comment on

This problem's starting to bug me now ;-)

So I've done some tests.

Specify the local port as part of the LocalAddr parameter ('1.2.3.4:8080')

Set something listening on a port:

perl -mHTTP::Daemon -e '$d=new HTTP::Daemon(LocalPort=>12345);while ($
+c=$d->accept){sleep 10;$c->send_file_response("index.html")}'
[download]

Try to connect to it:

perl -e 'use LWP::Simple;@LWP::Protocol::http::EXTRA_SOCK_OPTS = (Loca
+lAddr=>"localhost:54321");get("http://localhost:12345")'
[download]

Check netstat -a

tcp       71      0 mondas:12345            mondas:51575            ES
+TABLISHED
[download]

So we can use a string in the form 'x.x.x.x:port' with LocalAddr

Two processes trying to use the same outgoing port number
http://jonallen.info/cgi/delay.pl will wait 10 seconds, then print "Hello, World!" (to give me time to run netstat and set up processes on different machines).
We know now that specifying an local port number works. What would happen if, under high load, your server tried to send several XML 'pings' at once?
```
[jj@mondas jj]$ perl -le 'use LWP::Simple;@LWP::Protocol::http::EXTRA_
+SOCK_OPTS = (LocalAddr=>"192.168.1.1:54321");getprint("http://jonalle
+n.info/cgi/delay.pl");'
Hello, World!
[download]
```
At the same time, try to access a different remote server using the same local port
```
[jj@mondas jj]$ perl -e 'use LWP::Simple;@LWP::Protocol::http::EXTRA_S
+OCK_OPTS = (LocalAddr=>"192.168.1.1:54321");getprint("http://www.goog
+le.com");'
500 Can't connect to www.google.com:80 (Cannot assign requested addres
+s)
 <URL:http://www.google.com>
[download]
```
So if you are going to restrict the outgoing port numbers, be aware that in some conditions the local port you need will be in use. If you *really* need to do this, set up a range of ports and have your program try to use each one in turn and only fail if they are all in use.

Using the same port number on different aliased IP addresses

Machine has 192.168.1.10 aliased to 192.168.1.1

[root@mondas log]# ifconfig
eth0      Link encap:Ethernet  HWaddr 52:54:05:C5:13:7A
          inet addr:192.168.1.1  Bcast:192.168.1.255  Mask:255.255.255
+.0
          EtherTalk Phase 2 addr:65280/97
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:27996973 errors:0 dropped:2 overruns:0 frame:6
          TX packets:32099772 errors:484 dropped:0 overruns:0 carrier:
+968
          collisions:146707
          RX bytes:3038904039 (2898.1 Mb)  TX bytes:4085277291 (3896.0
+ Mb)

eth0:0    Link encap:Ethernet  HWaddr 52:54:05:C5:13:7A
          inet addr:192.168.1.10  Bcast:192.168.1.255  Mask:255.255.25
+5.0
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1

lo        Link encap:Local Loopback
          inet addr:127.0.0.1  Mask:255.0.0.0
          EtherTalk Phase 2 addr:0/0
          UP LOOPBACK RUNNING  MTU:16436  Metric:1
          RX packets:17172 errors:0 dropped:0 overruns:0 frame:0
          TX packets:17172 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0
          RX bytes:4381193 (4.1 Mb)  TX bytes:4381193 (4.1 Mb)
[download]

Start Apache as an unprivileged user (will bind to port 8080).

[jj@mondas jj]$ perl -e 'use LWP::Simple;@LWP::Protocol::http::EXTRA_S
+OCK_OPTS = (LocalAddr=>"192.168.1.1:8080");getprint("http://jonallen.
+info/cgi/delay.pl");'
500 Can't connect to jonallen.info:80 (Address already in use) <URL:ht
+tp://jonallen.info/cgi/delay.pl>

[jj@mondas jj]$ perl -e 'use LWP::Simple;@LWP::Protocol::http::EXTRA_S
+OCK_OPTS = (LocalAddr=>"192.168.1.10:8080");getprint("http://jonallen
+.info/cgi/delay.pl");'
500 Can't connect to jonallen.info:80 (Address already in use) <URL:ht
+tp://jonallen.info/cgi/delay.pl>
[download]

You can of course use the Listen and BindAddress directives in httpd.conf to force Apache to use only a certain IP alias. However the default configuration will bind to every IP address, so it is worth checking with netstat that nothing else is using the local port that you want to use.

Using the same port number for incoming & outgoing connections

Start the HTTP::Daemon one-liner (on 192.168.1.1). From another computer, connect to this daemon with a local port of 11111

perl -e 'use LWP::Simple;@LWP::Protocol::http::EXTRA_SOCK_OPTS = (Loca
+lAddr=>"192.168.1.8:11111");getprint("http://192.168.1.1:12345");'
[download]

Then (at the same time) from the machine running HTTP::Daemon, try to use the local port 11111:

perl -e 'use LWP::Simple;@LWP::Protocol::http::EXTRA_SOCK_OPTS = (Loca
+lAddr=>"192.168.1.1:11111");getprint("http://jonallen.info/cgi/delay.
+pl");'
[download]

Check netstat on 192.168.1.1

tcp        0      0 mondas.coldsoluti:11111 212.69.202.117:http     ES
+TABLISHED
tcp       73      0 mondas.coldsoluti:12345 lclus1.coldsoluti:11111 ES
+TABLISHED
[download]

So incoming connections do not restrict what ports you can use for outgoing connections.

This leads me to the conclusion that your code is fine, and as long as nothing else is listening on port 8080, it should work. Note however that if you try these sort of examples over the Internet, caches and proxies run by ISPs will change the local port numbers. So if machine 'A' opens a connection with a destination address of machine 'B' and a local port '22222', you cannot guarantee that when machine 'B' accepts the connection the remote port will be '22222'.

I would suggest that you disable your firewall (at least for outgoing connections), try your code again, and use netstat to find out exactly what it is doing.

In reply to Re: LWP and LocalIP/LocalPort by jj808
in thread LWP and LocalIP/LocalPort by jk2addict

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