete, or modify VLANs. Also, a VTP client does not save VLAN information and configuration in NVRAM. In client and server mode, VLAN information is synchronized between switches in the VTP domain.
What is VTP transparent mode?
In transparent mode, a switch can add, modify, and delete VLANs. This information is not transmitted to other switches in the VTP domain. They affect only the local switch. VTP transparent mode is used when a switch does not need to participate in the VTP domain but needs to propagate VTP information to other switches.
How often are VTP advertisements flooded throughout the management domain?
VTP advertisements are flooded throughout the management domain every 5 minutes or whenever a change occurs in VLAN configuration.
What is included in VTP advertisements?
VTP advertisements include the following:
VTP revision number
VLAN names and numbers
Information about switches that have ports assigned to each VLAN
What is one of the most important components of the VTP advertisement?
The revision number is one of the most important components of the VTP advertisement. Every time a VTP server modifies its VLAN configuration, it increments the configuration number by 1. The largest configuration number in the VTP domain contains the most current information. When a client receives a revision number higher than its current number, it updates its VLAN configuration.
On a Catalyst 1900 switch, how do you reset the configuration number?
To reset the configuration numbers on a Catalyst 1900, use the delete vtp privileged EXEC command, and then reset the switch.
What is VTP pruning?
By default, a trunk link carries traffic for all VLANs in the VTP domain. Even if a switch does not have any ports in a specific VLAN, traffic for that VLAN is carried across the trunk link. VTP pruning uses VLAN advertisements to determine when a trunk connection is needlessly flooding traffic to the trunk links that the traffic must use to access the appropriate network device.
How many VLANs with a separate spanning tree per VLAN does the Catalyst 1900 support?
The Catalyst 1900 supports 64 VLANs with a separate spanning tree per VLAN.
What VLAN number are CDP and VTP advertisements sent across?
CDP and VTP advertisements are sent on VLAN 1, which is also known as the management VLAN.
What must you remember before you create VLANs on a Catalyst switch?
Before you create VLANs on a Catalyst 1900 switch, the switch must be in VTP server mode or VTP transparent mode.
How do you configure the VTP operation mode on a Catalyst 1900?
To configure VTP on a Catalyst 1900, use the vtp [server transparent client] global configuration command:
Cat1900(config)#vtp server
How do you configure a VTP domain on a Catalyst 1900 switch?
To configure a VTP domain on a Catalyst 1900 switch, use the vtp domain domain-name global command:
Cat1900(config)#vtp domain cisco
How do you configure a VTP domain password on a Catalyst 1900?
Use the vtp password password global command to configure a VTP domain password. This example sets the VTP password to cisco:
Cat1900(config)#vtp password cisco
What does the show vtp privileged EXEC command display?
The show vtp privileged EXEC command displays the following:
VTP version
The number of existing VLANs on a switch and the maximum number of locally supported VLANs
VTP domain name, password, and operating mode
Whether VTP pruning is enabled
The last time VLAN configuration was modified.
Here's an example of show vtp output:
Cat1900#show vtp
VTP version: 1
Configuration revision: 0
Maximum VLANs supported locally: 1005
Number of existing VLANs: 5
VTP domain name : cisco
VTP password : cisco
VTP operating mode : Server
VTP pruning mode : Disabled
VTP traps generation : Enabled
Configuration last modified by: 192.168.0.2 at 00-00-0000 00:00:00
What command do you use to add a VLAN on a Catalyst switch?
To add a VLAN on a Catalyst switch, use the vlan vlan-number [name vlan_name] global command. The following example adds VLAN 10 with a name of Sales: Cat1900(config)#vlan 10 name Sales
What Catalyst 1900 command can you use to verify VLAN information?
To verify VLAN information, use the show vlan vlan-number privileged EXEC command.
How do you view spanning tree information for a particular VLAN?
A Catalyst 1900 switch can have a maximum of 64 VLANs with a separate instance of spanning tree per VLAN. To view spanning tree information for a particular VLAN use the "show spandtree vlan-id" command.
