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CHAPTER 4
Configuring Interfaces
This chapter describes basic interface configurations for your Layer 3 switch router. Also included are
sections about configuring virtual LANs (VLANs), packet-over-SONET interfaces, ATM uplink
interfaces, and port snooping.
Unless otherwise noted, the information in this chapter applies to the Catalyst 8540 CSR,
Catalyst 8510 CSR, and Catalyst 8540 MSR with Layer 3 functionality. For further information about
the commands used in this chapter, refer to the comma
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Chapter 4 Configuring Interfaces Overview of Interface Configuration Overview of Interface Configuration A router’s main function is to relay packets from one data link to another. To do that, the characteristics of the interfaces through which the packets are received and sent must be defined. Interface characteristics include, but are not limited to, IP address, address of the port, data encapsulation method, and media type. Many features are enabled on a per-interface basis. Interface co
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Chapter 4 Configuring Interfaces General Instructions for Configuring Interfaces Figure 4-1 Interface Port Identifier Format slot number / subslot number / interface number The port or interface The slot in which the The subslot in which the number on the interface interface module or port interface module or port module or port adapter. adapter is installed. adapter is installed. For a Slots are numbered Numbering always starts full-width interface at 0 and goes from left to starti
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Chapter 4 Configuring Interfaces About Layer 3 Switching Interfaces Step 3 Follow each interface command with the interface configuration commands required for your particular interface. The commands you enter define the protocols and applications that will run on the interface. The commands are collected and applied to the interface command until you enter another interface command, a command that is not an interface configuration command, or you enter end to return to privileged EXEC mode
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Chapter 4 Configuring Interfaces About Layer 3 Switching Interfaces Initially Configuring Gigabit Ethernet Interfaces To configure an IP address and autonegotiation on a Gigabit Ethernet interface, perform the following steps, beginning in global configuration mode: Command Purpose Step 1 Router(config)# interface gigabitethernet Enters Ethernet interface configuration mode to slot/subslot/interface configure the Gigabit Ethernet interface. Router(config-if)# Step 2 Router(config-if)# [no]
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Chapter 4 Configuring Interfaces About Layer 3 Switching Interfaces Initially Configuring Fast Ethernet Interfaces Use the following procedure to assign an IP address to the Fast Ethernet 10BaseT or 100BaseT interface of your switch router so that it can be recognized as a device on the Ethernet LAN. The Fast Ethernet interface supports 10-Mbps and 100-Mbps speeds with Cisco 10BaseT and 100BaseT routers, hubs, switches, and switch routers. Command Description Step 1 Router(config)# interfac
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Chapter 4 Configuring Interfaces About Layer 3 Switching Interfaces Examples The following example shows sample output from the show interface gigabitethernet command: Router# show interface gigabitethernet 0/0/0 GigabitEthernet0/0/0 is administratively down, line protocol is down Hardware is K1 Gigabit Port, address is 00d0.ba1d.3207 (bia 00d0.ba1d.3207) Internet address is 10.1.2.3/8 MTU 1500 bytes, BW 1000000 Kbit, DLY 10 usec, rely 255/255, load 1/255 Encapsulation ARPA, loopbac
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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 rout
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Chapter 4 Configuring Interfaces Configuring ISL VLAN Encapsulation Figure 4-2 Example of an ISL VLAN Bridging Configuration Bridge-group 1 1/0/1.1 1/0/0 VLAN 50 encap isl 50 encap isl 100 Campus Campus switch switch router router VLAN 100 3/0/1 1/0/1.2 Bridge-group 2 To configure the Layer 3 VLANs shown in Figure 4-2, perform the following steps, beginning in global configuration mode: Command Purpose Step 1 Router(config)# interface fastethernet Enters subinterface configuration mode. slot
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Chapter 4 Configuring Interfaces Configuring 802.1Q VLAN Encapsulation Example The following example shows how to configure the interfaces for VLAN bridging with ISL encapsulation shown in Figure 4-2: Router(config)# interface fastethernet 1/0/1.1 Router(config-subif)# encap isl 50 Router(config-subif)# bridge-group 1 Router(config-subif)# interface fastethernet 1/0/0 Router(config-if)# bridge-group 1 Router(config-if)# exit Router(config)# bridge 1 protocol ieee Router(config)# interface f
