OSPF

=Introduction=


 * Attributes:


 * OSPF Hello Packet has TTL=1. It cannot cross a hop.


 * Change AD in OSPF:
 * 1) router ospf 1
 * 2) distance 250 		   (useful in Protocol Migration)
 * 3) distance 255              (invalid; do not use these routes)


 * Metric Formula

This can be modifiable with cmd: router ospf 1 auto-cost reference-bandwidth 1000

Every 10 sec on Broadcast/Point-to-point network. Every 30 sec on NBMA Network 40 sec Broadcast/Point-to-point network. 120 sec NBMA Network
 * All Areas must connect to Area 0.
 * All routers in an area have same Topology Table.
 * ABR localizes updates to an Area.
 * Only ABR & ASBR can do Summarization in OSPF. In EIGRP Summarization can be done anywhere.
 * All Areas must connect to Area 0.
 * Hello message is sent:
 * Dead Timer is 4 times Hello message
 * On receiving a hello, If my Router-ID is already listed, reset Dead Timer, stop further processing, else start Neighbor relationship processing.

= OSPF Databases and Tables =

OSPF has 3 Databases used to create 3 Tables:

= Packet types in OSPF =

= DR BDR Election =
 * The DR serves as a common point for all adjacencies on a multiaccess segment
 * The BDR also maintains adjacencies with all routers in case the DR fails
 * Election does not occur on point-to-point or multipoint links
 * Default priority (0-255) is 1, Highest priority wins, 0 cannot be elected
 * In case of tie, Router with Highest Router ID wins election
 * DR preemption will not occur unless the current DR is reset

= Virtual Links =
 * Tunnel formed to join two areas across an intermediate
 * Both end routers must share a common area
 * At least one end must reside in area 0
 * Cannot traverse stub areas

R1> router ospf 1 R1> area 2 virtual-link 10.0.0.1

R2> router ospf 1 R2> area 2 virtual-link 10.0.0.2

10.0.0.1 & 10.0.0.2 are Router-IDs Area 2 is the area of the transit area. R1 & R2 are the ABRs of Area 2 & Area 3.

= What is a Demand Circuit =

Source: cisco.com


 * OSPF sends hellos every 10 seconds and refreshes its LSAs every 30 minutes.
 * These functions maintain neighbor relationships and ensure that the link-state databases are accurate and use far less bandwidth than similar functions in RIP & IGRP.
 * However, even this amount of traffic is undesirable on demand circuits. Using OSPF demand circuit options suppresses hello and LSA refresh functions.
 * OSPF can establish a demand link to form an adjacency and perform initial database synchronization, the adjacency remains active even after Layer 2 of the demand circuit goes down.


 * Cisco IOS version 12.1(2)T introduces the flooding reduction feature for OSPF.
 * This feature is intended to minimize traffic created by a periodic refresh of LSAs in OSPF domains with large number of LSAs.
 * Unlike the OSPF demand circuit feature, flooding reduction is usually configured on leased lines.
 * Flooding reduction uses same technique as demand circuits to suppress the periodic LSA refresh.
 * This feature is submitted for standardization into the IETF OSPF working group.


 * The main difference between flooding reduction and demand circuits is that former suppresses only periodic LSA refreshes; it does not suppress periodic hello packets.
 * Thus, the flooding reduction feature does not impair the detection of a neighbor router going down.

ip ospf demand-circuit

=Area Summary=

Contain LSAs of type 1, 2, 3, 4, and 5, and may contain an ASBR. The backbone is considered a standard area.
 * Standard areas:

Contain type 1, 2, and 3 LSAs. Block Type 5 LSAs. A default route is substituted for external routes.
 * Stub areas

Only contain type 1 and 2 LSAs, and a single type 3 LSA. Block LSAs Type 3,4,5. The type 3 LSA describes a default route, substituted for all external and inter-area routes.
 * Totally stubby areas

Implement stub or totally stubby functionality yet contain an ASBR. Type 7 LSAs generated by the ASBR are converted to type 5 by ABRs when entering Backbone Area to be flooded to the rest of the OSPF domain.
 * Not-so-stubby areas

