# Configuring the Physical Interface

This section describes how to complete the basic configuration for a Fast Ethernet, Gigabit Ethernet, or 10-Gigabit Ethernet interface. CLI examples are provided with the individual command descriptions.

To configure an Ethernet interface:

1. Select an Ethernet interface.
2. (Optional) Specify the line speed and duplex mode.
3. (Optional) Specify the MTU.
4. (Optional) Set the time interval at which the router records bit and packet rates.
5. (Optional) Associate a name with the interface.
6. (Optional) Validate MAC addresses on a per interface basis.
7. (Optional) Enable the debounce timer and set the time interval that the interface waits before reporting a state change to the upper-layer protocols.
8. (Optional) Modify the interval that the interface waits before reporting a state change to the upper-layer protocols.

debounce

- Use to enable the debounce configuration and set the interval, in seconds, for which an interface must maintain a given state—for example, up or down—before the interface reports the state change to the upper-layer protocols.

  | Note: Debounce configuration is supported for all Ethernet module combinations on E Series routers.

- When a link briefly goes up or down, the momentary loss of signal can cause a temporary service interrution for connection-oriented protocols such as PPPoE. Configuring the debounce interval prevents the router from prematurely tearing down and rebuilding the PPPoE connections during such brief network outages.
- Specify the interval, in seconds, for which an interface must maintain a given state before the state change is reported to the upper-layer links. The range is 1–5 seconds and the default interval is 1 second.
- Observe the following guidelines when you configure the debounce feature for Ethernet interfaces:
  - In networks where a link alternates between the up and down state for brief periods, we recommend that you set a longer debounce interval to prevent the router from prematurely and unnecessarily tearing down and rebuilding the PPPoE connections during brief network outages.
  - In networks where the interface changes to a down state and remains in the down state for long periods of time, we recommend that you set a shorter debounce interval to minimize the latency (delay) required for the interface to notify the upper-layer protocols of the state change. When you set a longer debounce interval, the latency increases.
  - We recommend that you disable the debounce feature in networks that require faster link status notifications to upper links.
  - The debounce feature is not supported for Ethernet interfaces on which either IEEE 802.3ad link aggregation is configured.
- The setting of the debounce command persists after you reboot the router.
- Example
  host1(config-if)#debounce 3
- Use the no version to restore the default behavior, which disables debounce on the interface.
- See debounce.

debounce-interval

- Use to modify the minimum time an Ethernet interface must maintain a given state—for example, up or down—before the interface notifies the upper-layer protocols of the state change. The interval can be in the range 1–5 seconds.

  | Note: Debounce configuration is supported for all Ethernet module combinations on E Series routers.

- You can configure this command only if you have enabled the debounce timer feature using the debounce command. After you enable this feature, you can use the debounce-interval command to modify the debounce interval.
- The setting of the debounce-interval command persists after you reboot the router.
- Example
  host1(config-if)#debounce—interval 4
- Use the no version to restore the default value, 1 second.
- See debounce-interval.

duplex

- Use to specify the duplex mode.
- This command also works on the Fast Ethernet port on the SRP module on all E Series routers. For more information, see JunosE System Basics Configuration Guide.

  | Note: If you set either the line speed or duplex mode to automatically negotiate by using the automatically negotiate keyword, the router negotiates both parameters. You can specify different values to prevent the router from negotiating these parameters. Automatic negotiation is not supported for the FE-8 SFP I/O module. For this I/O module, full duplex mode is the default.

- Example
  host1(config-if)#duplex full
- Use the no version to revert to the default, either automatically negotiate or full duplex (FE-8 SFP I/O module only)
- See duplex.

ethernet description

- Use to associate a text description of up to 64 characters with an Ethernet interface.
- This command does not work for the Fast Ethernet port on the SRP module.
- The description is displayed in the output for show configuration, show interfaces fastEthernet, show interfaces gigabitEthernet, and show interfaces tenGigabitEthernet commands.
- Example
  host1(config-if)#ethernet description abcd1234
- Use the no version to remove the description from the interface.
- See ethernet description.

interface fastEthernet

- Use to select a Fast Ethernet interface on a line module.
- You can also use it to select a Fast Ethernet management port on an SRP I/O module (ERX7xx models, ERX14xx models, and the ERX310 router) or an SRP IOA (E120 and E320 routers). For information about managing the Fast Ethernet port on the SRP module, see JunosE System Basics Configuration Guide.
- Use the slot/port [.subinterface] format for Fast Ethernet interfaces on ERX7xx models, ERX14xx models, and the ERX310 router . Use the slot/adapter/port format for the SRP IOA on the E120 or E320 routers; the port on the SRP IOA is always identified by 0.
- Example 1—Selects a Fast Ethernet interface on ERX7xx models, ERX14xx models, or the ERX310 router
  host1(config)#interface fastEthernet 1/0
- Example 2—Selects the Fast Ethernet management port on an E320 router
  host1(config)#interface fastEthernet 6/0/0
- Use the no version to remove IP from an interface or subinterface. You must issue the no version from the highest level down; you cannot remove an interface or subinterface if the one above it still exists.
- See interface fastEthernet.