VLANs are broadcast domains in a Layer 2 network. Each broadcast domain is like a distinct virtual bridge within the switch. Each virtual bridge you create in a switch defines a broadcast domain. By default, traffic from one VLAN cannot pass to another VLAN. Each of the users in a VLAN is also in the same IP subnet, and each switch port can belong to only one VLAN.
What are the three characteristics of a typical VLAN setup?
The three characteristics of a typical VLAN setup are:
Each logical VLAN is like a separate physical bridge.
VLANs can span multiple switches.
Trunks carry traffic for multiple VLANs.
What are trunk links?
By default, each port on a switch can belong to only one VLAN. For devices that are in VLANs (that span multiple switches) to talk to other devices in the same VLAN, you must use trunking or have a dedicated port per VLAN. Trunk links allow the switch to carry multiple VLANs across a single link.
What are the two methods you can use to assign a port to a VLAN?
The two methods to assign a port to a VLAN are
Statically
Dynamically
What is Inter-Switch Link (ISL)?
ISL is a Cisco proprietary protocol used to interconnect switches that have multiple VLANs. It maintains VLAN information as traffic goes between switches, allowing the traffic to enter the correct VLAN. ISL operates in a point-to-point environment.
At which layer of the OSI model does ISL function?
ISL functions at Layer 2 of the OSI model. It encapsulates a data frame with a new ISL header and CRC. Because ISL operates at Layer 2 of the OSI model, it is protocol-independent.
What type of tagging method does ISL use?
Many network professions refer to the way ISL tags frames as an external tagging mechanism. This is because ISL encapsulates each frame and does not modify the original packet.
Many network professions refer to the way ISL tags frames as an external tagging mechanism. This is because ISL encapsulates each frame and does not modify the original packet.
How many extra bytes does ISL add to an existing Ethernet frame?
ISL adds a 26-byte ISL header and a 4-byte CRC to each frame, extending each Ethernet frame by 30 bytes. ISL tagging is implemented in ASICs, so tagging is done at wire speed.
What is VTP?
VLAN Trunking Protocol (VTP) is a Layer 2 messaging protocol that maintains VLAN configuration consistency throughout a common administrative domain by managing VLANs' additions, deletions, and name changes across multiple switches. Without VTP, you would have to add VLAN information in all switches in your network.
What is a VTP domain?
A VTP domain is one or more interconnected switches that share the same VTP environment. A switch can be in only one VTP domain, and all VLAN information is propagated to all switches in the same VTP domain.
What are the three VTP modes?
The three VTP modes are
Server
Client
Transparent
What is VTP server mode?
A switch in VTP server mode can add, delete, and modify VLANs and other configuration parameters for the entire VTP domain. This is the default mode for all Catalyst switches. VLAN configurations are saved in NVRAM. When you change VLAN configuration in server mode, the change is dynamically propagated to all switches in the VTP domain.
What is VTP client mode?
In VTP client mode, a switch cannot create, delete, or modify VLANs. Also, a VTP client does not save VLAN information and configuration in NVRAM. In client and server mode, VLAN information is synchronized between switches in the VTP domain.
What is VTP transparent mode?
In transparent mode, a switch can add, modify, and delete VLANs. This information is not transmitted to other switches in the VTP domain. They affect only the local switch. VTP transparent mode is used when a switch does not need to participate in the VTP domain but needs to propagate VTP information to other switches.
How often are VTP advertisements flooded throughout the management domain?
VTP advertisements are flooded throughout the management domain every 5 minutes or whenever a change occurs in VLAN configuration.
What is included in VTP advertisements?
VTP advertisements include the following:
VTP revision number
VLAN names and numbers
Information about switches that have ports assigned to each VLAN
What is one of the most important components of the VTP advertisement?
The revision number is one of the most important components of the VTP advertisement. Every time a VTP server modifies its VLAN configuration, it increments the configuration number by 1. The largest configuration number in the VTP domain contains the most current information. When a client receives a revision number higher than its current number, it updates its VLAN configuration.
On a Catalyst 1900 switch, how do you reset the configuration number?
