2 * Copyright (c) 2016 Cisco Systems, Inc. and others. All rights reserved.
4 * This program and the accompanying materials are made available under the
5 * terms of the Eclipse Public License v1.0 which accompanies this distribution,
6 * and is available at http://www.eclipse.org/legal/epl-v10.html
9 package org.opendaylight.protocol.bgp.mode.spi;
11 import javax.annotation.Nonnull;
12 import org.opendaylight.protocol.bgp.mode.api.BestPathState;
13 import org.opendaylight.protocol.bgp.rib.spi.RouterId;
14 import org.opendaylight.yang.gen.v1.urn.opendaylight.params.xml.ns.yang.bgp.message.rev180329.path.attributes.attributes.OriginatorId;
15 import org.opendaylight.yang.gen.v1.urn.opendaylight.params.xml.ns.yang.bgp.types.rev180329.BgpOrigin;
17 public class AbstractBestPathSelector {
18 private final long ourAs;
19 protected RouterId bestOriginatorId = null;
20 protected BestPathState bestState = null;
22 protected AbstractBestPathSelector(final long ourAs) {
27 * RFC 4456 mandates the use of Originator IDs instead of Router ID for
30 * @param routerId routerID
31 * @param originatorId originator
32 * @return returns originators Id if present otherwise routerId
34 protected RouterId replaceOriginator(final RouterId routerId, final OriginatorId originatorId) {
35 return originatorId != null ? RouterId.forAddress(originatorId.getOriginator()) : routerId;
39 * Chooses best route according to BGP best path selection.
41 * @param state attributes of the new route
42 * @return true if the existing path is better, false if the new path is better
44 protected boolean isExistingPathBetter(@Nonnull final BestPathState state) {
45 // 0. draft-uttaro-idr-bgp-persistence-04 defines "depreferenced" paths
46 final boolean stateDepref = state.isDepreferenced();
47 if (this.bestState.isDepreferenced() != stateDepref) {
51 // 1. prefer path with accessible nexthop
52 // - we assume that all nexthops are accessible
54 * 2. prefer path with higher LOCAL_PREF
56 * FIXME: for eBGP cases (when the LOCAL_PREF is missing), we should assign a policy-based preference
57 * before we ever get here.
59 final Long bestLocal = this.bestState.getLocalPref();
60 final Long stateLocal = state.getLocalPref();
61 if (stateLocal != null) {
62 if (bestLocal == null) {
66 final Boolean bool = firstLower(stateLocal, bestLocal);
70 } else if (bestLocal != null) {
74 // 3. prefer learned path
75 // - we assume that all paths are learned
77 // 4. prefer the path with the shortest AS_PATH.
78 if (this.bestState.getAsPathLength() != state.getAsPathLength()) {
79 return this.bestState.getAsPathLength() < state.getAsPathLength();
82 // 5. prefer the path with the lowest origin type
83 // - IGP is lower than Exterior Gateway Protocol (EGP), and EGP is lower than INCOMPLETE
84 if (!this.bestState.getOrigin().equals(state.getOrigin())) {
85 final BgpOrigin bo = this.bestState.getOrigin();
86 final BgpOrigin no = state.getOrigin();
88 // This trick relies on the order in which the values are declared in the model.
89 return no.ordinal() > bo.ordinal();
91 // FIXME: we should be able to cache the best AS
92 final long bestAs = this.bestState.getPeerAs();
93 final long newAs = state.getPeerAs();
96 * Checks 6 and 7 are mutually-exclusive, as MEDs are comparable
97 * only when the routes originated from the same AS. On the other
98 * hand, when they are from the same AS, they are in the same iBGP/eBGP
102 if (bestAs == newAs) {
103 // 6. prefer the path with the lowest multi-exit discriminator (MED)
104 final Boolean cmp = firstLower(this.bestState.getMultiExitDisc(), state.getMultiExitDisc());
110 * 7. prefer eBGP over iBGP paths
112 * EBGP is peering between two different AS, whereas IBGP is between same AS (Autonomous System),
113 * so we just compare the AS numbers to our AS.
115 * FIXME: we should know this information from the peer directly.
117 if (this.ourAs != bestAs && this.ourAs == newAs) {
122 // 8. Prefer the path with the lowest IGP metric to the BGP next hop.
123 // - no next hop metric is advertised
126 * 9. When both paths are external, prefer the path that was received first (the oldest one).
128 * FIXME: we do not want to store an explicit timer for each set due to performance/memory
129 * constraints. Our caller has the information about which attributes have changed
130 * since the selection process has ran last time, which may be a good enough approximation,
131 * but its properties need to be analyzed.
135 * 10. Prefer the route that comes from the BGP router with the lowest router ID.
137 * This is normally guaranteed by the iteration order of our caller, which runs selection
138 * in the order of increasing router ID, but RFC-4456 Route Reflection throws a wrench into that.
140 * With RFC-5004, this gets a bit easier, because it completely eliminates step f) and later :-)
142 * RFC-5004 states that this algorithm should end here and select existing path over new path in the
143 * best path selection process. Benefits are listed in the RFC: @see http://tools.ietf.org/html/rfc500
144 * - This algorithm SHOULD NOT be applied when either path is from a BGP Confederation peer.
145 * - not applicable, we don't deal with confederation peers
146 * - The algorithm SHOULD NOT be applied when both paths are from peers with an identical BGP identifier
147 * (i.e., there exist parallel BGP sessions between two BGP speakers).
148 * - not applicable, BUG-2631 prevents parallel sessions to be created.
153 private static Boolean firstLower(final long first, final long second) {
154 return first < second ? Boolean.TRUE : first == second ? null : Boolean.FALSE;