Cannot install fail2ban on 11.04 (Natty)

I try to install fail2ban on 11.04. apt-get install returns a "package not found" error:

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root@ubuntu:/etc/apt# apt-get update
Ign http://us.archive.ubuntu.com natty InRelease
Ign http://us.archive.ubuntu.com natty-updates InRelease
Ign http://security.ubuntu.com natty-security InRelease
Hit http://us.archive.ubuntu.com natty Release.gpg
Hit http://security.ubuntu.com natty-security Release.gpg
Hit http://us.archive.ubuntu.com natty-updates Release.gpg
Hit http://security.ubuntu.com natty-security Release
Hit http://us.archive.ubuntu.com natty Release
Hit http://security.ubuntu.com natty-security/main Sources
Hit http://us.archive.ubuntu.com natty-updates Release
Hit http://security.ubuntu.com natty-security/restricted Sources
Hit http://security.ubuntu.com natty-security/main amd64 Packages
Hit http://security.ubuntu.com natty-security/restricted amd64 Packages
Ign http://security.ubuntu.com natty-security/main TranslationIndex
Ign http://security.ubuntu.com natty-security/restricted TranslationIndex
Hit http://us.archive.ubuntu.com natty/main Sources
Hit http://us.archive.ubuntu.com natty/restricted Sources
Hit http://us.archive.ubuntu.com natty/main amd64 Packages
Hit http://us.archive.ubuntu.com natty/restricted amd64 Packages
Ign http://us.archive.ubuntu.com natty/main TranslationIndex
Ign http://us.archive.ubuntu.com natty/restricted TranslationIndex
Hit http://us.archive.ubuntu.com natty-updates/main Sources
Hit http://us.archive.ubuntu.com natty-updates/restricted Sources
Hit http://us.archive.ubuntu.com natty-updates/main amd64 Packages
Hit http://us.archive.ubuntu.com natty-updates/restricted amd64 Packages
Ign http://us.archive.ubuntu.com natty-updates/main TranslationIndex
Ign http://us.archive.ubuntu.com natty-updates/restricted TranslationIndex
Ign http://security.ubuntu.com natty-security/main Translation-en_US
Ign http://security.ubuntu.com natty-security/main Translation-en
Ign http://us.archive.ubuntu.com natty/main Translation-en_US
Ign http://security.ubuntu.com natty-security/restricted Translation-en_US
Ign http://security.ubuntu.com natty-security/restricted Translation-en
Ign http://us.archive.ubuntu.com natty/main Translation-en
Ign http://us.archive.ubuntu.com natty/restricted Translation-en_US
Ign http://us.archive.ubuntu.com natty/restricted Translation-en
Ign http://us.archive.ubuntu.com natty-updates/main Translation-en_US
Ign http://us.archive.ubuntu.com natty-updates/main Translation-en
Ign http://us.archive.ubuntu.com natty-updates/restricted Translation-en_US
Ign http://us.archive.ubuntu.com natty-updates/restricted Translation-en
Reading package lists... Done

root@ubuntu:/etc/apt# ls -l sources.list.d; echo; cat sources.list
total 0

deb http://us.archive.ubuntu.com/ubuntu/ natty main restricted
deb-src http://us.archive.ubuntu.com/ubuntu/ natty main restricted

## Major bug fix updates produced after the final release of the
## distribution.
deb http://us.archive.ubuntu.com/ubuntu/ natty-updates main restricted
deb-src http://us.archive.ubuntu.com/ubuntu/ natty-updates main restricted

## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
## team. Also, please note that software in universe WILL NOT receive any
## review or updates from the Ubuntu security team.
#deb http://gb.archive.ubuntu.com/ubuntu/ natty universe
#deb-src http://gb.archive.ubuntu.com/ubuntu/ natty universe
#deb http://gb.archive.ubuntu.com/ubuntu/ natty-updates universe
#deb-src http://gb.archive.ubuntu.com/ubuntu/ natty-updates universe

## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
## team, and may not be under a free licence. Please satisfy yourself as to
## your rights to use the software. Also, please note that software in
## multiverse WILL NOT receive any review or updates from the Ubuntu
## security team.
#deb http://gb.archive.ubuntu.com/ubuntu/ natty multiverse
#deb-src http://gb.archive.ubuntu.com/ubuntu/ natty multiverse
#deb http://gb.archive.ubuntu.com/ubuntu/ natty-updates multiverse
#deb-src http://gb.archive.ubuntu.com/ubuntu/ natty-updates multiverse

## Uncomment the following two lines to add software from the 'backports'
## repository.
## N.B. software from this repository may not have been tested as
## extensively as that contained in the main release, although it includes
## newer versions of some applications which may provide useful features.
## Also, please note that software in backports WILL NOT receive any review
## or updates from the Ubuntu security team.
#deb http://gb.archive.ubuntu.com/ubuntu/ natty-backports main restricted universe multiverse
#deb-src http://gb.archive.ubuntu.com/ubuntu/ natty-backports main restricted universe multiverse

## Uncomment the following two lines to add software from Canonical's
## 'partner' repository. This software is not part of Ubuntu, but is
## offered by Canonical and the respective vendors as a service to Ubuntu
## users.
#deb http://archive.canonical.com/ubuntu natty partner
#deb-src http://archive.canonical.com/ubuntu natty partner

deb http://security.ubuntu.com/ubuntu natty-security main restricted
deb-src http://security.ubuntu.com/ubuntu natty-security main restricted
#deb http://security.ubuntu.com/ubuntu natty-security universe
#deb-src http://security.ubuntu.com/ubuntu natty-security universe
#deb http://security.ubuntu.com/ubuntu natty-security multiverse
#deb-src http://security.ubuntu.com/ubuntu natty-security multiverse

root@ubuntu:/etc/apt# apt-get install fail2ban
Reading package lists... Done
Building dependency tree
Reading state information... Done
E: Unable to locate package fail2ban
root@ubuntu:/etc/apt#
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fail2ban is listed at http://packages.ubuntu.com/natty/fail2ban.

If it matters, I'm trying this on an 11.04 image on a virtual machine at Rackspace. I.e., I'm using their 11.04 Natty image.

Thanks in advance!