Interfaces and Hardware Component Configuration Guide for Cisco 8000 Series Routers, Cisco IOS XR Releases

PDF

Interfaces and Hardware Component Configuration Guide for Cisco 8000 Series Routers, Cisco IOS XR Releases

Network interface speed and autonegotiation

Updated: July 31, 2026

Want to summarize with AI?

Describes autonegotiation as an IEEE 802.3 Ethernet standard that enables connected routers to determine the highest common transmission parameters, such as mode, speed, and flow control, to optimize link bandwidth utilization.

Autonegotiation is an IEEE 802.3 Ethernet standard that

enables a router to connect with its peer by automatically determining and negotiating to the highest common supported transmission parameters between them,
exchanges parameters, such as mode, speed, and flow control, between the two connected routers, and
supports autonegotiation on 1 G copper ports and 1 G SFP copper transceivers that allow an SFP port to connect to a copper Ethernet network at 1 Gbps using a standard RJ45 connector.

Table 1. Feature history table
Feature Name	Release Information	Feature Description
Network interface speed support with autonegotiation	Release 25.4.1	Introduced in this release on: Fixed Systems (8010 [ASIC: A100]) (select variants only) You can ensure compatibility between new and legacy routers by enabling autonegotiation on the Gigabit interfaces of the connected routers. This process allows the routers to exchange key parameters such as mode, speed, and flow control, enabling them to agree on common transmission settings. As a result, the link achieves optimal bandwidth utilization. This feature is supported on: 8011-4G24Y4H-I 8011-32Y8L2H2FH 8011-12G12X4Y-A/D

Network interface speed configuration methods

You can configure the network interface speed using one of these methods:

Note

Cisco recommends configuring network interface speed in autonegotiation mode.

Configure with speed option

When you configure a 1 Gbps network interface using the speed command, the interface is forced to operate at the specified value.

Procedure

Run the show interfaces GigabitEthernet interface-name command to check the existing speed.

Example:

#show interfaces GigabitEthernet 0/0/0/31
GigabitEthernet0/0/0/31 is up, line protocol is up
  Interface state transitions: 7
  Hardware is GigabitEthernet, address is 0035.1a00.e62c (bia 0035.1a00.e62c)
  Internet address is Unknown
  MTU 1514 bytes, BW 100000 Kbit (Max: 100000 Kbit)
     reliability 255/255, txload 0/255, rxload 0/255
  Encapsulation ARPA,
  Full-duplex, 1000 Mb/s, TFD, link type is force-up
  output flow control is off, input flow control is off
  Carrier delay (up) is 10 msec
  loopback not set,
  Last link flapped 00:00:30
  Last input 00:00:00, output 00:00:00
  Last clearing of "show interface" counters never
  30 second input rate 1000 bits/sec, 1 packets/sec
  30 second output rate 0 bits/sec, 1 packets/sec
     90943 packets input, 11680016 bytes, 0 total input drops
     0 drops for unrecognized upper-level protocol
     Received 0 broadcast packets, 90943 multicast packets
              0 runts, 0 giants, 0 throttles, 0 parity
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
     61279 packets output, 4347618 bytes, 0 total output drops
     Output 0 broadcast packets, 8656 multicast packets
     0 output errors, 0 underruns, 0 applique, 0 resets
     0 output buffer failures, 0 output buffers swapped out
8	carrier transitions

Checks the existing speed. Observe that the speed is 1000 Mbps.

Use interface GigabitEthernet interface-path-id , speed speed-value command to set the configuration that forces 1 Gbps interface speed to 100 Mbps.

Example:


 (config)#interface GigabitEthernet 0/0/0/31
 (config-if)#speed 100
 (config-if)#commit
 (config-if)#end

Sets the configuration that forces the 1 Gbps interface speed to 100 Mbps. If the remote end is not also configured for 100 Mbps, the link goes down.

