hsa: http server: fix http response format type error - vpp

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author	jiangxiaoming <jiangxiaoming@outlook.com>	2020-12-17 10:01:43 +0800
committer	xm j <jiangxiaoming@outlook.com>	2020-12-17 02:26:02 +0000
commit	88405809613b8255174e6c5fe257cfaec5af1e27 (patch)
tree	7721754478aae95c0af71ee00dbc5d0f280a9633 /docs/troubleshooting/mem.rst
parent	d6a1acebeae5adb157397b8088042a03f0fa5ee9 (diff)

hsa: http server: fix http response format type error

Type: fix Signed-off-by: jiangxiaoming <jiangxiaoming@outlook.com> Change-Id: I15e43ded1ccd1b06a5ce1822a260fd2dd7edf95f

Diffstat (limited to 'docs/troubleshooting/mem.rst')

0 files changed, 0 insertions, 0 deletions

/* * 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* source and thus to maintain the FI added by losing sources so it can be * installed should the winning source be withdrawn.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


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