Gigabit: MTU at 9000 not working... pls help

I can set the MTU to 9000, but I can't ping any size over 1472. FTP
transfers don't work either... If I go back to the 1500, I can then
ping sizes over 1472, and FTP works ok (only about 120Mbits). I am
using the bcm5700 modules, and just can't seem to get it! here is my
ifconfig:

eth1 Link encap:Ethernet HWaddr 00:02:A5:E7:1F:10
inet addr:192.168.3.2 Bcast:192.168.3.255
Mask:255.255.252.0
UP BROADCAST RUNNING MULTICAST MTU:9000 Metric:1
RX packets:38 errors:0 dropped:0 overruns:0 frame:0
TX packets:63 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:100
RX bytes:3148 (3.0 Kb) TX bytes:15880 (15.5 Kb)
Interrupt:17 Memory:fe000000-fe010000

/proc/net/nicinfo/eth1.info:

Description HP NC7770 Gigabit Server Adapter
Driver_Name bcm5700
Driver_Version 6.2.17
Bootcode_Version 2.04
PCI_Vendor 0x14e4
PCI_Device_ID 0x1645
PCI_Subsystem_Vendor 0x0e11
PCI_Subsystem_ID 0x007c
PCI_Revision_ID 0x15
PCI_Slot 4
PCI_Bus 0
PCI_Bus_Speed 32-bit PCI 33MHz
Memory 0xfe000000
IRQ 17
System_Device_Name eth1
Current_HWaddr 00:02:a5:e7:1f:10
Permanent_HWaddr 00:02:a5:e7:1f:10
Part_Number 284685-001

Link up
Auto_Negotiate on
Speed_Advertisement 10half 10full 100half 100full 1000half
1000full
Flow_Control_Advertisement pause
Speed 1000
Duplex full
Flow_Control receive/transmit
State up
MTU_Size 9000

Rx_Packets 41
Rx_Jumbo_Packets 0
Tx_Packets 68
Rx_Bytes 3370
Tx_Bytes 16334
Rx_Errors 0
Tx_Errors 0

Tx_Carrier_Errors 0
Tx_Abort_Excess_Coll 0
Tx_Abort_Late_Coll 0
Tx_Deferred_Ok 0
Tx_Single_Coll_Ok 0
Tx_Multi_Coll_Ok 0
Tx_Total_Coll_Ok 0
Tx_XON_Pause_Frames 0
Tx_XOFF_Pause_Frames 0

Rx_CRC_Errors 0
Rx_Short_Fragment_Errors 0
Rx_Short_Length_Errors 0
Rx_Long_Length_Errors 0
Rx_Align_Errors 0
Rx_Overrun_Errors 0
Rx_XON_Pause_Frames 0
Rx_XOFF_Pause_Frames 0

Tx_MAC_Errors 0
Rx_MAC_Errors 0

Tx_Checksum on
Rx_Checksum on
Scatter_Gather on
VLAN off

Tx_Desc_Count 100
Rx_Desc_Count 200
Rx_Jumbo_Desc_Count 128
Adaptive_Coalescing off
Rx_Coalescing_Ticks 18
Rx_Coalesced_Frames 6
Tx_Coalescing_Ticks 200
Tx_Coalesced_Frames 35
Stats_Coalescing_Ticks 1000000
Wake_On_LAN off

"Matthew E. Kozloski" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed) om...
> I can set the MTU to 9000, but I can't ping any size over 1472. FTP
> transfers don't work either... If I go back to the 1500, I can then
> ping sizes over 1472, and FTP works ok (only about 120Mbits). I am
> using the bcm5700 modules, and just can't seem to get it! here is my
> ifconfig:
>

Is this gigabit ethernet? Gigabit ethernet is still ethernet and the maximum
MTU is still 1500 bytes. I'm not sure anything has an MTU of 9000.


--
Andy Zhang

Remove "removethis" to reply by email

Andy Zhang wrote:
> "Matthew E. Kozloski" <(E-Mail Removed)> wrote in message
> news:(E-Mail Removed) om...
>
>>I can set the MTU to 9000, but I can't ping any size over 1472. FTP
>>transfers don't work either... If I go back to the 1500, I can then
>>ping sizes over 1472, and FTP works ok (only about 120Mbits). I am
>>using the bcm5700 modules, and just can't seem to get it! here is my
>>ifconfig:
>>
>
>
> Is this gigabit ethernet? Gigabit ethernet is still ethernet and the maximum
> MTU is still 1500 bytes. I'm not sure anything has an MTU of 9000.