Run the show controllers GigabitEthernet interface-path-id and show interfaces GigabitEthernet interface-path-id commands to verify if the speed is configured to 100 Mbps and autonegotiation is disabled.

Example:

#show controllers GigabitEthernet 0/0/0/31
Operational data for interface GigabitEthernet0/0/0/31:
State:
    Administrative state: enabled
    Operational state: Up
    LED state: Green On
Phy:
    Media type: Four-pair Category 5 UTP PHY, full duplex
    Optics:
        Vendor: CISCO
        Part number: SBCU-5740ARZ-CS1
        Serial number: AVC194525HW
        Wavelength: 0 nm
MAC address information:
    Operational address: 0035.1a00.e67c
    Burnt-in address: 0035.1a00.e62c
Autonegotiation disabled.

Operational values:
    Speed: 100 Mbps       /*Gig interface speed is set to 100 Mbps */
    Duplex: Full Duplex
    Flowcontrol: None
    Loopback: None (or external)
    MTU: 1514
    MRU: 1514
    Forward error correction: Disabled

#show interfaces GigabitEthernet 0/0/0/31
GigabitEthernet0/0/0/31 is up, line protocol is up
  Interface state transitions: 7
  Hardware is GigabitEthernet, address is 0035.1a00.e62c (bia 0035.1a00.e62c)
  Internet address is Unknown
  MTU 1514 bytes, BW 100000 Kbit (Max: 100000 Kbit)
     reliability 255/255, txload 0/255, rxload 0/255
  Encapsulation ARPA,
  Full-duplex, 100 Mb/s, TFD, link type is force-up
  output flow control is off, input flow control is off
  Carrier delay (up) is 10 msec
  loopback not set,
  Last link flapped 00:00:30
     0 output errors, 0 underruns, 0 applique, 0 resets
     0 output buffer failures, 0 output buffers swapped out
      carrier transitions

The show output confirms that GigabitEthernet0/0/0/31 is up and its line protocol is up. This occurs when both ends of the link are operating at 100 Mbps. If the remote end is not also configured for 100 Mbps, the link goes down.

Verifies that the speed is configured to 100 Mbps and autonegotiation is disabled.

Configure with negotiation auto option

Procedure

Set the configuration for interface speed to auto-negotiate. The router sets its interface speed to match the highest common speed supported by the peer router.

Example:

Router#configuration
 Router(config)#interface GigabitEthernet 0/0/0/31
 Router(config-if)#negotiation auto
 Router(config-if)#commit
 Router(config-if)#end

Sets the configuration for the interface speed to autonegotiate. The router sets its interface speed to match the highest common speed supported by the peer router. Autonegotiation is not enabled by default. Use the negotiation auto command to enable autonegotiation.

Run the show controllers GigabitEthernet interface-path-id and show interfaces GigabitEthernet interface-path-id commands to verify if the speed is autonegotiated.

Example:

Router#show interfaces GigabitEthernet 0/0/0/31
GigabitEthernet0/0/0/31 is up, line protocol is up
  Interface state transitions: 10
  Hardware is GigabitEthernet, address is 0035.1a00.e62c (bia 0035.1a00.e62c)
  Internet address is Unknown
  MTU 1514 bytes, BW 100000 Kbit (Max: 100000 Kbit)
     reliability 255/255, txload 0/255, rxload 0/255
  Encapsulation ARPA,
  Full-duplex, 100Mb/s, TFD, link type is autonegotiation
  output flow control is off, input flow control is off
  Carrier delay (up) is 10 msec
  loopback not set,
  Last link flapped 00:00:01
  Last input 00:00:00, output 00:00:00
  Last clearing of "show interface" counters never
  30 second input rate 1000 bits/sec, 1 packets/sec
  30 second output rate 0 bits/sec, 0 packets/sec
     91005 packets input, 11687850 bytes, 0 total input drops
     0 drops for unrecognized upper-level protocol
     Received 0 broadcast packets, 91005 multicast packets
              0 runts, 0 giants, 0 throttles, 0 parity
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
     61307 packets output, 4350024 bytes, 0 total output drops
     Output 0 broadcast packets, 8668 multicast packets
     0 output errors, 0 underruns, 0 applique, 0 resets
     0 output buffer failures, 0 output buffers swapped out
     15 carrier transitions

