Realtek USB ethernet adapter weirdness

Forum: Networking
Topic: Realtek USB ethernet adapter weirdness
started by: Ed_Nelson

Posted by Ed_Nelson on Oct. 12 2007,03:06

Hi all,

When I start DSL I can't access the internet. However, after I unplug and replug my USB ethernet adapter, I can connect.

First, some of my system specs:
Dual boot Windows98/Linux (flavor of the day, right now it's DSL)
Dell Latitude laptop
400 MHz PII
128 Mb RAM
6 Gb HD
Billion 5200S ADSL modem/router (provided by ISP)
Realtek RTL8150 USB ethernet adapter (I don't have an NIC card, that's why I use the adapter).

Here are the results of "ifconfig eth0" and "route" for the before and after unplug/replug scenarios:

BEFORE:
# ifconfig eth0 (just the first 3 lines)
Link encap: Ethernet HWaddr 00:E0:4C:03:38:08
inet addr:192.168.1.33 Bcast:192.168.1.255 Mask:255.255.255.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1

#route
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
58.8.37.1 * 255.255.255.255 UH 0 0 0 ppp0
192.168.1.0 * 255.255.255.0 U 0 0 0 eth0
default 192.168.1.1 0.0.0.0 UG 0 0 0 eth0

AFTER:
# ifconfig eth0
Link encap: Ethernet HWaddr 00:E0:4C:03:38:08
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1

#route
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
58.8.37.1 * 255.255.255.255 UH 0 0 0 ppp0
default ppp-58.8.37.1.r 0.0.0.0 UG 0 0 0 ppp0

So, while I'm very happy that I can connect to the internet with only the trivial step of unplug/replug, I am curious as to what's going on. Further, the issue isn't so trivial in other distros. In Slax, for example, when I unplug my USB cable the computer freezes ("kernel panic"). In Gentoo-based systems, nothing seems to happen (i.e. I still can't connect after replug). In Puppy, the whole unplug/replug is a non-issue since it works right out of the box.

Can anybody here help to explain this to me?

Thanks,
Gerry

Posted by roberts on Oct. 12 2007,04:21

Looks like upon boot your are assigned 192.168.1.33 ip address and its associated default route which is apparently not what you want?
Did you try to boot with the nodhcp boot option?

Posted by Ed_Nelson on Oct. 12 2007,09:23

Thanks roberts, booting with "nodhcp" did the trick!

Pardon my ignorance, but could you be so kind as to explain "why?"

Posted by roberts on Oct. 12 2007,14:07

DSL's default is to request an IP from any DHCP server by calling pump -i eth0. Why your router would respond with a bogus IP would be in the router configuration. DSL's default behaviour is usually not a problem but can sometimes interfere with proper network configuration. . One can always use nodhcp to stop such request.

Glad this worked for you.