VTP is a Cisco proprietary protocol that distributes VLAN information among Catalyst switches. VTP uses ISL or 802.1q encapsulated links to communicate. VTP’s purpose is to ease the administrative burden of managing VLANs, by managing the addition, deletion, and renaming of VLANs.
With VTP, a VTP domain is created for all Catalyst switches that are to be in an administrative domain. VTP operates through VTP messages (multicast messages) that are sent to a particular MAC address (01-00-0C-CC-CC-CC). VTP advertisements only travel through trunk ports and are carried only through VLAN 1.
VTP Switch Modes
Catalyst switches can be configured for one of three different VTP modes. The configuration command is as follows:
set vtp mode [server | client | transparent]
The VTP server maintains a full list of all VLANs within the VTP domain. Information is stored in NVRAM. The server can add, delete, and rename VLANs. The VTP client also maintains a full list of all VLANs. However, it does not store in NVRAM. The client cannot add, delete, or rename VLANs. Any changes made must be received from a VTP server advertisement. The VTPtransparent does not participate in VTP. However, it does pass on a VTP advertisement. VLAN, as defined, is only local to the switch and is stored in NVRAM.
VTP Pruning
A major feature of VTP is VTP pruning, which limits the distribution of broadcasts throughout the VTP domain. As shown in Figure 4-33, a VTP domain has VLANs 1, 2, and 3. If switch S3 does not have users in VLAN 1, no broadcasts are sent to switch S3.
!
interface fastethernet 1/1.3 encapsulation dot1q 30
ip address 192.168.3.1 255.255.255.0
Figure 4-33 VTP Pruning
VTP Configuration
To configure Catalysts for VTP, a VTP domain name is created, and the VTP mode is configured. Options such as VTP pruning can be configured for all or a range of VLANs. Example 4-16 configures VTP domain CCIE with pruning on all eligible ports. Enabling VTP pruning on the server only enables pruning in the VTP management domain. All other devices need to be configured for pruning.
Fast EtherChannel (FEC)
Cisco’s FEC provides a method to increase the bandwidth between two systems by bundling FE links. FEC also provides load sharing and redundancy capabilities. If a link fails in the FEC bundle, the other links take on the rest of the traffic load. Although this discussion focuses on FE, EtherChannel works for 10 Mbps Ethernet links and for GE links.
The requirements for EtherChannel are that all ports must be of the same speed, be in duplex mode, and belong to the same VLAN. Up to four ports are permitted in a bundle.
Example 4-16VTP Configuration
cat5000: (enable) set vtp domain ccie
VTP domain ccie modified
cat5000: (enable) set vtp mode server
VTP domain ccie modified cat5000: (enable)
cat5000: (enable) set vtp pruning enable
This command will enable the pruning function in the entire management domain. All devices in the management domain should be pruning-capable before enabling. Do you want to continue (y/n) [n]? y
VTP domain ccie modified
vlan 1 vlan 2 vlan 3
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FEC Configuration
On a router, FEC is configured by assigning interfaces to a port-channel with the channel-
groupnumbermode on command. The virtual interface is created with the interface port-
channelnumber command. Example 4-17 shows the FEC configuration of two FE interfaces
assigned to channel 1.
On the Catalyst switch, the configuration command is set port channel: cat5000: (enable) set port channel ?
Usage: set port channel <port_list> [on|off|desirable|auto] (example of port_list: 2/1-4 or 2/1-2 or 2/5,2/6)
CDP
CDP is a Cisco proprietary protocol that you use to obtain hardware platforms and addresses of neighboring Cisco devices. CDP is media and protocol independent, and it runs over any Layer- 2 protocol that supports SNAP frames including Ethernet, Frame Relay, and ATM. CDP allows network management stations to retrieve the device type and SNMP IP address of neighboring routers.
CDP is enabled by default. To disable CDP, use the no cdp run global command. CDP can be
disabled per interface with the no cdp enable interface command. In Catalyst OS (CatOS), the command to globally disable CDP is set cdp disable. In CatOS, to disable CDP on a port, use the set cdp disable [mod/port] command.
The router output in Example 4-18 shows the information that can be gathered from show cdp. Example 4-17FEC Configuration on a Router
ag1.hstttx.lab(config)#int fast 2/25
ag1.hstttx.lab(config-if)#channel-group ?
<1-256> Channel group number
ag1.hstttx.lab(config-if)#channel-group 1 mode on
Creating a port-channel interface Port-channel1 ag1.hstttx.lab(config-if)#int fast 2/26
ag1.hstttx.lab(config-if)#channel-group 1 mode on
ag1.hstttx.lab(config-if)#exit
ag1.hstttx.lab(config)#interface port-channel ?
<1-256> Port-channel interface number
ag1.hstttx.lab(config)#interface port-channel 1 channel-group 1 mode on
channel-group 1 mode on
To find out about neighboring Cisco routers or switches, use the show cdp neighbors com- mand, which gives summary information of each router. Example 4-19 shows the output of the
show cdp neighbors command. The router has two neighbors, called R7 and R9, which are
Cisco 2500 routers.
You use the same command on a Catalyst switch. Example 4-20 shows the output of the show
cdp neighbor command of a switch. This switch has six neighboring routers (one MC3810 and
five Cisco 2500s), which are marked with an R that describes router capabilities.
To get more detailed information about neighboring routers, use the show cdp neighbors detail
command, as shown in Example 4-21. From the output, you can gather neighbor information such as name, IP address, platform type, and IOS version.
Example 4-18Router show cdp Command Output
R8#show cdp ?
entry Information for specific neighbor entry interface CDP interface status and configuration neighbors CDP neighbor entries
traffic CDP statistics | Output modifiers <cr>
Example 4-19Router show cdp neighbors Command Output
R8#show cdp neighbors
Capability Codes: R - Router, T - Trans Bridge, B - Source Route Bridge S - Switch, H - Host, I - IGMP, r - Repeater
Device ID Local Intrfce Holdtme Capability Platform Port ID R7 Ser 1 133 R 2500 Ser 1 R9 Tok 0 176 R 2500 Tok 0
Example 4-20Switch show cdp neighbor Command Output
cat5000: (enable) show cdp neighbor
Capability Codes: R - Router, T - Trans Bridge, B - Source Route Bridge S - Switch, H - Host, I - IGMP, r - Repeater
Port Device-ID Port-ID Platform Capability --- --- --- --- -- 2/4 R3 Ethernet0 Cisco MC3810 R 2/5 R5 Ethernet0 cisco 2500 R 2/7 R7 Ethernet0 cisco 2500 R 2/9 R9 Ethernet0 cisco 2500 R 2/10 R10 Ethernet0 cisco 2500 R 2/11 R6 Ethernet0 cisco 2500 R Device ID Platform R7 2500 R9 2500 Platform Capability
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