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Jumbo Frames

dbuckley77
Level 1
Level 1

We have a hub and spoke network that consists of a 6807 core running VSS and mostly 2960X access layer switches with a few 2960Gs here and there.  The core does all the layer three stuff and there are some 10GB and 1gb links to the access layer switches.  We were wondering if it would b e beneficial to enable jumbo frame on all our part of our network and what the pros and cons may be.

3 Replies 3

many thing will be consider if you want to use Jumbo in all network 
are some host use jumbo frame ? are it connect to other host use jumbo ONLY or it connect to host use default 1500 ? 

Reza Sharifi
Hall of Fame
Hall of Fame

Usually, Jumbo frame is not needed in a campus environment with just users and phone connectivity. It is mostly enabled in datacenter, where storage devices and/or VMs are present. In general, you need to have a case for enabling it and not just randomly.

HTH

 

 

Joseph W. Doherty
Hall of Fame
Hall of Fame

Pros:

Better data utilization of link, i.e. 1460/1518 = (about) 96% vs. 8960/9018 = (about) 99%, an increase of about 3% if you use jumbo.

On many devices, improved throughput as PPS demands decrease as packet size increases; recall this may be true for your 2960X, but also recall, 6807 may have consistent PPS rate regardless of packet size; likely the 2960X is wire-rate, for all ports, even with minimum size packets, so this wouldn't matter, might (probably unlikely, though) make a difference on the 6807 if sup and its DFCs, if any, PPS is being exceeded because of lots and lots of minimum size packet traffic.

Cons:

There's no standard for what max MTU should be for jumbo.  Most vendors support 9K something, but the "something" can differ between platforms and cause MTU issues.

Jumbo packets increase store-and-forward, per switch, latency.  (Also why, I suspect, cut-through switching has reappeared.)

Jumbo packets, if corrupted, have bigger impact (whole, larger, packet needs to be resent).  In theory, corrupted larger packets are more likely to slip past packet/frame validation w/o detection (not a huge risk increase, at least for an Ethernet frame's FCS).

New chances to create in-flight fragmentation.

New chances to mismatch MTU on same L2 segment.

More "care and feeding" required.

Summary, unless you really, really need the extra 3% increased data transfer capacity, for most use cases, jumbo not worthwhile.

One use case where jumbo is "nice", if you have tunnels that would normally fragment 1500 byte packets (due to encapsulation overhead), jumbo allows such encapsulated packets to be sent without fragmentation.

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