I prefer Comer over Stevens:
Internetworking with TCP/IP Volume 1, Third Edition
P110. IP routing footnote (footnote at the bottom, which I found by looking up
IP Forwarding in the Index)
"Vendors also use the terms IP forwarding and IP switching to describe IP
Interestingly, most still refer to the needed information as IP routing
"...However, the TCP/IP standards draw a sharp distinction between the functions
of a host and those of a router, and sites that try to mix host and router
functions on a single machine
sometimes find that their multi-homed hosts engage in unexpected interactions.
For now, we will distinguish hosts from routers and assume that hosts do not
the router's function of transferring packets from one network to another."
Any typos are mine..
So, Comer says that routers transfer packets from one network to another,
which IP Forwarding on a Sun will do. Also, your quote from Stevens p.114
supports my point.
For those who must be getting tired of the arguement, again:
One of my Sun's that runs Firewall-1 will, with IP Forwarding enabled,
and Firewall-1 *unloaded* (crashed if you prefer, I won't get into that,)
and with only default routes, no advertising from the Sun box, not
listening to route updates, will pass packets between the inside
and outside networks. This acts enough like a router that you don't
really want it on. I would say that static or default routes would qualify
as Stevens' "routing policies" and they don't require RIP or OSPF
or any similar protocol.
---------- Previous Message ----------
To: Jerald.Josephs, Ryan.Russell
cc: firewalls, fw-1-mailinglist
From: kenneth_kron @ INS.COM (Kenneth kron) @ smtp
Date: 02/24/97 12:35:51 PM
Subject: Re:Routing vs IP forwarding (was FW Solaris and routing)
Come on guys.
IP forwarding is not routing. A system becomes a "router" when it starts
IP forwarding but everytime a system sends an IP packet it *routes*, it
decides which of it's interfaces to use to transmit the packet and whether
to forward it to a router or send it directly to it's destination.
Now when a system starts "IP forwarding" it not only makes routing
decisions for itself but will provide that same service for other systems.
So all IP stacks route (they choose between direct sending and using a
default router). Systems that are performing "IP forwarding" are usually
To quite Stevens in "TCP/IP Illustrated Vol. 1"
"The routing done by IP, when it searches the routing table and decides
which interface to send a packet out, is a *routing mechanism*. This
differs from a *routing policy* which is a set of rules that decides which
routes go into the routing table." page 112
"Here we purposely call *sun* a router and not a host because when it's
used as a default router, its IP forwarding function is being used, not its
host functionality" page 114
I believe what you two were actually arguing about was (per Stevens
1) IP forwarding
2) Routing policy
3) Route broadcasting
(though to be honest I didn't read the entire thread)
At 04:32 PM 2/21/97 -0800, Jerald Josephs wrote:
>Okay, now that we have clarified the argument, I *still* disagree
>with you because I understand that the routing of a packet is the
>intelligent movement of a packet based upon data obtained from a table
>of known routes.
[... stuff deleted...]
>> From: Ryan Russell/SYBASE
>> <Ryan .
>> Date: 21 Feb 97 16:04:27 EDT
>> My original argument was that IP Forwarding *IS* routing, which you
>> disagreed with.
[ ... More stuff deleted ...]
Kenneth Kron Information Security Consultant
International Network Services, Mountain View Office
Voice Mail: 415-858-4764,
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