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 com.google.common.primitives.UnsignedInteger;
12 import javax.annotation.Nonnull;
13 import org.opendaylight.protocol.bgp.mode.api.BestPathState;
14 import org.opendaylight.protocol.bgp.rib.spi.RouterIds;
15 import org.opendaylight.yang.gen.v1.urn.opendaylight.params.xml.ns.yang.bgp.message.rev180329.path.attributes.attributes.OriginatorId;
16 import org.opendaylight.yang.gen.v1.urn.opendaylight.params.xml.ns.yang.bgp.types.rev180329.BgpOrigin;
18 public class AbstractBestPathSelector {
19 private final long ourAs;
20 protected UnsignedInteger bestOriginatorId = null;
21 protected BestPathState bestState = null;
23 protected AbstractBestPathSelector(final long ourAs) {
28 * RFC 4456 mandates the use of Originator IDs instead of Router ID for
31 * @param routerId routerID
32 * @param originatorId originator
33 * @return returns originators Id if present otherwise routerId
35 protected UnsignedInteger replaceOriginator(final UnsignedInteger routerId, final OriginatorId originatorId) {
36 if (originatorId != null) {
37 return RouterIds.routerIdForAddress(originatorId.getOriginator().getValue());
44 * Chooses best route according to BGP best path selection.
46 * @param state attributes of the new route
47 * @return true if the existing path is better, false if the new path is better
49 protected boolean isExistingPathBetter(@Nonnull final BestPathState state) {
50 // 1. prefer path with accessible nexthop
51 // - we assume that all nexthops are accessible
53 * 2. prefer path with higher LOCAL_PREF
55 * FIXME: for eBGP cases (when the LOCAL_PREF is missing), we should assign a policy-based preference
56 * before we ever get here.
58 if (this.bestState.getLocalPref() == null && state.getLocalPref() != null) {
61 if (this.bestState.getLocalPref() != null && state.getLocalPref() == null) {
64 if (state.getLocalPref() != null && state.getLocalPref() > this.bestState.getLocalPref()) {
67 if (state.getLocalPref() != null && state.getLocalPref() < this.bestState.getLocalPref()) {
70 // 3. prefer learned path
71 // - we assume that all paths are learned
73 // 4. prefer the path with the shortest AS_PATH.
74 if (this.bestState.getAsPathLength() != state.getAsPathLength()) {
75 return this.bestState.getAsPathLength() < state.getAsPathLength();
78 // 5. prefer the path with the lowest origin type
79 // - IGP is lower than Exterior Gateway Protocol (EGP), and EGP is lower than INCOMPLETE
80 if (!this.bestState.getOrigin().equals(state.getOrigin())) {
81 final BgpOrigin bo = this.bestState.getOrigin();
82 final BgpOrigin no = state.getOrigin();
84 // This trick relies on the order in which the values are declared in the model.
85 return no.ordinal() > bo.ordinal();
87 // FIXME: we should be able to cache the best AS
88 final Long bestAs = this.bestState.getPeerAs();
89 final Long newAs = state.getPeerAs();
92 * Checks 6 and 7 are mutually-exclusive, as MEDs are comparable
93 * only when the routes originated from the same AS. On the other
94 * hand, when they are from the same AS, they are in the same iBGP/eBGP
98 if (bestAs.equals(newAs)) {
99 // 6. prefer the path with the lowest multi-exit discriminator (MED)
100 if (this.bestState.getMultiExitDisc() != null || state.getMultiExitDisc() != null) {
101 final Long bmed = this.bestState.getMultiExitDisc();
102 final Long nmed = state.getMultiExitDisc();
107 * 7. prefer eBGP over iBGP paths
109 * EBGP is peering between two different AS, whereas IBGP is between same AS (Autonomous System),
110 * so we just compare the AS numbers to our AS.
112 * FIXME: we should know this information from the peer directly.
114 if (this.ourAs != bestAs && this.ourAs == newAs) {
119 // 8. Prefer the path with the lowest IGP metric to the BGP next hop.
120 // - no next hop metric is advertised
123 * 9. When both paths are external, prefer the path that was received first (the oldest one).
125 * FIXME: we do not want to store an explicit timer for each set due to performance/memory
126 * constraints. Our caller has the information about which attributes have changed
127 * since the selection process has ran last time, which may be a good enough approximation,
128 * but its properties need to be analyzed.
132 * 10. Prefer the route that comes from the BGP router with the lowest router ID.
134 * This is normally guaranteed by the iteration order of our caller, which runs selection
135 * in the order of increasing router ID, but RFC-4456 Route Reflection throws a wrench into that.
137 * With RFC-5004, this gets a bit easier, because it completely eliminates step f) and later :-)
139 * RFC-5004 states that this algorithm should end here and select existing path over new path in the
140 * best path selection process. Benefits are listed in the RFC: @see http://tools.ietf.org/html/rfc500
141 * - This algorithm SHOULD NOT be applied when either path is from a BGP Confederation peer.
142 * - not applicable, we don't deal with confederation peers
143 * - The algorithm SHOULD NOT be applied when both paths are from peers with an identical BGP identifier
144 * (i.e., there exist parallel BGP sessions between two BGP speakers).
145 * - not applicable, BUG-2631 prevents parallel sessions to be created.