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Diffstat (limited to 'vnet/vnet/fib/fib.h')
| -rw-r--r-- | vnet/vnet/fib/fib.h | 652 |
1 files changed, 0 insertions, 652 deletions
diff --git a/vnet/vnet/fib/fib.h b/vnet/vnet/fib/fib.h deleted file mode 100644 index 7cf1d136935..00000000000 --- a/vnet/vnet/fib/fib.h +++ /dev/null @@ -1,652 +0,0 @@ -/* - * Copyright (c) 2016 Cisco and/or its affiliates. - * Licensed under the Apache License, Version 2.0 (the "License"); - * you may not use this file except in compliance with the License. - * You may obtain a copy of the License at: - * - * http://www.apache.org/licenses/LICENSE-2.0 - * - * Unless required by applicable law or agreed to in writing, software - * distributed under the License is distributed on an "AS IS" BASIS, - * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. - * See the License for the specific language governing permissions and - * limitations under the License. - */ -/** - * \brief - * A IP v4/6 independent FIB. - * - * The main functions provided by the FIB are as follows; - * - * - source priorities - * - * A route can be added to the FIB by more than entity or source. Sources - * include, but are not limited to, API, CLI, LISP, MAP, etc (for the full list - * see fib_entry.h). Each source provides the forwarding information (FI) that - * is has determined as required for that route. Since each source determines the - * FI using different best path and loop prevention algorithms, it is not - * correct for the FI of multiple sources to be combined. Instead the FIB must - * choose to use the FI from only one source. This choose is based on a static - * priority assignment. For example; - * IF a prefix is added as a result of interface configuration: - * set interface address 192.168.1.1/24 GigE0 - * and then it is also added from the CLI - * ip route 192.168.1.1/32 via 2.2.2.2/32 - * then the 'interface' source will prevail, and the route will remain as - * 'local'. - * The requirement of the FIB is to always install the FI from the winning - * source and thus to maintain the FI added by losing sources so it can be - * installed should the winning source be withdrawn. - * - * - adj-fib maintenance - * - * When ARP or ND discover a neighbour on a link an adjacency forms for the - * address of that neighbour. It is also required to insert a route in the - * appropriate FIB table, corresponding to the VRF for the link, an entry for - * that neighbour. This entry is often referred to as an adj-fib. Adj-fibs - * have a dedicated source; 'ADJ'. - * The priority of the ADJ source is lower than most. This is so the following - * config; - * set interface address 192.168.1.1/32 GigE0 - * ip arp 192.168.1.2 GigE0 dead.dead.dead - * ip route add 192.168.1.2 via 10.10.10.10 GigE1 - * will forward traffic for 192.168.1.2 via GigE1. That is the route added - * by the control plane is favoured over the adjacency discovered by ARP. - * The control plane, with its associated authentication, is considered the - * authoritative source. - * To counter the nefarious addition of adj-fib, through the nefarious injection - * of adjacencies, the FIB is also required to ensure that only adj-fibs whose - * less specific covering prefix is connected are installed in forwarding. This - * requires the use of 'cover tracking', where a route maintains a dependency - * relationship with the route that is its less specific cover. When this cover - * changes (i.e. there is a new covering route) or the forwarding information - * of the cover changes, then the covered route is notified. - * - * Overlapping sub-nets are not supported, so no adj-fib has multiple paths. - * The control plane is expected to remove a prefix configured for an interface - * before the interface changes VRF. - * So while the following config is accepted: - * set interface address 192.168.1.1/32 GigE0 - * ip arp 192.168.1.2 GigE0 dead.dead.dead - * set interface ip table GigE0 2 - * it does not result in the desired behaviour. - * - * - attached export. - * - * Further to adj-fib maintenance above consider the following config: - * set interface address 192.168.1.1/24 GigE0 - * ip route add table 2 192.168.1.0/24 GigE0 - * Traffic destined for 192.168.1.2 in table 2 will generate an ARP request - * on GigE0. However, since GigE0 is in table 0, all adj-fibs will be added in - * FIB 0. Hence all hosts in the sub-net are unreachable from table 2. To resolve - * this, all adj-fib and local prefixes are exported (i.e. copied) from the - * 'export' table 0, to the 'import' table 2. There can be many import tables - * for a single export table. - * - * - recursive route resolution - * - * A recursive route is of the form: - * 