To reset the configuration numbers on a Catalyst 1900, use the delete vtp privileged EXEC command, and then reset the switch.
What is VTP pruning?
By default, a trunk link carries traffic for all VLANs in the VTP domain. Even if a switch does not have any ports in a specific VLAN, traffic for that VLAN is carried across the trunk link. VTP pruning uses VLAN advertisements to determine when a trunk connection is needlessly flooding traffic to the trunk links that the traffic must use to access the appropriate network device.
How many VLANs with a separate spanning tree per VLAN does the Catalyst 1900 support?
The Catalyst 1900 supports 64 VLANs with a separate spanning tree per VLAN.
What VLAN number are CDP and VTP advertisements sent across?
CDP and VTP advertisements are sent on VLAN 1, which is also known as the management VLAN.
What must you remember before you create VLANs on a Catalyst switch?
Before you create VLANs on a Catalyst 1900 switch, the switch must be in VTP server mode or VTP transparent mode.
How do you configure the VTP operation mode on a Catalyst 1900?
To configure VTP on a Catalyst 1900, use the vtp [server transparent client] global configuration command:
Cat1900(config)#vtp server
How do you configure a VTP domain on a Catalyst 1900 switch?
To configure a VTP domain on a Catalyst 1900 switch, use the vtp domain domain-name global command:
Cat1900(config)#vtp domain cisco
How do you configure a VTP domain password on a Catalyst 1900?
Use the vtp password password global command to configure a VTP domain password. This example sets the VTP password to cisco:
Cat1900(config)#vtp password cisco
What does the show vtp privileged EXEC command display?
The show vtp privileged EXEC command displays the following:
VTP version
The number of existing VLANs on a switch and the maximum number of locally supported VLANs
VTP domain name, password, and operating mode
Whether VTP pruning is enabled
The last time VLAN configuration was modified.
Here's an example of show vtp output:
Cat1900#show vtp
VTP version: 1
Configuration revision: 0
Maximum VLANs supported locally: 1005
Number of existing VLANs: 5
VTP domain name : cisco
VTP password : cisco
VTP operating mode : Server
VTP pruning mode : Disabled
VTP traps generation : Enabled
Configuration last modified by: 192.168.0.2 at 00-00-0000 00:00:00
What command do you use to add a VLAN on a Catalyst switch?
To add a VLAN on a Catalyst switch, use the vlan vlan-number [name vlan_name] global command. The following example adds VLAN 10 with a name of Sales: Cat1900(config)#vlan 10 name Sales
What Catalyst 1900 command can you use to verify VLAN information?
To verify VLAN information, use the show vlan vlan-number privileged EXEC command.
How do you view spanning tree information for a particular VLAN?
A Catalyst 1900 switch can have a maximum of 64 VLANs with a separate instance of spanning tree per VLAN. To view spanning tree information for a particular VLAN use the "show spandtree vlan-id" command.
Quick
Notes - TCP / IP
What are the four layers of the TCP/IP layer model?
The
four layers of the TCP/IP layer model are:
Application (process)
Host-to-host (transport)
Internet
Network Access (physical and data link)
What two protocols function at the transport (host-to-host) layer of the TCP/IP model?
Application (process)
Host-to-host (transport)
Internet
Network Access (physical and data link)
What two protocols function at the transport (host-to-host) layer of the TCP/IP model?
The
two protocols that function at the host-to-host layer of the TCP/IP model are
TCP and UDP. (TCP is a connection-oriented, reliable protocol. UDP is a
connectionless and unacknowledged protocol.)
What are the protocol numbers for TCP and UDP?
What are the protocol numbers for TCP and UDP?
The
protocol number for TCP is 6. The protocol number for UDP is 17.
How many bytes are in the header for TCP and UDP packets?
How many bytes are in the header for TCP and UDP packets?
A
TCP header contains 20 bytes, and a UDP header contains 8 bytes.
What are TCP and UDP port numbers?
What are TCP and UDP port numbers?
