net: remove policy-routing.txt documentation

It dates back from 2.1.16 and is obsolete since 2.1.68 when the current
rule system has been introduced.
Signed-off-by: Vincent Bernat <vincent@bernat.im>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/networking/policy-routing.txt

-Classes
--------
-
-	"Class" is a complete routing table in common sense.
-	I.e. it is tree of nodes (destination prefix, tos, metric)
-	with attached information: gateway, device etc.
-	This tree is looked up as specified in RFC1812 5.2.4.3
-	1. Basic match
-	2. Longest match
-	3. Weak TOS.
-	4. Metric. (should not be in kernel space, but they are)
-	5. Additional pruning rules. (not in kernel space).
-	
-	We have two special type of nodes:
-	REJECT - abort route lookup and return an error value.
-	THROW  - abort route lookup in this class.
-
-
-	Currently the number of classes is limited to 255
-	(0 is reserved for "not specified class")
-
-	Three classes are builtin:
-
-	RT_CLASS_LOCAL=255 - local interface addresses,
-	broadcasts, nat addresses.
-
-	RT_CLASS_MAIN=254  - all normal routes are put there
-	by default.
-
-	RT_CLASS_DEFAULT=253 - if ip_fib_model==1, then
-	normal default routes are put there, if ip_fib_model==2
-	all gateway routes are put there.
-
-
-Rules
------
-	Rule is a record of (src prefix, src interface, tos, dst prefix)
-	with attached information.
-
-	Rule types:
-	RTP_ROUTE - lookup in attached class
-	RTP_NAT   - lookup in attached class and if a match is found,
-		    translate packet source address.
-	RTP_MASQUERADE - lookup in attached class and if a match is found,
-		    masquerade packet as sourced by us.
-	RTP_DROP   - silently drop the packet.
-	RTP_REJECT - drop the packet and send ICMP NET UNREACHABLE.
-	RTP_PROHIBIT - drop the packet and send ICMP COMM. ADM. PROHIBITED.
-
-	Rule flags:
-	RTRF_LOG - log route creations.
-	RTRF_VALVE - One way route (used with masquerading)
-
-Default setup:
-
-root@amber:/pub/ip-routing # iproute -r
-Kernel routing policy rules
-Pref Source             Destination        TOS Iface   Cl
-   0 default            default            00  *       255
- 254 default            default            00  *       254
- 255 default            default            00  *       253
-
-
-Lookup algorithm
-----------------
-
-	We scan rules list, and if a rule is matched, apply it.
-	If a route is found, return it.
-	If it is not found or a THROW node was matched, continue
-	to scan rules.
-
-Applications
-------------
-
-1.	Just ignore classes. All the routes are put into MAIN class
-	(and/or into DEFAULT class).
-
-	HOWTO:  iproute add PREFIX [ tos TOS ] [ gw GW ] [ dev DEV ]
-		[ metric METRIC ] [ reject ] ... (look at iproute utility)
-
-		or use route utility from current net-tools.
-		
-2.	Opposite case. Just forget all that you know about routing
-	tables. Every rule is supplied with its own gateway, device
-	info. record. This approach is not appropriate for automated
-	route maintenance, but it is ideal for manual configuration.
-
-	HOWTO:  iproute addrule [ from PREFIX ] [ to PREFIX ] [ tos TOS ]
-		[ dev INPUTDEV] [ pref PREFERENCE ] route [ gw GATEWAY ]
-		[ dev OUTDEV ] .....
-
-	Warning: As of now the size of the routing table in this
-	approach is limited to 256. If someone likes this model, I'll
-	relax this limitation.
-
-3.	OSPF classes (see RFC1583, RFC1812 E.3.3)
-	Very clean, stable and robust algorithm for OSPF routing
-	domains. Unfortunately, it is not widely used in the Internet.
-
-	Proposed setup:
-	255 local addresses
-	254 interface routes
-	253 ASE routes with external metric
-	252 ASE routes with internal metric
-	251 inter-area routes
-	250 intra-area routes for 1st area
-	249 intra-area routes for 2nd area
-	etc.
-	
-	Rules:
-	iproute addrule class 253
-	iproute addrule class 252
-	iproute addrule class 251
-	iproute addrule to a-prefix-for-1st-area class 250
-	iproute addrule to another-prefix-for-1st-area class 250
-	...
-	iproute addrule to a-prefix-for-2nd-area class 249
-	...
-
-	Area classes must be terminated with reject record.
-	iproute add default reject class 250
-	iproute add default reject class 249
-	...
-
-4.	The Variant Router Requirements Algorithm (RFC1812 E.3.2)
-	Create 16 classes for different TOS values.
-	It is a funny, but pretty useless algorithm.
-	I listed it just to show the power of new routing code.
-
-5.	All the variety of combinations......
-
-
-GATED
------
-
-	Gated does not understand classes, but it will work
-	happily in MAIN+DEFAULT. All policy routes can be set
-	and maintained manually.
-
-IMPORTANT NOTE
---------------
-	route.c has a compilation time switch CONFIG_IP_LOCAL_RT_POLICY.
-	If it is set, locally originated packets are routed
-	using all the policy list. This is not very convenient and
-	pretty ambiguous when used with NAT and masquerading.
-	I set it to FALSE by default.
-
-
-Alexey Kuznetov
-kuznet@ms2.inr.ac.ru