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Chapter 4 Configuring Interfaces Configuring 802.1Q VLAN Encapsulation Figure 4-3 Example of Bridging Between Native and Non-Native 802.1Q VLANs Bridge-group 1 1/0/1.1 1/0/0 Native VLAN 1 encap dot1q 1 native encap dot1q 100 Campus Campus switch switch router router Non-native VLAN 100 3/0/1 1/0/1.2 Bridge-group 2 To configure the bridging between native VLAN 1 and non-native VLAN 100 depicted in Figure 4-3, perform the following steps: Command Purpose Step 1 Router(config)# interface faste
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Chapter 4 Configuring Interfaces Monitoring VLAN Operation Example The following example shows how to configure the bridging between native and non-native 802.1Q VLANs shown in Figure 4-3: Router(config)# interface fastethernet 1/0/1.1 Router(config-subif)# encap dot1q 1 native Router(config-subif)# bridge-group 1 Router(config-subif)# interface fastethernet 1/0/0 Router(config-if)# bridge-group 1 Router(config-if)# exit Router(config)# bridge 1 protocol ieee Router(config)# interface faste
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Chapter 4 Configuring Interfaces About the POS OC-12c Uplink Interface Because SONET/SDH (Synchronous Digital Hierarchy) is by definition a point-to-point circuit, PPP is well suited for use over SONET links. The octet stream is mapped into the SONET/SDH synchronous payload envelope (SPE) in accordance with RFC 2615, “PPP over SONET/SDH,” and RFC 2615, “PPP in HDLC-like Framing.” Octet boundaries are aligned with the SPE octet boundaries, and the PPP frames are located by row within the SPE
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Chapter 4 Configuring Interfaces Configuring the POS OC-12c Uplink Interface (Catalyst 8540) Figure 4-5 shows an example of a service provider application of the POS OC-12c uplink interface module. Here traffic is aggregated from Catalyst 8500 CSRs over POS OC-12c interfaces to Cisco 12000 GSRs. POS OC-48 interfaces on the Cisco 12000 gigabit switch routers then provide the uplinks to the Internet backbone. Figure 4-5 POS for Aggregated Traffic Uplink to Internet Internet Backbone OC-48c/STM
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Chapter 4 Configuring Interfaces Configuring the POS OC-12c Uplink Interface (Catalyst 8540) Default Configuration Table 4-1 shows the default configuration of an enabled POS OC-12c uplink interface. To change any of these values, see the instructions in the following sections, “Initially Configuring the POS Interface” and “Customizing the Configuration.” Table 4-1 POS OC-12c Uplink Interface Default Configuration Values Parameter Configuration Command Default Value Keepalive [no] keepalive
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Chapter 4 Configuring Interfaces Configuring the POS OC-12c Uplink Interface (Catalyst 8540) To initially configure the POS OC-12c uplink interface, perform the following steps, beginning in global configuration mode: Command Purpose Step 1 Router(config)# ip routing Enables IP routing. Step 2 Router(config)# interface pos Enters interface configuration mode and specifies the POS slot/subslot/interface interface to configure. Router(config-if)# Step 3 Router(config-if)# ip address Assigns a
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Chapter 4 Configuring Interfaces Configuring the POS OC-12c Uplink Interface (Catalyst 8540) Additional Configurations To configure additional properties to match those of the interface at the far end, perform the following steps, beginning in global configuration mode: Command Purpose Step 1 Router(config-if)# no keepalive Turns off keepalive messages. Keepalive messages, though not required, are recommended. Step 2 Router(config-if)# no cdp enable Turns off CDP, which is not required. Ste
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Chapter 4 Configuring Interfaces Configuring the POS OC-12c Uplink Interface (Catalyst 8540) Configuring Framing The default framing mode for the POS OC-12c uplink interface is SONET STS-12c. You can also configure the interface for SDH STM-4, which is more widely used in Europe. To configure the framing mode on the POS OC-12c uplink interface, perform the following steps, beginning in global configuration mode: Command Purpose Step 1 Router(config)# interface pos Enters interface configura
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Chapter 4 Configuring Interfaces Configuring the POS OC-12c Uplink Interface (Catalyst 8540) The value of the c2 byte is determined as follows: • If the value of the c2 byte has not been explicitly configured with the pos flag command, the SONET framer sends the following values: – For Cisco HDLC encapsulation with or without SPE scrambling: 0xCF – For PPP encapsulation with scrambling: 0x16 (RFC 2615) – For PPP encapsulation without scrambling: 0xCF (RFC 2615) • If the value of the c2 byte
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Chapter 4 Configuring Interfaces Configuring the POS OC-12c Uplink Interface (Catalyst 8540) Configuring SONET Alarms The OC-12c POS uplink interface supports SONET alarm monitoring. To configure alarm monitoring, perform the following steps, beginning in global configuration mode: Command Purpose Step 1 Router(config)# interface pos Enters interface configuration mode and specifies the POS slot/subslot/interface interface to configure. Router(config-if)# Step 2 Router(config-if)# pos repor