interface gigabitEthernet

- Use to select a Gigabit Ethernet interface.

  | Note: On the GE I/O module, you can configure only the primary port, 0. The router automatically uses the redundant port, 0R, if the primary port fails. On the GE-2 SFP I/O module, you can configure only the primary ports, 0 and 1. The router automatically uses the corresponding redundant port, 0R or 1R, if the primary port fails. On the OC3-2 GE APS I/O module, you can configure only port 2. Ports 0 and 1 are reserved for OC3/STM1 ATM interfaces. This I/O module does not support redundant ports in the current release. On the ES2-S1 GE-4 IOA, you can configure all four ports. On the ES2-S1 GE-8 IOA, you can configure all eight ports.

- Use the slot/port [.subinterface] format for Gigabit Ethernet interfaces on ERX7xx models, ERX14xx models, or the ERX310 router; use the slot/adapter/port format for Gigabit Ethernet interfaces on the E120 and E320 routers.
- Example 1—Selects a Gigabit Ethernet interface on ERX7xx models, ERX14xx models, and the ERX310 router
  host1(config)#interface gigabitEthernet 1/0 host1(config)#interface gigabitEthernet 2/1
- Example 2—Selects a Gigabit Ethernet interface on the E320 router
  host1(config)#interface gigabitEthernet 4/0/1
- Use the no version to remove IP from an interface. You must issue the no version from the highest level down; you cannot remove an interface or subinterface if the one above it still exists.
- See interface gigabitEthernet.

interface tenGigabitEthernet

- Use to select a 10-Gigabit Ethernet interface on the E120 or E320 router.

  | Note: On the ES2-S2 10GE PR IOA, you can configure only the primary port, 0. The router automatically uses the redundant port, 0R, if the primary port fails.

- Use the slot/adapter/port format.
- Example—Selects a 10-Gigabit Ethernet interface on the ES2-S1 10GE IOA
  host1(config)#interface tenGigabitEthernet 4/0/0
- Use the no version to remove IP from an interface. You must issue the no version from the highest level down; you cannot remove an interface or subinterface if the one above it still exists.
- See interface tenGigabitEthernet.

ip mac-validate

- Use to enable or disable MAC address validation on a per interface basis.
- Use the strict keyword to prevent transmission of IP packets that do not reside in the validation table.
- Use the loose keyword to enable IP packets to pass through even though the packets do not have entries in the validation table. Only packets that have matching IP–MAC pair entries in the table are validated.
- The default behavior is not to perform MAC address validation.
- Example
  host1(config)#interface gigabitEthernet 2/0 host1(config-if)#ip address 4.4.4.2 255.255.255.0 host1(config-if)#ip mac-validate strict host1(config-if)#exit
- Use the no version to disable the command.

  | Note: For additional information about MAC address validation, see the arp validate command description in JunosE IP, IPv6, and IGP Configuration Guide.

- See ip mac-validate.

load-interval

- Use to set the time interval at which the router calculates bit and packet rate counters.
- This command does not work for the Fast Ethernet port on the SRP module.
- Specify a multiple of 30 seconds, in the range 30–300 seconds.
- The default value is 300 seconds.
- Example
  host1(config-if)#load-interval 90
- Use the no version to restore the default time interval, 300 seconds.
- See load-interval.

mtu

- Use to specify the MTU for an interface.
- Specify a value in the range 64–9188 bytes. The range for FE-8 I/O modules is 64–9042 bytes.
- This command does not work for the Fast Ethernet port on the SRP module.
- Example
  host1(config-if)#mtu 9000
- Use the no version to specify the default, 1518.
- See mtu.

speed

- Use to specify the line speed.
- This command also works on the Fast Ethernet port on the SRP module on all E Series routers. For more information, see JunosE System Basics Configuration Guide.

  | Note: If you set either the line speed or duplex mode to automatically negotiate by using the automatically negotiate keyword, the router negotiates both parameters. You can specify different values to prevent the router from negotiating these parameters. Automatic negotiation is not supported for the FE-8 SFP I/O module. For this I/O module, the default speed is 100 Mbps.

- Example
  host1(config-if)#speed 10
- Use the no version to revert to the default, either automatically negotiate or 100 Mbps (FE-8 SFP I/O module only).
- See speed.