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keepitsimpleengineer
Asked: 2015-12-15 05:14:09 +0800 CST

How can I get the NIC to respond to jumbo packets when MTU is set to 4000

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I have a mythbuntu 14.04 server. 

# uname -a
Linux KISE-055 3.16.0-55-generic #74~14.04.1-Ubuntu SMP Tue Nov 17 10:15:59 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux

I have the MTU set to 4000 vice 1500 to get jumbo packets...

# ip link
...
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 4000 qdisc pfifo_fast state UP mode DEFAULT group default qlen 1000
link/ether 90:fb:a6:eb:d7:f3 brd ff:ff:ff:ff:ff:ff

I set the MTU in /etc/network/interfaces

# cat /etc/network/interfaces
auto lo
iface lo inet loopback
#primary wired interface
auto eth0
iface eth0 inet dhcp
post-up /sbin/ifconfig eth0 mtu 4000

Which can be seen in the output of 'ifconfig'...

~$ ifconfig
eth0      Link encap:Ethernet  HWaddr 90:fb:a6:eb:d7:f3
      inet addr:192.168.0.55  Bcast:192.168.0.255  Mask:255.255.255.0
      inet6 addr: fe80::92fb:a6ff:feeb:d7f3/64 Scope:Link
  ⇛ ⇛ UP BROADCAST RUNNING MULTICAST  MTU:4000  Metric:1  ⇚ ⇚
      RX packets:43654 errors:0 dropped:0 overruns:0 frame:0
      TX packets:41807 errors:0 dropped:0 overruns:0 carrier:0
      collisions:0 txqueuelen:1000
      RX bytes:29877609 (29.8 MB)  TX bytes:21276131 (21.2 MB)

lo        Link encap:Local Loopback
      inet addr:127.0.0.1  Mask:255.0.0.0
      inet6 addr: ::1/128 Scope:Host
      UP LOOPBACK RUNNING  MTU:65536  Metric:1
      RX packets:2010 errors:0 dropped:0 overruns:0 frame:0
      TX packets:2010 errors:0 dropped:0 overruns:0 carrier:0
      collisions:0 txqueuelen:0
      RX bytes:279223 (279.2 KB)  TX bytes:279223 (279.2 KB)

But the system does not respond to jumbo packets from other computers on the LAN. So all it's clients must use an MTU of 1500 to talk to the server.

Here's the nic...