=LSA=


 * LSA Details:


 * Type 1 - Router LSAs

Sent from a router to other routers in the same area. It contains information regarding the routers interfaces in the same area, relevant interfaces IPs, its adjacent routers on those interfaces and sub networks

Generated by the DR on a multi access segment Represents the pseudonode (designated router) for a multiaccess link. Provides similar information to an LSA type 1 for the multi access segment and subnet which it belongs
 * Type 2 - Network LSAs

Generated by ABRs Contain the subnets & costs but omit the topological data from all subnets in one area and sent to another area via the ABR
 * Type 3 - Network Summary LSA

Generated by ___ Represents ASBRs and are identical in structure to a type 3 LSA and sent when crossing an AS boundary
 * Type 4 - ASBR summary LSA

Generated by ASBRs describe a route external to the OSPF domain
 * Type 5 - AS external LSA

Generated by the ASBR in an NSSA area Used in stub areas in place of a type 5 LSA.
 * Type 7 - NSSA External LSA


 * LSA as per Areas :-

=Adjacency=


 * OSPF neighbor requirements:
 * 1) Router should be in same area
 * 2) Router should have same authentication config
 * 3) Router should be on same subnet
 * 4) Router have same hello/dead interval
 * 5) Router have matching stub flags


 * Difference between Adjacency & Neighbor:
 * 1) Only Adjacent Routers can sync Link State DB
 * 2) Point-to-Point Links: If Neighbors, Adjcency automatically established
 * 3) Broadcast Link: Adjacency established with DR & BDR only, rest are in 2-way state
 * 4) Point-to-Multipoint:_________
 * 5) Neighbor means Physical Connectivity(Direct)
 * 6) Adjacency means Database Syncronization
 * 7) Neighbor Requirements:
 * 8) Hello exchange => Subnet Mask, Subnet Number, Hello/Dead Interval, Area ID, Authentication must match.
 * 9) Exchange hellos but not LSAs(2-Way State).
 * 10) Adjacency Requirements:
 * 11) Exchange LSAs
 * 12) Both routers are in Stable(Full) State.
 * 13) Still final LSDB is same even in Neighbors as well as Adjacent routers.

OSPF Neighbor Relationship
1. Determine you own Router-ID: Highest Active Interface IP < HIghest Active Loopback Interface IP < Router-ID Command Router-ID is determined during 1st neighbor establishment process. It only changes when: - OSPF process is restarted (# clear ip ospf process) - Rebooted Router

2. Add Interfaces to Link State Database (Network command):


 * Neighbor States

= R&S Quick Notes = The Neighbor IP used with OSPF distance command is the Neighbors Router-ID. “area range” summarize type 3 LSA’. “summary-address” summarize type 5 & 7 LSA’s. Auto-cost reference BW (Default = 100mb), formula = Ref-BW/Int-Bw. Switches do no support the interface command “ip ospf {pid} area {area-id}”. OSPF path selection: O > O*IA > O*E1 > O*E2. Using E1 metric type : Packets will be routed out the closest exit point of the network. Using E2 metric type : If you want packets to exit your network at the closest point to their external destination. Don’t forget with hub and spoke topology, “ip ospf priority 0″. PITFALL, when forbid to use RID, Loopbacks created later on might change the DR on you network after a reload. PITFALL, when forbid to use RID, Later requested to configure the same loopback on two routers, could break your adjacencies, as two router cant peer with the same RID. “no capability transit” – Mimics OSPFv1 behaviour for all data traffic to pass through Area-0. “max-metric” – Configures OSPF stub configurations “max-lsa” – Limit amount of non-local LSA’s “timers throttle lsa all” – Slow down update rate. “timers pacing lsa-group” – Group more LSA’s together in updates. “no ip ospf flood-reduction” – Disables every 30-min LSA DB refresh. “ip ospf database filter all out” – Breaks RFC, Stop sending LSA’s, but still receive LSA’s

