Configuring Ethernet Interfaces
This section describes how to configure the Gigabit and Ten Gigabit Ethernet interface modules and includes information about verifying the configuration.
Limitations and Restrictions
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Interface module A900-IMA8Z in slot 0 with A900-RSP3C-200-S supports a maximum of 6 ports at 10GE speed and needs explicit enablement using the hw-module subslot 0/0 A900-IMA8Z mode 6-port command.
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VRF-Aware Software Infrastructure (VASI) interface commnads interface vasileft and interface vasiright are not supported .
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Interface modules have slot restrictions, see NCS 4200 Hardware Installation Guides.
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MPLS MTU is not supported.
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On the RSP3 module, MTU value configured for a BDI interface should match with the MTU configuration for all the physical interfaces, which have a service instance associated with this BDI.
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To replace the configured interface module with a different interface module in a particular slot, run the hw-module subslot slot-num default command.
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Giant counters are not supported.
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Mixed configurations of features are not supported on the same port. For example, one OC-3 port can have only CEM (CESoP or SAToP), ATM, IMA or DS3 configurations, but not a combination of these features on a single port.
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Ingress counters are not incremented for packets of the below packet format on the RSP3 module for the 10 Gigabit Ethernet interfaces, 100 Gigabit Ethernet interfaces, and 40 Gigabit Ethernet interfaces:
MAC header---->Vlan header---->Length/Type
When these packets are received on the RSP3 module, the packets are not dropped, but the counters are not incremented.
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If the IM is shutdown using hw-module subslot shutdown command, then the IM goes out-of-service. You should perform a Stateful Switchover (SSO) in the interim, as the IM needs to be re-inserted for successful reactivation.
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Following are some of the IMs that are not supported on certain slots when IPsec license is enabled:
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The below IMs are not supported on the Slot 11 on the Cisco ASR 907 router:
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SPA_TYPE_ETHER_IM_8x10GE
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SPA_TYPE_ETHER_IM_2x40GE
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The below IMs are not supported on the Slot 2 on the Cisco ASR 903 router for RSP3-200 and RSP3-400:
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SPA_TYPE_ETHER_IM_8xGE_SFP_1x10GE
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SPA_TYPE_ETHER_IM_8xGE_CU_1x10GE
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SPA_TYPE_ETHER_IM_1x10GE
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SPA_TYPE_ETHER_IM_8x10GE
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SPA_TYPE_OCX_IM_OC3OC12
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SPA_TYPE_ETHER_IM_8xGE_SFP
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SPA_TYPE_ETHER_IM_8xGE_CU
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CTS signal goes down, when control signal frequency is configured more than 5000 ms and timeout setting is more than 20,000 ms (4x control_frequency), which is greater than the OIR time (~20s) for a selected subordinate to complete an OIR cycle. This results in the primary being unaware that the subordinate is down and CTS of all subordinates are down too. To avoid this situation, ensure that the timeout is shorter than the OIR time of the subordinate. Set the control frequency to less than or equal to 5000 ms and the timeout setting to less than or equal to 20,000 ms before you perform OIR.
Configuring an Interface
This section lists the required configuration steps to configure Gigabit and Ten Gigabit Ethernet interface modules.
Procedure
| Command or Action | Purpose | |||||
|---|---|---|---|---|---|---|
| Step 1 |
configure terminal Example: |
Enters global configuration mode. |
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| Step 2 |
Do one of the following:
Example:Example:Example: |
Specifies the Gigabit Ethernet or Ten Gigabit Ethernet interface to configure and enters interface configuration mode, where:
|
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| Step 3 |
ip address ip-address mask {secondary } | dhcp {client-id interface-name }{hostname host-name }] Example: |
Sets a primary or secondary IP address for an interface that is using IPv4, where:
|
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| Step 4 |
no negotiation auto Example: |
(Optional) Disables automatic negotitation.
|
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| Step 5 |
speed { 10 | 100 | 1000 } Example: |
(Optional) Specifies the speed for an interface to transmit at 10, 100, and 1000 Mbps (1 Gbps), where the default is 1000 Mbps. |
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| Step 6 |
mtu bytes Example: |
(As Required) Specifies the maximum packet size for an interface, where:
The default is 1500 bytes; the range is from 1500 to 9216. |
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| Step 7 |
standby [group-number ] ip [ip-address [secondary ]] Example: |
Creates or enables the Hot Standby Router Protocol (HSRP) group using its number and virtual IP address, where:
|
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| Step 8 |
no shutdown Example: |
Enables the interface. |
Specifying the Interface Address on an Interface Module
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 enableConfiguring Hot Standby Router Protocol
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.
