Listing directories lags due to some Dup Acks

  • Jeremy Jacque
    Jeremy Jacque


    When listing a big directory , the screen may lag. By analyzing  some tcpdump captures it's look like many duplicate acks are generated by sshd.

    I'm using an IBM PPC 9110-51A , AIX 5.3 TL8 SP2 , Openssh- .

    It only happens when connecting to a remote server (even if on SDSL link with 15ms ping).
    It seems to be due to the SSH server because when connecting with telnet, there is no dup acks or when connecting to a linux PC with SSH, there is also no dup acks.

    I tried some network improvement/customizing:

    - no -o tcp_sendspace=262144
    - no -o tcp_recvspace=131072
    - no -o sb_max=2097152
    - chdev -l en0 -a remmtu=1500
    - no -o tcp_nodelayack=1
    - no -o rfc1323=1
    - no-o sack=1

    I renice'd the sshd process (-5) and optimized the sshd_config :
    UseDNS no , no X11 Forwarding ,…
    but there are still dup acks (or Retransmissions).
    If someone could help me ??

    Thanks in advance.
    Best Regards,