PROTOR Knowledge Base

PROTOR Redhat Note: Using SMT229 Ethernet Trams for RedHat 7.2

Author:	Don Davies
Date:	13-May-2002

When using a PROTOR host system based on RedHat 7.2 there is a problem talking to an RMDAS units using SMT229 Ethernet Trams as the communication interface. By default the units do not respond to "ping" commands or to PROTOR software. The SMT229 Trams have a problem with SYSV network protocols and require the MTU discovery bit to be turned off ( or more accurately the "MTU No Discovery" bit turned on ).

MTU discovery is controlled by the file

               /proc/sys/net/ipv4/ip_no_pmtu_disc

By default this file contains "0". One way of disabling MTU discovery add the following line to a startup script prior to starting PROTOR.

               echo 1 > /proc/sys/net/ipv4/ip_pmtu_nodisc

A cleaner solution is to add an entry into the file /etc/sysctl.conf. This file is actioned during the network startup from script /etc/init.d/network. Prior to modification the file looks like :

  # Disables packet forwarding
  net.ipv4.ip_forward = 0
  # Enables source route verification
  net.ipv4.conf.default.rp_filter = 1
  # Disables the magic-sysrq key
  kernel.sysrq = 0

Modify this file to add the setup of the MTU discovery bit for PROTOR so that it looks like :

  # Disables packet forwarding
  net.ipv4.ip_forward = 0
  #  Disable MTU Discovery for PROTOR Ethernet Trams
  net.ipv4.ip_no_pmtu_disc = 1
  # Enables source route verification
  net.ipv4.conf.default.rp_filter = 1
  # Disables the magic-sysrq key
  kernel.sysrq = 0

With this bit set you should now be able to "ping" RMDAS units containing Ethernet Trams.

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