 #show controllers GigabitEthernet 0/0/0/31
Operational data for interface GigabitEthernet0/0/0/31:

State:
    Administrative state: enabled
    Operational state: Up
    LED state: Green On

Phy:
    Media type: Four-pair Category 5 UTP PHY, full duplex
    Optics:
        Vendor: CISCO
        Part number: SBCU-5740ARZ-CS1
        Serial number: AVC194525HW
        Wavelength: 0 nm

MAC address information:
    Operational address: 0035.1a00.e67c
    Burnt-in address: 0035.1a00.e62c

Autonegotiation enabled:
    No restricted parameters

Operational values:
    Speed: 100 Mbps
    Duplex: Full Duplex
    Flowcontrol: None
    Loopback: None (or external)
    MTU: 1514
    MRU: 1514
    Forward error correction: Disabled

Verifies that the speed is autonegotiated.

Configure with speed and negotiation auto options

Procedure

Set the configuration for Gigabit interface speed to 100 Mbps and autonegotiate other parameters. The interface speed at remote end is set to 100 Mbps.

Example:


Router(config)#interface GigabitEthernet 0/0/0/31
Router(config-if)#negotiation auto
Router(config-if)#speed 100
Router(config-if)#end

Sets the configuration for the Gigabit interface speed to 100 Mbps and autonegotiates the other parameters. The interface speed at the remote end is set to 100 Mbps. The interface does not attempt to negotiate the speed with its peer; it simply tries to establish a link at 100 Mbps. The autonegotiation process might still occur for other parameters like duplex and flow control, but the speed itself is fixed by the speed command.

Use the show controllers GigabitEthernet interface-path-id and show interfaces GigabitEthernet interface-path-id command to verify if the link is up, speed is forced to 100 Mbps, and auto-negotiation is enabled.

Example:

Router#show interfaces GigabitEthernet 0/0/0/31
GigabitEthernet0/0/0/31 is up, line protocol is up
  Interface state transitions: 9
  Hardware is GigabitEthernet, address is 0035.1a00.e62c (bia 0035.1a00.e62c)
  Internet address is Unknown
  MTU 1514 bytes, BW 100000 Kbit (Max: 100000 Kbit)
     reliability 255/255, txload 0/255, rxload 0/255
  Encapsulation ARPA,
  Full-duplex, 100 Mb/s, TFD, link type is autonegotiation
  output flow control is off, input flow control is off
  Carrier delay (up) is 10 msec
  loopback not set,
  Last link flapped 00:00:03
  Last input 00:00:00, output 00:00:00
  Last clearing of "show interface" counters never
  30 second input rate 0 bits/sec, 1 packets/sec
  30 second output rate 0 bits/sec, 0 packets/sec
     90968 packets input, 11683189 bytes, 0 total input drops
     0 drops for unrecognized upper-level protocol
     Received 0 broadcast packets, 90968 multicast packets
              0 runts, 0 giants, 0 throttles, 0 parity
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
     61287 packets output, 4348541 bytes, 0 total output drops
     Output 0 broadcast packets, 8664 multicast packets
     0 output errors, 0 underruns, 0 applique, 0 resets
     0 output buffer failures, 0 output buffers swapped out
     12 carrier transitions

The show output confirms that GigabitEthernet0/0/0/31 is up and line protocol is up. This occurs because the speed at both ends is 100 Mbps.