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. |
Restrictions
HSRPv2 is not supported.
Verifying HSRP
To verify the HSRP information, use the show standby command in EXEC mode:
Router# show standby
Ethernet0 - Group 0
Local state is Active, priority 100, may preempt
Hellotime 3 holdtime 10
Next hello sent in 0:00:00
Hot standby IP address is 198.92.72.29 configured
Active router is local
Standby router is 198.92.72.21 expires in 0:00:07
Standby virtual mac address is 0000.0c07.ac00
Tracking interface states for 2 interfaces, 2 up:
UpSerial0
UpSerial1
Modifying the Interface MTU Size
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.
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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.
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.
Limitations
In EtherLike-MIB, the dot3StatsFrameTooLongs frames count in SNMP increases when the frame packet size is more than the default MTU.
Interface MTU Configuration Guidelines
When configuring the interface MTU size, consider the following guidelines:
- The default interface MTU
size accommodates a 1500-byte packet, plus 22 additional bytes to cover the
following additional overhead:
- Layer 2 header—14 bytes
- Dot1q header—4 bytes
- CRC—4 bytes
- Interface MTU is not supported on BDI Interface
Configuring Interface MTU
To modify the MTU size on an interface, use the following command in interface configuration mode:
|
Command |
Purpose |
|---|---|
|
mtu bytes |
Configures the maximum packet size for an interface, where:
The default is 1500 bytes and the maximum configurable MTU is 9216 bytes. |
To return to the default MTU size, use the no form of the command.
Note |
When IP FRR over BDI is configured, the maximum allowed packet size is 1504 bytes. |
When the BGP-PIC core is enabled, a packet destined to a prefix that is learnt through eBGP, is dropped if the packet size is greater than 1504 bytes. To work around this limitation, do one of the following:
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Disable the BGP-PIC core,
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Use the static route, or
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Use routed-port instead of BDI.
Verifying the MTU Size
To verify the MTU size for an interface, use the show interfaces gigabitethernet privileged EXEC command and observe the value shown in the “MTU” field.
The following example shows an MTU size of 1500 bytes for interface port 0 (the second port) on the Gigabit Ethernet interface module installed in slot 1:
Router# show interfaces gigabitethernet 0/1/0
GigabitEthernet0/1/0 is up, line protocol is up
Hardware is NCS4200-1T8LR-PS, 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 22/255
Encapsulation ARPA, loopback not set
Keepalive set (10 sec)
Configuring the Encapsulation Type
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. |
Configuring Autonegotiation on an Interface
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.
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.
Enabling Autonegotiation
To enable autonegotiation on a Gigabit Ethernet interface, use the following command in interface configuration mode:
|
Command |
Purpose |
|---|---|
|
negotiation auto |
Enables autonegotiation on a Gigabit Ethernet interface. Advertisement of flow control occurs. |
Disabling Autonegotiation
Autonegotiation is automatically enabled and can be disabled on Gigabit Ethernet interfaces . During autonegotiation, advertisement for flow control, speed, and duplex occurs, depending on the media (fiber or copper) in use.
Speed and duplex configurations can be advertised using autonegotiation. The values that are negotiated are:
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For Gigabit Ethernet interfaces using RJ-45 ports and for Copper (Cu) SFP ports—10, 100, and 1000 Mbps for speed and full-duplex mode. Link speed is not negotiated when using fiber interfaces.
To disable autonegotiation, use the following command in interface configuration mode:
|
Command |
Purpose |
|---|---|
|
no negotiation auto
|
Disables autonegotiation on Gigabit Ethernet interfaces. No advertisement of flow control occurs. |
Configuring Carrier Ethernet Features
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.
Saving the Configuration
To save your running configuration to NVRAM, use the following command in privileged EXEC configuration mode:
|
Command |
Purpose |
|---|---|
|
copy running-config startup-config
|
Writes the new configuration to NVRAM. |
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.
Shutting Down and Restarting an Interface
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.
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Command |
Purpose |
|---|---|
|
shutdown
no shutdown |
Restarts, stops, or starts an interface. |
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