Line Async setting to allow RTU device data to go through

rlortiz · ‎09-10-2008

I have a remote site customer with a Cisco 2620XM router with a NM-16 network module and they are testing it out to do some IP to serial port conversion. They are polling a device called an RTU (remote terminal unit) which is connected via the async cable. RTU is used by all utility companies everywhere to calculate voltage and other information.

They are polling that RTU by using socket (IP of the router and the raw TCP port). They tested this functionality using a Dymec Dynastar 1500 hardened router. They ran into a problem where Dymec router was truncating the data into 129 bytes. There was a configuration option under the serial line where we were able to change it to 500 bytes and it worked. According to Dymec's definition of that parameter, it is called "Max port forward limit" Indicates when packets will be forwarded: either every x bytes (1-1024) or according to X.3 values.

So, when they tested this witch Cisco router they ran into the same problem, here Ci

sco is truncating the message to 2 bytes only.

We need to know what the equivalent parameter is in Cisco's line (line 33 in our case) or global command where we can achieve the same result.

line 33

exec-timeout 0 0

buffer-length 500

absolute-timeout 500

no exec

length 512

width 512

transport input all

parity odd

stopbits 1

speed 1200

Here is a more descriptive definition of the problem as seen by their RTU engineers:

The message coming back is being broken up into two byte messages which cause the message being rejected by the master.

They had similar problems with the Dymec DynaStar 1500 terminal server that was breaking the serial messages up into 129 bytes. In that case, they were able to change the parameter (MAX port forward limit ). They set it higher than the max serial messages that are sent by the RTU, which did fix the problem.

The question is whether or not the CISCO router has a parameter that can be changed to force it to send the complete serial messages as one packet.

mchin345 · ‎09-16-2008

1. Truncating data from a webserver on the outside to a server on his dmz. This server is running an internal application. I checked for giants on the interfaces and none appeared. To increase MTU size to 65534 and try to pass the data again but it is still truncated. Changed MTU back to 1500. Cust reports there is a router on the outside (belongs to the ISP) and talked to the ISP who claims they are not doing any truncating on the router. Cust claims this data is not truncated when using other firewalls. This is in a test environment at the moment.

2. The system uses log files for temporary data storage and for error messages and state information. Because log files reside on the same disk as the database, you must monitor them; also, you must manage their size by periodically truncating them to ensure that the database has enough room to operate. This procedure describes how to truncate the Sybase database .log file.

http://www.cisco.com/en/US/docs/security/security_management/vms/ips_mc/2.2/user/guide/AppB.html#wp267206