= Concept Recap =

Protocol Number = 89, TTL=1, DES IP = 224.0.0.5 & 6 Network Types: PTP: No DR, BDR and ospf packets are sent to MC address. Broadcast: (ethernet, token ring, FDDI) DR, BDR election occurs and communicates using .5 and .6 address. DR and BDR listen to .5 and .6 addresses. NBMA network: (Frame relay, ATM) Manual configuration of neighbors and DR/BDR. All communication via unicast Point to multipoint: No DR and BDR. Neighbor statement not necessary. Unicast Virtual link: Packets are unicast. OSPF packet types: Hello – type 1 Database description – type 2 LS request – type 3 LS update – type 4 LS ACK – type 5 To bring neighborship up, following fields should be matched: Hello interval, Dead interval, area ID, network mask, option fields and authentication, if any Neighborship will not form via secondary address. Other words, router will not generate hello packet with SRC IP = secondary IP. DR/BDR election: Highest Priority Tie, highest router ID       Tie, highest interface address. No preempt. So, first come will elect as DR, BDR, DRother. So, always start the router which has to be DR and then BDR and then other routers. Priority=0 means ineligible to become DR/BDR. When interface comes up, it sets DR,BDR to 0.0.0.0 and wait for ‘wait timer’= router dead interval. Within that period, if it receives hello with DR/BDR filled, accept those. Else if the time period elapse, move to BDR and then to DR.   Timers: Default H=10 sec and D= 40 sec InfTransDelay = 1 sec. change by “ip ospf transmit-delay’ RxmtInterval = 5 sec. Change by “ip ospf retramit-delay’ Neighbor state machine: Down: at initial Attempt: Only in NBMA Init: Hello packet received. But couldn’t see our ID in its active neighbor list. 2-way:Could see our ID in neighbor list Exstart: Start electing master/slave to exchange DBD packets. Highest router ID becomes master. Exchange: exchange the LSA headers using DBD packets. Loading: Syn the LSD using LS request and LS update. In real scenario, both Exchange and loading occurs parallel. Full: Database was sync-ed. DBD packet: Have Interface MTU settings. Initial(I) bit, More (M) bit and Master/Slave (MS) bit First DBD packet sent with I/M/MS = 1/1/1 with seq =x Neighbor sends DBD with I/M/MS = 1/1/1 with seq = y           After master selection, slave send DBD with I/M/MS = 0/1/0 with seq = master seq + 1. Retransmission packets are always unicast. Use stub concept and summarization to reduce memory and CPU utilization. Sequence number, checksum and age uniquely defines as LSA: Seq #: From 0×80000001 to 0x7fffffff If the seq# reaches 0x7ffffff, router flushes those LSA with age = MAXage. Checksum: Calculated entire LSA except age field. Checksum is verified every 5 mins as it resides in LSD. Age: 0 to 3600 (1 Hr-MaxAge) Age increments when it resides in LSA and also incremented by ‘Infdelay’ value as it transits an interface. Virtual Links: Must be configured between 2 ABRs alone. Transit area must have full routing information. Transit area cannot be stub. Usually it is the worst design and needs to be changed. Can temporarily deploy to avoid partitioned area. LSA types: Router LSA: Type-1. Generated by all routers with all active networks which has ospf configured. Show ip ospf database router LSAs are flooded within an area only. Above command should have same output in all routers in an area. Seq #,checksum etc should be same. Network LSA: Type-2: Generated by the DR with network ID of the BC network. Show ip ospf database network No metric field as in router LSA. LSAs are flooded within an area only. N/w summary LSA: Type-3: Generated by ABR to advertise the networks in another area. If there are multiple routes to a destination, ABR advertise only the lowest cost route to its area along with cost metric. Means, intra area routers use distance-vector protocol to know about inter-area routes. Show ip ospf database summary ASBR summary LSA: Type-4; Same as summary LSA except the destination advertised by ABR is ASBR. Show ip ospf database asbr-summary AS external LSA: Type-5; Advertise routes external to OSPF domain. Typically redistribution of RIP, ISIS etc Show ip ospf database external Not associated with any area. Group-Membership LSA: Type-6; Used in MOSPF- multicast ospf NSSA external LSA: Type-7; originated by ASBR within NSSA Show ip ospf database nssa-external Flooded within NSSA region only. ASBR can set/reset “P-bit” under “options field” of every LSA. Only if NSSA-ABR receives type-7 LSA with P-bit set, it will translate into type-5 LSA and flood to other areas. External Attribute LSA: Type-8. Can be used as alternative to iBGP Not deployed yet. Opaque LSA: Type- 9,10,11 Extension to OSPF. Used for TE in MPLS. Areas: Backbone area: Area-0. Need for inter-area communication. If there is