I would like to ask you for your personal opinions and experience regarding Jumbo Frames in DC-LAN.
We´ve installed a DC-LAN with Juniper Components: MX960 as Campus Core Switches, SRX3600 as Firewalls for Inter-VRF Traffic, DC-Access Stacks with EX4200/4550 and MC-LAG to a pair of MX-Cores. At the moment we use default mtu-sizes for both L2 and L3. All Backbone Links and Uplinks are AEs with N x 10G. Actually we don´t support Jumbo Frames. The Backbone is a multiservice Core including support for Voice and Multicast.
To introduce Jumbo Frames I would follow up the following strategy:
1) Enable alle Backbone Links / Uplinks to support larger frame sizes on Layer-2 (set Ethernet MTU on AEs to 9216). This is a prerequiste to allow larger frame sizes between Server Access Stacks, but this alone will not allow Jumbo frames on Access Ports to work. The operational risk should be minimal because this will not change the traffic mix in the Core.
2) Stay with Layer-3 mtu on the default (1500 bytes), so all Routing Stuff including ospf mtu negotiation will not be affected.
3) Group the applications with request for Jumbo-Frames in dedicated VLANs (e.g. LAN attached Storage, iSCSI, etc). The goal for the expected Jumbo frames is not to leave the VLAN boundary. In case this will neccessary, we need to make sure that MTU discovery end-2-end will work and the Routers do not need to do fragmentation. This might be tricky if the possible destinations are not known or behind a multiservice-WA N. Jumbo Frames should be kept within a VLAN as much as possible to avoid fragmentation or drops on the routers.
4) Adust Qos/Buffers to make sure that Jumbo frames are not in priority queues and will not delay short realtime traffic pakets (such as voice RTP)
5) Enable L2-MTU on dedicated Access Ports for Jumbo Frames (also 9216) making sure you control sources and destinations of Jumbo Frames as good as possible
This is just a theoretical approach, so I would like that you guys share your experience from the practice with me. Thx for any comments or suggestions in advance.