Cisco Systems 8510 CSR, 8540 CSR appendix About Virtual LANs, Configuring ISL Vlan Encapsulation

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Chapter 4 Configuring Interfaces

About Virtual LANs

About Virtual LANs

Virtual LANs enable network managers to group users logically rather than by physical location. A virtual LAN (VLAN) is an emulation of a standard LAN that allows data transfer and communication to occur without the traditional restraints placed on the network. It can also be considered a broadcast domain set up within a switch. With VLANs, switches can support more than one subnet (or VLAN) on each switch, and give routers and switches the opportunity to support multiple subnets on a single physical link. A group of devices on a LAN are configured so that they communicate as if they were attached to the same LAN segment, when they are actually located on different segments. Layer 3 switching supports up to 255 VLANs per system.

VLANs enable efficient traffic separation and provide excellent bandwidth utilization. VLANs also alleviate scaling issues by logically segmenting the physical LAN structure into different subnetworks so that packets are switched only between ports within the same VLAN. This can be very useful for security, broadcast containment, and accounting.

Layer 3 switching software supports a port-based VLAN on a trunk port, which is a port that carries the traffic of multiple VLANs. Each frame transmitted on a trunk link is tagged as belonging to only one VLAN.

Layer 3 switching software supports VLAN frame encapsulation through the Inter-Switch Link (ISL) protocol and the 802.1Q standard.

Note The four adjacent ports (such as 0 through 3, or 4 through 7) on a 10/100 interface must all use the same VLAN encapsulation; that is, either 802.1Q and native, or ISL and native.

Configuring ISL VLAN Encapsulation

ISL is a Cisco protocol for interconnecting multiple switches and maintaining VLAN information as traffic travels between switches.

The VLAN configuration example shown in Figure 4-2depicts the following:

•Fast Ethernet port 1/0/0 and subinterface 1/0/1.1 on the switch router are in bridge group 1. They are part of VLAN 50, which uses ISL encapsulation.

•Fast Ethernet port 3/0/1 and subinterface 1/0/1.2 are in bridge group 2. They are part of VLAN 100, which uses ISL encapsulation.

•Fast Ethernet port 1/0/1 is configured as an ISL trunk.

 

Layer 3 Switching Software Feature and Configuration Guide

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78-6235-04, Cisco IOS Release 12.0(10)W5(18)

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Contents Configuring Interfaces Interface Port Identifier Overview of Interface ConfigurationMedia Access Control Address Routerconfig# interface gigabitethernet 1/0/1 General Instructions for Configuring InterfacesRouter# configure terminal About Layer 3 Switching Interfaces Initially Configuring Gigabit Ethernet Interfaces Command PurposeAbout the Enhanced Gigabit Ethernet Interfaces Catalyst ExampleCommand Description Initially Configuring Fast Ethernet InterfacesVerifying the Ethernet Interface Configuration Router# show interface fastethernet 1/0/0 ExamplesRouter# show interface gigabitethernet 0/0/0 Configuring ISL Vlan Encapsulation About Virtual LANsEnters subinterface configuration mode Routerconfig-subif#Configure the Fast Ethernet main interface Routerconfig-if# Routerconfig# bridge bridge-group protocol ieeeConfiguring 802.1Q Vlan Encapsulation Routerconfig# interface fastethernet 1/0/1.1Routerconfig-subif#interface fastethernet 1/0/0 Routerconfig-subif#interface fastethernet 3/0/1Bridge-group IeeeMonitoring Vlan Operation About Packet over Sonet CatalystAbout the POS OC-12c Uplink Interface POSConfiguring the POS OC-12c Uplink Interface Catalyst Parameter Configuration Command Default Value Default ConfigurationInitially Configuring the POS Interface Automatic Reverting of Clock Source Ip-address subnet-maskHdlc ppp Line internalSetting the MTU Size Customizing the ConfigurationAdditional Configurations Configuring Framing Configuring Sonet OverheadSdh sonet Value j0 value sls0 valueScramble-atm Configuring POS SPE ScramblingScrambling is on by default Configuring Sonet Alarms Alarm Description Configuring Sonet Delay TriggersAlarm Verifying the POS Configuration Lais pais plop prdi slofSlos Triggers line path millisecondRouter# show protocols pos 1/0/0 Router# show controllers pos 2/0/0 LOP = PLM-PRouter# show controller pos 2/0/0 detail Smdr About ATM Uplinks Catalyst About the ATM Uplink InterfaceConfiguring the ATM Uplink Interface Catalyst Configuration OverviewNo loopback No atm sonet stm-1 for OC-3Initially Configuring the ATM Uplink Interface No atm clock internalAtm vc-per-vp Parameter ValueConfiguring the Clock Source Configuring Sonet Framing Routerconfig-if# atm sonetStm-1 ATM interface or to STM-4 for the OC-12c interfaceOverhead c2 byte j0 bytes Msg line j1 16byte exp-msgSls0 is part of the payload pointer byte Line msg line 64byte exp-msgConfiguring Loopback Configuring Virtual Circuits Configuring CDPConfiguring the Maximum VCs per VP Creating a PVCMapping a Protocol Address to a PVC Vpi vci aal-encapIp-address atm-vc vcd NameSwitch Router B Verifying the ATM ConfigurationSwitch Router a 5CB Configuring Interfaces About Port Snooping About Port SnoopingConfiguring Snooping Restrictions on Port SnoopingAbout the Snooping Destination Port About the Snooping Source PortDirection receive transmit both Source-portMonitoring Snooping Show snoop interfaceDestination-port Show snoop78-6235-04, Cisco IOS Release 12.010W518
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