Purpose
Assuming that all the routers are correctly configured for OSPF, you can verify which neighbors are adjacent and what type of LSAs are contained in the OSPF link-state database. In addition, you can examine the set of routes installed in the forwarding table to verify that the routing protocol process (rpd) has relayed the correct information into the forwarding table.
Figure 12 illustrates an example OSPF network topology used in this topic.
Figure 12: OSPF Network Topology
The network consists of various types of routers that form adjacencies with neighboring OSPF routers. Once these adjacencies are in place, each router generates and floods LSAs into the network. The LSAs are placed into the link-state database on each router where the shortest path first (SPF) algorithm is calculated to find the best path to each router in the network. The network in Figure 12 should have the following adjacencies and LSA distribution:
To verify that routers are adjacent and have the correct exchange of LSAs, follow these steps:
To verify that routers are adjacent and able to exchange OSPF data.
To verify that routers are adjacent and able to exchange OSPF data, enter the following CLI operational mode command:
The following sample output shows the adjacencies that formed for all routers in Figure 12:
user@R1> show ospf neighbor Address Interface State ID Pri Dead 10.1.12.2 so-0/0/0.0 Full 10.0.0.2 128 36 user@R2> show ospf neighbor Address Interface State ID Pri Dead 10.1.23.2 so-0/0/1.0 Full 10.0.0.3 128 32 10.1.24.2 so-0/0/3.0 Full 10.0.0.4 128 33 10.1.12.1 so-0/0/0.0 Full 10.0.0.1 128 33 user@R3> show ospf neighbor Address Interface State ID Pri Dead 10.1.34.2 so-0/0/0.0 Full 10.0.0.4 128 36 10.1.23.1 so-0/0/1.0 Full 10.0.0.2 128 38 10.1.36.2 so-0/0/3.0 Full 10.0.0.6 128 33 user@R4> show ospf neighbor Address Interface State ID Pri Dead 10.1.34.1 so-0/0/0.0 Full 10.0.0.3 128 31 10.1.24.1 so-0/0/3.0 Full 10.0.0.2 128 36 10.1.45.2 so-0/0/2.0 Full 10.0.0.5 128 39 user@R5> show ospf neighbor Address Interface State ID Pri Dead 10.1.45.1 so-0/0/2.0 Full 10.0.0.4 128 35 user@R6> show ospf neighbor Address Interface State ID Pri Dead 10.1.36.1 so-0/0/3.0 Full 10.0.0.3 128 31
The sample output shows that ABR routers R2, R3, and R4 have formed adjacencies with routers in all areas to which they are directly connected. Internal routers (R1, R5, and R6) have formed an adjacency with the other router inside their local area.
Adjacencies are formed after OSPF hello packets are sent and received by neighbors. Adjacencies determine the type of LSAs sent and received, and what topological database updates are sent. When adjacencies are established, pairs of adjacent routers synchronize their topological databases.
Table 31 lists and describes the fields in the show ospf neighbor command.
Table 31: Output Fields for the show ospf neighbor Command
You can determine if the correct types of LSAs are sent and received throughout the OSPF network by examining the entire OSPF link-state database. Figure 13 illustrates the flooding scope of LSAs generated and flooded in the example OSPF network.
Figure 13: LSA Flooding Scopes
This network should have the following distribution of LSAs:
Because all routers in this network have SONET interfaces configured for Point-to-Point (PPP) encapsulation, all OSPF adjacencies are point-to-point, which results in Type 2 network LSAs not appearing in this network. Type 2 network LSAs are only advertised by a designated router, which is only present on broadcast or non-broadcast multiaccess (NBMA) networks.
