To configure or monitor Ethernet interfaces, you need to specify the physical location of the interface module and interface in the CLI. The interface address format is slot/subslot/port, where:

• slot—The chassis slot number in the chassis where the interface module is installed.

Note	The interface module slot number is always 0.

• subslot—The subslot where the interface module is installed. Interface module subslots are numbered from 0 to 5 for ASR 903 and from 0 to 15 for ASR 907, from bottom to top.
• port—The number of the individual interface port on an interface module.

The following example shows how to specify the first interface (0) on an interface module installed in the first interface module slot:

Router(config)# interface GigabitEthernet 0/0/0
 no ip address
 shutdown
 negotiation auto
 no cdp enable

Hot Standby Router Protocol (HSRP) provides high network availability because it routes IP traffic from hosts without relying on the availability of any single router. You can deploy HSRP in a group of routers to select an active router and a standby router. (An active router is the router of choice for routing packets; a standby router is a router that takes over the routing duties when an active router fails, or when preset conditions are met).

HSRP is enabled on an interface by entering the standby [group-number ] ip [ip-address [secondary ]] command. The standby command is also used to configure various HSRP elements. This document does not discuss more complex HSRP configurations. For additional information on configuring HSRP, see to the HSRP section of the Cisco IP Configuration Guide publication that corresponds to your Cisco IOS XE software release. In the following HSRP configuration, standby group 2 on Gigabit Ethernet port 0/1/0 is configured at a priority of 110 and is also configured to have a preemptive delay should a switchover to this port occur:

Router(config)#interface GigabitEthernet 0/1/0 
Router(config-if)#standby 2 ip 192.168.1.200 
Router(config-if)#standby 2 priority 110 
Router(config-if)#standby 2 preempt

The maximum number of different HSRP groups that can be created on one physical interface is 4. If additional groups are required, create 4 groups on the physical interface, and the remaining groups on the BDI or on another physical interface.

The maximum number of HSRP or VRRP groups allowed are:

• RSP1A —128 HSRP or VRRP groups. 128 HSRP or VRRP groups restriction implies that the maximum number of different interfaces that can be configured with VRRP or HSRP is 128. You cannot configure HSRP or VRRP for more than 128 interfaces but you can configure upto 256 HSRP or VRRP groups in those 128 interfaces.

• RSP1B —256 HSRP or VRRP groups

• RSP2A-64 and RSP2-128—128 HSRP or VRRP groups, prior to Cisco IOS Release XE 3.15S

• RSP2A-64 and RSP2-128 —256 HSRP or VRRP groups, starting Cisco IOS Release XE 3.15S

• RSP3-200 and RSP3-400—255 HSRP or VRRP groups, starting Cisco IOS Release XE 3.18.1SP

Note

TCAM space utilization changes when HSRP groups are configured on the router. If HSRP groups are configured the TCAM space is utilized. Each HSRP group takes 1 TCAM entry. The “Out of TCAM” message may be displayed if total number of TCAM space used by HSRP groups and prefixes on the router exceeds scale limit.

Note	HSRP state flaps with sub-second “Hello” or “Dead” timers.

Note	The maximum number of unique MTU values that can be configured on the physical interfaces on the chassis is 8. Use the show platform hardware pp active interface mtu command to check the number of values currently configured on the router. This is not applicable on Cisco ASR 900 RSP3 Module.

The Cisco IOS software supports three different types of configurable maximum transmission unit (MTU) options at different levels of the protocol stack:

• Interface MTU—The interface module checks the MTU value of incoming traffic. Different interface types support different interface MTU sizes and defaults. The interface MTU defines the maximum packet size allowable (in bytes) for an interface before drops occur. If the frame is smaller than the interface MTU size, but is not smaller than the minimum frame size for the interface type (such as 64 bytes for Ethernet), then the frame continues to process.
• IP MTU—Can be specified on an interface. If an IP packet exceeds the IP MTU size, then the packet is fragmented.

  When the value of the IP MTU is 9216 bytes and the packet is sent with 9214 bytes, 18 bytes are added to the packet by FPGA. The total size of the packet then becomes 9232 bytes. The maximum supported MTU of the packet without fragmentation in ASIC is 9232, so there is no traffic loss with a packet size of 9214. When IP MTU is 9216, and the packet is sent with either 9215 or 9216 bytes, 18 bytes are added to the packet by FPGA. The total size of the packet then becomes 9233 or 9234 bytes respectively. As the packet size exceeds the maximum supported MTU size of the packet without fragmentation, the packet is dropped.

  When the traffic with packet size greater than 9216 bytes is sent and the MTU is configured as 9216 bytes, the packet is fragmented. Hence, the packet loss is prevented.

  Note	The IP MTU configured on BDI should not be greater than the Layer2 MTU configured on the underlying Layer2 interface. For Cisco ASR 900 RSP3 Module the IP MTU configured on a BDI should be equal to the Layer2 MTU configured on the underlying Layer 2 interface.

• MPLS MTU—If the MPLS MTU is set to a value, for example, 1500 bytes, the value is programmed as 1504 bytes at the hardware level to allow the addition of one label. Consider the case of pseudowire. If the packet size of Layer 2 traffic sent with four bytes of Frame Check Sequence (FCS) to the pseudowire is 1500 bytes, then and four bytes of pseudowire control word and one pseudowire label (label size is four bytes) is added to the packet, the packet size is now 1508 bytes with FCS. However, note that while calculating the packet size, FCS is not considered. So the calculated packet size is 1504 bytes, which is equal to the MPLS MTU programmed in the hardware. This packet is forwarded as expected.

