by Archive-name: linux/howto/mini/slip+proxyarp
Last-modified: 14 Oct 95
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*** The `Linux SLIP+proxyARP mini-HOWTO' is posted automatically by the
*** direct any comments or questions about this HOWTO to the author,
- --- BEGIN Linux SLIP+proxyARP mini-HOWTO part 1/1 ---
Using SLIP And Proxy ARP To Connect
A Local Ethernet LAN To An Internet Connected LAN
February 4, 1994
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$Id: slip-arp,v 1.2 1995/02/04 20:57:08 davek Exp $
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0. Introduction
1. The Final Result
2. Setting It Up
3. Kernel And Software
4. Summary
5. Outstanding Issues And Questions
6. Acknowledgments
7. Further Reading
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0. Introduction
Very quickly, I have a small Ethernet LAN at home that I want to
be connected to the Internet. Since, I do not have my own network
address I wanted to piggyback on the office's network address. I
succeeded using SLIP and proxy ARP. This document quickly describes
how I did it.
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1. The Final Result
First, I'll present the final result and then describe how to get there.
The final network is all on a Class C network (a.b.c.0):
Internet
|
o-------+---------+----------------o <- Remote Ethernet
| .126
NetBlazer
| .215 <- SLIP (via 14.4 modem)
gw
| .253
o-----------------+--------+-------o <- Local Ethernet
| .254
mus
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2. Setting It Up
The keys to getting this working are routing and proxy ARP.
Here is gw's routing table:
Kernel routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
a.b.c.254 * 255.255.255.255 UH 0 0 5628 eth0
a.b.c.253 * 255.255.255.255 UH 0 0 0 eth0
a.b.c.126 * 255.255.255.255 UH 0 0 22 sl0
127.0.0.0 * 255.0.0.0 U 0 0 32 lo
default a.b.c.126 * UG 0 0 9 sl0
This table was created with the following commands:
1. The SLIP connection was established which created the default
gateway entry and the a.b.c.126 entry.
2. ifconfig eth0 a.b.c.253
3. route add a.b.c.253 eth0
4. route add a.b.c.254 eth0
Gw is now set up to talk to both eth0 and sl0. (This might be a good
time to note that my kernel has IP forwarding configured.) The reason for
the explicit route of a.b.c.253 may not be needed, but ping .253 from .253
without the route causes the ping to take the default route out the SLIP
link.
Here is mus's routing table:
Kernel routing table
Destination Gateway Genmask Flags MSS Window Use Iface
a.b.c.253 * 255.255.255.255 UH 1436 0 59 eth0
127.0.0.0 * 255.0.0.0 U 1936 0 52 lo
default a.b.c.253 * UG 1436 0 21661 eth0
This table was created with the following commands:
1. ifconfig eth0 a.b.c.254
2. route add a.b.c.253 eth0
3. route add default gw 192.68.22.253
Now, at this point I attempted to ping the NetBlazer. I could see the
packets being sent out the modem (SD was flashing), but there was no
response. This was good since it indicated that gw was getting packets
in on eth0 (Ethernet) and sending them out sl0 (SLIP).
The next step is to get the other side of the SLIP connection (NetBlazer)
to recognize and know how to talk to me. This was done by using its
proxy arp command.
Usage: proxy <hostid> ether|token|<interface> <mac-addr>
proxy a.b.c.253 ether 00:c0:6d:11:66:d3
proxy a.b.c.254 ether 00:c0:6d:11:66:e4
At this point I was able to ping the Internet from mus. And all was well
with the world. :)
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3. Kernel And Software
The kernel used on gw was 1.1.88 with IP Forwarding configured. This
is required. The kernel on mus was also 1.1.88, but IP Forwarding
was not configured. This does not matter.
It's also worth noting that PPP could have been used instead of
SLIP just as easily.
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4. Summary
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5. Outstanding Issues And Questions
The main question I have came up while writing this. When I checked
the ARP table on the NetBlazer, my ARP entries were no longer there, but
everything was still working. I readded the entry for mus and it made
no difference. If anyone has ideas on this, let me know.
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6. Acknowledgments
post Dec 21, 1994 "A Guide on Using SLIP with ProxyARP..." I'm not
so sure that my document is anything more than a rehash of what he
wrote other than I'm using a NetBlazer on the Internet side and he
had a modem attached to a computer. Anyway, thanks, John!
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7. Further Reading
Dawson, Terry; "NET-2-HOWTO."
Garnett, John; "A (client) SLIP Guide for Linux."
Lots of other HOWTO's.
- --
| UUCP: emory!melupl!davek Whois: DK87 |
- --- END Linux SLIP+proxyARP mini-HOWTO part 1/1 ---
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