only one area, no need for area-0 All types of LSAs except type-7 can be seen. Stub area: Single exist point for inter-area communication. But still can have more than one ABR. Have info about OSPF domain areas. Both intra and inter-area routes. No info about external (other domain) routes. Hence, ABR sends a default route. Type-1,2 and 3 LSAs can be seen. All the routers should have “E-bit” set to 0 in their hello packets to form adjacency. Command: “area x stub” Totally stubby area: Router has info about its area alone. No info about inter-area routes. Can see type-1, type-2 LSAs and single default route type-3 LSA by ABR. Command: ‘area x stub no-summary’ NSSA: Same property as stub area (not totally-stub area) with exception of allowing other domain routes as Lype-7 LSA. No default route from ABR. (unless ‘default-info originate’ CLI configured where N2 default route (or) ‘area x nssa no-summary’ configured. In later, IA routes will not be available and default route has IA tag) Can see Type-1,2,3,4 and type-7 LSAs. Command: ‘area x nssa’. Path types: Intra-area paths Inter-area paths. Denoted by “IA” in show ip route. E1: Cost = advertised by ASBR + cost to ASBR E2: Cost = advertised by ASBR. Enabled by default. If there is only one ASBR in OSPF, there is no necessity of adding cost to ASBR. Hence E2 is default. If there are more than on ASBR, enable E1. Authentication: No authentication: Type-0 Simple password: Type-1 MD5 password: Type-2 Few points: Router LSA of ABR will have “B-bit” set in router-lsa packet Router LSA of ASBR will have “E-bit” set in router-lsa packet When NSSA ABR, translates type-7 LSA to type-5 LSA, it advertise with “Advertising Router” field set to its own router ID and it changes to ASBR. It could be confirmed by seeing “E” bit set in router LSA packet. “Options field” in OSPF hello, DBD and every LSA: From MSB DN – used in MPLS VPN. To detect loop. O- Set to indicate routers’ opaque LSA support. DC- OSPF over Demand circuit. EA – external attribute support N/P bit N bit in hello: Set to indicate support for NSSA external LSAs. Mismatch will not bring adjacency P-bit in NSSA external LSA header: to inform ABR to translate T-7 to T-5 LSAs. MC – set to indicate multicast ospf capability E – E bit=0 to indicate stub area. MT – set to indicate Multi-topology OSPF support. Under development. Troubleshooting point of view: few Neighborship not coming UP: Check for Hello packet parameter match Network ID in correct area?? Access-list blocking OSPF packets?? Packet dropped on the way to CP incase if interface multicast count is incrementing?? Check Stub-area configuration?? Virtual link via stub area?? Neighborship UP but no advertised routes in database: Enable debug and check for LSupdate packets. Routes in OSPF database but not in routing table: Routes via another protocol which has AD less than OSPFs?? One end of router has “ip ospf network PTP’ whereas other end router has default BC network type. In case of external routes not installed in routing table, check whether the forwarding address is reachable. If not, configure ‘suppress-fa’ option at the NSSA ABR. If an LSA has less age or high sequence number among others, we need to look for why this network was keep flapping and flooding updates. Might be reason for high CPU utilization. Observations: ABR with area-1 and area-2 only. Routes from area-1 are not leaked into area-2 using type-3 network summary LSA. Authentication: Configure ‘ip ospf authentication’ to change to type-1. No user-defined password possible. For loopback IP to become router-id either remove and reapply the ospf configuration or configure ‘router-id’ command. DBD packet can have multiple LSA headers each can be of different type.(T1/T2) When we change the network type to ‘point-point’, the interface will send a hello with DR,BDR =0 and no neighbor IDs in active neighbor field. This makes other end router to move to init. In BC network: DBD, LS request and LS updates are exchanged via unicast. LS update (repeat) and LS ACK are sent to 224.0.0.5 In PTP, all communications via 224.0.0.5 Changing hello packet parameters (hello interval, dead interval etc) on one end makes the other end router to ignore those hello packets which has modified parameters. Both side of router configured with priority =0 with default n/w type, they will stuck in 2way/DRother. In an already existing stub network, if we change to totally stub, border router send an update with IA routes’ age= 3600 for flushing from database. Same as in ‘clear ip ospf process’ Redistributing RIP to ospf in a router which is inside a stub network: “%OSPF-4-ASBR_WITHOUT_VALID_AREA: Router is currently an ASBR while having only one area which is a stub area” Summarization has no effect of external routes (E1/E2).

