Strange byte gets added to the first packet

Putchakayala, Prabhat S. psp at mitre.org
Tue Jan 12 08:59:28 PST 2010


Hello list,

I have a small WANProxy scenario setup on a single computer for preliminary tests and I noticed some odd behavior. After a TCP connection is made, the first packet has a random byte inserted at the beginning of it after it passes through one of the proxies. Here is a brief example using netcat. The server is started on port 4001, and the client makes requests to port 3000. Our config files are attached to the end, but here is a summary:

WANProxy 1: listening on port 3000, forwarding to port 4000. Applying the codec in both directions
WANProxy 2: listening on port 4000, forwarding to port 4001. Applying the codec in both directions

The server: $ nc -lp 4001
The client: $ nc localhost 3000

The following message is typed in the server: testing
The following message appears in the client: �testing

In case it fails to show up in this message, the byte in front of the second “testing” is \xef

Our best guess is that some of the information needed for deduplication is left in the packet. We did a more complicated test using two computers on the network rather than just one, and the same thing happens. Anyone know what we are doing wrong?

Thanks a lot!
Prabhat

Here are our config files:

Server:
create codec codec0
set codec0.codec XCodec
activate codec0

create interface if0
set if0.family IPv4
set if0.host "127.0.0.1"
set if0.port "4000"
activate if0

create peer peer0
set peer0.family IPv4
set peer0.host "localhost"
set peer0.port "4001"
activate peer0

create proxy proxy0
set proxy0.interface if0
set proxy0.decoder codec0
set proxy0.peer peer0
set proxy0.encoder codec0
activate proxy0

Client:
create codec codec0
set codec0.codec XCodec
activate codec0

create interface if0
set if0.family IPv4
set if0.host "127.0.0.1"
set if0.port "3000"
activate if0

create peer peer0
set peer0.family IPv4
set peer0.host "localhost"
set peer0.port "4000"
activate peer0

create proxy proxy0
set proxy0.interface if0
set proxy0.decoder codec0
set proxy0.peer peer0
set proxy0.encoder codec0
activate proxy0
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