To determine if the correct LSAs appear in the different areas of the OSPF AS, enter the following CLI operational mode command:
user@R2> show
ospf database OSPF link state database, area 0.0.0.0
Type ID Adv Rtr Seq Age Opt Cksum Len
Router *10.0.0.2 10.0.0.2 0x80000049 1555 0x2 0xd72a 84
Router 10.0.0.3 10.0.0.3 0x80000038 1395 0x2 0xef0e 84
Router 10.0.0.4 10.0.0.4 0x80000041 914 0x2 0x46a9 84
Summary *10.0.0.1 10.0.0.2 0x80000047 1855 0x2 0xf509 28
Summary 10.0.0.5 10.0.0.4 0x8000003c 2114 0x2 0xd72c 28
Summary 10.0.0.6 10.0.0.3 0x80000033 1995 0x2 0xe527 28
Summary *10.1.12.0 10.0.0.2 0x80000047 786 0x2 0x5d98 28
Summary 10.1.36.0 10.0.0.3 0x80000035 2426 0x2 0x727c 28
Summary 10.1.45.0 10.0.0.4 0x8000003d 1021 0x2 0xf8e3 28
ASBRSum *10.0.0.1 10.0.0.2 0x80000046 355 0x2 0xe915 28
ASBRSum 10.0.0.6 10.0.0.3 0x80000032 1526 0x2 0xd933 28
OSPF link state database, area 0.0.0.1
Type ID Adv Rtr Seq Age Opt Cksum Len
Router 10.0.0.1 10.0.0.1 0x80000058 858 0x0 0x5c26 60
Router *10.0.0.2 10.0.0.2 0x80000048 1986 0x0 0xecbd 48
Summary *10.0.0.2 10.0.0.2 0x80000039 1686 0x0 0x1cf2 28
Summary *10.0.0.3 10.0.0.2 0x80000038 2286 0x0 0x1eef 28
Summary *10.0.0.4 10.0.0.2 0x80000038 955 0x0 0x14f8 28
Summary *10.0.0.5 10.0.0.2 0x80000038 186 0x0 0x14f6 28
Summary *10.0.0.6 10.0.0.2 0x80000038 2155 0x0 0xaff 28
Summary *10.1.23.0 10.0.0.2 0x80000046 655 0x0 0x4e9 28
Summary *10.1.24.0 10.0.0.2 0x80000046 486 0x0 0xf8f3 28
Summary *10.1.34.0 10.0.0.2 0x80000039 1255 0x0 0xae40 28
Summary *10.1.36.0 10.0.0.2 0x80000039 55 0x0 0x9854 28
Summary *10.1.45.0 10.0.0.2 0x80000039 1086 0x0 0x35ae 28
NSSA *0.0.0.0 10.0.0.2 0x80000044 2455 0x0 0xd821 36
NSSA 10.0.0.100 10.0.0.1 0x80000051 2916 0x8 0x797c 36
OSPF AS SCOPE link state database
Type ID Adv Rtr Seq Age Opt Cksum Len
Extern *10.0.0.100 10.0.0.2 0x8000005e 1386 0x2 0xcf20 36
Extern 10.0.0.101 10.0.0.6 0x8000002b 333 0x2 0x9791 36
user@ R3 > show ospf database
OSPF link state database, area 0.0.0.0
Type ID Adv Rtr Seq Age Opt Cksum Len
Router 10.0.0.2 10.0.0.2 0x80000049 1668 0x2 0xd72a 84
Router *10.0.0.3 10.0.0.3 0x80000038 1506 0x2 0xef0e 84
Router 10.0.0.4 10.0.0.4 0x80000041 1027 0x2 0x46a9 84
Summary 10.0.0.1 10.0.0.2 0x80000047 1968 0x2 0xf509 28
Summary 10.0.0.5 10.0.0.4 0x8000003c 2227 0x2 0xd72c 28
Summary *10.0.0.6 10.0.0.3 0x80000033 2106 0x2 0xe527 28
Summary 10.1.12.0 10.0.0.2 0x80000047 900 0x2 0x5d98 28
Summary *10.1.36.0 10.0.0.3 0x80000036 6 0x2 0x707d 28
Summary 10.1.45.0 10.0.0.4 0x8000003d 1134 0x2 0xf8e3 28
ASBRSum 10.0.0.1 10.0.0.2 0x80000046 468 0x2 0xe915 28
ASBRSum *10.0.0.6 10.0.0.3 0x80000032 1638 0x2 0xd933 28
OSPF link state database, area 0.0.0.3
Type ID Adv Rtr Seq Age Opt Cksum Len
Router *10.0.0.3 10.0.0.3 0x80000036 2406 0x2 0x3452 48
Router 10.0.0.6 10.0.0.6 0x8000002f 445 0x2 0x1850 60