=LAB=


 * OSPF Neighbor Establishment Debug
 * OSPF MTU Mismatch Debug
 * Packet Captures

Troubleshooting

 * If OSPF is stuck in INIT State, check Netmask, Hello/Dead Timer, Area ID, Authentication password.


 * On a shared/ethernet network, only 2 router, DR & BDR will form full relationship, all others will stay in 2-way state.

Matching MTU is not a Adjacency Requirement, but is required to successfully pass Database Descriptor Packets
 * If OSPF is stuck in ExStart State, MTU mismatch may be the cause, as it is requirement to successfully pass DBD Packets.

Mar 1 00:10:09.535: %OSPF-5-ADJCHG: Process 1, Nbr 10.10.10.1 on Ethernet0/0 from EXSTART to DOWN, Neighbor Down: Too many retransmissions
 * In OSPF, MTU Mismatch causes neighbors swinging between ExStart state to Down state

Basic OSPF Lab


GNS3 Project: File:CBT Nuggets OSPF Lab.zip

Objectives
1. Config OSPF: R1 will act as ASBR by redistributing static routes into OSPF. Metric of these routes should not increase as they pass through network and should have initial OSPF cost of 200. All routers have should have router-id as their hostname. 2. Find out which router is DR & BDR. 3. R1 should become DR, R2 & R3 should not be DR or BDR. Find out relation between R1 & R2; R2 & R3. 4. Implement summarization on ABRs to make routing table most efficient 5. Implement summarization on ASBRs; Summary routes should have same attributes as original routes. 6. Change Metric to accurately calculate cost for Gigabit Ethernet links.

Configurations
R1 Config: ! interface Ethernet0/0 ip address 172.30.0.1 255.255.255.0 half-duplex ! ! router ospf 1 router-id 1.1.1.1 log-adjacency-changes auto-cost reference-bandwidth 1000 summary-address 172.16.0.0 255.255.252.0 redistribute static metric 200 subnets network 172.30.0.1 0.0.0.0 area 0 ! ! ip route 172.16.0.0 255.255.255.0 Null0 ip route 172.16.1.0 255.255.255.0 Null0 ip route 172.16.2.0 255.255.255.0 Null0 ip route 172.16.3.0 255.255.255.0 Null0 !

R2 Config: ! interface Ethernet0/0 ip address 172.30.0.2 255.255.255.0 ip ospf priority 0 half-duplex ! interface Serial1/0 ip address 172.30.10.2 255.255.255.0 serial restart-delay 0 ! ! router ospf 1 router-id 2.2.2.2 log-adjacency-changes auto-cost reference-bandwidth 1000 area 10 range 10.10.0.0 255.255.252.0 network 172.30.0.2 0.0.0.0 area 0 network 172.30.10.2 0.0.0.0 area 10 ! !

