In this simple lab setup I will demonstrate OSPF LSA types. Area 40 and area 50 are connecting to the backbone area 0.
- Area 40 is a regular area injecting routes redistributed from EIGRP process 1.
- Area 50 is a Not So Stubby Area and is redistributing routes from another OSPF process 2.
- LSA Type 1: Router LSA.
- LSA Type 2: Network LSA.
- LSA Type 3: Summary LSA.
- LSA Type 4: Summary ASBR LSA.
- LSA Type 5: Autonomous system external LSA.
- LSA Type 6: Multicast OSPF LSA.
- LSA Type 7: Not-so-stubby area LSA.
- LSA Type 8: External attribute LSA for BGP.
On R1, R2 and R3 are in a Broadcast network and R2 has a priority of 100 which makes it the DR. R3 has become the BDR because of the higher router-id.
Output 1.1
R2#show ip ospf neighbor
Neighbor ID Pri State Dead Time Address Interface
1.1.1.1 1 FULL/DROTHER 00:00:37 10.0.123.1 Ethernet0/2
3.3.3.3 1 FULL/BDR 00:00:31 10.0.123.3 Ethernet0/2
R3#show ip ospf interface ethernet 0/3
Ethernet0/3 is up, line protocol is up
Internet Address 10.0.123.3/24, Area 0, Attached via Network Statement
Process ID 1, Router ID 3.3.3.3, Network Type BROADCAST, Cost: 10
Topology-MTID Cost Disabled Shutdown Topology Name
0 10 no no Base
Transmit Delay is 1 sec, State BDR, Priority 1
Designated Router (ID) 2.2.2.2, Interface address 10.0.123.2
Backup Designated router (ID) 3.3.3.3, Interface address 10.0.123.3
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
oob-resync timeout 40
Hello due in 00:00:03
Supports Link-local Signaling (LLS)
Cisco NSF helper support enabled
IETF NSF helper support enabled
Index 1/1, flood queue length 0
Next 0x0(0)/0x0(0)
Last flood scan length is 1, maximum is 1
Last flood scan time is 0 msec, maximum is 0 msec
Neighbor Count is 2, Adjacent neighbor count is 2
Adjacent with neighbor 1.1.1.1
Adjacent with neighbor 2.2.2.2 (Designated Router)
Suppress hello for 0 neighbor(s)
When we look at the routing table of R2, we see a number of routes learned through OSPF. Let's deep dive into understanding what each route means.
Output 1.2
R2#show ip route ospf
Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route, H - NHRP, l - LISP
a - application route
+ - replicated route, % - next hop override
Gateway of last resort is not set
10.0.0.0/8 is variably subnetted, 4 subnets, 3 masks
O IA 10.0.14.0/24 [110/20] via 10.0.123.1, 00:53:14, Ethernet0/2
O IA 10.0.35.0/30 [110/20] via 10.0.123.3, 00:57:34, Ethernet0/2
44.0.0.0/32 is subnetted, 1 subnets
O E2 44.44.44.44 [110/20] via 10.0.123.1, 00:45:20, Ethernet0/2
55.0.0.0/32 is subnetted, 1 subnets
O E1 55.55.55.55 [110/21] via 10.0.123.3, 00:42:16, Ethernet0/2
- 10.0.14.0/24 is learned from Area 40 which is a regular area and this is a type 3 LSA because of IA.
- 10.0.35.0/30 is learned from Area 50
- 44.44.44.44/32 is a loopback configured on R4 (ASBR) which is EIGRP and the route is redistributed into OSPF with the default metric-type 2.
- 55.55.55.55/32 is a route learned through Area 50 which is a Not-so-stubby-area (NSSA), the route has been redistributed from an OSPF process 2 into process 1 with a metric-type 1 configured.
When we look at this route on R3 which is an ABR receiving this route from R5, this is what we see.
Output 1.3
R3#show ip route ospf
Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route, H - NHRP, l - LISP
a - application route
+ - replicated route, % - next hop override
Gateway of last resort is not set
10.0.0.0/8 is variably subnetted, 5 subnets, 3 masks
O IA 10.0.14.0/24 [110/20] via 10.0.123.1, 00:51:15, Ethernet0/3
44.0.0.0/32 is subnetted, 1 subnets
O E2 44.44.44.44 [110/20] via 10.0.123.1, 00:51:15, Ethernet0/3
55.0.0.0/32 is subnetted, 1 subnets
O N1 55.55.55.55 [110/11] via 10.0.35.2, 00:49:03, Ethernet0/0
This route 55.55.55.55/32 is a Type-7 LSA route because Area 50 is configured as NSSA. On R3 we see this route as N2 but when the route is propagated within Area 0 it appears as a Type 5. As you may see from Output 1.2 above, the route is an E1 since it was redistributed with the metric-type 1.
Output 1.4
R3#
router ospf 1
router-id 5.5.5.5
area 50 nssa
redistribute ospf 2 metric-type 1 subnets ! Here you can see that OSPF 2 is redistributed into OSPF 1 with metric-type 1 and that area 50 is NSSA.
network 10.0.35.0 0.0.0.3 area 50
Let's validate our findings with show ip ospf database topology.
R3#show ip ospf database topology OSPF Router with ID (3.3.3.3) (Process ID 1) Base Topology (MTID 0) Router Link States (Area 0) ! Type-1 Router LSA Link ID ADV Router Age Seq# Checksum Link count 1.1.1.1 1.1.1.1 447 0x80000007 0x00AC60 1 2.2.2.2 2.2.2.2 878 0x80000005 0x006F97 1 3.3.3.3 3.3.3.3 1935 0x80000007 0x0036C2 1 Net Link States (Area 0) ! Type-2 Network LSA Link ID ADV Router Age Seq# Checksum 10.0.123.2 2.2.2.2 622 0x80000004 0x00BDCD Summary Net Link States (Area 0) ! Type-3 Summary LSA Link ID ADV Router Age Seq# Checksum 10.0.14.0 1.1.1.1 447 0x80000003 0x00AE66 10.0.35.0 3.3.3.3 947 0x80000003 0x007882 Summary ASB Link States (Area 0) ! Type-4 The external route originated from R4 when passed through R1 and received on R3. Link ID ADV Router Age Seq# Checksum 4.4.4.4 1.1.1.1 184 0x80000003 0x000517 Router Link States (Area 50) ! Type-1 from within Area 50 Link ID ADV Router Age Seq# Checksum Link count 3.3.3.3 3.3.3.3 1935 0x80000006 0x001E60 2 5.5.5.5 5.5.5.5 1905 0x80000006 0x004C2A 2 Summary Net Link States (Area 50) ! Type-3 from Area 50 Link ID ADV Router Age Seq# Checksum 10.0.14.0 3.3.3.3 1935 0x80000003 0x007C80 10.0.123.0 3.3.3.3 1935 0x80000003 0x006435 Type-7 AS External Link States (Area 50) ! Type-7 for the route redistributed from R5 OSPF process 2. Link ID ADV Router Age Seq# Checksum Tag 55.55.55.55 5.5.5.5 1905 0x80000003 0x00DD2A 0 Type-5 AS External Link States ! Type-5 For the routes learned through ABRs. Link ID ADV Router Age Seq# Checksum Tag 44.44.44.44 4.4.4.4 189 0x80000003 0x007B62 0 55.55.55.55 3.3.3.3 1935 0x80000003 0x00AE6B 0
Definitions from Cisco.com