Poor TCP throughput across a LES

[kevinhobson2000]

HI All,

I have a issue with throughput across a sub millisecond LES link.  Topology below:

Nexus3k -------------------------------------------- LES ---------------------------------------- Nexus3k

    |                                                                                                                              |

    |                                                                                                                              |

    |                                                                                                                              |

Server 1                                                                                                                 Server 2

Tests done below:

1.  Server 1 through switch to laptop on another port 500 meg.

2.  Server 2 through switch to laptop on another port 500 meg

3.  Server 1 to Server 2 17 meg.

4. Laptop on the LES Patch to Server 2 17 meg.

5. Laptop to Laptop at each patch 500 Meg.

I have done a capture and see a few retransmissions which indicates that acks are being lost somewhere in the path.

So i am thinking im going to have to find out if the packet reaches its destination and if so where the ack is being lost.

The only other thing i can think of is that the Windows Server Stack is the problem as the laptops are mac's.

I will build a couple of ubuntu boxes and see if i have the same issue.

Just throwing this out there for any suggestions.

Cheers

Kev

[kevinhobson2000]

Hi All,

I get full throughput when testing fomr ubuntu to ubuntu.

So seems to be windows tcp stack that is causing this.

Cheers

[Joseph W. Doherty]

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Posting

Windows OSs, before their nextGen TCP stack, often are rate limited due to that stack's default RWIN.  (If this is cause, manual RWIN tuning sometimes will dramatically improve performance.)

With Windows platforms, performance might also be constrained by NIC's hardware or its driver.  You might check if NIC's manufacturer has newer driver.