Add the rt linux 4.1.3-rt3 as base

[kvmfornfv.git] / kernel / Documentation / networking / policy-routing.txt

diff --git a/kernel/Documentation/networking/policy-routing.txt b/kernel/Documentation/networking/policy-routing.txt
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+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