Creating a virtual interface to get more ephemeral ports (CentOS 5)

MediocreGopher · 01-25-2011, 08:36 PM

OS: CentOS 5.5 i386 Live CD (for testing purposes). Uses kernel 2.6.18-194.

I'm attempting to generate a boat-ton of connections (at least 100k) to a remote server. I wrote a script to do so (in erlang), it works fine. However, I run out of ephemeral ports and start getting address-in-use errors. I set my local port range to 1024-65535 (by echoing into /proc/sys/net/ipv4/ip_local_port_range), but that still maxes out at about 60k connections. From what I understand, opening up a new interface and giving it an ip address should work.

My problem is that I can't do so. Whenever I try I lose internet. Here's what usually happens:

Code:

[root@livecd ~]# curl --interface eth0 google.com
<HTML><HEAD><meta http-equiv="content-type" content="text/html;charset=utf-8">
<TITLE>301 Moved</TITLE></HEAD><BODY>
<H1>301 Moved</H1>
The document has moved
<A HREF="http://www.google.com/">here</A>.
</BODY></HTML>
[root@livecd ~]# /sbin/ifconfig
eth0      Link encap:Ethernet  HWaddr 00:21:85:E5:0F:B6  
          inet addr:172.16.202.132  Bcast:172.16.202.255  Mask:255.255.255.0
          inet6 addr: fe80::221:85ff:fee5:fb6/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:434562 errors:0 dropped:0 overruns:0 frame:0
          TX packets:916856 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:87592629 (83.5 MiB)  TX bytes:65593430 (62.5 MiB)
          Interrupt:90 Base address:0x4000 

lo        Link encap:Local Loopback  
          inet addr:127.0.0.1  Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:16436  Metric:1
          RX packets:1556 errors:0 dropped:0 overruns:0 frame:0
          TX packets:1556 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0 
          RX bytes:128016 (125.0 KiB)  TX bytes:128016 (125.0 KiB)

[root@livecd ~]# /sbin/ifconfig eth0:1 172.16.202.135
[root@livecd ~]# /sbin/ifconfig
eth0      Link encap:Ethernet  HWaddr 00:21:85:E5:0F:B6  
          inet addr:172.16.202.132  Bcast:172.16.202.255  Mask:255.255.255.0
          inet6 addr: fe80::221:85ff:fee5:fb6/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:434623 errors:0 dropped:0 overruns:0 frame:0
          TX packets:916900 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:87612074 (83.5 MiB)  TX bytes:65596722 (62.5 MiB)
          Interrupt:90 Base address:0x4000 

eth0:1    Link encap:Ethernet  HWaddr 00:21:85:E5:0F:B6  
          inet addr:172.16.202.135  Bcast:172.16.255.255  Mask:255.255.0.0
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          Interrupt:90 Base address:0x4000 

lo        Link encap:Local Loopback  
          inet addr:127.0.0.1  Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:16436  Metric:1
          RX packets:1556 errors:0 dropped:0 overruns:0 frame:0
          TX packets:1556 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0 
          RX bytes:128016 (125.0 KiB)  TX bytes:128016 (125.0 KiB)

[root@livecd ~]# curl --interface eth0 google.com

[root@livecd ~]# curl --interface eth0:1 google.com

[root@livecd ~]#

The first two commands show that I have internet and what my setup is. The third sets up a new interface (I think), and the last ones show the results (the two curl commands timeout).

Am I not setting up the connection correctly? I've tried doing it with the /etc/sysconfig/network-scripts files as well, but still no luck.

xeleema · 01-25-2011, 09:47 PM

Greetingz!

Sounds like you have a routing problem;

Code:

luser@lhost$ netstat -rn
Kernel IP routing table
Destination     Gateway         Genmask         Flags   MSS Window  irtt Iface
192.168.1.0     0.0.0.0         255.255.255.0   U         0 0          0 eth0
169.254.0.0     0.0.0.0         255.255.0.0     U         0 0          0 eth0
0.0.0.0         192.168.1.1     0.0.0.0         UG        0 0          0 eth0
luser@lhost$

I'm running CentOS 5.5

Code:

luser@lhost$ uname -a ; cat /etc/*release
Linux lhost 2.6.18-194.8.1.el5 #1 SMP Thu Jul 1 19:04:48 EDT 2010 x86_64 x86_64 x86_64 GNU/Linux
CentOS release 5.5 (Final)
luser@lhost$

And that seems to work for me;

Code:

luser@lhost$ sudo ifconfig eth0:1 192.168.1.122 
luser@lhost$ ifconfig -a | grep eth0
eth0      Link encap:Ethernet  HWaddr xx:xx:xx:xx:xx:xx
eth0:1    Link encap:Ethernet  HWaddr xx:xx:xx:xx:xx:xx

luser@lhost$ curl --interface eth0 google.com
<HTML><HEAD><meta http-equiv="content-type" content="text/html;charset=utf-8">
<TITLE>301 Moved</TITLE></HEAD><BODY>
<H1>301 Moved</H1>
The document has moved
<A HREF="http://www.google.com/">here</A>.
</BODY></HTML>
luser@lhost$ curl --interface eth0:1 google.com
<HTML><HEAD><meta http-equiv="content-type" content="text/html;charset=utf-8">
<TITLE>301 Moved</TITLE></HEAD><BODY>
<H1>301 Moved</H1>
The document has moved
<A HREF="http://www.google.com/">here</A>.
</BODY></HTML>
luser@lhost$