ADSL as backup Internet Connection

ADSL as backup Internet Connection

Post by Chris Taniguch » Sat, 09 Oct 1999 04:00:00



 Hi all,

 My company presently has a T-1 connected to the Internet via an ISP.
 The ISP provides mail exchange and DNS, the LAN has email server, FTP,
 web, etc.  Normal stuff.  What we'd like to do is have a backup
 connection to the Internet using ADSL from a different ISP.  When the
 T-1 goes down, or there is connection problems at the T-1 ISP, I'd like
 to be able to connect the LAN to the ADSL line and have all services
 available as usual albeit perhaps at a bit slower speed.  The best
 scenario would be one where there would no changes necessary at the
 desktops, little or none on the LAN servers (email server, ftp, web).

 I'm thinking I could use a linux box with 2 NICs as the emergency
 router.  One NIC is connected to the ADSL and one NIC is connected to
 the LAN.  The ADSL NIC is given an IP address via DHCP by the ISP,
 although if necessary we could request a static IP.  The LAN NIC I
would
 give the same IP number as used by the Cisco router on the T-1.  Of
 course, the LAN-side NIC on the Linux box would be left disconnected
 until it was needed.  I would disconnect the Cisco router from the LAN
 and plug in the Linux box when something went wrong with the T-1.

 I'm trying to think through all the various gotchas, like would mail
 exchange still work, DNS, etc.  Do you see anything wrong with my
 solution?

 Thanks, Chris.

 
 
 

1. Internet connection lost after x hours (DHCP, aDSL)

If I leave my computer on for a while -- let's say overnight -- then  I
log back on later, I can't access the internet.  I'm connected to a
router, and I'm using DHCP.

If I run 'ipconfig', everything looks fine:

eth0      Link encap:Ethernet  HWaddr 00:10:A4:84:EB:85
           inet addr:192.168.2.3  Bcast:192.168.2.255  Mask:255.255.255.0
           inet6 addr: fe80::210:a4ff:fe84:eb85/10 Scope:Link
           UP BROADCAST NOTRAILERS RUNNING MULTICAST  MTU:1500  Metric:1
           RX packets:50468 errors:0 dropped:0 overruns:0 frame:0
           TX packets:39321 errors:0 dropped:0 overruns:0 carrier:0
           collisions:0 txqueuelen:100
           RX bytes:46521342 (44.3 Mb)  TX bytes:7554248 (7.2 Mb)
           Interrupt:11 Base address:0x1800 Memory:e8120000-e8120038

   When I try to get to my router through a browser, the connection gets
refused. (To get to my router, I go to: 192.168.2.1).  It works after a
reboot, as does the internet.

If I run 'ifdown eth0', it works.  Then, when I try 'ifup eth0', I
receive the message: 'Starting DHCP Client Daemon on eth0... . . . . . .
. no IP address yet... backgrounding.'  If I run 'ipconfig' again, I get:

eth0      Link encap:Ethernet  HWaddr 00:10:A4:84:EB:85
           inet6 addr: fe80::210:a4ff:fe84:eb85/10 Scope:Link
           UP BROADCAST NOTRAILERS RUNNING MULTICAST  MTU:1500  Metric:1
           RX packets:50468 errors:0 dropped:0 overruns:0 frame:0
           TX packets:39321 errors:0 dropped:0 overruns:0 carrier:0
           collisions:0 txqueuelen:100
           RX bytes:46521342 (44.3 Mb)  TX bytes:7561066 (7.2 Mb)
           Interrupt:11 Base address:0x1800 Memory:e8120000-e8120038

Eventually, I have to give up and reboot, and then it works.  Any ideas?

I'm using an IBM ThinkPad T21 with SuSE 8.0 Professional.  Also, and I
don't know if this is related, when I ran 'uptime' this morning, it said
that it had been up for ten hours and twenty-one minutes.  However, I
know that I've had the computer on for at least twenty-one hours.  Has
anyone seen this before?

This does not happen to my desktop, which is connected to the same
router.  There, I am using an AMD Athlon XP 1800+ w/ 1gig of RAM and an
ECS K7S5A motherboard (using the onboard SiS 900 ethernet).  Same OS --
SuSE 8.0 Pro.

Shawn

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