tcp profile for heavy packet loss

I'm not sure any congestion control setting is going to help where there is 'heavy packet loss'. What's causing that loss?

 

 

You can modify the TCP Profile and reduce the number of retransmissions from the default of 8 to something lower but of course this means your application will have to handle the data loss. I think it's standard (i.e. in the TCP/IP standard and thus not configurable) for the time between each retransmission to be double that of the previous one, so a value of 4 for instance would probably result in retransmission after 1s, 2s, 4s and finally 8s.

 

 

You might want to investigate the other options in the TCP Profile as some of these might also be beneficial, however, I'd suggest you ultimately need to resolve the root cause of the packet loss.

thanks. definitely true it needs to figure out the packet loss ultimately. but it is in the network of my vendor, I can not even traceroute to them. (really secure!) before that, packet loss has to be mitigated.

 

Is there a way to tune the maximum 64s of retransmission interval to 8 seconds?

 

Scalable is said to be better, but i cannot find a doc about that.

 

 

 

thanks. definitely true it needs to figure out the packet loss ultimately. but it is in the network of my vendor, I can not even traceroute to them. (really secure!) before that, packet loss has to be mitigated.

 

Is there a way to tune the maximum 64s of retransmission interval to 8 seconds?

 

Scalable is said to be better, but i cannot find a doc about that.

 

 

 

thanks. definitely true it needs to figure out the packet loss ultimately. but it is in the network of my vendor, I can not even traceroute to them. (really secure!) before that, packet loss has to be mitigated.

 

Is there a way to tune the maximum 64s of retransmission interval to 8 seconds?

 

Scalable is said to be better, but i cannot find a doc about that.

 

 

 

Fair enough. To reduce the maximum retransmission interval to 8s you'll have to modify the default TCP Profile (or ideally create a new custom one) and reduce the number of retransmissions from 8 to 4. This will result in a max retransmission interval of 8s but obviously means only 4 retransmissions are attempted and past that the source client will have to retransmit or recover as appropriate.

 

There's no way to independently modify the retransmission interval alone, as far as I'm aware.

 

tried setting of "Keep Alive Interval" to 8 sec. disappointed with there are not other tunable parameters for keepalive.

Did it work? Why didn't you change the max. retransmission interval?

 

 

Other parameters can't be changed as they must be standards compliant.

the "max. retransmission interval" is not seen in my LTM. without this "max. retransmission interval" configureable, "Keep Alive Interval" is the only one could be likely to help.

 

keepalive message can be seen, but not able to set how many times to send out keepalive mesg.

Apologies, I should have wrote "Maximum Segment Retransmissions".

Posted By szkwg on 10/08/2012 03:22 PM

 

at this moment my ltm is using 'High Speed'. when there are heavy packet loss, the retransmission timeout goes to 32 seconds, and sometimes goes to 64 seconds. And this causes a whole transaction takes more than 4 minutes to finish, which usually just needs 2 seconds.

 

Wondering if 'Scalable' will be better?

 

Can the maximum retransmission timeout be set to lower value?

 

 

Hi Szkwg,

 

first of all, thank you for this interesting post. If i may, i would like to ask some questions:

 

- what is the average RTT of your link? RTO is normally calculated by RTT measurements, see also http://www.ietf.org/rfc/rfc2988.txt

 

- are those retransmission you are seeing timeout based? I am asking as i would expect dupacks to arrive, causing fast retransmissions.

 

Would you be happy to share an example tcpdump here ?

 

 

To answer your initial question, i would recommend the wom-tcp-wan-optimized profile.

 

regards,

 

Christian