Enabling jumbo frames on WAN link

[Borman Bravo]

Should I expect any impact on applications after enabling jumbo frames? I have two sites connected over a 10Gb link terminated at 6509's on each site, an SRDF deployment requirement calls for the enabling of jumbo frames across the WAN and LAN on the path between the EMC devices, has anyone experienced any issues after enabling jumbo frames? Thanks in advance.

[Steve Lyons]

Jumbo frame support is required for frame sizes over the standard 1500 byte mtu. An example of why this is required is MPLS. MPLS requires an additional 4-bytes. To enable support for mpls packets jumbo frame support should be enabled. If your application requires frame sizes above 1500 bytes then jumbo frame support is required.

Refer to the following link and search for additional features:

http://www.cisco.com/en/US/prod/collateral/routers/ps5854/product_data_sheet0900aecd8016be8d.html

[Borman Bravo]

Stelyons, thanks but my question is not about how to configure jumbo frames, that I know, the question is if I should expect any impact on some applications?

[Steve Lyons]

You should not experience any problems if all the infrastructure is set to the same mtu size. Although, without knowing your topology it would be impossible to predict. I would recommend anytime you make significant changes, like mtu adjustments, always baseline your network performance prior to these change and then monitor after you make these changes. I have seen bgp affected by MTU mismatches (finite state machine errors). Also scenarios where the MTU of packets arriving at an interface configured with a smaller MTU will be dropped, i.e.: MTU mismatch. I would recommend consulting with your Cisco Support Engineer for network design related questions.

Steve Lyons