Can't push/pull to bitbucket via SSH using IPv6

Question

When I can push/pull to bitbucket:

• From my work computer via ssh key id_rsa_bitbucket_work
• From my laptop, but only when logged into VPN (Cisco AnyConnect) via ssh key id_rsa_bitbucket. My VPN has a static IP.
• Always using https.

When I cannot push/pull to bitbucket:

• From my laptop anytime VPN is not connected, via ssh key ida_rsa_bitbucket.
• From my laptop on my work network network when not on VPN, even though I'm nominally on the same network I would be with VPN.

The appropriate entry in my ~/.ssh/config is:

Host bitbucket
     HostName bitbucket.org
     User git
     IdentityFile ~/.ssh/id_rsa_bitbucket

Connecting to github repositories via SSH always works, regardless of what network/VPN I am going through.

I have checked to make sure that:

• My SSH agent is running and has the correct keys loaded.
• My SSH agent is handing out the same key regardless of VPN settings.

The output from ssh -Tv bitbucket when NOT logged in to VPN is:

OpenSSH_6.9p1, LibreSSL 2.1.8
debug1: Reading configuration data /Users/fcarter/.ssh/config
debug1: /Users/fcarter/.ssh/config line 1: Applying options for bitbucket
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: /etc/ssh/ssh_config line 21: Applying options for *
debug1: /etc/ssh/ssh_config line 56: Applying options for *
debug1: Connecting to bitbucket.org [2401:1d80:1010::150] port 22.
debug1: Connection established.
debug1: identity file /Users/fcarter/.ssh/id_rsa_bitbucket type 1
debug1: key_load_public: No such file or directory
debug1: identity file /Users/fcarter/.ssh/id_rsa_bitbucket-cert type -1
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_6.9
debug1: Remote protocol version 2.0, remote software version conker_1.0.284-7b46313 app-127
debug1: no match: conker_1.0.284-7b46313 app-127
debug1: Authenticating to bitbucket.org:22 as 'git'
debug1: SSH2_MSG_KEXINIT sent
debug1: SSH2_MSG_KEXINIT received
debug1: kex: server->client aes128-ctr hmac-sha2-256 none
debug1: kex: client->server aes128-ctr hmac-sha2-256 none
debug1: expecting SSH2_MSG_KEX_ECDH_REPLY
debug1: Server host key: ssh-rsa SHA256:zzXQOXSRBEiUtuE8AikJYKwbHaxvSc0ojez9YXaGp1A
debug1: Host 'bitbucket.org' is known and matches the RSA host key.
debug1: Found key in /Users/fcarter/.ssh/known_hosts:12
debug1: SSH2_MSG_NEWKEYS sent
debug1: expecting SSH2_MSG_NEWKEYS
debug1: SSH2_MSG_NEWKEYS received
debug1: SSH2_MSG_SERVICE_REQUEST sent
debug1: SSH2_MSG_SERVICE_ACCEPT received
debug1: Authentications that can continue: publickey
debug1: Next authentication method: publickey
debug1: Offering RSA public key: /Users/fcarter/.ssh/id_rsa_bitbucket
debug1: Server accepts key: pkalg ssh-rsa blen 535
debug1: Authentication succeeded (publickey).
Authenticated to bitbucket.org ([2401:1d80:1010::150]:22).
debug1: channel 0: new [client-session]
debug1: Entering interactive session.
debug1: Sending environment.
debug1: Sending env LANG = en_US.UTF-8
debug1: channel 0: free: client-session, nchannels 1
Transferred: sent 4048, received 1776 bytes, in 10.1 seconds
Bytes per second: sent 401.8, received 176.3
debug1: Exit status -1

It appears to connect and authenticate (via IPv6?), but exits with an error.

