[ale] Weird DSL modem issue

[Chris Fowler]

I spent an hour today trying to use a DSL modem in a lab to route to a
different network.  Please do not ask why!  I am doing work for a
telephone company in their lab and they have some weird connections to
mimic remote sites.


Anyway.

I am 192.168.130.2 on a 130.0/24.  The modem is at 130.253 and a cisco
router is at 130.254.  for me to go to the Internet I use 130.253.
130.253 is my default gateway.  For me to go to 110.0 I use still sue
130.253.

Here is traceroute

 [tomcat at sam-defalt tmp]$ traceroute -n 192.168.110.2
traceroute to 192.168.110.2 (192.168.110.2), 30 hops max, 40 byte
packets
 1  10.0.5.2  21.811 ms  24.711 ms  24.674 ms
 2  192.168.130.253  45.623 ms  47.584 ms  53.546 ms
 3  192.168.130.254  53.530 ms  53.513 ms  57.449 ms
 4  192.168.110.2  53.463 ms  57.379 ms  57.350 ms

Watch this!
[tomcat at sam-defalt tmp]$ strace -e trace=connect,read,write /tmp/test.pl
https://192.168.110.2/

... some stuff

connect(3, {sa_family=AF_INET, sin_port=htons(443),
sin_addr=inet_addr("192.168.110.2")}, 16) = 0
read(4, "#\363?\307\327\210,\330Z\4G\372\264\260 \1\330\222\264\203'\7
\313\227\226$^\326w\212_<"..., 48) = 48
write(3, "\200g\1\3\1\0N\0\0\0\20\0\0009\0\0008\0\0005\0\0\26\0\0\23\0\0
\n\7\0\300"..., 105) = 105
read(3, 

So we successfully connect.  We write but we are blocking in read!

No, I'll tell my device that 192.168.110.0/24 is at 130.254 (Cisco )
instead

[tomcat at sam-defalt tmp]$ traceroute -n 192.168.110.2
traceroute to 192.168.110.2 (192.168.110.2), 30 hops max, 40 byte
packets
 1  10.0.5.2  22.837 ms  26.783 ms  53.740 ms
 2  192.168.130.254  53.738 ms  53.782 ms  53.784 ms
 3  192.168.110.2  53.676 ms  53.682 ms  53.676 ms

No watch this!

connect(3, {sa_family=AF_INET, sin_port=htons(443),
sin_addr=inet_addr("192.168.110.2")}, 16) = 0
read(4, "\217\344\226\273\352\347\276\377\0206H\366^7\231\4k\360Z\243?\5
\37\240\260\31\2619d\2506\311"..., 48) = 48
write(3, "\200g\1\3\1\0N\0\0\0\20\0\0009\0\0008\0\0005\0\0\26\0\0\23\0\0
\n\7\0\300"..., 105) = 105
read(3, "\26\3\1\0J\2\0", 7)            = 7

See, no blocking in read and we get a page back.

The lab techs said nothing funny is going on but I get a feeling that
this modem is running some sort of "protection" program that is doing
this.

Does anyone have any clue what that might be?