- L2VPN Protocol-Based CLIs
- Any Transport over MPLS
- L2VPN Interworking
- L2VPN Pseudowire Preferential Forwarding
- L2VPN Multisegment Pseudowires
- MPLS Quality of Service
- QoS Policy Support for L2VPN ATM PVPs
- MPLS Pseudowire Status Signaling
- L2VPN VPLS Inter-AS Option B
- AToM Static Pseudowire Provisioning
- MPLS MTU Command Changes
- L2VPN Pseudowire Redundancy
- L2VPN Pseudowire Switching
- VPLS MAC Address Withdrawal
- Hot Standby Pseudowire Support for ATM and TDM Access Circuits
- Configuring Virtual Private LAN Services
- Routed Pseudo-Wire and Routed VPLS
- VPLS Autodiscovery BGP Based
- QoS Policies for VFI Pseudowires
- VPLS BGP Signaling L2VPN Inter-AS Option B
- Loop-Free Alternate Fast Reroute with L2VPN
Contents
- MPLS MTU Command Changes
- Finding Feature Information
- Information About MPLS MTU Command Changes
- MPLS MTU Values During Upgrade
- Guidelines for Setting MPLS MTU and Interface MTU Values
- MPLS MTU Values for Ethernet Interfaces
- How to Configure MPLS MTU Values
- Setting the Interface MTU and MPLS MTU Values
- Setting the MPLS MTU Value on an Ethernet Interface
- Setting the MPLS MTU Value to the Maximum on L3VPN Profiles
- Configuration Examples for Setting the MPLS MTU Values
- Example Setting the Interface MTU and MPLS MTU
- Example Setting the MPLS MTU Value on an Ethernet Interface
- Example Setting the MPLS MTU Value to the Maximum MTU on L3VPN profiles
- Additional References
- Feature Information for MPLS MTU Command Changes
MPLS MTU Command Changes
This document explains the change in the behavior of the mplsmtu command for the following Cisco IOS releases:
- 12.2(27)SBC and later
- 12.2(33)SRA and later
- 12.2(33)SXH and later
- 12.4(11)T and later
- 15.0(1)M1
- 15.1(2)S
You cannot set the Multiprotocol Label Switching (MPLS) maximum transmission unit (MTU) to a value larger than the interface MTU value. This eliminates problems such as dropped packets, data corruption, and high CPU rates from occurring when the MPLS MTU value settings are larger than the interface MTU values. Cisco IOS software allows the MPLS MTU value to be higher than the interface MTU value only for interfaces that have a default interface MTU value of 1580 or less.
 Note | In Cisco IOS Release 15.0(1)M1, you can configure the interface MTU on PA-1FE and PA-2FE port adapters (PAs). The range of values is from 1500 to 1530. Before this enhancement, the MTU of those interfaces was not configurable, and any attempt to configure the interface MTU displayed the following message: %Interface{InterfaceName}doesnotsupportusersettablemtu. |
- Finding Feature Information
- Information About MPLS MTU Command Changes
- How to Configure MPLS MTU Values
- Configuration Examples for Setting the MPLS MTU Values
- Additional References
- Feature Information for MPLS MTU Command Changes
Finding Feature Information
Your software release may not support all the features documented in this module. For the latest caveats and feature information, see Bug Search Tool and the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the feature information table at the end of this module.
Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.
Information About MPLS MTU Command Changes
- MPLS MTU Values During Upgrade
- Guidelines for Setting MPLS MTU and Interface MTU Values
- MPLS MTU Values for Ethernet Interfaces
MPLS MTU Values During Upgrade
If you have configuration files with MPLS MTU values that are larger than the interface MTU values and you upgrade to Cisco IOS Release 12.2(27)SBC, 12.2(33)SRA, 12.4(11)T, 12.2(33)SXH, or later releases, the software does not change the MPLS MTU value. When you reboot the router, the software accepts the values that are set for the MPLS MTU and the interface MTU. The following error message is displayed during system initialization:
Setting the mpls mtu to xxxx on interface x/x, which is higher than the interface MTU xxxx. This could lead to packet forwarding problems including packet drops. You must set the MPLS MTU values equal to or lower than the interface MTU values.