Summary *10.0.0.1 10.0.0.3 0x80000036 906 0x2 0x1cf1 28
Summary *10.0.0.2 10.0.0.3 0x80000036 738 0x2 0x806 28
Summary *10.0.0.3 10.0.0.3 0x80000033 1806 0x2 0xf917 28
Summary *10.0.0.4 10.0.0.3 0x80000033 1038 0x2 0xf915 28
Summary *10.0.0.5 10.0.0.3 0x80000033 306 0x2 0xf913 28
Summary *10.1.12.0 10.0.0.3 0x80000036 606 0x2 0x8381 28
Summary *10.1.23.0 10.0.0.3 0x80000036 438 0x2 0xfffa 28
Summary *10.1.24.0 10.0.0.3 0x80000036 1338 0x2 0xfef9 28
Summary *10.1.34.0 10.0.0.3 0x80000036 138 0x2 0x8669 28
Summary *10.1.45.0 10.0.0.3 0x80000033 1206 0x2 0x1dc9 28
ASBRSum *10.0.0.1 10.0.0.3 0x80000035 2238 0x2 0x10fd 28
ASBRSum *10.0.0.2 10.0.0.3 0x80000035 1938 0x2 0xfb12 28
OSPF AS SCOPE link state database
Type ID Adv Rtr Seq Age Opt Cksum Len
Extern 10.0.0.100 10.0.0.2 0x8000005e 1500 0x2 0xcf20 36
Extern 10.0.0.101 10.0.0.6 0x8000002b 445 0x2 0x9791 36
user@ R4 > show ospf database
OSPF link state database, area 0.0.0.0
Type ID Adv Rtr Seq Age Opt Cksum Len
Router 10.0.0.2 10.0.0.2 0x80000049 1711 0x2 0xd72a 84
Router 10.0.0.3 10.0.0.3 0x80000038 1550 0x2 0xef0e 84
Router *10.0.0.4 10.0.0.4 0x80000041 1068 0x2 0x46a9 84
Summary 10.0.0.1 10.0.0.2 0x80000047 2011 0x2 0xf509 28
Summary *10.0.0.5 10.0.0.4 0x8000003c 2268 0x2 0xd72c 28
Summary 10.0.0.6 10.0.0.3 0x80000033 2150 0x2 0xe527 28
Summary 10.1.12.0 10.0.0.2 0x80000047 942 0x2 0x5d98 28
Summary 10.1.36.0 10.0.0.3 0x80000036 50 0x2 0x707d 28
Summary *10.1.45.0 10.0.0.4 0x8000003d 1175 0x2 0xf8e3 28
ASBRSum 10.0.0.1 10.0.0.2 0x80000046 511 0x2 0xe915 28
ASBRSum 10.0.0.6 10.0.0.3 0x80000032 1681 0x2 0xd933 28
OSPF link state database, area 0.0.0.2
Type ID Adv Rtr Seq Age Opt Cksum Len
Router *10.0.0.4 10.0.0.4 0x8000003f 875 0x0 0x5913 48
Router 10.0.0.5 10.0.0.5 0x8000002e 1263 0x0 0x5a03 60
Summary *0.0.0.0 10.0.0.4 0x80000019 768 0x0 0x4be3 28
Summary *10.0.0.1 10.0.0.4 0x80000040 575 0x0 0x20e4 28
Summary *10.0.0.2 10.0.0.4 0x80000040 468 0x0 0xcf8 28
Summary *10.0.0.3 10.0.0.4 0x8000003f 275 0x0 0x401 28
Summary *10.0.0.4 10.0.0.4 0x8000003d 168 0x0 0xf313 28
Summary *10.0.0.6 10.0.0.4 0x8000003d 2075 0x0 0xf30f 28
Summary *10.1.12.0 10.0.0.4 0x8000003f 1968 0x0 0x8973 28
Summary *10.1.23.0 10.0.0.4 0x8000003f 1775 0x0 0x10e1 28
Summary *10.1.24.0 10.0.0.4 0x8000003d 1668 0x0 0xfef4 28
Summary *10.1.34.0 10.0.0.4 0x8000003d 1475 0x0 0x9059 28
Summary *10.1.36.0 10.0.0.4 0x8000003d 1368 0x0 0x8462 28
OSPF AS SCOPE link state database
Type ID Adv Rtr Seq Age Opt Cksum Len
Extern 10.0.0.100 10.0.0.2 0x8000005e 1542 0x2 0xcf20 36
Extern 10.0.0.101 10.0.0.6 0x8000002b 488 0x2 0x9791 36
The sample output shows that all the ABRs have the correct distribution of LSAs. Area 0.0.0.0 for all routers has Type 1 router, Type 3 summary, and Type 4 ASBR summary LSAs. Each ABR has an OSPF AS scope link-state database that includes Type 5 external LSAs.