1.1.1.1/32 via 10.10.10.10 - * i.e. a route for which no egress interface is provided. In order to forward - * traffic to 1.1.1.1/32 the FIB must therefore first determine how to forward - * traffic to 10.10.10.10/32. This is recursive resolution. - * Recursive resolution, just like normal resolution, proceeds via a longest - * prefix match for the 'via-address' 10.10.10.10. Note it is only possible - * to add routes via an address (i.e. a /32 or /128) not via a shorter mask - * prefix. There is no use case for the latter. - * Since recursive resolution proceeds via a longest prefix match, the entry - * in the FIB that will resolve the recursive route, termed the via-entry, may - * change as other routes are added to the FIB. Consider the recursive - * route shown above, and this non-recursive route: - * 10.10.10.0/24 via 192.168.16.1 GigE0 - * The entry for 10.10.10.0/24 is thus the resolving via-entry. If this entry is - * modified, to say; - * 10.10.10.0/24 via 192.16.1.3 GigE0 - * Then packet for 1.1.1.1/32 must also be sent to the new next-hop. - * Now consider the addition of; - * 10.10.10.0/28 via 192.168.16.2 GigE0 - * The more specific /28 is a better longest prefix match and thus becomes the - * via-entry. Removal of the /28 means the resolution will revert to the /24. - * The tracking to the changes in recursive resolution is the requirement of - * the FIB. When the forwarding information of the via-entry changes a back-walk - * is used to update dependent recursive routes. When new routes are added to - * the table the cover tracking feature provides the necessary notifications to - * the via-entry routes. - * The adjacency constructed for 1.1.1.1/32 will be a recursive adjacency - * whose next adjacency will be contributed from the via-entry. Maintaining - * the validity of this recursive adjacency is a requirement of the FIB. - * - * - recursive loop avoidance - * - * Consider this set of routes: - * 1.1.1.1/32 via 2.2.2.2 - * 2.2.2.2/32 via 3.3.3.3 - * 3.3.3.3/32 via 1.1.1.1 - * this is termed a recursion loop - all of the routes in the loop are - * unresolved in so far as they do not have a resolving adjacency, but each - * is resolved because the via-entry is known. It is important here to note - * the distinction between the control-plane objects and the data-plane objects - * (more details in the implementation section). The control plane objects must - * allow the loop to form (i.e. the graph becomes cyclic), however, the - * data-plane absolutely must not allow the loop to form, otherwise the packet - * would loop indefinitely and never egress the device - meltdown would follow. - * The control plane must allow the loop to form, because when the loop breaks, - * all members of the loop need to be updated. Forming the loop allows the - * dependencies to be correctly setup to allow this to happen. - * There is no limit to the depth of recursion supported by VPP so: - * 9.9.9.100/32 via 9.9.9.99 - * 9.9.9.99/32 via 9.9.9.98 - * 9.9.9.98/32 via 9.9.9.97 - * ... turtles, turtles, turtles ... - * 9.9.9.1/32 via 10.10.10.10 Gig0 - * is supported to as many layers of turtles is desired, however, when - * back-walking a graph (in this case from 9.9.9.1/32 up toward 9.9.9.100/32) - * a FIB needs to differentiate the case where the recursion is deep versus - * the case where the recursion is looped. A simple method, employed by VPP FIB, - * is to limit the number of steps. VPP FIB limit is 16. Typical BGP scenarios - * in the wild do not exceed 3 (BGP Inter-AS option C). - * - * - Fast Convergence - * - * After a network topology change, the 'convergence' time, is the time taken - * for the router to complete a transition to forward traffic using the new - * topology. The convergence time is therefore a summation of the time to; - * - detect the failure. - * - calculate the new 'best path' information - * - download the new best paths to the data-plane. - * - install those best best in data-plane forwarding. - * The last two points are of relevance to VPP architecture. The download API is - * binary and batch, details are not discussed here. There is no HW component to - * programme, installation time is bounded by the memory allocation and table - * lookup and insert access times. - * - * 'Fast' convergence refers to a set of technologies that a FIB can employ to - * completely or partially restore forwarding whilst the convergence actions - * listed above are ongoing. Fast convergence technologies are further - * sub-divided into Prefix Independent Convergence (PIC) and Loop Free - * Alternate path Fast re-route (LFA-FRR or sometimes called IP-FRR) which - * affect recursive and non-recursive routes respectively. - * - * LFA-FRR - * - * Consider the network topology below: - * - * C - * / \ - * X -- A --- B - Y - * | | - * D F - * \ / - * E - * - * all links are equal cost, traffic is passing from X to Y. the best path is - * X-A-B-Y. There are two alternative paths, one via C and one via E. An - * alternate path is considered to be loop free if no other router on that path - * would forward the traffic back to the sender. Consider router C, its best - * path to Y is via B, so if A were to send traffic destined to Y to C, then C - * would forward that traffic to B - this is a loop-free alternate path. In - * contrast consider router D. D's shortest path to Y is via A, so if A were to - * send traffic destined to Y via D, then D would send it back to A; this is - * not a loop-free alternate path. There are several points of note; - * - we are considering the pre-failure routing topology - * - any equal-cost multi-path between A and B is also a LFA path. - * - in order for A to calculate LFA paths it must be aware of the best-path - * to Y from the perspective of D. These calculations are thus limited to - * routing protocols that have a full view of the network topology, i.e. - * link-state DB protocols like OSPF or an SDN controller. LFA protected - * prefixes are thus non-recursive. - * - * LFA is specified as a 1 to 1 redundancy; a primary path has only one LFA - * (a.k.a. backup) path. To my knowledge this limitation is one of complexity - * in the calculation of and capacity planning using a 1-n redundancy. - * - * In the event that the link A-B fails, the alternate path via C can be used. - * In order to provide 'fast' failover in the event of a failure, the control - * plane will download both the primary and the backup path to the FIB. It is - * then a requirement of the FIB to perform the failover (a.k.a cutover) from - * the primary to the backup path as quickly as possible, and particularly - * without any other control-plane intervention. The expectation is cutover is - * less than 50 milli-seconds - a value allegedly from the VOIP QoS. Note that - * cutover time still includes the fault detection time, which in a vitalised - * environment could be the dominant factor. Failure detection can be either a - * link down, which will affect multiple paths on a multi-access interface, or - * via a specific path heartbeat (i.e. BFD). - * At this time VPP does not support LFA, that is it does not support the - * installation of a primary and backup path[s] for a route. However, it does - * support ECMP, and VPP FIB is designed to quickly remove failed paths from - * the ECMP set, however, it does not insert shared objects specific to the - * protected resource into the forwarding object graph, since this would incur - * a forwarding/performance cost. Failover time is thus route number dependent. - * Details are provided in the implementation section below. - * - * PIC - * - * PIC refers to the concept that the converge time should be independent of - * the number of prefixes/routes that are affected by the failure. PIC is - * therefore most appropriate when considering networks with large number of - * prefixes, i.e. BGP networks and thus recursive prefixes. There are several - * flavours of PIC covering different locations of protection and failure - * scenarios. An outline is given below, see the literature for more details: - * - * Y/16 - CE1 -- PE1---\ - * | \ P1---\ - * | \ PE3 -- CE3 - X/16 - * | - P2---/ - * Y/16 - CE2 -- PE2---/ - * - * CE = customer edge, PE = provider edge. external-BGP runs between customer - * and provider, internal-BGP runs between provider and provider. - * - * 1) iBGP PIC-core: consider traffic from CE1 to X/16 via CE3. On PE1 there is - * are routes; - * X/16 (and hundreds of thousands of others like it) - * via PE3 - * and - * PE3/32 (its loopback address) - * via 10.0.0.1 Link0 (this is P1) - * via 10.1.1.1 Link1 (this is P2) - * the failure is the loss of link0 or link1 - * As in all PIC scenarios, in order to provide prefix independent convergence - * it must be that the route for X/16 (and all other routes via PE3) do not - * need to be updated in the FIB. The FIB therefore needs to update a single - * object that is shared by all routes - once this shared object is updated, - * then all routes using it will be instantly updated to use the new forwarding - * information. In this case the shared object is the resolving route via PE3. - * Once the route via PE3 is updated via IGP (OSPF) convergence, then all - * recursive routes that resolve through it are also updated. VPP FIB - * implements this scenario via a recursive-adjacency. the X/16 and it sibling - * routes share a recursive-adjacency that links to/points at/stacks