 Caution | If you do not set the MPLS MTU less than or equal to the interface MTU, data corruption, dropped packets, and high CPU conditions can occur. |
Guidelines for Setting MPLS MTU and Interface MTU Values
When configuring the network to use MPLS, set the core-facing interface MTU values greater than the edge-facing interface MTU values using one of the following methods:
- Set the interface MTU values on the core-facing interfaces to a higher value than the interface MTU values on the customer-facing interfaces to accommodate any packet labels, such as MPLS labels, that an interface might encounter. Make sure that the interface MTUs on the remote end interfaces have the same interface MTU values. The interface MTU values on both ends of the link must match.
- Set the interface MTU values on the customer-facing interfaces to a lower value than the interface MTU on the core-facing interfaces to accommodate any packet labels, such as MPLS labels, that an interface might encounter. When you set the interface MTU on the edge interfaces, ensure that the interface MTUs on the remote end interfaces have the same values. The interface MTU values on both ends of the link must match.
Changing the interface MTU can also modify the IP MTU, Connectionless Network Service (CLNS) MTU, and other MTU values because they depend on the value of the interface MTU. The Open Shortest Path First (OSPF) routing protocol requires that the IP MTU values match on both ends of the link. Similarly, the Intermediate System-to-Intermediate System (IS-IS) routing protocol requires that the CLNS MTU values match on both ends of the link. If the values on both ends of the link do not match, IS-IS or OSPF cannot complete initialization.
If the configuration of the adjacent router does not include the mplsmtuand mtu commands, add these commands to the router.
Note | The MPLS MTU setting is displayed only in the show running-config output if the MPLS MTU value is different from the interface MTU value. If the values match, only the interface MTU value is displayed. |
If you attempt to set the MPLS MTU value higher than the interface MTU value, the software displays the following error message, which prompts you to set the interface MTU to a higher value before you set the MPLS MTU value:
% Please increase interface mtu to xxxx and then set mpls mtu
Note | In Cisco IOS Release 15.1(2)S, the mplsmtu command was modified. This command was made available in L3VPN encapsulation configuration mode. The maximum keyword was replaced with the max keyword. The override keyword and the bytes argument were removed from the GRE tunnel interface. To set MPLS MTU to the maximum MTU on L3VPN profiles, use the mplsmtu command in L3VPN encapsulation configuration mode. |
MPLS MTU Values for Ethernet Interfaces
If you have an interface with a default interface MTU value of 1580 or less (such as an Ethernet interface), the mplsmtu command provides an overridekeyword, which allows you to set the MPLS MTU to a value higher than the interface MTU value. The override keyword is not available for interface types that do not have a default interface MTU value of 1580 or less. For configuration details, see the Setting the MPLS MTU Value on an Ethernet Interface.
Setting the MPLS MTU value higher than the Ethernet interface MTU value can lead to dropped packets, data corruption, or high CPU rates. When you set the MPLS MTU value higher than the Ethernet interface MTU value, the software displays the following message:
%MFI-30-MPLS_MTU_SET: Setting the mpls mtu to xxxx on Ethernet x/x, which is higher than the interface MTU xxxx. This could lead to packet forwarding problems including packet drops. Most drivers will be able to support baby giants and will gracefully drop packets that are too large. Certain drivers will have packet forwarding problems including data corruption. Setting the mpls mtu higher than the interface mtu can lead to packet forwarding problems and may be blocked in a future release.
