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Contributor
Posts: 47
Registered: ‎07-21-2009

FCIP parameter question

Hello,

   I have a couple of Brocade 7500 talking to each other using FCIP tunnels.  We are seeing retransmissions but networking is not seeing any packet drops. There is a parameter called Min Retransmit Time with a default value of 100ms. We are thinking, maybe we are running over this limit which is causing retransmissions. Has anybody every played with this parameter or if what we are thinking could be a probable cause of retransmissions or if we are just looking in the wrong direction.

Any help is appreciated.


Moeen

Regular Contributor
Posts: 178
Registered: ‎04-21-2008

Re: FCIP parameter question

Hi Moeen,

How many tcp retransmits do you have ?

FYI here is a drawing of retransmits on ge interface on one of my 7500 :

BESD100-tcpretransmit-Pge0.gif

I don't have any issues with FCIP flows

Hope this helps

Kind regards,

--

david

Contributor
Posts: 47
Registered: ‎07-21-2009

Re: FCIP parameter question

Here is latest stats.

Performance stats:
                8691577231 output packets
                   5671 pkt/s 30s avg, 15772 pkt/s lifetime avg
                8414301449756 output Bytes
                   5015530 Bps 30s avg, 15269246 Bps lifetime avg
                1111952660 packets lost (retransmits)
                   4.30% loss rate 30s avg
                6515082828 input packets
                   4081 pkt/s 30s avg, 11822 pkt/s lifetime avg
                1558970946184 input Bytes
                   539726 Bps 30s avg, 2829030 Bps lifetime avg

Tunnel has been up for 6 days and 9 hours.  The loss rate goes up to as much as 16% at times..

By the way, what are you using for the graph ?

Valued Contributor
Posts: 931
Registered: ‎12-30-2009

Re: FCIP parameter question

By the way, what are you using for the graph ?

Graph is produced by RRDTool. Data collection is probably done by SNMP with tools like Cacti.

Regular Contributor
Posts: 178
Registered: ‎04-21-2008

Re: FCIP parameter question

here stats from mine :

Performance stats:
                25411149126 output packets
                   14885 pkt/s 30s avg, 23556 pkt/s lifetime avg
                28504168177784 output Bytes
                   12255456 Bps 30s avg, 26423355 Bps lifetime avg
                321625 packets lost (retransmits)
                   0.00% loss rate 30s avg
                24231790657 input packets
                   15404 pkt/s 30s avg, 22462 pkt/s lifetime avg
                23101403295932 input Bytes
                   14352944 Bps 30s avg, 21414993 Bps lifetime avg

very few retransmits compared to yours ... Min Retransmit Time is default value (100).

As said by Dion, I use rrdtool (a GREAT tool, thanks Tobi !) and my data collection tool is .... as simple  as snmpwalk on FCIP MIB.

One thing you may consider : how did you configure MTU size on IP interfaces ?

Kind regards,

--

david

Frequent Contributor
Posts: 76
Registered: ‎02-13-2010

Re: FCIP parameter question

You rate is 12% of retransmissions. This is too much. Actually retransmissions on the TCP protocol are normal and expected but in your case retransmissions are too high.

This is because poor quality of the link. Network issue. Talk to your IP network administrator to solve the issue.

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