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NSX vxlan mtu size and cisco switches

Hello,

There is a need to set up NSX in our environment. The NSX will be installed on hosts running on HP Virtual Connect, administered by the System team. HP Virtual Connect switches connect to Nexus 5672UP, which in turn connects to 6509 (Version 12.2(18)SXF17a) that access as the L3 switch in the domain.

I have created an SVI on the 6509 for the VXLAN, and this vlan is propagated all the way to the hosts running NSX. Here is my question:

VMWare vxlan requires MTU 1600. Is this something that will be used only in the host part of the setup or do I need to enable MTU size 1600, throughout the whole domain? If this is the case, where do I set the MTU size? Do I change the system MTU on 6509? Do I set the MTU on the SVI? Do I set it on all the interfaces leading to the hosts? Do I enable jumbo frames on the Nexus 5K?

 

MTU always results in a great headache, so any info will be highly appreciated.

 

Thank you in advance,

Katerina

 

4 Replies 4

nazimkha
Level 4
Level 4
Hi Katerina,

From your post I understand you have built a VXLAN based fabric with Nexus 9K switches. The border leaf switches connect to the Catalyst 6509 which acts as a core.

Now the questions are :
Does the VLAN gateway reside on the Catalyst 6509 or it is configured on the leaf switches ?

You may have to set jumbo mtu on all interfaces

Hi,
We are planning to deploy vmware nsx and the vxlan is used for the virtual endpoints (vtep) inside the nsx configuration. There are no nexus 9k, just nexus 5k where the esxi hosts connect, through HP virtual connect switches. The L3 gateway for ips assigned to vtep is the 6509. I don’t understand if i need to adjust the mtu size in all the domain to 1600 and where to adjust it if needed.

Thanks

Generally for a VXLAN fabric, we set the jumbo mtu in the VXLAN underlay.

In this case, since the NSX is adding the VXLAN header so it has to be enabled for the entire domain everywhere the VXLAN encapsulated packet is forwarded

adding mtu to a VXLAN switching network can be done as per this link :
https://www.cisco.com/c/en/us/td/docs/switches/datacenter/pf/configuration/guide/b-pf-configuration/IP-Fabric-Underlay-Options.html

Thank you for the link. I will surely consult it.

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