[1739] in linux-net channel archive
Re: Static vs dynamic routing from ISP
daemon@ATHENA.MIT.EDU (Jonathan Bradshaw)
Tue Jan 30 07:19:23 1996
From: Jonathan Bradshaw <jonathan@nrgup.com>
To: ecloud@goodnet.com (Shawn Ruttledge)
Date: Mon, 29 Jan 1996 22:46:38 -0500 (EST)
Cc: linux-net@vger.rutgers.edu
In-Reply-To: <199601292015.NAA04494@goodguy.goodnet.com> from "Shawn Ruttledge" at Jan 29, 96 01:15:19 pm
> The question remains then: is it true or not that a typical ISP does
> dynamic routing and that the result of it is that any addresses which appear
> under the assigned one will be seen as new addresses and automatically added
> to the routing tables? Or do they enforce subnetting, ie check to see if
> a "new" address ought to be under the ISP's subnet before adding it?
No, the typical ISP does STATIC ROUTING. Dynamic routing has too many
headaches associated with it. Terminal servers may have dynamic routes
defined, but as a whole, static routes are much easier to administer for
an ISP.
I have 6 IP addresses assigned to my dialin. Its a static route.
> OK, so assuming that it's not possible for me to get packets back that
> are directed to the ethernet addresses I have assigned my machines, what
> do I do? How about proxy arp? As I understand it, proxy arp forces a
> mapping of tcp/ip addresses to ethernet addresses. But it is superior to
> static routing somehow isn't it? I don't understand the difference really.
No, you get your ISP to assign you more IP addresses and route them to you.
You really are making this ALOT harder than it is because you are assuming
the Internet runs on dynamic routing tables. It doesn't.
Ok, here is how it works for me.
198.70.144.154 is my gateway. That is the address my Linux box uses as
the "primary" ppp0 interface.
ppp0 Link encap:Point-Point Protocol
inet addr:198.70.144.154 P-t-P:206.53.251.30 Mask:255.255.255.0
UP POINTOPOINT RUNNING MTU:1500 Metric:1
RX packets:24412 errors:18 dropped:18 overruns:0
TX packets:20163 errors:0 dropped:0 overruns:0
eth0 Link encap:10Mbps Ethernet HWaddr 02:60:8C:AF:7F:3E
inet addr:198.70.37.233 Bcast:198.70.37.239 Mask:255.255.255.248
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:79110 errors:0 dropped:0 overruns:0
TX packets:90071 errors:0 dropped:0 overruns:0
Interrupt:5 Base address:0x300 Memory:c8000-ca000
198.70.37.233 thru 198.70.37.238 have a static route via the 198.70.144.154
gateway as setup on the ISP end. Now, if you do the binary, that happens
to be the subnet 198.70.37.232 with a subnet mask of 198.70.37.248 (I think)
That is, when a packet for 198.70.37.233 comes into the ISP routers, it
sends it to 198.70.144.154 (the gateway). Linux, being configured for
packet forwarding, gets the packet through the ppp0 link and checks its
STATIC routing tables for where it should go.
Kernel routing table
Destination Gateway Genmask Flags MSS Window Use Iface
iq-ind-ts020.iq * 255.255.255.255 UH 1500 0 0 ppp0
198.70.37.232 * 255.255.255.248 U 1500 0 2 eth0
loopback * 255.0.0.0 U 2000 0 5 lo
default iq-ind-ts020.iq * UG 1500 0 187 ppp0
198.70.37.233 is the Linux ethernet card (see the above ifconfig) so it
ends up staying on the Linux box. However, 234 thru 238 will be sent out
the ethernet card to my LAN (my Win95 box is 234).
Unless you have a really nice (or knowledgable) ISP admin, you are probably
barking up an empty tree. Doing this setup is a pain for them and I pay
$100/month for it plus $125 setup charge.
--
Jonathan M. Bradshaw | Jonathan@NrgUp.Com | http://WWW.NrgUp.Com/jonathan
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Software Administrator, Boehringer Mannheim Corporation, Indianapolis, IN
Please note my opinions do not necessarily represent those of my employer
