Firewalling execute nodes: Avoid LOWPORT/HIGHPORT, use IN_LOWPORT/IN_HIGHPORT

We all know why firewalls are setup. Typical firewall configurations minimize inbound connections and allow unrestricted outbound connections.

Condor primarily uses ephemeral ports for inbound connections. To assist configuration with firewalls, it has long provided LOWPORT and HIGHPORT configuration options to constrain the port range it uses. Going beyond port range management, Condor has grown to include the Condor Connection Broker (CCB), to reverse connections when components are entirely hidden by firewalls, and condor_shared_port, to reduce the inbound port footprint on a machine to one.

Unfortunately, there is a disconnect in the typical firewall configuration and what LOWPORT/HIGHPORT configuration expresses. LOWPORT/HIGHPORT constraints both inbound and outbound port usage.

On an execute node, Condor will run a condor_master, a condor_startd and a few condor_starter processes, one per job. All must be able to accept connections. For a node that can run 4 jobs, the minimum number of inbound ports open in the node’s firewall is 6, one for each of the 6 potential processes. However, those processes will use more than just one port during its lifetime. In fact, the processes may have 3 open connections at some point. Using LOWPORT/HIGHPORT, that means setting a range that is 3 times wider than is necessary. It is possible to reduce that because not all processes will use all 3 connections at once, until they do. Going low is fragile.

Luckily, Condor provides IN_LOWPORT/IN_HIGHPORT and OUT_LOWPORT/OUT_HIGHPORT. For a typical firewall configuration, ignore the OUT_’s and use the IN_’s, e.g. IN_LOWPORT = 10000, IN_HIGHPORT = 10005. You will be much happier.

Port usage running 4 jobs with configuration,

ALL_DEBUG = D_NETWORK
IN_LOWPORT = 10000
IN_HIGHPORT = 10015
OUT_LOWPORT = 20000
OUT_HIGHPORT = 20015

Looks like,

MasterLog:08/08/10 09:25:10 Sock::bindWithin - bound to 10012...
MasterLog:08/08/10 09:25:13 Sock::bindWithin - bound to 10000...
MasterLog:08/08/10 09:25:18 Sock::bindWithin - bound to 20009...
StartLog:08/08/10 09:25:24 Sock::bindWithin - bound to 20015...
StartLog:08/08/10 09:25:24 Sock::bindWithin - bound to 20007...
StartLog:08/08/10 09:25:28 Sock::bindWithin - bound to 20003...
StartLog:08/08/10 09:25:34 Sock::bindWithin - bound to 10007...
StartLog:08/08/10 09:25:34 Sock::bindWithin - bound to 10013...
StartLog:08/08/10 09:25:34 Sock::bindWithin - bound to 10006...
StartLog:08/08/10 09:25:34 Sock::bindWithin - bound to 10015...
StarterLog.slot1:08/08/10 09:25:34 Sock::bindWithin - bound to 20007...
StarterLog.slot1:08/08/10 09:25:34 Sock::bindWithin - bound to 20008...
StarterLog.slot2:08/08/10 09:25:34 Sock::bindWithin - bound to 20003...
StarterLog.slot2:08/08/10 09:25:34 Sock::bindWithin - bound to 20013...
StarterLog.slot3:08/08/10 09:25:34 Sock::bindWithin - bound to 20011...
StarterLog.slot3:08/08/10 09:25:34 Sock::bindWithin - bound to 20012...
StarterLog.slot4:08/08/10 09:25:34 Sock::bindWithin - bound to 20013...
StarterLog.slot4:08/08/10 09:25:34 Sock::bindWithin - bound to 20004...

That’s 6 inbound ports and 12 outbound ports, with a few reused.

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One Response to “Firewalling execute nodes: Avoid LOWPORT/HIGHPORT, use IN_LOWPORT/IN_HIGHPORT”

  1. Getting Started: Multiple node Condor pool with firewalls « Spinning Says:

    […] headaches for firewalls as large ranges of ports need to be opened for communication. There are ways to control the ephemeral range used. Unfortunately, doing so just reduced the port range some, did not guarantee Condor was on the […]

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