#show controllers GigabitEthernet 0/0/0/31
Operational data for interface GigabitEthernet0/0/0/31:

State:
    Administrative state: enabled
    Operational state: Up
    LED state: Green On

Phy:
    Media type: Four-pair Category 5 UTP PHY, full duplex
    Optics:
        Vendor: CISCO
        Part number: SBCU-5740ARZ-CS1
        Serial number: AVC194525HW
        Wavelength: 0 nm

MAC address information:
    Operational address: 0035.1a00.e67c
    Burnt-in address: 0035.1a00.e62c

Autonegotiation enabled:
    Speed restricted to: 100 Mbps  /* autonegotiation is enabled and speed is forced to 100 Mbps*/

Operational values:
    Speed: 100 Mbps
    Duplex: Full Duplex
    Flowcontrol: None
    Loopback: None (or external)
    MTU: 1514
    MRU: 1514
    Forward error correction: Disabled

Verifies that the link is up, the speed is forced to 100 Mbps, and autonegotiation is enabled.

QoS with autonegotiated speeds

QoS with autonegotiated speeds is a congestion management feature that

manages congestion on interfaces that automatically adjust their speed—such as 10 Mbps or 100 Mbps—to connect with legacy devices,
addresses reduced bandwidth and increased congestion potential when operating at lower speeds, and
prioritizes critical applications, controls bandwidth allocation, and minimizes packet loss or delay, even when connecting to legacy devices or working in mixed-speed environments.

Table 2. Feature history table
Feature Name	Release Information	Feature Description
QoS with auto-negotiated speeds	Release 25.3.1	Introduced in this release on: Fixed Systems (8010 [ASIC: A100]) (select variants only) You can now maintain optimal network efficiency by applying QoS on Gigabit Ethernet interfaces that operate at lower speeds through autonegotiation. Autonegotiation detects and matches the highest common speed between connected routers, allowing seamless interoperability. With this enhancement, you can use QoS on interfaces connecting to legacy devices that support only 10 Mbps or 100 Mbps speeds. This capability improves traffic management, leading to enhanced network performance and reliability across diverse deployment scenarios. This feature is supported on 8011-4G24Y4H-I.

Benefits of QoS with autonegotiated speeds

Applying QoS policies on interfaces that operate at autonegotiated speeds provides the following benefits.

Maximized bandwidth utilization: When an interface autonegotiates to a higher speed, the QoS policy dynamically scales up its allocations and limits. This ensures that the newly available bandwidth is fully leveraged by all traffic classes according to their defined priorities, preventing under-utilization of network resources.
Optimized resource allocation at lower speeds: If an interface autonegotiates down to a lower speed, QoS mechanisms, such as shapers and bandwidth allocations, automatically adjust downward, preventing enforcement of rates that exceed physical link capacity. This minimizes packet drops, control plane overhead, and inconsistent state conditions.

Supported interfaces for QoS with autonegotiation

QoS with autonegotiation is supported on the following interface types.

Gigabit Ethernet interfaces that need to connect to legacy devices operating at 10 Mbps or 100 Mbps speeds.
Bundle interfaces that include Gigabit Ethernet interfaces operating at autonegotiated speeds of 10 Mbps, 100 Mbps, or 1 Gbps.

Restrictions for QoS with autonegotiated speeds

Absolute rate values, such as fixed, specific numerical bandwidth or rate limits, cannot be configured on bundle interfaces.
Hierarchical QoS (HQoS) policies are not supported on 10 or 100 M ports on main and sub-interfaces of 8011-4G24Y4H-I, 8011-32Y8L2H2FH, and 8011-32Y8L2H2FH (ASIC: A100) systems.

Enable QoS with autonegotiated speeds

The purpose of this task is to enable QoS with autonegotiated speeds using relative values on Cisco IOS XR routers.

Before you begin

Confirm that the interface you intend to configure supports autonegotiation and QoS.

