Cabal can't open a TCP connection

Dear ghc-devs Cabal can't open a TCP connection from my Linux box. It used to work fine. Here's what it says: cabal -v3 update Downloading the latest package list from hackage.haskell.org Sending: GET http://hackage.haskell.org/packages/archive/00-index.tar.gz HTTP/1.1 User-Agent: cabal-install/1.16.0.2 Host: hackage.haskell.org proxy uri host: , port: Creating new connection to cabal: openTCPConnection: host lookup failure for "" simonpj@cam-05-unx:~/code/HEAD$ cabal --version cabal-install version 1.16.0.2 using version 1.16.0.3 of the Cabal library simonpj@cam-05-unx:~/code/HEAD$ Can anyone help me work out what to do? git works just fine, so the internet is connected all right. Thanks Simon