Miscellaneous questions ======================= How can I open a UDP or TCP port in SLC5 or SLC6? ------------------------------------------------- There are two options. However, they are incompatible (at least in SLC5). Either use always one method or the other, but not both: * Modify /etc/sysconfig/iptables and restart the iptables service (open port 4241): .. code-block:: sh -A INPUT -m state --state NEW -m tcp -p tcp --dport 4241 -j ACCEPT sudo /sbin/service iptables restart * Install xsudo, and then open a TCP port using the Redhat firewall configuration GUI: .. code-block:: sh wget http://cmsdaq0/cmscdb/cmsswrep/i386_slc4/xsudo-2.0.2-0.noarch.rpm sudo rpm -iv xsudo-2.0.2-0.noarch.rpm xsudo /usr/bin/system-config-firewall How can I simulate deterministic and non-deterministic packet loss and delay? ----------------------------------------------------------------------------- It is very easy, just use the ``tc`` command. see `examples in stackoverflow <http://stackoverflow.com/a/615757>`_. Common examples (for ``eth0``): * Drop 0.1% of outgoing packets: * If other rules have already been applied to ``eth0`` : ``sudo /sbin/tc qdisc add dev eth0 root netem loss 0.1%`` * Otherwise : ``sudo /sbin/tc qdisc change dev eth0 root netem loss 0.1%`` * Find out what rules are applied already : ``sudo /sbin/tc -s qdisc ls dev eth0`` * Remove rules : ``sudo /sbin/tc qdisc del dev eth0 root`` N.B. The ``tc`` command with netem only applies these rules (e.g. packet dropping) to **outgoing** packets ... * See the ''How can I use netem on incoming traffic?'' FAQ section `here <http://www.linuxfoundation.org/collaborate/workgroups/networking/netem>`__ for details on how to also apply rules to the incoming traffic. Another useful resource (also contains instructions for doing same thing with ``iptables``) can be found `here <http://sandilands.info/sgordon/dropping-packets-in-ubuntu-linux-using-tc-and-iptables>`__.