Note | Theoverride keyword is supported in Cisco IOS Release 12.2(27)SBC, 12.2(33)SRA, 12.4(11)T, 12.2(33)SXH, and later releases, but may not be supported in a future release. |
How to Configure MPLS MTU Values
The following sections explain how to configure MPLS MTU and interface MTU values:
- Setting the Interface MTU and MPLS MTU Values
- Setting the MPLS MTU Value on an Ethernet Interface
- Setting the MPLS MTU Value to the Maximum on L3VPN Profiles
Setting the Interface MTU and MPLS MTU Values
Use the following steps to set the interface MTU and the MPLS MTU.
Note | In Cisco IOS Release 15.0(1)M1, you can configure the interface MTU on PA-1FE and PA-2FE port adapters. The range of values is from 1500 to 1530. Before this enhancement, the MTU of those interfaces was not configurable. |
1.
enable
2.
configure
terminal
3.
interface
type
slot
/
port
4.
mtu
bytes
5.
mpls
mtu
bytes
6.
end
DETAILED STEPS
Setting the MPLS MTU Value on an Ethernet Interface
Use the following steps to set the MPLS MTU value on an Ethernet interface.
1.
enable
2.
configure
terminal
3.
interface
type
slot
/
port
4.
mpls
mtu
override
bytes
5.
end
DETAILED STEPS
Setting the MPLS MTU Value to the Maximum on L3VPN Profiles
Use the following steps to set the MPLS MTU value to the maximum on L3VPN profiles.
1.
enable
2.
configure
terminal
3.
l3vpn
encapsulation
ip
profile
4.
mpls
mtu
max
5.
end
DETAILED STEPS
| Command or Action | Purpose | |
|---|---|---|
| Step 1 |
enable
Example: Router> enable |
Enables privileged EXEC mode.
|
| Step 2 |
configure
terminal
Example: Router# configure terminal |
Enters global configuration mode. |
| Step 3 |
l3vpn
encapsulation
ip
profile
Example: Router(config)# l3vpn encapsulation ip profile1 |
Configures an L3VPN encapsulation profile and enters the L3VPN encapsulation configuration mode. |
| Step 4 |
mpls
mtu
max
Example: Router(config-l3vpn-encap-ip)# mpls mtu max |
Sets the MPLS MTU value to the maximum MTU on the L3VPN profile. |
| Step 5 |
end
Example: Router(config-l3vpn-encap-ip)# end |
Exits L3VPN encapsulation configuration mode and returns to privileged EXEC mode. |
Configuration Examples for Setting the MPLS MTU Values
- Example Setting the Interface MTU and MPLS MTU
- Example Setting the MPLS MTU Value on an Ethernet Interface
- Example Setting the MPLS MTU Value to the Maximum MTU on L3VPN profiles
Example Setting the Interface MTU and MPLS MTU
The following example shows how to set the interface and MPLS MTU values. The serial interface in the following configuration examples is at the default interface MTU value. The MPLS MTU value is not set. The interface settings are as follows:
interface Serial 4/0 ip unnumbered Loopback0 mpls traffic-eng tunnels mpls ip serial restart-delay 0 ip rsvp bandwidth 2000 2000 end
The following example attempts to set the MPLS MTU value to 1520. This returns an error because MPLS MTU cannot be set to a value greater than the value of the interface MTU.
Router# configure terminal Enter configuration commands, one per line. End with CNTL/Z. Router(config)# interface serial 4/0 Router(config-if)# mpls mtu 1520 % Please increase interface mtu to 1520 and then set mpls mtu
The following example first sets the interface MTU to 1520 and then sets the MPLS MTU to 1520:
Router(config-if)# mtu 1520 Router(config-if)# mpls mtu 1520
The following example shows the new interface MTU value. The MPLS MTU value is not displayed because it is equal to the interface value.
Router# show running-config interface serial 4/0 Building configuration... interface Serial4/0 mtu 1520 ip unnumbered Loopback0 mpls traffic-eng tunnels mpls ip serial restart-delay 0 ip rsvp bandwidth 2000 2000 end
The following example sets the MPLS MTU value to 1510:
Router(config-if)# mpls mtu 1510
The following example shows the new interface MTU value. The MPLS MTU value is displayed because it is different than the interface MTU value.