on the - * normal adjacency contributed by the route for PE3. Once this shared - * recursive adj is re-linked then all routes are switched to using the new - * forwarding information. This is shown below; - * - * pre-failure; - * X/16 --> R-ADJ-1 --> ADJ-1-PE3 (multi-path via P1 and P2) - * - * post-failure: - * X/16 --> R-ADJ-1 --> ADJ-2-PE3 (single path via P1) - * - * note that R-ADJ-1 (the recursive adj) remains in the forwarding graph, - * therefore X/16 (and all its siblings) is not updated. - * X/16 and its siblings share the recursive adj since they share the same - * path-list. It is the path-list object that contributes the recursive-adj - * (see next section for more details) - * - * - * 2) iBGP PIC-edge; Traffic from CE3 to Y/16. On PE3 there is are routes; - * Y/16 (and hundreds of thousands of others like it) - * via PE1 - * via PE2 - * and - * PE1/32 (PE1's loopback address) - * via 10.0.2.2 Link0 (this is P1) - * PE2/32 (PE2's loopback address) - * via 10.0.3.3 Link1 (this is P2) - * - * the failure is the loss of reachability to PE2. this could be either the - * loss of the link P2-PE2 or the loss of the node PE2. This is detected either - * by the withdrawal of the PE2's loopback route or by some form of failure - * detection (i.e. BFD). - * VPP FIB again provides PIC via the use of the shared recursive-adj. Y/16 and - * its siblings will again share a path-list for the list {PE1,PE2}, this - * path-list will contribute a multi-path-recursive-adj, i.e. a multi-path-adj - * with each choice therein being another adj; - * - * Y/16 -> RM-ADJ --> ADJ1 (for PE1) - * --> ADJ2 (for PE2) - * - * when the route for PE1 is withdrawn then the multi-path-recursive-adjacency - * is updated to be; - * - * Y/16 --> RM-ADJ --> ADJ1 (for PE1) - * --> ADJ1 (for PE1) - * - * that is both choices in the ECMP set are the same and thus all traffic is - * forwarded to PE1. Eventually the control plane will download a route update - * for Y/16 to be via PE1 only. At that time the situation will be: - * - * Y/16 -> R-ADJ --> ADJ1 (for PE1) - * - * In the scenario above we assumed that PE1 and PE2 are ECMP for Y/16. eBGP - * PIC core is also specified for the case were one PE is primary and the other - * backup - VPP FIB does not support that case at this time. - * - * 3) eBGP PIC Edge; Traffic from CE3 to Y/16. On PE1 there is are routes; - * Y/16 (and hundreds of thousands of others like it) - * via CE1 (primary) - * via PE2 (backup) - * and - * CE1 (this is an adj-fib) - * via 11.0.0.1 Link0 (this is CE1) << this is an adj-fib - * PE2 (PE2's loopback address) - * via 10.0.5.5 Link1 (this is link PE1-PE2) - * the failure is the loss of link0 to CE1. The failure can be detected by FIB - * either as a link down event or by the control plane withdrawing the connected - * prefix on the link0 (say 10.0.5.4/30). The latter works because the resolving - * entry is an adj-fib, so removing the connected will withdraw the adj-fib, and - * hence the recursive path becomes unresolved. The former is faster, - * particularly in the case of Inter-AS option A where there are many VLAN - * sub-interfaces on the PE-CE link, one for each VRF, and so the control plane - * must remove the connected prefix for each sub-interface to trigger PIC in - * each VRF. Note though that total PIC cutover time will depend on VRF scale - * with either trigger. - * Primary and backup paths in this eBGP PIC-edge scenario are calculated by - * BGP. Each peer is configured to always advertise its best external path to - * its iBGP peers. Backup paths therefore send traffic from the PE back into the - * core to an alternate PE. A PE may have multiple external paths, i.e. multiple - * directly connected CEs, it may also have multiple backup PEs, however there - * is no correlation between the two, so unlike LFA-FRR, the redundancy model is - * N-M; N primary paths are backed-up by M backup paths - only when all primary - * paths fail, then the cutover is performed onto the M backup paths. Note that - * PE2 must be suitably configured to forward traffic on its external path that - * was received from PE1. VPP FIB does not support external-internal-BGP (eiBGP) - * load-balancing. - * - * As with LFA-FRR the use of primary and backup paths is not currently - * supported, however, the use of a recursive-multi-path-adj, and a suitably - * constrained hashing algorithm to choose from the primary or backup path sets, - * would again provide the necessary shared object and hence the prefix scale - * independent cutover. - * - * Astute readers will recognise that both of the eBGP PIC scenarios refer only - * to a BGP free core. - * - * Fast convergence implementation options come in two