client：Mac 10.8，server：Ubuntu 10.04 LTS 64bit

I use 'ssh-keygen -t rsa' generate public/private keys.

First, I input: ssh -i /Users/phenix/.ssh/poponet_rsa root@popo.net, I can login to the server with the private key 'poponet_rsa'

Next, I create a config file: /Users/phenix/.ssh/config, with content:

Host popo
    Hostname popo.net
    User root
    PreferredAuthentications publickey
    IdentityFile /Users/phenix/.ssh/poponet_rsa

and I input ssh root@popo.net, the Terminal ask me the password.

Next, I change poponet_rsa filename to id_rsa, and input ssh root@popo.net, OK, I login.

My question: ssh cannot use the IdentityFile config in file ~/.ssh/config, why?

$ ssh -vvv root@popo.net
OpenSSH_5.9p1, OpenSSL 0.9.8r 8 Feb 2011
debug1: Reading configuration data /Users/phenix/.ssh/config
debug1: /Users/phenix/.ssh/config line 1: Applying options for popo.net
debug1: /Users/phenix/.ssh/config line 2: Applying options for popo.net
debug1: Reading configuration data /etc/ssh_config
debug1: /etc/ssh_config line 20: Applying options for *
debug2: ssh_connect: needpriv 0
debug1: Connecting to popo.net [111.111.111.111] port 22.
debug1: Connection established.
debug3: Incorrect RSA1 identifier
debug3: Could not load "/Users/phenix/.ssh/id_rsa" as a RSA1 public key
debug1: identity file /Users/phenix/.ssh/id_rsa type -1
debug1: identity file /Users/phenix/.ssh/id_rsa-cert type -1
debug1: identity file /Users/phenix/.ssh/id_dsa type -1
debug1: identity file /Users/phenix/.ssh/id_dsa-cert type -1
debug1: Remote protocol version 2.0, remote software version OpenSSH_5.3p1 Debian-3ubuntu7
debug1: match: OpenSSH_5.3p1 Debian-3ubuntu7 pat OpenSSH*
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_5.9
debug2: fd
ssh rsa private-key
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