Wireshark - SACK_PERM=1
<p>We are capturing a file transfer from machine 1 to machine 2 via Wireshark. While I am unable to capture any/few retransmission errors, other guy is able to capture around 10 to 15 retransmission errors and underrun errors.</p>

<p>On analysing the wire-shark capture, I find that the major difference is that <code>SACK_PERM</code> flag is not set in my capture, whereas <code>SACK_PERM=1</code> in other capture.</p>

<p>Below is</p>

<p><code>8535   7.272671    172.23.165.254  10.108.32.29    TCP 62</code> [TCP Retransmission] <code>29537 → 389 [SYN] Seq=0 Win=8192 Len=0 MSS=1460 SACK_PERM=1</code></p>

<p>Can anyone explain the effects of <code>SACK_PERM</code> <code>flag</code> in a network transmission?</p>

<p>Thanks in advance.</p>