I agree with zentara that using Net::SSH2 would be the way to go. However, if for some reason (like not being able to get libssh2 installed) you want/need to use Net::SSH::Perl, you could try forcing SSH protocol 2, i.e.

my %args = (user=>'aaa', password=>'bbb', ssh_args => [ protocol => 2 
+]);
my $ftp = new Net::SFTP('http://www.test.com',%args);
...
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This suggestion is based on:

client DES3 server aes128-cbc,3des-cbc,...
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Somehow, the client side seems to be under the false impression it's supposed to use SSH protocol 1 — at least that's what I would infer from it proposing the protocol 1 cipher name 'DES3' (the corresponding protocol 2 name would be '3des-cbc'), while the server is only offering protocol 2 cipher names to choose from. OTOH, as Net::SSH::Perl is proposing DES3, you apparently already have the respective Crypt:: module installed. IOW, you (or your customer) should in theory be able to use '3des-cbc' without installing additional modules, once you get client and server to agree on using that cipher...  Just an idea (untested).