02:00.0 Ethernet controller: Realtek Semiconductor Co., Ltd. RTL8111/8168/8411 PCI Express Gigabit Ethernet Controller (rev 03)
    Subsystem: Foxconn International, Inc. Device 0e22
    Control: I/O+ Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr- Stepping- SERR+ FastB2B- DisINTx+
    Status: Cap+ 66MHz- UDF- FastB2B- ParErr- DEVSEL=fast >TAbort- <TAbort- <MAbort- >SERR- <PERR- INTx-
    Latency: 0, Cache Line Size: 64 bytes
    Interrupt: pin A routed to IRQ 47
    Region 0: I/O ports at e800 [size=256]
    Region 2: Memory at fafff000 (64-bit, prefetchable) [size=4K]
    Region 4: Memory at faff8000 (64-bit, prefetchable) [size=16K]
    Expansion ROM at fdfe0000 [disabled] [size=128K]
    Capabilities: [40] Power Management version 3
            Flags: PMEClk- DSI- D1+ D2+ AuxCurrent=375mA PME(D0+,D1+,D2+,D3hot+,D3cold+)
            Status: D0 NoSoftRst+ PME-Enable- DSel=0 DScale=0 PME-
    Capabilities: [50] MSI: Enable+ Count=1/1 Maskable- 64bit+
            Address: 00000000fee0200c  Data: 4142
    Capabilities: [70] Express (v2) Endpoint, MSI 01
            DevCap: MaxPayload 256 bytes, PhantFunc 0, Latency L0s <512ns, L1 <64us
                    ExtTag- AttnBtn- AttnInd- PwrInd- RBE+ FLReset-
            DevCtl: Report errors: Correctable- Non-Fatal- Fatal- Unsupported-
                    RlxdOrd- ExtTag- PhantFunc- AuxPwr- NoSnoop-
                    MaxPayload 128 bytes, MaxReadReq 512 bytes
            DevSta: CorrErr+ UncorrErr- FatalErr- UnsuppReq+ AuxPwr+ TransPend-
            LnkCap: Port #0, Speed 2.5GT/s, Width x1, ASPM L0s L1, Exit Latency L0s <512ns, L1 <64us
                    ClockPM+ Surprise- LLActRep- BwNot-
            LnkCtl: ASPM Disabled; RCB 64 bytes Disabled- CommClk+
                    ExtSynch- ClockPM- AutWidDis- BWInt- AutBWInt-
            LnkSta: Speed 2.5GT/s, Width x1, TrErr- Train- SlotClk+ DLActive- BWMgmt- ABWMgmt-
            DevCap2: Completion Timeout: Not Supported, TimeoutDis+, LTR-, OBFF Not Supported
            DevCtl2: Completion Timeout: 50us to 50ms, TimeoutDis-, LTR-, OBFF Disabled
            LnkCtl2: Target Link Speed: 2.5GT/s, EnterCompliance- SpeedDis-
                     Transmit Margin: Normal Operating Range, EnterModifiedCompliance- ComplianceSOS-
                     Compliance De-emphasis: -6dB
            LnkSta2: Current De-emphasis Level: -6dB, EqualizationComplete-, EqualizationPhase1-
                     EqualizationPhase2-, EqualizationPhase3-, LinkEqualizationRequest-
    Capabilities: [ac] MSI-X: Enable- Count=4 Masked-
            Vector table: BAR=4 offset=00000000
            PBA: BAR=4 offset=00000800
    Capabilities: [cc] Vital Product Data
            Unknown small resource type 00, will not decode more.
    Capabilities: [100 v1] Advanced Error Reporting
            UESta:  DLP- SDES- TLP- FCP- CmpltTO- CmpltAbrt- UnxCmplt- RxOF- MalfTLP- ECRC- UnsupReq- ACSViol-
            UEMsk:  DLP- SDES- TLP- FCP- CmpltTO- CmpltAbrt- UnxCmplt- RxOF- MalfTLP- ECRC- UnsupReq- ACSViol-
            UESvrt: DLP+ SDES+ TLP- FCP+ CmpltTO- CmpltAbrt- UnxCmplt- RxOF+ MalfTLP+ ECRC- UnsupReq- ACSViol-
            CESta:  RxErr- BadTLP- BadDLLP- Rollover- Timeout- NonFatalErr+
            CEMsk:  RxErr- BadTLP- BadDLLP- Rollover- Timeout- NonFatalErr+
            AERCap: First Error Pointer: 00, GenCap+ CGenEn- ChkCap+ ChkEn-
    Capabilities: [140 v1] Virtual Channel
            Caps:   LPEVC=0 RefClk=100ns PATEntryBits=1
            Arb:    Fixed- WRR32- WRR64- WRR128-
            Ctrl:   ArbSelect=Fixed
            Status: InProgress-
            VC0:    Caps:   PATOffset=00 MaxTimeSlots=1 RejSnoopTrans-
                    Arb:    Fixed- WRR32- WRR64- WRR128- TWRR128- WRR256-
                    Ctrl:   Enable+ ID=0 ArbSelect=Fixed TC/VC=ff
                    Status: NegoPending- InProgress-
    Capabilities: [160 v1] Device Serial Number 16-00-00-00-68-4c-e0-00
    Kernel driver in use: r8169
networking

1 Answers

  1. I have a question about your environment, What kind of switch do you have? and is the switch configured to Jumbo Frames.

    • 0