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When I connect my 64-bit Windows 7 to a OS X server using \servername, my transfer rates are around 400KB/s.

However, when I do the same thing using \ (which is the IP of the server), transfer rates jump to 30MB/s.

All of this happens via a gigabit ethernet cable with my wireless disabled

I heard Samba itself "doesn't use DNS", but if that's the case, how am I able to connect to the server in the first place?

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You may need to see if "servername" maps to some other IP address than, and then figure out what route through your network your packets would take if you connected to that other IP address.

For example, your address of suggests to me that you're running a NAT gateway on your network. Let's say "servername" is an unqualified DNS hostname (fully qualified, it might be If points to the public IP address of your NAT box, then when you connect to \servername, your traffic from your client to that server is going out through your NAT box towards its public port (outbound NAT), then just before your NAT box sends it out its public port, it realizes that that's its own IP address, and then does inbound NAT (a.k.a. port mapping, port forwarding) to send that traffic to your server. This process of outbound and inbound NAT on the same traffic flow is called "hairpin NAT". I wouldn't usually expect hairpin NAT to destroy your throughput quite that bad (30MB/s to 400KB/s), but if it's a cheap home gateway I suppose it could happen. It could be that introducing a hairpin NAT between your client and server is screwing up TCP congestion avoidance and retransmit algorithms in some way.

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When you use the IP address directly, NetBIOS naming is not used, so there may be some problems with NetBIOS (WINS, etc.) on your network. This document describes NetBIOS in detail and will likely be of interest to you in tracking down the problem:

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Rarely does resolution have anything to do with SMB. – surfasb Feb 19 '11 at 8:37
"Rarely" doesn't justify voting down my answer. If it turns out that this is the issue, then this answer is especially relevant. In working with networks over the years, I've found that NetBIOS naming is in fact an important part of making things work quickly and reliably, and the link I referenced agrees with that too. – Randolf Richardson Feb 19 '11 at 16:46

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