Method for testing for network errors

network-link-testing.txt

Method for testing for network errors
=====================================

Background
----------
A WAN link is suspected of error in transport. Evidence of this is
suggested by periodic warnings of errors from our NetApp replication
jobs and intermittent failures in SIP messaging. These errors are
occurring on separate VLANs that pass data over separate equipment as
they move deeper in to the LAN infrastructure. The only common link is
the Carrier Ethernet WAN link.

Testing method
--------------

Netcat will be used to transfer a file between two locations and the
output checked for consistency.

A "server" and "client" laptop are connected to switches on two sides of
a WAN link. The WAN link is a Carrier Ethernet service delivery composed
of aggregated DS0-based (DS1 and DS3) links terminated on Overture ISG
equipment. The Overture equipment hands off Ethernet to Cisco 3560
8-port switches on both ends. The server and client laptops are
connected directly to these switches on both ends. No other equipment is
present in the link between the two.

The connection stack looks like:

[server]
<--C3560-->
<--Overture ISG-->
<--DS0 link-->
<--Overture ISG-->
<--C3560-->
[client]

A (roughly) 490 MB test file is available for transfer. The file is a
tar-gzipped collection of G.711 audio data, which shouldn't be
compressible much further when transmitted by file transfer tools. The
file name is '35.tgz'.

Netcat will be used to transfer the file between client/server; chosen
for it's simplicity and lack of high-level error correction.

On the server:

cat 35.tgz | pv -b | nc -l 3333

On the client:

nc 10.0.0.1 3333 > 35.tgz

After transfering the file `md5sum` is used on both client and server to
verify the contents of the file.