R3 Config: ! interface Ethernet0/0 ip address 172.30.0.3 255.255.255.0 ip ospf priority 0 half-duplex ! ! interface Serial1/0 ip address 172.30.20.3 255.255.255.0 serial restart-delay 0 ! ! router ospf 1 router-id 3.3.3.3 log-adjacency-changes auto-cost reference-bandwidth 1000 area 20 range 10.20.0.0 255.255.252.0 network 172.30.0.3 0.0.0.0 area 0 network 172.30.20.3 0.0.0.0 area 20 ! !

R4 Config: interface Loopback1 ip address 10.20.0.1 255.255.255.0 ! interface Loopback2 ip address 10.20.1.1 255.255.255.0 ! interface Loopback3 ip address 10.20.2.1 255.255.255.0 ! interface Loopback4 ip address 10.20.3.1 255.255.255.0 ! ! interface Serial1/0 ip address 172.30.20.4 255.255.255.0 serial restart-delay 0 ! ! router ospf 1 router-id 4.4.4.4 log-adjacency-changes auto-cost reference-bandwidth 1000 network 10.0.0.0 0.255.255.255 area 20 network 172.30.20.4 0.0.0.0 area 20 ! !

R5 Config: ! interface Loopback1 ip address 10.10.0.1 255.255.255.0 ip ospf network point-to-point ! interface Loopback2 ip address 10.10.1.1 255.255.255.0 ! interface Loopback3 ip address 10.10.2.1 255.255.255.0 ! interface Loopback4 ip address 10.10.3.1 255.255.255.0 ! ! interface Serial1/0 ip address 172.30.10.5 255.255.255.0 serial restart-delay 0 ! ! router ospf 1 router-id 5.5.5.5 log-adjacency-changes auto-cost reference-bandwidth 1000 network 10.10.0.0 0.0.255.255 area 10 network 172.30.10.5 0.0.0.0 area 10 ! !

Command Line Outputs

 * show ip interface brief

R1# show ip interface brief Interface                 IP-Address      OK? Method Status               Protocol Ethernet0/0               172.30.0.1      YES manual up                    up      Ethernet0/1                unassigned      YES unset  administratively down down Ethernet0/2               unassigned      YES unset  administratively down down Ethernet0/3               unassigned      YES unset  administratively down down Serial1/0                 unassigned      YES unset  administratively down down Serial1/1                 unassigned      YES unset  administratively down down Serial1/2                 unassigned      YES unset  administratively down down Serial1/3                 unassigned      YES unset  administratively down down
 * R1:

R2#show ip interface brief Interface                 IP-Address      OK? Method Status               Protocol Ethernet0/0               172.30.0.2      YES manual up                    up      Ethernet0/1                unassigned      YES unset  administratively down down Ethernet0/2               unassigned      YES unset  administratively down down Ethernet0/3               unassigned      YES unset  administratively down down Serial1/0                 172.30.10.2     YES manual up                    up      Serial1/1                  unassigned      YES unset  administratively down down Serial1/2                 unassigned      YES unset  administratively down down Serial1/3                 unassigned      YES unset  administratively down down
 * R2:

R3#show ip interface brief Interface                 IP-Address      OK? Method Status               Protocol Ethernet0/0               172.30.0.3      YES manual up                    up      Ethernet0/1                unassigned      YES unset  administratively down down Ethernet0/2               unassigned      YES unset  administratively down down Ethernet0/3               unassigned      YES unset  administratively down down Serial1/0                 172.30.20.3     YES manual up                    up      Serial1/1                  unassigned      YES unset  administratively down down Serial1/2                 unassigned      YES unset  administratively down down Serial1/3                 unassigned      YES unset  administratively down down
 * R3:

R4# show ip interface brief Interface                 IP-Address      OK? Method Status               Protocol Ethernet0/0               unassigned      YES unset  administratively down down Ethernet0/1               unassigned      YES unset  administratively down down Ethernet0/2               unassigned      YES unset  administratively down down Ethernet0/3               unassigned      YES unset  administratively down down Serial1/0                 172.30.20.4     YES manual up                    up      Serial1/1                  unassigned      YES unset  administratively down down Serial1/2                 unassigned      YES unset  administratively down down Serial1/3                 unassigned      YES unset  administratively down down Loopback1                 10.20.0.1       YES manual up                    up      Loopback2                  10.20.1.1       YES manual up                    up      Loopback3                  10.20.2.1       YES manual up                    up      Loopback4                  10.20.3.1       YES manual up                    up
 * R4:

