2 * Copyright (c) 2013 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
8 package org.opendaylight.protocol.bgp.rib.spi;
10 import com.google.common.annotations.VisibleForTesting;
11 import com.google.common.base.Preconditions;
12 import com.google.common.net.InetAddresses;
13 import java.util.Arrays;
14 import java.util.Comparator;
15 import java.util.List;
17 import org.opendaylight.protocol.bgp.rib.spi.AbstractAdjRIBsIn.RIBEntryData;
18 import org.opendaylight.yang.gen.v1.urn.ietf.params.xml.ns.yang.ietf.inet.types.rev100924.AsNumber;
19 import org.opendaylight.yang.gen.v1.urn.opendaylight.params.xml.ns.yang.bgp.message.rev130919.PathAttributes;
20 import org.opendaylight.yang.gen.v1.urn.opendaylight.params.xml.ns.yang.bgp.message.rev130919.path.attributes.as.path.Segments;
21 import org.opendaylight.yang.gen.v1.urn.opendaylight.params.xml.ns.yang.bgp.types.rev130919.BgpOrigin;
22 import org.opendaylight.yang.gen.v1.urn.opendaylight.params.xml.ns.yang.bgp.types.rev130919.as.path.segment.c.segment.AListCase;
23 import org.opendaylight.yang.gen.v1.urn.opendaylight.params.xml.ns.yang.bgp.types.rev130919.as.path.segment.c.segment.ASetCase;
26 * This comparator is intended to implement BGP Best Path Selection algorithm, as described at
28 * @see http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080094431.shtml
30 * @param <T> Actual object state reference
32 public final class BGPObjectComparator implements Comparator<RIBEntryData<?, ?>> {
33 private final AsNumber ourAS;
35 public BGPObjectComparator(final AsNumber ourAs) {
36 this.ourAS = Preconditions.checkNotNull(ourAs);
40 public int compare(final RIBEntryData<?, ?> e1, final RIBEntryData<?, ?> e2) {
51 final PathAttributes o1 = e1.getPathAttributes();
52 final PathAttributes o2 = e2.getPathAttributes();
53 if (o1.equals(o2) && Arrays.equals(e1.getPeer().getRawIdentifier(), e2.getPeer().getRawIdentifier())) {
57 // 1. prefer path with accessible nexthop
58 // - we assume that all nexthops are accessible
60 // 2. prefer path with higher LOCAL_PREF
61 if ((o1.getLocalPref() != null || o2.getLocalPref() != null)
62 && (o1.getLocalPref() != null && !o1.getLocalPref().equals(o2.getLocalPref()))) {
63 return o1.getLocalPref().getPref().compareTo(o2.getLocalPref().getPref());
66 // 3. prefer learned path
67 // - we assume that all paths are learned
69 // 4. prefer the path with the shortest AS_PATH.
70 if (!o1.getAsPath().equals(o2.getAsPath())) {
71 final Integer i1 = countAsPath(o1.getAsPath().getSegments());
72 final Integer i2 = countAsPath(o2.getAsPath().getSegments());
73 return i2.compareTo(i1);
76 // 5. prefer the path with the lowest origin type
77 // - IGP is lower than Exterior Gateway Protocol (EGP), and EGP is lower than INCOMPLETE
78 if (!o1.getOrigin().equals(o2.getOrigin())) {
79 if (o1.getOrigin().getValue().equals(BgpOrigin.Igp)) {
82 if (o2.getOrigin().getValue().equals(BgpOrigin.Igp)) {
85 if (o1.getOrigin().getValue().equals(BgpOrigin.Egp)) {
92 // 6. prefer the path with the lowest multi-exit discriminator (MED)
93 if ((o1.getMultiExitDisc() != null || o2.getMultiExitDisc() != null)
94 && (o1.getMultiExitDisc() != null && !o1.getMultiExitDisc().equals(o2.getMultiExitDisc()))) {
95 return o2.getMultiExitDisc().getMed().compareTo(o1.getMultiExitDisc().getMed());
98 // 7. prefer eBGP over iBGP paths
99 // EBGP is peering between two different AS, whereas IBGP is between same AS (Autonomous System).
100 final AsNumber first = getPeerAs(o1.getAsPath().getSegments());
101 final AsNumber second = getPeerAs(o2.getAsPath().getSegments());
102 if ((first != null || second != null) && (first != null && !first.equals(second))) {
103 if (first.equals(this.ourAS)) {
106 if (second == null || second.equals(this.ourAS)) {
111 // 8. Prefer the path with the lowest IGP metric to the BGP next hop.
112 // - no next hop metric is advertized
114 // 9. When both paths are external, prefer the path that was received first (the oldest one).
115 // if (first.equals(this.ourAS) && second.equals(this.ourAS)) {
116 // FIXME: do we have a way how to determine which one was received first?
119 // 10. Prefer the route that comes from the BGP router with the lowest router ID.
120 // The router ID is the highest IP address on the router, with preference given to loopback addresses.
121 // If a path contains route reflector (RR) attributes, the originator ID is substituted for the router ID in the
122 // path selection process.
123 byte[] oid1 = e1.getPeer().getRawIdentifier();
124 byte[] oid2 = e2.getPeer().getRawIdentifier();
125 if (o1.getOriginatorId() != null) {
126 oid1 = InetAddresses.forString(o1.getOriginatorId().getOriginator().getValue()).getAddress();
128 if (o2.getOriginatorId() != null) {
129 oid2 = InetAddresses.forString(o2.getOriginatorId().getOriginator().getValue()).getAddress();
131 if (!Arrays.equals(oid1, oid2)) {
132 return compareByteArrays(oid1, oid2);
134 // 11. prefer the path with the minimum cluster list length
137 if (o1.getClusterId() != null) {
138 cluster1 = o1.getClusterId().getCluster().size();
140 if (o2.getClusterId() != null) {
141 cluster2 = o2.getClusterId().getCluster().size();
143 if (cluster1 != cluster2) {
144 return ((Integer) cluster1).compareTo(cluster2);
147 // 12. Prefer the path that comes from the lowest neighbor address.
148 // FIXME: do we know this?
153 private static int countAsPath(final List<Segments> segments) {
154 // an AS_SET counts as 1, no matter how many ASs are in the set.
156 boolean setPresent = false;
157 for (final Segments s : segments) {
158 if (s.getCSegment() instanceof ASetCase) {
161 final AListCase list = (AListCase) s.getCSegment();
162 count += list.getAList().getAsSequence().size();
165 return (setPresent) ? ++count : count;
168 private static AsNumber getPeerAs(final List<Segments> segments) {
169 if (segments.size() == 0) {
172 final AListCase first = (AListCase) segments.get(0).getCSegment();
173 return first.getAList().getAsSequence().get(0).getAs();
177 public static int compareByteArrays(final byte[] byteOne, final byte[] byteTwo) {
178 for (int i = 0; i < byteOne.length; i++) {
179 final int res = Byte.compare(byteOne[i], byteTwo[i]);