Note that Type 2 network LSAs are not found in this topology because both broadcast or NMBA network types are not present.
NSSA area 0.0.0.1, in the output for R2, has Type 1 router, Type 3 summary, and Type 7 NSSA LSAs. Stub area 0.0.0.2, in the output for R4, has Type 1 router and Type 3 summary LSAs. Non-backbone area 0.0.0.3, in the output for R3, has Type 1 router, Type 3 summary, Type 4 ASBR, and Type 5 external LSAs.
All areas have a Type 1 router LSA because the Type 1 LSA is generated for each router that has interfaces in that area. Because this LSA has an area flooding scope, it remains within its own particular area and is not seen in other areas. For example, in the link-state database for area 0.0.0.2, there are two router LSAs: one for R4 and one for R5.
The ABR for that area places the routing information contained within the Type 1 LSA into a Type 3 summary or Type 4 ASBR summary LSA and forwards it across the area boundary. Whether the area receives a Type 3 or Type 4 summary LSA depends on whether the area is a stub area. Type 3 summary LSAs appear in all areas, but Type 4 LSAs only appear in non-stub areas as indicated in the link-state databases for areas 0.0.0.1, 0.0.0.2, and 0.0.0.3.
Each ABR router has a Type 5 AS external LSA used to advertise any networks external to the OSPF AS. This LSA is flooded by the ABRs to each non-stub router in the entire AS. For example, within area 0.0.0.0, Type 5 LSAs exist for areas 0.0.0.1 and 0.0.0.3. Both of these areas are connected to routers (external router A and external router B) from other ASs, which results in the injection of external routes into the OSPF AS. However, there are no Type 5 LSAs in stub areas 0.0.0.1 and 0.0.0.2.
A Type 7 NSSA external LSA appears in NSSA area 0.0.0.1 and is used within the NSSA to advertise an external router. This LSA is flooded to each router in the NSSA and is not sent to other adjacent areas. For example, only area 0.0.0.1 has a Type 7 LSA. Because a Type 7 LSA does not traverse area boundaries, the ABR in the NSSA (R2) translates the Type 7 LSA into a Type 5 LSA that is forwarded to all areas (with the exception of stub areas).
The sample output shows that each router has two databases, indicating that it is an ABR between the backbone and a non-backbone, stub, or NSSA area. All of the addresses preceded by an asterisk (*) are LSAs that originated with the router from which the output was taken.
You can determine if the LSAs that appear in the link-state database of a router are correct by examining the route to the destination. In this step, three routes are examined. The first example shows the route from R5 to external router A, the second shows the route from R6 to external router A, and the third shows the route from R4 to R6.
To examine a route in an OSPF AS, enter one or all of the following CLI commands:
Sample Output 1
The following sample output shows the path from R5 to external router A:
user@R5> show route 10.0.0.100
inet.0: 23 destinations, 25 routes (23 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both
0.0.0.0/0 *[OSPF/10] 01:58:42, metric 11
> via so-0/0/2.0
user@R5> show ospf database
OSPF link state database, area 0.0.0.2
Type ID Adv Rtr Seq Age Opt Cksum Len
Router 10.0.0.4 10.0.0.4 0x8000002b 140 0x0 0x81fe 48
Router *10.0.0.5 10.0.0.5 0x8000001f 526 0x0 0x78f3 60