Procedure

	1.	Configure the interface to allow auto-negotiation. Example: `Router(config)#interface GigabitEthernet0/0/0/28 Router(config)#negotiation auto` Configures the interface to allow autonegotiation.
	2.	Define the class-maps for traffic classification. Example: `Router(config)#class-map match-any voice_traffic Router(config-cmap)#match dscp ef Router(config-cmap)#end-class-map Router(config)#class-map match-any data_traffic Router(config-cmap)#match dscp af21 Router(config-cmap)#end-class-map`
	3.	Define the policy map using bandwidth percentages. Example: `Router(config)#policy-map adaptive_qos_policy Router(config-pmap)#class voice_traffic Router(config-pmap)#priority level 1 Router(config-pmap)#bandwidth percent 20 ! Allocates 20% of the negotiated link speed Router(config-pmap)#class data_traffic Router(config-pmap)#bandwidth percent 50 ! Allocates 50% of the negotiated link speed Router(config-pmap)#class class-default Router(config-pmap)#end-policy-map` We recommend using the percentile of port speed for interfaces with auto-negotiated speeds, as this allows the policy map to automatically adjust to any changes in speed.
	4.	Apply the policy to the auto-negotiating interface. Example: `Router(config)#interface GigabitEthernet0/0/0/28 Router(config)#service-policy output adaptive_qos_policy` Applies the policy to the autonegotiating interface.
	5.	Execute the show qos inconsistency detail location location command to identify any conflict between a configured QoS policy and the interface’s current operational state. Example: Router# show qos inconsistency detail location 0/rp0/cpu0 Fri Mar 28 14:53:36.542 UTC Inconsistency Type: Policer conform rate greater than parent reference rate ============================================================================ Interface Direction Policy Name ---------------------------------------------------------------------------- GigabitEthernet0/0/0/28 input p1-ing-negative Inconsistency Type: Shape bandwidth rate greater than parent reference rate ============================================================================ Interface Direction Policy Name ---------------------------------------------------------------------------- GigabitEthernet0/0/0/28 output p1-negative

Autonegotiation parameters

These parameters are crucial for Ethernet transmission because they directly define how data is sent and received over the link, impacting performance, efficiency, and reliability.

Speed – 1G copper ports and 1G SFP copper transceivers support autonegotiation, allowing them to establish the highest common speed and duplex mode with connected routers.
Duplex – Full.
Pause – Receive part (RX) and Transmit part (TX).

Configuration guidelines and restrictions for autonegotiation and speed

Speed and autonegotiation guidelines

Speed can be manually set or configured to autonegotiate with the remote interface.
In autonegotiation mode, the interface automatically determines whether to operate at 10 Mbps, 100 Mbps, or 1 Gbps based on the capabilities of the connected device.
Other settings such as full duplex and pause are also negotiated during this process.
Autonegotiation is an optional function of the Fast Ethernet standard that enables devices to automatically exchange information about speed and duplex abilities.
It is especially useful for ports where devices with different capabilities are connected and disconnected regularly.
Autonegotiation is enabled, by default, on integrated copper ports and copper transceivers on most devices.
Do not enable autonegotiation when you configure a link on K100-based systems. Ensure autonegotiation is disabled on both ends of the link.
For Cisco 8711-32FH-M routers, an autonegotiation mismatch between source and destination interfaces does not cause the link to go down; the link remains active. To avoid potential loss of traffic due to an autonegotiation mismatch, enable autonegotiation on both source and destination interfaces.

Need help?

Open a support case

(Requires a Cisco Service Contract)

The documentation set for this product strives to use bias-free language. For the purposes of this documentation set, bias-free is defined as language that does not imply discrimination based on age, disability, gender, racial identity, ethnic identity, sexual orientation, socioeconomic status, and intersectionality. Exceptions may be present in the documentation due to language that is hardcoded in the user interfaces of the product software, language used based on RFP documentation, or language that is used by a referenced third-party product. Learn more about how Cisco is using Inclusive Language.