  However, if another label is added to this packet, the packet size becomes 1508 bytes without FCS. This value is greater than programmed MTU value, so this packet is dropped. This restriction applies not only to pseudowire, but to the entire MPLS network.

  To ensure that packets are not dropped, MPLS MTUs should be set considering the maximum size of the label stack that is added to the packet in the network.

Encapsulation methods and MPLS MTU labels add additional overhead to a packet. For example, Subnetwork Access Protocol (SNAP) encapsulation adds an 8-byte header, dot1q encapsulation adds a 2-byte header, and each MPLS label adds a 4-byte header (n labels x 4 bytes).

For the Gigabit Ethernet interface module on the chassis, the default MTU size is 1500 bytes. The maximum configurable MTU is 9216 bytes. The interface module automatically adds an additional 22 bytes to the configured MTU size to accommodate some of the additional overhead.

MPLS MTU configuration is supported starting with Cisco IOS XE Release 3.10.2 and later. The platform mpls mtu-enable command is introduced to enable MPLS MTU on the router.

The only encapsulation supported by the interface modules is IEEE 802.1Q encapsulation for virtual LANs (VLANs).

Note	VLANs are only supported on Ethernet Virtual Connection (EVC) service instances and Trunk Ethernet Flow Point (EFP) interfaces. For more information about how to configure these features, see the Configuring Ethernet Virtual Connections on the Cisco ASR 900 Series Router document.

Gigabit Ethernet interfaces use a connection-setup algorithm called autonegotiation. Autonegotiation allows the local and remote devices to configure compatible settings for communication over the link. Using autonegotiation, each device advertises its transmission capabilities and then agrees upon the settings to be used for the link.

For the Gigabit Ethernet interfaces on the chassis, flow control is autonegotiated when autonegotiation is enabled. Autonegotiation is enabled by default.

The Copper SFP does not auto-negotiate full duplex with 8-port Gigabit Ethernet RJ45 (Copper) Interface Module (8X1GE) with speed 100 configured.

When enabling autonegotiation, consider these guidelines:

• If autonegotiation is disabled on one end of a link, it must be disabled on the other end of the link. If one end of a link has autonegotiation disabled while the other end of the link does not, the link will not come up properly on both ends.
• Flow control is enabled by default.
• Flow control will be on if autonegotiation is disabled on both ends of the link.

For information about configuring an Ethernet interface as a layer 2 Ethernet virtual circuit (EVC) or Ethernet flow point (EFP), see the Ethernet Virtual Connections Configuration. .

To save your running configuration to NVRAM, use the following command in privileged EXEC configuration mode:

Router# copy running-config startup-config

For information about managing your system image and configuration files, refer to the Cisco IOS Configuration Fundamentals Configuration Guide and Cisco IOS Configuration Fundamentals Command Reference publications that correspond to your Cisco IOS software release.

You can shut down and restart any of the interface ports on an interface module independently of each other. Shutting down an interface stops traffic and enters the interface into an “administratively down” state.

If you are preparing for an OIR of an interface module, it is not necessary to independently shut down each of the interfaces prior to deactivation of the module.

router#configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
router(config)
router(config)#interface GigabitEthernet 0/1/0
router(config-if)#shutdown 

router#configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
router(config)
router(config)#interface GigabitEthernet 0/1/0
router(config-if)#no shutdown 

You can use the following commands in EXEC mode to automatically stop traffic on the affected interfaces and deactivate them along with the interface module in preparation for OIR:

To find detailed interface information on a per-port basis for the Gigabit Ethernet interface module, use the show interfaces gigabitethernet command.

The following example provides sample output for interface port 0 on the interface module located in slot 1:

Router# show interfaces GigabitEthernet0/1/0
GigabitEthernet0/1/0 is up, line protocol is up
  Hardware is A900-IMA8T , address is d0c2.8216.0590 (bia d0c2.8216.0590)
  MTU 1500 bytes, BW 1000000 Kbit/sec, DLY 10 usec,
     reliability 255/255, txload 1/255, rxload 1/255
  Encapsulation ARPA, loopback not set
  Keepalive set (10 sec)
  Full Duplex, 1000Mbps, link type is auto, media type is RJ45
  output flow-control is off, input flow-control is off
  ARP type: ARPA, ARP Timeout 04:00:00
  Last input never, output 08:59:45, output hang never
  Last clearing of show interface counters 09:00:18
  Input queue: 0/375/0/0 (size/max/drops/flushes); Total output drops: 0
  Queueing strategy: fifo
  Output queue: 0/40 (size/max)
  5 minute input rate 0 bits/sec, 0 packets/sec
  5 minute output rate 0 bits/sec, 0 packets/sec
     11 packets input, 704 bytes, 0 no buffer
     Received 11 broadcasts (0 IP multicasts)
     0 runts, 0 giants, 0 throttles
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
     0 watchdog, 0 multicast, 0 pause input
     0 packets output, 0 bytes, 0 underruns
     0 output errors, 0 collisions, 0 interface resets
     0 unknown protocol drops
     0 babbles, 0 late collision, 0 deferred
     0 lost carrier, 0 no carrier, 0 pause output
     0 output buffer failures, 0 output buffers swapped out