Summary 0.0.0.0 10.0.0.4 0x80000005 32 0x0 0x73cf 28
Summary 10.0.0.1 10.0.0.4 0x8000002b 2132 0x0 0x4acf 28
Summary 10.0.0.2 10.0.0.4 0x8000002b 1940 0x0 0x36e3 28
Summary 10.0.0.3 10.0.0.4 0x8000002a 1832 0x0 0x2eeb 28
Summary 10.0.0.4 10.0.0.4 0x80000028 1640 0x0 0x1efd 28
Summary 10.0.0.6 10.0.0.4 0x80000029 1340 0x0 0x1cfa 28
Summary 10.1.12.0 10.0.0.4 0x8000002b 1232 0x0 0xb15f 28
Summary 10.1.23.0 10.0.0.4 0x8000002b 1040 0x0 0x38cd 28
Summary 10.1.24.0 10.0.0.4 0x80000029 932 0x0 0x27e0 28
Summary 10.1.34.0 10.0.0.4 0x80000029 740 0x0 0xb845 28
Summary 10.1.36.0 10.0.0.4 0x80000029 632 0x0 0xac4e 28
Sample Output 2
The following sample output shows the route from R6 to external router A:
user@R6> show route 10.0.0.100
inet.0: 29 destinations, 31 routes (29 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both
10.0.0.100/32 *[OSPF/150] 16:52:11, metric 0, tag 0
> via so-0/0/3.0
user@R6> show ospf database
OSPF link state database, area 0.0.0.3
Type ID Adv Rtr Seq Age Opt Cksum Len
Router 10.0.0.3 10.0.0.3 0x8000001d 502 0x2 0x6639 48
Router *10.0.0.6 10.0.0.6 0x80000019 807 0x2 0x443a 60
Summary 10.0.0.1 10.0.0.3 0x8000001c 1570 0x2 0x50d7 28
Summary 10.0.0.2 10.0.0.3 0x8000001c 1402 0x2 0x3ceb 28
Summary 10.0.0.3 10.0.0.3 0x80000019 2470 0x2 0x2efc 28
Summary 10.0.0.4 10.0.0.3 0x80000019 1702 0x2 0x2efa 28
Summary 10.0.0.5 10.0.0.3 0x80000019 970 0x2 0x2ef8 28
Summary 10.1.12.0 10.0.0.3 0x8000001c 1270 0x2 0xb767 28
Summary 10.1.23.0 10.0.0.3 0x8000001c 1102 0x2 0x34e0 28
Summary 10.1.24.0 10.0.0.3 0x8000001c 2002 0x2 0x33df 28
Summary 10.1.34.0 10.0.0.3 0x8000001c 802 0x2 0xba4f 28
Summary 10.1.45.0 10.0.0.3 0x80000019 1870 0x2 0x51af 28
ASBRSum 10.0.0.1 10.0.0.3 0x8000001c 370 0x2 0x42e4 28
ASBRSum 10.0.0.2 10.0.0.3 0x8000001c 70 0x2 0x2ef8 28
OSPF AS SCOPE link state database
Type ID Adv Rtr Seq Age Opt Cksum Len
Extern 10.0.0.100 10.0.0.2 0x80000042 384 0x2 0x804 36
Extern *10.0.0.101 10.0.0.6 0x80000015 807 0x2 0xc37b 36
Extern 10.1.13.0 10.0.0.2 0x80000041 234 0x2 0x481e 36
Extern 10.1.15.0 10.0.0.2 0x80000041 233 0x2 0x3232 36
Extern 100.168.64.0 10.0.0.2 0x80000041 82 0x2 0xe0f7 36
Sample Output 3
The following sample output shows the route from R4 to R6:
user@R4> show route 10.0.0.6
inet.0: 27 destinations, 31 routes (27 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both
10.0.0.6/32 *[OSPF/10] 17:02:28, metric 2
> via so-0/0/0.0
user@R4> show ospf database
OSPF link state database, area 0.0.0.0
Type ID Adv Rtr Seq Age Opt Cksum Len
Router 10.0.0.2 10.0.0.2 0x8000002f 632 0x2 0xc10 84
Router 10.0.0.3 10.0.0.3 0x8000001e 2271 0x2 0x24f3 84
Router *10.0.0.4 10.0.0.4 0x80000022 1582 0x2 0x848a 84
Summary 10.0.0.1 10.0.0.2 0x8000002d 789 0x2 0x2aee 28
Summary *10.0.0.5 10.0.0.4 0x8000001e 982 0x2 0x140e 28
Summary 10.0.0.6 10.0.0.3 0x8000001a 302 0x2 0x180e 28
Summary 10.1.12.0 10.0.0.2 0x8000002c 1847 0x2 0x937d 28
Summary 10.1.36.0 10.0.0.3 0x8000001c 771 0x2 0xa463 28
Summary *10.1.45.0 10.0.0.4 0x8000001f 1789 0x2 0x35c5 28
ASBRSum 10.0.0.1 10.0.0.2 0x8000002b 1533 0x2 0x20f9 28
ASBRSum 10.0.0.6 10.0.0.3 0x80000018 2402 0x2 0xe19 28
OSPF link state database, area 0.0.0.2
Type ID Adv Rtr Seq Age Opt Cksum Len
Router *10.0.0.4 10.0.0.4 0x80000020 1282 0x0 0x97f3 48
Router 10.0.0.5 10.0.0.5 0x80000018 1685 0x0 0x86ec 60
Summary *10.0.0.1 10.0.0.4 0x80000021 1189 0x0 0x5ec5 28
