[j-nsp] RFC2544 on Juniper MX960 10G ports

[Alex]

Chris,
Line rate on one 10G port could be different from line-rate on another 10G 
port because Ethernet is not bit-synchronous.
LAN-PHY 10GBASE-S allowed transmitter clock tolerance is 10.3125Gbd +/1 
100ppm (parts per million) and LAN-PHY 10GBASE-S allowed receiver clock 
tolerance is also 10.3125Gbd +/- 100ppm. See IEEE 802.3-2008 spec sections 
52.5.1 and 52.5.2.
So in reality the Rx on ingress port could run at 10.31353125Gbd and Tx on 
egress port could run at 10.31146875Gbd. This 0.0020625Gbd=2.0625Mbd 
difference causes ingress buffer to grow until there is no more room and 
eventually an "overspill" and packet drop. Please run Your tests at 99% line 
rate, I am sure there will be no packet loss at all.
Rgds
Alex


----- Original Message ----- 
From: "Chris Evans" <chrisccnpspam2 at gmail.com>
To: "Joerg Staedele" <js at tnib.de>
Cc: "juniper-nsp" <juniper-nsp at puck.nether.net>
Sent: Sunday, March 14, 2010 7:28 PM
Subject: Re: [j-nsp] RFC2544 on Juniper MX960 10G ports


> Joerg,
>
> The hardware we have in our lab is the 20xSFP + 2x10Gig.. JTAC says this
> 'should' work but obviously it doesn't.. I tested it on an EX switch and 
> it
> had no issues.. In a simple L2 mode the MX lost about 47% packets at 
> 64byte
> 10Gig line rates. In L3 mode is lost about 5.2%.. This is when testing 
> full
> duplex flows. This was with 9.6R3.8.. There is a known PR related to this
> issue.
>
> Hope to have some resolution sometime this week..
>
> On Sun, Mar 14, 2010 at 3:14 PM, Joerg Staedele <js at tnib.de> wrote:
>
>> Hi,
>>
>> so this means that this Linecard is not able to do line-rate forwarding
>> with small frame sizes? What about other cards (20xSFP+2x10G) .. I guess
>> they use exactly the same PFE hardware? So they have this limitation 
>> aswell?
>>
>> I am really confused now because in every document you read that the 
>> DPCE's
>> are able to do line-rate at any frame-size?
>>
>> Regards,
>>  Joerg
>>
>> -----Original Message-----
>> From: juniper-nsp-bounces at puck.nether.net [mailto:
>> juniper-nsp-bounces at puck.nether.net] On Behalf Of Jonathan Lassoff
>> Sent: Sunday, March 14, 2010 6:55 PM
>> To: Serge Vautour
>> Cc: juniper-nsp
>> Subject: Re: [j-nsp] RFC2544 on Juniper MX960 10G ports
>>
>> Excerpts from Serge Vautour's message of Thu Feb 18 16:28:44 -0800 2010:
>> > Hello,
>> >
>> > We recently used a traffic generator to run RFC2544 tests against a
>> Juniper MX960. The 1G ports work flawlessly. 0% packet loss at all frame
>> sizes.
>> >
>> > The 10G ports  (4x10G "R" card) didn't do as well. They dropped up to 
>> > 25%
>> packets with certain small frames (ex: 70 byte frames). The packet loss 
>> goes
>> away almost completely for frames larger than 100 bytes. Our SE tells us
>> this is normal and is due to how the MX chops the frames up into 64 byte
>> cells inside the PFE. The 4x10G cards have 4 separate PFEs (1 per 10G 
>> port)
>> and each of them has 10G of bandwidth. 10G of small frames essentially
>> creates more than 10G of traffic inside the PFE. That explanation may not 
>> be
>> 100% correct but I think it paints the right picture.
>> >
>> > Now the questions. Is this a problem on production networks with real
>> world traffic? What about on VPN networks with alot of small frames like
>> VoIP? Has anyone seen this problem creep it's head in production?
>>
>> Isn't the minimum Ethernet frame size 64 bytes? I think Ethernet II /
>> Ethernet 802.3 requires this.
>>
>> Wouldn't this make the problem moot if you're just running Ethernet?
>>
>> Might be a problem with small ATM cells?
>>
>> Cheers,
>> jof
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