The output from ssh -Tv bitbucket when logged into my VPN is:

OpenSSH_6.9p1, LibreSSL 2.1.8
debug1: Reading configuration data /Users/fcarter/.ssh/config
debug1: /Users/fcarter/.ssh/config line 1: Applying options for bitbucket
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: /etc/ssh/ssh_config line 21: Applying options for *
debug1: /etc/ssh/ssh_config line 56: Applying options for *
debug1: Connecting to bitbucket.org [2401:1d80:1010::151] port 22.
debug1: connect to address 2401:1d80:1010::151 port 22: Permission denied
debug1: Connecting to bitbucket.org [104.192.143.3] port 22.
debug1: Connection established.
debug1: identity file /Users/fcarter/.ssh/id_rsa_bitbucket type 1
debug1: key_load_public: No such file or directory
debug1: identity file /Users/fcarter/.ssh/id_rsa_bitbucket-cert type -1
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_6.9
debug1: Remote protocol version 2.0, remote software version conker_1.0.284-7b46313 app-125
debug1: no match: conker_1.0.284-7b46313 app-125
debug1: Authenticating to bitbucket.org:22 as 'git'
debug1: SSH2_MSG_KEXINIT sent
debug1: SSH2_MSG_KEXINIT received
debug1: kex: server->client aes128-ctr hmac-sha2-256 none
debug1: kex: client->server aes128-ctr hmac-sha2-256 none
debug1: expecting SSH2_MSG_KEX_ECDH_REPLY
debug1: Server host key: ssh-rsa SHA256:zzXQOXSRBEiUtuE8AikJYKwbHaxvSc0ojez9YXaGp1A
debug1: Host 'bitbucket.org' is known and matches the RSA host key.
debug1: Found key in /Users/fcarter/.ssh/known_hosts:12
debug1: SSH2_MSG_NEWKEYS sent
debug1: expecting SSH2_MSG_NEWKEYS
debug1: SSH2_MSG_NEWKEYS received
debug1: SSH2_MSG_SERVICE_REQUEST sent
debug1: SSH2_MSG_SERVICE_ACCEPT received
debug1: Authentications that can continue: publickey
debug1: Next authentication method: publickey
debug1: Offering RSA public key: /Users/fcarter/.ssh/id_rsa_bitbucket
debug1: Server accepts key: pkalg ssh-rsa blen 535
debug1: Authentication succeeded (publickey).
Authenticated to bitbucket.org ([104.192.143.3]:22).
debug1: channel 0: new [client-session]
debug1: Entering interactive session.
debug1: Sending environment.
debug1: Sending env LANG = en_US.UTF-8
logged in as faustin315.

You can use git or hg to connect to Bitbucket. Shell access is disabled.
debug1: client_input_channel_req: channel 0 rtype exit-status reply 0
debug1: channel 0: free: client-session, nchannels 1
Transferred: sent 4048, received 1984 bytes, in 0.2 seconds
Bytes per second: sent 16284.6, received 7981.4
debug1: Exit status 0

It appears to connect and authenticate (via IPv4?) and everything is fine.

Update: After finding this issue on bitbucket's site, I tried adding 104.192.143.2 bitbucket.org to my /etc/hosts file. This did not fix the issue.

Answer 1

Updated after lots of help from Bitbucket support:

After much more research, the problem appears to be on my router's end (Linksys E3200) and is somehow related to IPv6. I have no trouble accessing IPv6-only sites, and everything works fine with github (this is because github is IPv4 only). However, there is something being filtered out that SSH needs to work properly. If I jack directly into my modem and run ssh -Tvv bitbucket it authenticates properly over IPv6.

In order to work around the problem (while I shop for a new router), I am forcing connections to bitbucket to only use IPv4 by adding AddressFamily inet to my ~/.ssh/config file (thanks to: https://stackoverflow.com/a/35113901/7735643). So the updated entry for bitbucket now reads:

Host bitbucket
     HostName bitbucket.org
     User git
     IdentityFile ~/.ssh/id_rsa_bitbucket
     AddressFamily inet