This is an incomplete draft.  GCB is no longer part of HTCondor; this is only preserved for historic purposes.

GCB, or Generic Connection Brokering, allows HTCondor installations behind firewalls and NATs to communicate with machines on the other side.  Two sets of machines behind different firewalls can even communicate.

(It is possible to put large holes in your firewall or NAT to allow incoming and outgoing connections instead of using GCB.)

For example, assume that you have existing use of GCB brokers on the machines
192.168.0.101, 192.168.0.102, and 192.168.0.103.

*:*TODO* Document standing up the GCB brokers
*:The following goes in your HTCondor configuration file.  These setting must be visible to all HTCondor machines that need to use the GCB broker.  If a daemon communicates with machines outside of your firewall or NAT for any reason, it will need GCB configured.
{code}
# Turn on GCB
# Note: this automatically turns on BIND_ALL_INTERFACES.
NET_REMAP_ENABLE=TRUE

# The only valid option is GCB here.
NET_REMAP_SERVICE = GCB

# IP addresses of GCB brokers.  Also add it to $(ETC)/GCB-routing-table,
# or else GCB routed connections will be unnecessarily slow.
NET_REMAP_INAGENT = 192.168.0.101, 192.168.0.102, 192.168.0.103

# This is used to determine which IP addresses are GCB brokers, potentially
# allowing us to be more clever and avoid the broker.
NET_REMAP_ROUTE = $(ETC)/GCB-routing-table

# This is used to identify machines that can route to each other without
# hitting any NATs, firewalls, or the like.  This lets us skip GCB entirely in
# these circumstances.  It's an arbitrary string used in comparisons; it only
# needs to be unique among all daemons talking to this pool.
PRIVATE_NETWORK_NAME = my.network.example.internal
{endcode}


*: Create a GCB-routing-table containing the following:
{code}
# All GCB broker addresses set in NET_REMAP_INAGENT should be
# listed here with "/32 GCB" appended.  This significantly
# improves local scalability.  It is safe to list brokers you are
# not using.

192.168.0.100
192.168.0.101
192.168.0.102
192.168.0.103
192.168.0.104
192.168.0.105
{endcode}