Summary *10.0.0.2 10.0.0.4 0x80000021 889 0x0 0x4ad9 28
Summary *10.0.0.3 10.0.0.4 0x80000020 682 0x0 0x42e1 28
Summary *10.0.0.4 10.0.0.4 0x8000001e 1489 0x0 0x32f3 28
Summary *10.0.0.6 10.0.0.4 0x8000001f 589 0x0 0x30f0 28
Summary *10.1.12.0 10.0.0.4 0x80000021 382 0x0 0xc555 28
Summary *10.1.23.0 10.0.0.4 0x80000021 289 0x0 0x4cc3 28
Summary *10.1.24.0 10.0.0.4 0x80000020 82 0x0 0x39d7 28
Summary *10.1.34.0 10.0.0.4 0x8000001f 2089 0x0 0xcc3b 28
Summary *10.1.36.0 10.0.0.4 0x8000001f 1882 0x0 0xc044 28
OSPF AS SCOPE link state database
Type ID Adv Rtr Seq Age Opt Cksum Len
Extern 10.0.0.100 10.0.0.2 0x80000042 484 0x2 0x804 36
Extern 10.0.0.101 10.0.0.6 0x80000015 910 0x2 0xc37b 36
Extern 10.1.13.0 10.0.0.2 0x80000041 333 0x2 0x481e 36
Extern 10.1.15.0 10.0.0.2 0x80000041 332 0x2 0x3232 36
Extern 100.168.64.0 10.0.0.2 0x80000041 182 0x2 0xe0f7 36
Sample output 1 shows an OSPF default route (0.0.0.0/0) with a preference value of 10. In the area 0.0.0.2 link-state database, a Type 3 summary LSA advertises the default route.
Sample output 2 shows an OSPF route with a preference value of 150. In the AS scope link-state database, an external Type 5 LSA indicates that the route from R6 to external router A is through R2, the advertising router. By default, routes resulting from OSPF external LSAs are installed with a preference value of 150.
Sample output 3 shows an OSPF route with a preference value of 10. In the area 0.0.0.0 link-state database, a summary Type 3 LSA indicates that the route from R4 to R6 is through R3, the advertising router.
The LSAs placed into the link-state database are used by the router to run the Dijkstra algorithm (also called the shortest path first algorithm). This computation uses the link-state database as a source, resulting in a loop-free topology using the best metric from the local router to all nodes in the OSPF network.
You can display the set of routes installed in the forwarding table to verify that the routing protocol process (rpd) has relayed the correct information into the forwarding table. This is especially important when there are network problems, such as connectivity. In this procedure, you verify that the routes displayed in Step 2 appear in the forwarding table for router R5.
To examine the forwarding table for a router, enter the following CLI command:
user@R5> show route forwarding-table
destination 10.0.0.3 Routing table: inet Internet: Destination Type RtRef Next hop Type Index NhRef Netif 10.0.0.3/32 user 0 10.1.15.0 ucst 285 7 so-0/0/1.0 user@R5> show route forwarding-table destination 10.0.0.3 Routing table: inet Internet: Destination Type RtRef Next hop Type Index NhRef Netif 10.0.0.3/32 user 0 10.1.56.0 ucst 281 9 so-0/0/0.0
The sample output shows the selected next hop between routers R5 and R3 sent from the inet routing table and installed into the forwarding table. The first instance shows the route through R1 and the second instance shows the route through R6. In both instances, the preferred route displayed in Step 2 is installed in the forwarding table.
In general, the sample output includes the destination address and destination type, the next-hop address and next-hop type, the number of references to the next hop, an index number into an internal next-hop database, and the interface used to reach the next hop.