Router# show running-config interface serial 4/0 Building configuration... interface Serial4/0 mtu 1520 ip unnumbered Loopback0 mpls mtu 1510 mpls traffic-eng tunnels mpls ip serial restart-delay 0 ip rsvp bandwidth 2000 2000 end
Example Setting the MPLS MTU Value on an Ethernet Interface
Caution | Setting the MPLS MTU to a value higher than the Ethernet interface MTU value can lead to dropped packets, data corruption, or high CPU rates. |
The following example shows how to set the MPLS MTU values on an Ethernet interface. The Ethernet interface in the following configuration examples is at the default interface MTU value. The MPLS MTU value is not set. The interface settings are as follows:
interface Ethernet 2/0 ip unnumbered Loopback0 mpls traffic-eng tunnels mpls ip serial restart-delay 0 ip rsvp bandwidth 2000 2000 end
The following example uses the override keyword to set the MPLS MTU to 1520, which is higher than the Ethernet interface’s MTU value:
Router(config-if)# mpls mtu override 1520 %MFI-30-MPLS_MTU_SET: Setting the mpls mtu to 1520 on Ethernet2/0, which is higher than the interface MTU 1500. This could lead to packet forwarding problems including packet drops.
The following example shows the new MPLS MTU value:
Router# show running-config interface ethernet 2/0 Building configuration... interface Ethernet 2/0 mtu 1500 ip unnumbered Loopback0 mpls mtu 1520 mpls traffic-eng tunnels mpls ip serial restart-delay 0 ip rsvp bandwidth 2000 2000 end
Example Setting the MPLS MTU Value to the Maximum MTU on L3VPN profiles
The following example shows how to set the MPLS MTU value to the maximum MTU on L3VPN profiles:
Router# configure terminal Router(config)# l3vpn encapsulation ip profile1 Router(config-l3vpn-encap-ip)# mpls mtu max
Additional References
Related Documents
|
Related Topic |
Document Title |
|---|---|
|
Cisco IOS commands |
|
|
MPLS commands |
|
MIBs
|
MIBs |
MIBs Link |
|---|---|
|
None. |
To locate and download MIBs for selected platforms, Cisco IOS releases, and feature sets, use Cisco MIB Locator found at the following URL: |
Technical Assistance
|
Description |
Link |
|---|---|
|
The Cisco Support and Documentation website provides online resources to download documentation, software, and tools. Use these resources to install and configure the software and to troubleshoot and resolve technical issues with Cisco products and technologies. Access to most tools on the Cisco Support and Documentation website requires a Cisco.com user ID and password. |
http://www.cisco.com/cisco/web/support/index.html
|
Feature Information for MPLS MTU Command Changes
The following table provides release information about the feature or features described in this module. This table lists only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise, subsequent releases of that software release train also support that feature.
Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.
|
Feature Name |
Releases |
Feature Information |
|---|---|---|
|
MPLS MTU Command Changes |
12.2(27)SBC 12.2(28)SB 12.2(33)SRA 12.2(33)SXH 12.4(11)T 15.0(1)M1 15.1(2)S |
This document explains the changes to the mplsmtu command. You cannot set the MPLS MTU value larger than the interface MTU value, except for Ethernet interfaces. In 12.2(28)SB, support was added for the Cisco 10000 router. In 12.2(33)SRA, support was added for the Cisco 7600 series router. This feature was integrated into Cisco IOS Release 12.4(11)T. This feature was integrated into Cisco IOS Release 12.2(33)SXH. In 15.0(1)M1, you can configure the interface MTU on PA-1FE and PA-2FE port adapters. In 15.1(2)S, the mplsmtu command was made available in L3VPN encapsulation configuration mode. The maximum keyword was replaced with the max keyword. The override keyword and the bytes argument were removed from the GRE tunnel interface. |