Change control plane MTU on Cisco ACI - experience ?

[goranje]

Hello all,

We have multi site ACI environment and due to smaller MTU size configured in part of ISN network we need to decrease control plane MTU on both sites, so we do not have issue with MP-BGP neighbor ship between SPINES, that are located in different sites.

(this part of ISN with smaller MTU is using only for backup if primary part of ISN have some issues. So if there is no issues on ISN we have fully function Multi Site ACI deployment in production) 

According Cisco documentation Control plane MTU can be change  under system settings on each site.

BUut there is a note:

" Note:     The global MTU setting shown in figure above applies also to the control plane protocols used inside the ACI fabric (IS-IS, COOP, MP-BGP VPNv4) and to the OSPF protocol used between the spines and the ISN devices. However, no significant performance impact has been noticed when reducing the maximum size for those control plane frames."

Because this change will impact all routings protocol in fabric including COOP, i can assume that IS-IS, MPB-BGP neighbor ships will be reestablish and ...,  the question is:

Do some one have experience how the change will impact all network and services in moment of change of MTU?

Will services on the ACI have some disturbance, some outage, or it will went smoothly  ?

Best regards,

[Tarakesh Jetti]

Hi,

Could you please provide us the 

APIC version:

MSO/NDO version: 

You can also learn more about Cisco ACI through our live Ask the Experts (ATXs) session. Check out the ATXs Resources [https://community.cisco.com/t5/data-center-and-cloud-knowledge/cisco-aci-ask-the-experts-resources/ta-p/4394491] to view the latest schedule for upcoming sessions, as well as the useful references, e.g. online guides, FAQs.
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Thanks and regards,

Tarakesh

Customer Success Specialist - CX Team.

[Tarakesh Jetti]

Hi, 

Modifying Interface MTU Size

The maximum transmission unit (MTU) size specifies the maximum frame size that an Ethernet port can process. For transmissions to occur between two ports, you must configure the same MTU size for both ports. A port drops any frames that exceed its MTU size.

Cisco NX-OS allows you to configure MTU on an interface, with options to configure it on different level in the protocol stack. By default, each interface has an MTU of 1500 bytes, which is the IEEE 802.3 standard for Ethernet frames. Larger MTU sizes are possible for more efficient processing of data to allow different application requirements. The larger frames, are also called jumbo frames, can be up to 9216 bytes in size.

MTU is configured per interface, where an interface can be a Layer 2 or a Layer 3 interface. For a Layer 2 interface, you can configure the MTU size with one of two values, the value system default MTU value or the system jumbo MTU value. The system default MTU value is 1500 bytes. Every Layer 2 interface is configured with this value by default. You can configure an interface with the default system jumbo MTU value, that is 9216 bytes. To allow an MTU value from 1500 through 9216, you must adjust the system jumbo MTU to an appropriate value where interface can be configured with the same value

We would request you to raise a Cisco TAC case to know more about the configurational issues. 

If you find my reply solved your question or issue, kindly click the 'Accept as Solution' button and vote it as helpful.

You can also learn more about Cisco ACI through our live Ask the Experts (ATXs) session. Check out the ATXs Resources [https://community.cisco.com/t5/data-center-and-cloud-knowledge/cisco-aci-ask-the-experts-resources/ta-p/4394491] to view the latest schedule for upcoming sessions, as well as the useful references, e.g. online guides, FAQs.

Thanks and regards,

Tarakesh

Customer Success Specialist - CX Team.

[arambasil]

The maximum transmission unit (MTU) defines the largest data packet that can be transmitted over a network connection. For successful data transfer between two devices, both ends must have the same MTU size configured. If a data packet exceeds the MTU size of the receiving device, it will be dropped.

Cisco NX-OS provides the flexibility to configure MTU at various levels within the network stack. The default MTU size for Ethernet interfaces is 1500 bytes, adhering to the IEEE 802.3 standard. Larger MTUs, known as jumbo frames, can be employed to enhance data transmission efficiency and cater to specific application requirements. Jumbo frames can reach a maximum size of 9216 bytes.

ILT20