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Forums › LAN (ethernet/Wifi/routers/Bluetooth) › Is 10GbE SFP+ backwards compatible with 1GbE SFP


18 posts

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Topic # 115068 12-Mar-2013 17:12
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Hi everyone

We have a server with on-board 10GbE SFP ethernet but a switch with only 1GbE SFP ports and we're unable to get traffic over the link. Using Linux ethtool I can set the server to run the interface at 1Gb (ethtool -s eth0 speed 1000) but without luck. We're using a SFP+ cable which I believe is backward compatible with SFP.

The server is a HP DL380p Gen8 with NetXtreme II 10GbE controllers.
The switch is a Cisco 3560.

Neither supplier has been much help.

Hopefully someone out there works with this stuff every day and knows right off what we're doing wrong. Any help is appreciated.

Thanks
  Shane

P.S. What's the point of (expensive) SFP ports that only run at 1GbE anyway?

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341 posts

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  Reply # 778699 12-Mar-2013 17:20
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As a general rule, SFP and SFP+ are not compatible. You'll also generally find that you can't have 10 GbE at one end and 1 GbE at the other, even if you're rate limiting the port speed, as the wavelengths will differ.

In general, when dealing with fibre, everything must be exactly the same. It's not remotely plug-n-play.

The purpose of using fibre for 1 GbE comes down to distance. If you're not going over 70m or so, you'll have a much easier time just using Cat6.



18 posts

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  Reply # 778720 12-Mar-2013 17:57
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The cable is copper, but it sounds like your answer will still apply since SFP seems incapable of negotiation. So if 10GbE running at 1GbE is really just throttled 10GbE when we're out of luck, until we upgrade the switch. Right?

 
 
 
 


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  Reply # 778742 12-Mar-2013 18:51
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Hi, depending on brand you can put SFP in SFP+ ports, but not the otherway around.

Cyril

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  Reply # 778764 12-Mar-2013 19:39
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So do you have Copper 10G (Just standard Cat6 Cables) or do you have SPF+ Ports with Fibre SPF+ Adapters?

I don't think Copper will Autoneg to 1G (depends on the Adapters) and with Fibre SPF it will need SPF+ 10G SPF+'s on both ends

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  Reply # 778767 12-Mar-2013 19:42
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or are they SFP twinax cables?

Cyril



18 posts

Geek


  Reply # 778793 12-Mar-2013 20:50
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cyril7: bugga, I was sure I read somewhere that SFP+ cables were backwards compatible with SFP. It's HP brand. No idea, never heard of twinax.

LennonNZ: The cable itself may be cat6 but it states that it is copper and that it is SFP+. ethtool reports that autoneg is not supported, which is why I was setting the DL380 to 1GB speed.

1GbE RJ45 is just so simple :)

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  Reply # 778809 12-Mar-2013 21:24
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Ah.. sounds like a TwinAx Cable. (10GSFP+Cu) Copper Cable with Directly Attached SPF+'s at each end.

Like this?? http://www.amazon.com/Diablo-Cable-24AWG-Copper-Twinax/dp/B005WX2FSU

You'll need a switch which has SPF+ Slots. Cheap? Nope..

I don't even think your 3560 would have 10G of backplane anyway...

You should be able to find a switch with 2 to 4 10G SPF+ Slots and 24 GigE Copper quiet easily..





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  Reply # 781030 13-Mar-2013 11:48
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OK, thanks guys. It looks like we wasted a bit of money. We can just keep using the 1GbE (RJ45) PCIe card and switch to the 10GbE SFP when we replace the Cisco, which I expect is a long way off.

Real shame since the 8 disk raid6 array can push 650MB/s. There's always bonding as a stepping stone.

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  Reply # 783046 17-Mar-2013 18:10
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SFP+ active cables are not backward compatible as far as I know. 10GbaseT (ie Cat6A cable) is backward compatible with 1000baseT (ie cat6 cable), but 10GbaseSX and 10GbaseLX are only compatible with themselves. You could get SFP and SFP+ modules that have RJ45 sockets for standard gigabit ethernet (baseT), or just get a matching module for the SFP+ side. So for example if your SFP is 1000baseSX then you also need that for the SFP+ module.




Qualified in business, certified in fibre, stuck in copper, have to keep going  ^_^

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