[Bug 194238] New: Ping attempted with MTU 9000 transmits fragmented packets of size 1500

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=194238

            Bug ID: 194238
           Summary: Ping attempted with MTU 9000 transmits fragmented
                    packets of size 1500
           Product: Base System
           Version: 10.0-RELEASE
          Hardware: amd64
                OS: Any
            Status: Needs Triage
          Severity: Affects Many People
          Priority: ---
         Component: kern
          Assignee: freebsd-bugs at FreeBSD.org
          Reporter: praveenchoudary.gokina at emulex.com

Setup Details:

Machine1:

OS:  FreeBSD 10.0

We are using below Emulex skyhawk adapter.

oce3 at pci0:4:0:3:        class=0x020000 card=0xe8fe10df chip=0x072010df rev=0x10
hdr=0x00
    vendor     = 'Emulex Corporation'
    device     = 'OneConnect NIC (Skyhawk)'
    class      = network
    subclass   = ethernet
    bar   [10] = type Prefetchable Memory, range 64, base 0xfa700000, size
16384, enabled
    bar   [18] = type Prefetchable Memory, range 64, base 0xfa620000, size
131072, enabled
    bar   [20] = type Prefetchable Memory, range 64, base 0xfa600000, size
131072, enabled


Machine2:
OS:  FreeBSD 10.0

We are using below Emulex skyhawk adapter.
oce1 at pci0:5:0:1:        class=0x020000 card=0xe80010df chip=0x072010df rev=0x10
hdr=0x00
    vendor     = 'Emulex Corporation'
    device     = 'OneConnect NIC (Skyhawk)'
    class      = network
    subclass   = ethernet
    bar   [10] = type Prefetchable Memory, range 64, base 0xfa780000, size
16384, enabled
    bar   [18] = type Prefetchable Memory, range 64, base 0xfa720000, size
131072, enabled
    bar   [20] = type Prefetchable Memory, range 64, base 0xfa700000, size
131072, enabled


Both the adapters are connected directly without switch.

Both the interfaces are configured with mtu=9000 

When we send jumbo frames from machine1 to machine2, packets are getting
fragmented to 1500bytes.

To reproduce, we can use "ping -s 9000 <peer ipaddr> " on Machine1.

tcpdump on Machine1 shows packets of length 1500 bytes.

We are observing this behavior even with other adapters like Intel

igb0 at pci0:2:0:0:        class=0x020000 card=0x152115d9 chip=0x15218086 rev=0x01
hdr=0x00
    vendor     = 'Intel Corporation'
    device     = 'I350 Gigabit Network Connection'
    class      = network
    subclass   = ethernet
    bar   [10] = type Memory, range 32, base 0xfbc20000, size 131072, enabled
    bar   [18] = type I/O Port, range 32, base 0xe020, size 32, enabled
    bar   [1c] = type Memory, range 32, base 0xfbc44000, size 16384, enabled

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