SFTP -

Good Day everyone,

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I have an issue here.

Essentially, we have a sftp communication between two servers (Server A and Server B), crossing wan with a Wan interface MTU of 1400/MSS 1360

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Server A is able to establish SFTP PUT for both Large and small files.

GET only works for small files but not large files, unless we reduce the buffer size drastically (way way below the default of 32000+ bytes).

3 Way Handshake shows MSS 1460

Windows Size of 65535, after approximately 30 numbers of (1448 TCP len packets + an 848 TCP len packet), wireshark shows

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TCP DUP ACK

TCP DUP ACK

TCP DUP ACK

FAST Retransmission

TCP DUP ACK

TCP DUP ACK

TCP DUP ACK

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Is this an issue of MTU mismatched ? Or am i completely off track from the root cause ?
Firewall was replaced, prior to the issue happening.