Gigabit supports up to 9000, but the switch and any other devices in the
network have to be configured to support it. I know that our Cisco
switches don't have it enabled by default.

Also the documentation says that the BCM5705 chip does not support Jumbo
MTUs. I don't know what chip the HP NC7770 uses.

Regards, Ian

Andy Zhang wrote:

> Is this gigabit ethernet? Gigabit ethernet is still ethernet and the
> maximum MTU is still 1500 bytes. I'm not sure anything has an MTU of 9000.
>

Token ring can go to 16K and probably more. There is also a method of
sending multiple ethernet frames at once over gigabit. This means that the
individual frames are the same as at lower speeds, but because multiple
frames are sent as a group, the network becomes more efficient.

--

Fundamentalism is fundamentally wrong.

To reply to this message, replace everything to the left of "@" with
james.knott.

Although not part of the 802.3xxx standard, many gigabit cards and
switches, ethernet mind you, support what is known as a jumbo frame or
packet. The largest jumbo frame is 9014 bytes. You loose 14 bytes to
overhead, and get to keep an MTU of 9000 (that is if you card and
switches support it). My cards and switches do support it... At
least that is what the manufacturer is saying (I am begining to wonder
about the switch though).

Matthew E. Kozloski wrote:
> Although not part of the 802.3xxx standard, many gigabit cards and
> switches, ethernet mind you, support what is known as a jumbo frame or
> packet. The largest jumbo frame is 9014 bytes. You loose 14 bytes to
> overhead, and get to keep an MTU of 9000 (that is if you card and
> switches support it). My cards and switches do support it... At
> least that is what the manufacturer is saying (I am begining to wonder
> about the switch though).

The switch may support it but have it turned off by default. Have you
checked its configuration?

Regards, Ian

Ian Northeast wrote:
> Matthew E. Kozloski wrote:
>> Although not part of the 802.3xxx standard, many gigabit cards and
>> switches, ethernet mind you, support what is known as a jumbo frame
>> or packet. The largest jumbo frame is 9014 bytes. You loose 14
>> bytes to overhead, and get to keep an MTU of 9000 (that is if you
>> card and switches support it). My cards and switches do support
>> it... At least that is what the manufacturer is saying (I am
>> begining to wonder about the switch though).
>
> The switch may support it but have it turned off by default. Have you
> checked its configuration?
>
> Regards, Ian

Out of curiosity, does increasing the MTU have a noticable beneficial
effect? I have a client using Fibre gigabit (Cisco 1000SX GBIC's in a
Catalyst 2948XL) and we've not altered the MTU. One of the gigabit servers
runs MS SQL server, one runs Exchange 5.5, another runs Metaframe 1.8 on
NT4.

Would this be a worthwhile modification? Also they're using the Cisco 80xx
8-port gigabit Switch (sorry, can't remember the model exactly).

thanks,

Carl

Netgear LIED TO ME! I have an email from their support that says it
does in fact support the 9000MTU. Well, it doesn't work for me - I
called to complain, and found out that it DOES NOT support anything
higher than 1500. I used to love the netgear products...

Carl Farrington wrote:

> Out of curiosity, does increasing the MTU have a noticable beneficial
> effect? I have a client using Fibre gigabit (Cisco 1000SX GBIC's in a
> Catalyst 2948XL) and we've not altered the MTU. One of the gigabit servers
> runs MS SQL server, one runs Exchange 5.5, another runs Metaframe 1.8 on
> NT4.

I don't actually know as my network admins havn't enabled jumbo frames
on the switches. However, when I ran some contrived tests (priming
filesystem cache, writing to /dev/null) between a pair of IBM x Series
servers with, IIRC, dual 2.0GHz Xeons and Intel EtherExpress Pro1000
NICs, running SuSE 8.1 (again IIRC) connected to the same Cisco 6000
switch, I got about 112MByte/s out of FTP. As this is pretty close to
the theoretical limit, I doubt that enabling jumbo frames would improve
it significantly. Perhaps it would in different circumstances.

Interestingly I can't get that speed out of mega expensive p Series 690
boxes with 1.4GHz Power 4 CPUs and IBM's own gigabit NICs running AIX
5.1 connected to the same switch. I got about 80MB/s out of them. It
would be nice to have a go with Linux on these boxes but I doubt I'll
get a chance.

Regards, Ian

Carl Farrington wrote:

> Out of curiosity, does increasing the MTU have a noticable beneficial
> effect?

That depends on your traffic. If mainly short bursts of data, no. If large
blocks of data, yes.

--

Fundamentalism is fundamentally wrong.

To reply to this message, replace everything to the left of "@" with
james.knott.