ssh cannot use the IdentityFile config in file ~/.ssh/config

Question

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 [email protected], 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 [email protected], the Terminal ask me the password.

Next, I change poponet_rsa filename to id_rsa, and input ssh [email protected], OK, I login.

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

$ ssh -vvv [email protected]
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 3 setting O_NONBLOCK
debug3: load_hostkeys: loading entries for host "popo.net" from file "/Users/phenix/.ssh/known_hosts"
debug3: load_hostkeys: found key type RSA in file /Users/phenix/.ssh/known_hosts:1
debug3: load_hostkeys: loaded 1 keys
debug3: order_hostkeyalgs: prefer hostkeyalgs: [email protected],[email protected],ssh-rsa
debug1: SSH2_MSG_KEXINIT sent
debug1: SSH2_MSG_KEXINIT received
debug2: kex_parse_kexinit: **too much init, i delete them.**
debug2: mac_setup: found hmac-md5
debug1: kex: server->client aes128-ctr hmac-md5 none
debug2: mac_setup: found hmac-md5
debug1: kex: client->server aes128-ctr hmac-md5 none
debug1: SSH2_MSG_KEX_DH_GEX_REQUEST(1024<1024<8192) sent
debug1: expecting SSH2_MSG_KEX_DH_GEX_GROUP
debug2: dh_gen_key: priv key bits set: 135/256
debug2: bits set: 468/1024
debug1: SSH2_MSG_KEX_DH_GEX_INIT sent
debug1: expecting SSH2_MSG_KEX_DH_GEX_REPLY
debug1: Server host key: RSA xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx
debug3: load_hostkeys: loading entries for host "popo.net" from file "/Users/phenix/.ssh/known_hosts"
debug3: load_hostkeys: found key type RSA in file /Users/phenix/.ssh/known_hosts:1
debug3: load_hostkeys: loaded 1 keys
debug3: load_hostkeys: loading entries for host "111.111.111.111" from file "/Users/phenix/.ssh/known_hosts"
debug3: load_hostkeys: found key type RSA in file /Users/phenix/.ssh/known_hosts:1
debug3: load_hostkeys: loaded 1 keys
debug1: Host 'popo.net' is known and matches the RSA host key.
debug1: Found key in /Users/phenix/.ssh/known_hosts:1
debug2: bits set: 516/1024
debug1: ssh_rsa_verify: signature correct
debug2: kex_derive_keys
debug2: set_newkeys: mode 1
debug1: SSH2_MSG_NEWKEYS sent
debug1: expecting SSH2_MSG_NEWKEYS
debug2: set_newkeys: mode 0
debug1: SSH2_MSG_NEWKEYS received
debug1: Roaming not allowed by server
debug1: SSH2_MSG_SERVICE_REQUEST sent
debug2: service_accept: ssh-userauth
debug1: SSH2_MSG_SERVICE_ACCEPT received
debug2: key: /Users/phenix/.ssh/id_rsa (0x0)
debug2: key: /Users/phenix/.ssh/id_dsa (0x0)
debug1: Authentications that can continue: publickey,password
debug3: start over, passed a different list publickey,password
debug3: preferred publickey,keyboard-interactive,password
debug3: authmethod_lookup publickey
debug3: remaining preferred: keyboard-interactive,password
debug3: authmethod_is_enabled publickey
debug1: Next authentication method: publickey
debug1: Trying private key: /Users/phenix/.ssh/id_rsa
debug1: key_parse_private_pem: PEM_read_PrivateKey failed
debug1: read PEM private key done: type <unknown>
debug2: no passphrase given, try next key
debug1: Trying private key: /Users/phenix/.ssh/id_dsa
debug3: no such identity: /Users/phenix/.ssh/id_dsa
debug2: we did not send a packet, disable method
debug3: authmethod_lookup password
debug3: remaining preferred: ,password
debug3: authmethod_is_enabled password
debug1: Next authentication method: password
[email protected]'s password: 

Answer 1

I found the answer to my problem here: https://superuser.com/a/436015.

In short, IdentitiesOnly yes needs to be specified on either the host or the global SSH client configuration because otherwise, unspecified keys may also be tried, including keys in the ssh-agent if one is running.