To
pass information (such as e-mail) to upper layers, TCP and UDP use port
numbers. These port numbers are used to keep track of different conversations
among different hosts at the same time. Originating source port numbers are
dynamically assigned by the source host, which is a number greater than 1023.
What is the number range for "well-known" port numbers?
What is the number range for "well-known" port numbers?
Defined
in RFC 1700, the well-known port numbers are 1 to 1023.
What are the steps for the TCP three-way handshake?
The steps for the TCP three-way handshake are as follows:
Step 1. The source host sends a SYN to the destination host.
Step 2. The destination host replies with a SYN/ACK to the source host.
Step 3. The source host replies with an ACK.
What are some protocols that operate at the TCP/IP Internet layer?
What are the steps for the TCP three-way handshake?
The steps for the TCP three-way handshake are as follows:
Step 1. The source host sends a SYN to the destination host.
Step 2. The destination host replies with a SYN/ACK to the source host.
Step 3. The source host replies with an ACK.
What are some protocols that operate at the TCP/IP Internet layer?
Some
protocols that operate at the TCP/IP Internet layer are
IP
ICMP
ARP
RARP
IP
ICMP
ARP
RARP
What is the Internet Protocol (IP)?
IP
is a connectionless protocol that provides best-effort delivery routing of
datagrams.
What is the Internet Control Message Protocol (ICMP)?
What is the Internet Control Message Protocol (ICMP)?
ICMP
is a management protocol for IP. ICMP messages are carried in IP datagrams and
are used to send error and control messages. An example of a utility that uses
ICMP is ping.
What is the Address Resolution Protocol (ARP)?
What is the Address Resolution Protocol (ARP)?
ARP
is used to resolve a known IP address to a MAC address. In order for a host to
communicate with another host, it must know the MAC address of the destination
host (if they are on the same network) or next hop router. This is the reason
for ARP.
What is the Reverse Address Resolution Protocol (RARP)?
What is the Reverse Address Resolution Protocol (RARP)?
RARP
is a protocol used to find the IP address of a station that knows its MAC
address. It is mainly used for diskless workstations that boot up and need an
IP address. An RARP request is a broadcast packet.
What are the IP address ranges for Class A, Class B, and Class C addresses?
What are the IP address ranges for Class A, Class B, and Class C addresses?
The
address ranges are as follows: Class A 1.0.0.0 to 126.0.0.0Class B 128.0.0.0 to
191.255.0.0Class C 192.0.0.0 to 223.255.255.0
What does RFC 1918 define?
What does RFC 1918 define?
RFC
1918 defines reserved (private) networks and addresses that are not routed on
the Internet. These addresses are 10.0.0.0 to 10.255.255.255, 172.16.0.0 to
172.31.255.255, and 192.168.0.0 to 192.168.255.255. They are used as internal
private addresses. Private addresses are widely used today, along with proxy
servers and Network Address Translation to assist with "stretching"
the current IP address space.
Cisco IOS software supports what three kinds of broadcasts?
Cisco IOS software supports what three kinds of broadcasts?
The
three kinds of broadcasts that Cisco IOS software supports are:
Flooding
Directed broadcast
All-subnet broadcast
Flooded broadcasts are local broadcasts that have an address of 255.255.255.255. They are not propagated by a router.
Direct broadcasts are directed to a specific network. They contain all 1s in the host portion of the address. Routers forward these broadcasts. An example is 192.168.0.255/24.
All-subnet broadcast are broadcast messages to all hosts within a subnet and to all subnets within a network. An example is 192.168.255.255/24. With Cisco IOS release 12.0, a router does not forward all subnet broadcasts. You can use the ip directed-broadcast command to enable all subnet broadcasts.
Flooding
Directed broadcast
All-subnet broadcast
Flooded broadcasts are local broadcasts that have an address of 255.255.255.255. They are not propagated by a router.
Direct broadcasts are directed to a specific network. They contain all 1s in the host portion of the address. Routers forward these broadcasts. An example is 192.168.0.255/24.
