Adjusting the networking MTU on Mac OS X

My wife is newly involved with a Arbonne, a network selling cosmetics company. They set up in Australia a few months ago. She has an a website . Anyway the web site did not work from Mac OS X or Linux from our home, only Windows (running in VM Ware). The problem was seen in all browsers, curl and wget. Not a problem I have seen before.
The issue, viewed from wget, looks like:
Using wget we get:
=> `index.html.1′
Caching =>
Connecting to||:80… connected.
Created socket 4.
Releasing 0x00516290 (new refcount 1).
—request begin—
GET / HTTP/1.0
User-Agent: Wget/1.10.2
Accept: */*
Connection: Keep-Alive
—request end—
HTTP request sent, awaiting response…
—response begin—
HTTP/1.1 200 OK
Server: Lotus-Domino
Date: Tue, 28 Aug 2007 22:36:16 GMT
Connection: close
Content-Type: text/html
Content-Length: 14036
Last-Modified: Sun, 01 Jul 2007 21:15:36 GMT
Accept-Ranges: bytes
—response end—
200 OK
Length: 14,036 (14K) [text/html]
0% [ ] 0 –.–K/s
i.e. the response is always stuck on 0%. You never get any data.
A colleague, Dave Whitla, suggested that our default MTU of 1500 bytes could be at issue. Not all networking equipment deals properly with fragments. See
The default MTU on Mac OS X is 1500. I adjusted the MTU to 1000 bytes and sure enough, the problems were resolved.
On Mac the MTU can be adjusted to 1000 bytes using:
sudo ifconfig en1 mtu 1000
You then to stop and start the interface. You then get:
en1: flags=8863 mtu 1000
tunnel inet –>
inet6 fe80::216:cbff:feb9:7131%en1 prefixlen 64 scopeid 0x5
inet netmask 0xffffff00 broadcast
ether 00:16:cb:b9:71:31
media: autoselect status: active
supported media: autoselect
vlan: 0 parent interface:
bond interfaces:
MTU can also be on the server side. See