subversion uses ssh. If ssh blocked from A to C, but A-> B and B->C is not blocked, setup tunneing:

1. on A:

/etc/subversion/config

in the [tunnel] section, add:

ssh = $SVN_SSH ssh -o ControlMaster=no <machine B’s hostname> ssh -o ControlMaster=no

2. on B:

/etc/ssh/ssh_config

HostbasedAuthentication yes
EnableSSHKeysign yes

3. on C

/etc/ssh/sshd_config

HostbasedAuthentication yes

RSAAuthentication yes

ssh-keyscan -t rsa <C’s hostname> >> /etc/ssh/ssh_known_hosts

Add C’s hostname to :   /etc/ssh/shosts.equiv