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 http://arbonnebrisbane.myarbonne.com.au . 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:
http://www.myarbonne.com.au/
=> `index.html.1′
Resolving www.myarbonne.com.au… 208.179.207.104
Caching www.myarbonne.com.au => 208.179.207.104
Connecting to www.myarbonne.com.au|208.179.207.104|:80… connected.
Created socket 4.
Releasing 0x00516290 (new refcount 1).
—request begin—
GET / HTTP/1.0
User-Agent: Wget/1.10.2
Accept: */*
Host: www.myarbonne.com.au
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 http://en.wikipedia.org/wiki/Maximum_transmission_unit
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 192.168.0.119 netmask 0xffffff00 broadcast 192.168.0.255
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 http://help.expedient.net/broadband/mtu.shtml

Published
Categorized as Mac OS X

By Greg Luck

As Terracotta’s CTO, Greg (@gregrluck) is entrusted with understanding market and technology forces and the business drivers that impact Terracotta’s product innovation and customer success. He helps shape company and technology strategy and designs many of the features in Terracotta’s products. Greg came to Terracotta on the acquisition of the popular caching project Ehcache which he founded in 2003. Prior to joining Terracotta, Greg served as Chief Architect at Australian online travel giant Wotif.com. He also served as a lead consultant for ThoughtWorks on accounts in the United States and Australia, was CIO at Virgin Blue, Tempo Services, Stamford Hotels and Resorts and Australian Resorts and spent seven years as a Chartered Accountant in KPMG’s small business and insolvency divisions. He is a regular speaker at conferences and contributor of articles to the technical press.