flavours: - * 1) Insert switches into the data-path. The switch represents the protected - * resource. If the switch is 'on' the primary path is taken, otherwise - * the backup path is taken. Testing the switch in the data-path comes with - * an associated performance cost. A given packet may encounter more than - * one protected resource as it is forwarded. This approach minimises - * cutover times as packets will be forwarded on the backup path as soon - * as the protected resource is detected to be down and the single switch - * is tripped. However, it comes at a performance cost, which increases - * with each shared resource a packet encounters in the data-path. - * This approach is thus best suited to LFA-FRR where the protected routes - * are non-recursive (i.e. encounter few shared resources) and the - * expectation on cutover times is more stringent (<50msecs). - * 2) Update shared objects. Identify objects in the data-path, that are - * required to be present whether or not fast convergence is required (i.e. - * adjacencies) that can be shared by multiple routes. Create a dependency - * between these objects at the protected resource. When the protected - * resource fails, each of the shared objects is updated in a way that all - * users of it see a consistent change. This approach incurs no performance - * penalty as the data-path structure is unchanged, however, the cutover - * times are longer as more work is required when the resource fails. This - * scheme is thus more appropriate to recursive prefixes (where the packet - * will encounter multiple protected resources) and to fast-convergence - * technologies where the cutover times are less stringent (i.e. PIC). - * - * Implementation: - * --------------- - * - * Due to the requirements outlined above, not all routes known to FIB - * (e.g. adj-fibs) are installed in forwarding. However, should circumstances - * change, those routes will need to be added. This adds the requirement that - * a FIB maintains two tables per-VRF, per-AF (where a 'table' is indexed by - * prefix); the forwarding and non-forwarding tables. - * - * For DP speed in VPP we want the lookup in the forwarding table to directly - * result in the ADJ. So the two tables; one contains all the routes (a - * lookup therein yields a fib_entry_t), the other contains only the forwarding - * routes (a lookup therein yields an ip_adjacency_t). The latter is used by the - * DP. - * This trades memory for forwarding performance. A good trade-off in VPP's - * expected operating environments. - * - * Note these tables are keyed only by the prefix (and since there 2 two - * per-VRF, implicitly by the VRF too). The key for an adjacency is the - * tuple:{next-hop, address (and it's AF), interface, link/ether-type}. - * consider this curious, but allowed, config; - * - * set int ip addr 10.0.0.1/24 Gig0 - * set ip arp Gig0 10.0.0.2 dead.dead.dead - * # a host in that sub-net is routed via a better next hop (say it avoids a - * # big L2 domain) - * ip route add 10.0.0.2 Gig1 192.168.1.1 - * # this recursive should go via Gig1 - * ip route add 1.1.1.1/32 via 10.0.0.2 - * # this non-recursive should go via Gig0 - * ip route add 2.2.2.2/32 via Gig0 10.0.0.2 - * - * for the last route, the lookup for the path (via {Gig0, 10.0.0.2}) in the - * prefix table would not yield the correct result. To fix this we need a - * separate table for the adjacencies. - * - * - FIB data structures; - * - * fib_entry_t: - * - a representation of a route. - * - has a prefix. - * - it maintains an array of path-lists that have been contributed by the - * different sources - * - install an adjacency in the forwarding table contributed by the best - * source's path-list. - * - * fib_path_list_t: - * - a list of paths - * - path-lists may be shared between FIB entries. The path-lists are thus - * kept in a DB. The key is the combined description of the paths. We share - * path-lists when it will aid convergence to do so. Adding path-lists to - * this DB that are never shared, or are not shared by prefixes that are - * not subject to PIC, will increase the size of the DB unnecessarily and - * may lead to increased search times due to hash collisions. - * - the path-list contributes the appropriate adj for the entry in the - * forwarding table. The adj can be 'normal', multi-path or recursive, - * depending on the number of paths and their types. - * - since path-lists are shared there is only one instance of the multi-path - * adj that they [may] create. As such multi-path adjacencies do not need a - * separate DB. - * The path-list with recursive paths and the recursive adjacency that it - * contributes forms the backbone of the fast convergence architecture (as - * described previously). - * - * fib_path_t: - * - a description of how to forward the traffic (i.e. via {Gig1, K}). - * - the path describes the intent on how to forward. This differs from how - * the path resolves. I.e. it might not be resolved at all (since the - * interface is deleted or down). - * - paths have different types, most notably recursive or non-recursive. - * - a fib_path_t will contribute the appropriate adjacency object. It is from - * these contributions that the DP graph/chain for the route is built. - * - if the path is recursive and a recursion loop is detected, then the path - * will contribute the special DROP adjacency. This way, whilst the control - * plane graph is looped, the data-plane graph does not. - * - * we build a graph of these objects; - * - * fib_entry_t -> fib_path_list_t -> fib_path_t -> ... - * - * for recursive paths: - * - * fib_path_t -> fib_entry_t -> .... - * - * for non-recursive paths - * - * fib_path_t -> ip_adjacency_t -> interface - * - * These objects, which constitute the 'control plane' part of the FIB are used - * to represent the resolution of a route. As a whole this is referred to as the - * control plane graph. There is a separate DP graph to represent the forwarding - * of a packet. In the DP graph each object represents an action that is applied - * to a packet as it traverses the graph. For example, a lookup of a IP address - * in the forwarding table could result in the following graph: - * - * recursive-adj --> multi-path-adj --> interface_A - * --> interface_B - * - * A packet traversing this FIB DP graph would thus also traverse a VPP node - * graph of: - * - * ipX_recursive --> ipX_rewrite --> interface_A_tx --> etc - * - * The taxonomy of objects in a FIB graph is as follows, consider; - * - * A --> - * B --> D - * C --> - * - * Where A,B and C are (for example) routes that resolve through D. - * parent; D is the parent of A, B, and C. - * children: A, B, and C are children of D. - * sibling: A, B and C are siblings of one another. - * - * All shared objects in the FIB are reference counted. Users of these objects - * are thus expected to use the add_lock/unlock semantics (as one would - * normally use malloc/free). - * - * WALKS - * - * It is necessary to walk/traverse the graph forwards (entry to interface) to - * perform a collapse or build a recursive adj and backwards (interface - * to entry) to perform updates, i.e. when interface state changes or when - * recursive route resolution updates occur. - * A forward walk follows simply by navigating an object's parent pointer to - * access its parent object. For objects with multiple parents (e.g. a - * path-list), each parent is walked in turn. - * To support back-walks direct dependencies are maintained between objects, - * i.e. in the relationship, {A, B, C} --> D, then object D will maintain a list - * of 'pointers' to its children {A, B, C}. Bare C-language pointers are not - * allowed, so a pointer is described in terms of an object type (i.e. entry, - * path-list, etc) and index - this allows the object to be retrieved from the - * appropriate pool. A list is maintained to achieve fast convergence at scale. - * When there are millions or recursive prefixes, it is very inefficient to - * blindly walk the tables looking for entries that were affected by a given - * topology change. The lowest hanging fruit when optimising is to remove - * actions that are not required, so all back-walks only traverse objects that - * are directly affected by the change. - * - * PIC Core and fast-reroute rely on FIB reacting quickly to an interface - * state change to update the multi-path-adjacencies that use this interface. - * An example graph is shown below: - * - * E_a --> - * E_b --> PL_2 --> P_a --> Interface_A - * ... --> P_c -\ - * E_k --> \ - * Interface_K - * / - * E_l --> / - * E_m --> PL_1 --> P_d -/ - * ... --> P_f --> Interface_F - * E_z --> - * - * E = fib_entry_t - * PL = fib_path_list_t - * P = fib_path_t - * The subscripts are arbitrary and serve only to distinguish object instances. - * This CP graph result in the following DP graph: - * - * M-ADJ-2 --> Interface_A - * \ - * -> Interface_K - * / - * M-ADJ-1 --> Interface_F - * - * M-ADJ = multi-path-adjacency. - * - * When interface K goes down a back-walk is started over its dependants in the - * control plane graph. This back-walk will reach PL_1 and PL_2 and result in - * the calculation of new adjacencies that have interface K removed. The walk - * will continue to the entry objects and thus the forwarding table is updated - * for each prefix with the new adjacency. The DP graph then becomes: - * - * ADJ-3 --> Interface_A - * - * ADJ-4 --> Interface_F - * - * The eBGP PIC scenarios described above relied on the update of a path-list's - * recursive-adjacency to provide the shared point of cutover. This is shown - * below - * - * E_a --> - * E_b --> PL_2 --> P_a --> E_44 --> PL_a --> P_b --> Interface_A - * ... --> P_c -\ - * E_k --> \ - * \ - * E_1 --> PL_k -> P_k --> Interface_K - * / - * E_l --> / - * E_m --> PL_1 --> P_d -/ - * ... --> P_f --> E_55 --> PL_e --> P_e --> Interface_E - * E_z --> - * - * The failure scenario is the removal of entry E_1 and thus the paths P_c and - * P_d become unresolved. To achieve PIC the two shared recursive path-lists, - * PL_1 and PL_2 must be updated to remove E_1 from the recursive-multi-path- - * adjacencies that they contribute, before any entry E_a to E_z is updated. - * This means that as the update propagates backwards (right to left) in the - * graph it must do so breadth first not depth first. Note this approach leads - * to convergence times that are dependent on the number of path-list and so - * the number of combinations of egress PEs - this is desirable as this - * scale is considerably lower than the number of prefixes. - * - * If we consider another section of the graph that is similar to the one - * shown above where there is another prefix E_2 in a similar position to E_1 - * and so also has many dependent children. It is reasonable to expect that a - * particular network failure may simultaneously render E_1 and E_2 unreachable. - * This means that the update to withdraw E_2 is download immediately after the - * update to withdraw E_1. It is a requirement on the FIB to not spend large - * amounts of time in a back-walk whilst processing the update for E_1, i.e. the - * back-walk must not reach as far as E_a and its siblings. Therefore, after the - * back-walk has traversed one generation (breadth first) to update all the - * path-lists it should be suspended/back-ground and further updates allowed - * to be handled. Once the update queue is empty, the suspended walks can be - * resumed. Note that in the case that multiple updates affect the same entry - * (say E_1) then this will trigger multiple similar walks, these are merged, - * so each child is updated only once. - * In the presence of more layers of recursion PIC is still a desirable - * feature. Consider an extension to the diagram above, where more recursive - * routes (E_100 -> E_200) are added as children of E_a: - * - * E_100 --> - * E_101 --> PL_3 --> P_j-\ - * ... \ - * E_199 --> E_a --> - * E_b --> PL_2 --> P_a --> E_44 --> ...etc.. - * ... --> P_c -\ - * E_k \ - * E_1 --> ...etc.. - * / - * E_l --> / - * E_m --> PL_1 --> P_d -/ - * ... --> P_e --> E_55 --> ...etc.. - * E_z --> - * - * To achieve PIC for the routes E_100->E_199, PL_3 needs to be updated before - * E_b -> E_z, a breadth first traversal at each level would not achieve this. - * Instead the walk must proceed intelligently. Children on PL_2 are sorted so - * those Entry objects that themselves have children appear first in the list, - * those without later. When an entry object is walked that has children, a - * walk of its children is pushed to the front background queue. The back - * ground queue is a priority queue. As the breadth first traversal proceeds - * across the dependent entry object E_a to E_k, when the first entry that does - * not have children is reached (E_b), the walk is suspended and placed at the - * back of the queue. Following this prioritisation method shared path-list - * updates are performed before all non-resolving entry objects. - * The CPU/core/thread that handles the updates is the same thread that handles - * the back-walks. Handling updates has a higher priority than making walk - * progress, so a walk is required to be interruptable/suspendable when new - * updates are available. - * !!! TODO - this section describes how walks should be not how they are !!! - * - * In the diagram above E_100 is an IP route, however, VPP has no restrictions - * on the type of object that can be a dependent of a FIB entry. Children of - * a FIB entry can be (and are) GRE & VXLAN tunnels endpoints, L2VPN LSPs etc. - * By including all object types into the graph and extending the back-walk, we - * can thus deliver fast convergence to technologies that overlay on an IP - * network. - * - * If having read all the above carefully you are still thinking; 'i don't need - * all this %&$* i have a route only I know about and I just need to jam it in', - * then fib_table_entry_special_add() is your only friend. - */ - -#ifndef __FIB_H__ -#define __FIB_H__ - -#include <vnet/fib/fib_table.h> -#include <vnet/fib/fib_entry.h> -#include <vnet/fib/ip4_fib.h> -#include <vnet/fib/ip6_fib.h> - -#endif |