Well although I generally use Firefox I had to upgrade to IE7 today as a customer has spotted a problem with our website (www.ippatrol.com) whereby a redirect was looping.
It turns out IE7 is a little more picky about the REFRESH meta tag.
In all previous versions of IE and Firefox the following worked.
<meta equiv="REFRESH" content="1; anotherpage.html">
Under IE7 this just causes the page to constantly refresh. Adding the URL option fixes the issue.
<meta equiv="REFRESH" content="1; URL=anotherpage.html">
I've also seen comments on various blogs that this tag doesn't work or is disabled in IE7 and that somewhere in IE7 is an option to turn support on and off. I haven't seen this issue but then I only redirect internally within the site so perhaps it only takes affect when you redirect off site.
Just in case I've added some javascript code to do the redirect as well. Hopefully one or other method will fire otherwise the visitor can click on the link displayed to get to the contact page.
The second issue I had with IE7 was that PDF's no longer worked and just came up with a page error saying object required.
I quickly guessed this might be because my Acrobat Reader was also well out of date (V6.0.2 from 2004) even though it works fine in Firefox and worked in IE6.
So I bit the bullet and upgraded to Acrobat Reader V7.0 and now both Firefox and IE7 work with PDFs.
I have to say I am quite impressed with the speed of IE7 and the speed of the new version of Acrobat Reader. There are a few enhancements in IE7 most of which are just catching up with Firefox plus a few others which are useful if annoying such as the certificate checker/warnings and the fact that such errors are displayed on the address bar if you decide to ignore them - a nice reminder.
I did however notice that the IE7 pop up blocker is turned off by default which I find a little odd. The phishing facility warns you that its not turned on the first time you start IE7 but for some reason the pop up blocker doesn't - not very consistent or helpful.
Friday 21 December 2007
Monday 10 December 2007
Sendmail backup mx relay
I have used sendmail for a number of years. We use it on our main mail server and on our backup mx servers.
Up until recently we simply allowed the backup mx servers to relay all mail to the domains they serve. Unfortunately spammers tend to target backup mx servers in the belief they are less well protected.
One of the side effects of this is that you end up accepting mail for lots of invalid addresses, which not only results in more spam (as the spammer thinks the address is valid) but also means you then end up trying to send non delivery receipts to some random reply address when the backup mx tries to deliver the mail to the main server and gets refused as the address doesn't exist.
I finally worked out that there is a nice feature in sendmail to only relay certain addresses thus refusing all the other junk and preventing the erroneous non delivery receipts.
By default we used to add the following to out access database
TO:dcl.co.uk RELAY
which simply means relay all email addressed to the domain dcl.co.uk
It is possible to be more selective but first you have to add the following to your sendmail configuration (sendmail.mc). Suggest you save a copy of sendmail.cf first for later comparison.
dnl #
dnl #Use access db with undocumented feature
dnl #
define(`_RELAY_FULL_ADDR_', `1')
Then do a make. Compare your new sendmail.cf with your old one just to ensure you've not lost anything.
You can now specify specific email addresses in the TO field rather than just the domain.
It means you have to remember to update your backup mx servers whenever you add or remove an email account but that is a small price to pay for the empty mail queues. I guess you could easily automate it.
Don't for get to rebuild your access database once you've edited the text file.
# hash /etc/mail/access.db < /etc/mail/access
PS. I also set DoubleBounceAddress to nothing (O DoubleBounceAddress=) to get rid of all those non delivery receipts of non delivery receipts!
Up until recently we simply allowed the backup mx servers to relay all mail to the domains they serve. Unfortunately spammers tend to target backup mx servers in the belief they are less well protected.
One of the side effects of this is that you end up accepting mail for lots of invalid addresses, which not only results in more spam (as the spammer thinks the address is valid) but also means you then end up trying to send non delivery receipts to some random reply address when the backup mx tries to deliver the mail to the main server and gets refused as the address doesn't exist.
I finally worked out that there is a nice feature in sendmail to only relay certain addresses thus refusing all the other junk and preventing the erroneous non delivery receipts.
By default we used to add the following to out access database
TO:dcl.co.uk RELAY
which simply means relay all email addressed to the domain dcl.co.uk
It is possible to be more selective but first you have to add the following to your sendmail configuration (sendmail.mc). Suggest you save a copy of sendmail.cf first for later comparison.
dnl #
dnl #Use access db with undocumented feature
dnl #
define(`_RELAY_FULL_ADDR_', `1')
Then do a make. Compare your new sendmail.cf with your old one just to ensure you've not lost anything.
You can now specify specific email addresses in the TO field rather than just the domain.
It means you have to remember to update your backup mx servers whenever you add or remove an email account but that is a small price to pay for the empty mail queues. I guess you could easily automate it.
Don't for get to rebuild your access database once you've edited the text file.
# hash /etc/mail/access.db < /etc/mail/access
PS. I also set DoubleBounceAddress to nothing (O DoubleBounceAddress=) to get rid of all those non delivery receipts of non delivery receipts!
Saturday 8 December 2007
TCP Window Scaling
It appears the lastest versions of Linux and Windows both enable TCP windows scaling by default. This in itself shouldn't present a problem and should improve connection speeds to sites as larger tcp packets can be negotiated.
If however the site you are trying to access if behind and old firewall or router then you might find after upgrading to Windows Vista or a recent version of Linux (Redhat 6 for example) that some sites either crawl along or simply fail. This doesn't necessarily mean your computer is at fault. It could be your router - when did you last flash the rom?
But it could mean that a firewall or router sat somewhere between you and the site is causing the issue.
If you want to prove that its tcp window scaling causing the problem you can turn it off and see if it 'solves' the problem. If it does I suggest you get in touch with the site owner and ask them to get their firewall or router upgraded. Don't forget to turn Windows Scaling option back on after!
How to disable in Windows Vista and Linux
See Wikipedia for more details
If however the site you are trying to access if behind and old firewall or router then you might find after upgrading to Windows Vista or a recent version of Linux (Redhat 6 for example) that some sites either crawl along or simply fail. This doesn't necessarily mean your computer is at fault. It could be your router - when did you last flash the rom?
But it could mean that a firewall or router sat somewhere between you and the site is causing the issue.
If you want to prove that its tcp window scaling causing the problem you can turn it off and see if it 'solves' the problem. If it does I suggest you get in touch with the site owner and ask them to get their firewall or router upgraded. Don't forget to turn Windows Scaling option back on after!
How to disable in Windows Vista and Linux
See Wikipedia for more details
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