All-subnet broadcast are broadcast messages to all hosts within a subnet and to all subnets within a network. An example is 192.168.255.255/24. With Cisco IOS release 12.0, a router does not forward all subnet broadcasts. You can use the ip directed-broadcast command to enable all subnet broadcasts.
How do you assign an IP address to a Cisco router?
To
assign an IP address to a router, use the ip address address subnet-mask
interface configuration command. Here's an example:
RouterB(config)#inter e0
RouterB(config-if)#ip address 172.16.0.1 255.255.0.0
RouterB(config-if)#no shut
Note: By default all interfaces on a Cisco router are administratively disabled. To enable them you must use the "no shut" interface command.
How do you manually assign IP addresses to host names in a Cisco router?
RouterB(config)#inter e0
RouterB(config-if)#ip address 172.16.0.1 255.255.0.0
RouterB(config-if)#no shut
Note: By default all interfaces on a Cisco router are administratively disabled. To enable them you must use the "no shut" interface command.
How do you manually assign IP addresses to host names in a Cisco router?
The
ip host name [tcp-port-number] address [address] global configuration command
lets you assign IP addresses to host names in a Cisco router. [tcp-port-number]
is an optional parameter; the default value is Telnet. Here's an example:
RouterB(config)#ip host cisco 172.16.0.1
What Cisco IOS command can you use to program the router to use a DNS server to resolve host names?
RouterB(config)#ip host cisco 172.16.0.1
What Cisco IOS command can you use to program the router to use a DNS server to resolve host names?
The
ip name-server server-address [[server-address2]...[server-address6]] command
lets you program the Cisco router to resolve host names with a DNS server.
Here's an example:
RouterB(config)#ip name-server 172.16.0.250
RouterB(config)#ip name-server 172.16.0.250
If you enter a command that a Cisco router does not recognize, the
router tries to resolve the command you just entered with a DNS server. How do
you turn off this DNS domain lookup?
To
turn off DNS domain lookup, use the no ip domain-lookup global command.
Here's
an example: RouterB#enb
Translating "enb"...domain server (255.255.255.255)% Unknown command or computer name, or unable to find computer address
RouterB#config t
Enter configuration commands, one per line. End with CNTL/Z.
RouterB(config)#no ip domain-lookup
Translating "enb"...domain server (255.255.255.255)% Unknown command or computer name, or unable to find computer address
RouterB#config t
Enter configuration commands, one per line. End with CNTL/Z.
RouterB(config)#no ip domain-lookup
For different VLANs to communicate with each other, they need to be
routed (a router!). To perform inter-VLAN routing, what two things must occur?
To
perform inter-VLAN routing, the following must occur:
The router must know how to reach all VLANs being interconnected.
The router must have a separate physical connection on the router for each VLAN, or trunking must be enabled on a single physical connection.
The router must know how to reach all VLANs being interconnected.
The router must have a separate physical connection on the router for each VLAN, or trunking must be enabled on a single physical connection.
How do you enable ISL trunking on a Cisco router?
To
enable ISL trunking on a Cisco router, you must do the following:
Step 1 Configure subinterfaces on the router's physical Fast Ethernet or Gigabit interface. (ISL trunking works only on Fast Ethernet or Gigabit interfaces.)
Step 2 Assign an IP address to the subinterface.
Step 3 Enable ISL encapsulation for the particular VLAN with the encapsulate isl vlan# subinterface command.
Here's an example:
RouterB(config)#int f0/0
RouterB(config-subif)#ip address 172.16.0.1 255.255.0.0
RouterB(config-subif)#encapsulation isl 1
Step 1 Configure subinterfaces on the router's physical Fast Ethernet or Gigabit interface. (ISL trunking works only on Fast Ethernet or Gigabit interfaces.)
Step 2 Assign an IP address to the subinterface.
Step 3 Enable ISL encapsulation for the particular VLAN with the encapsulate isl vlan# subinterface command.
Here's an example:
RouterB(config)#int f0/0
RouterB(config-subif)#ip address 172.16.0.1 255.255.0.0
RouterB(config-subif)#encapsulation isl 1
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