R5#show ip interface brief Interface                 IP-Address      OK? Method Status               Protocol Ethernet0/0               unassigned      YES unset  administratively down down Ethernet0/1               unassigned      YES unset  administratively down down Ethernet0/2               unassigned      YES unset  administratively down down Ethernet0/3               unassigned      YES unset  administratively down down Serial1/0                 172.30.10.5     YES manual up                    up      Serial1/1                  unassigned      YES unset  administratively down down Serial1/2                 unassigned      YES unset  administratively down down Serial1/3                 unassigned      YES unset  administratively down down Loopback1                 10.10.0.1       YES manual up                    up      Loopback2                  10.10.1.1       YES manual up                    up      Loopback3                  10.10.2.1       YES manual up                    up      Loopback4                  10.10.3.1       YES manual up                    up
 * R5:


 * Routing Tables:

172.16.0.0/16 is variably subnetted, 5 subnets, 2 masks S      172.16.0.0/24 is directly connected, Null0 O      172.16.0.0/22 is a summary, 01:05:49, Null0 S      172.16.1.0/24 is directly connected, Null0 S      172.16.2.0/24 is directly connected, Null0 S      172.16.3.0/24 is directly connected, Null0 172.30.0.0/24 is subnetted, 3 subnets O IA   172.30.20.0 [110/747] via 172.30.0.3, 00:53:45, Ethernet0/0 C      172.30.0.0 is directly connected, Ethernet0/0 O IA   172.30.10.0 [110/747] via 172.30.0.2, 00:53:46, Ethernet0/0 10.0.0.0/22 is subnetted, 2 subnets O IA   10.10.0.0 [110/748] via 172.30.0.2, 00:53:46, Ethernet0/0 O IA   10.20.0.0 [110/748] via 172.30.0.3, 00:53:46, Ethernet0/0
 * R1:

172.16.0.0/22 is subnetted, 1 subnets O E2   172.16.0.0 [110/200] via 172.30.0.1, 00:53:15, Ethernet0/0 172.30.0.0/24 is subnetted, 3 subnets O IA   172.30.20.0 [110/747] via 172.30.0.3, 00:53:15, Ethernet0/0 C      172.30.0.0 is directly connected, Ethernet0/0 C      172.30.10.0 is directly connected, Serial1/0 10.0.0.0/8 is variably subnetted, 6 subnets, 3 masks O      10.10.1.1/32 [110/648] via 172.30.10.5, 00:53:15, Serial1/0 O      10.10.0.0/24 [110/648] via 172.30.10.5, 00:53:17, Serial1/0 O      10.10.0.0/22 is a summary, 00:53:17, Null0 O      10.10.3.1/32 [110/648] via 172.30.10.5, 00:53:17, Serial1/0 O      10.10.2.1/32 [110/648] via 172.30.10.5, 00:53:17, Serial1/0 O IA   10.20.0.0/22 [110/748] via 172.30.0.3, 00:53:17, Ethernet0/0
 * R2:

172.16.0.0/22 is subnetted, 1 subnets O E2   172.16.0.0 [110/200] via 172.30.0.1, 00:53:37, Ethernet0/0 172.30.0.0/24 is subnetted, 3 subnets C      172.30.20.0 is directly connected, Serial1/0 C      172.30.0.0 is directly connected, Ethernet0/0 O IA   172.30.10.0 [110/747] via 172.30.0.2, 00:53:37, Ethernet0/0 10.0.0.0/8 is variably subnetted, 6 subnets, 2 masks O IA   10.10.0.0/22 [110/748] via 172.30.0.2, 00:53:37, Ethernet0/0 O      10.20.3.1/32 [110/648] via 172.30.20.4, 00:53:38, Serial1/0 O      10.20.2.1/32 [110/648] via 172.30.20.4, 00:53:38, Serial1/0 O      10.20.1.1/32 [110/648] via 172.30.20.4, 00:53:38, Serial1/0 O      10.20.0.0/22 is a summary, 00:53:38, Null0 O      10.20.0.1/32 [110/648] via 172.30.20.4, 00:53:38, Serial1/0
 * R3:

172.16.0.0/22 is subnetted, 1 subnets O E2   172.16.0.0 [110/200] via 172.30.20.3, 00:53:42, Serial1/0 172.30.0.0/24 is subnetted, 3 subnets C      172.30.20.0 is directly connected, Serial1/0 O IA   172.30.0.0 [110/747] via 172.30.20.3, 00:53:42, Serial1/0 O IA   172.30.10.0 [110/1394] via 172.30.20.3, 00:53:42, Serial1/0 10.0.0.0/8 is variably subnetted, 5 subnets, 2 masks O IA   10.10.0.0/22 [110/1395] via 172.30.20.3, 00:53:42, Serial1/0 C      10.20.2.0/24 is directly connected, Loopback3 C      10.20.3.0/24 is directly connected, Loopback4 C      10.20.0.0/24 is directly connected, Loopback1 C      10.20.1.0/24 is directly connected, Loopback2
 * R4:

172.16.0.0/22 is subnetted, 1 subnets O E2   172.16.0.0 [110/200] via 172.30.10.2, 00:53:27, Serial1/0 172.30.0.0/24 is subnetted, 3 subnets O IA   172.30.20.0 [110/1394] via 172.30.10.2, 00:53:27, Serial1/0 O IA   172.30.0.0 [110/747] via 172.30.10.2, 00:53:27, Serial1/0 C      172.30.10.0 is directly connected, Serial1/0 10.0.0.0/8 is variably subnetted, 5 subnets, 2 masks C      10.10.0.0/24 is directly connected, Loopback1 C      10.10.1.0/24 is directly connected, Loopback2 C      10.10.2.0/24 is directly connected, Loopback3 C      10.10.3.0/24 is directly connected, Loopback4 O IA   10.20.0.0/22 [110/1395] via 172.30.10.2, 00:53:29, Serial1/0
 * R5:


 * Topology Tables

R1#sh ip ospf database
 * R1:

OSPF Router with ID (1.1.1.1) (Process ID 1)

Router Link States (Area 0)

Link ID        ADV Router      Age         Seq#       Checksum Link count 1.1.1.1        1.1.1.1         1583        0x80000009 0x0029FC 1 2.2.2.2        2.2.2.2         1320        0x80000007 0x00EB34 1 3.3.3.3        3.3.3.3         1425        0x8000000E 0x009F70 1

Net Link States (Area 0)

Link ID        ADV Router      Age         Seq#       Checksum 172.30.0.1     1.1.1.1         82          0x80000004 0x0098B2

Summary Net Link States (Area 0)

Link ID        ADV Router      Age         Seq#       Checksum 10.10.0.0      2.2.2.2         1320        0x80000005 0x00A2F2 10.20.0.0      3.3.3.3         1425        0x80000003 0x001079 172.30.10.0    2.2.2.2         1320        0x80000004 0x0008CB 172.30.20.0    3.3.3.3         1425        0x8000000A 0x006F50

Type-5 AS External Link States

Link ID        ADV Router      Age         Seq#       Checksum Tag 172.16.0.0     1.1.1.1         82          0x80000006 0x003AEE 0

R2#sh ip ospf database
 * R2:

OSPF Router with ID (2.2.2.2) (Process ID 1)

Router Link States (Area 0)

Link ID        ADV Router      Age         Seq#       Checksum Link count 1.1.1.1        1.1.1.1         1600        0x80000009 0x0029FC 1 2.2.2.2        2.2.2.2         1335        0x80000007 0x00EB34 1 3.3.3.3        3.3.3.3         1442        0x8000000E 0x009F70 1

Net Link States (Area 0)

Link ID        ADV Router      Age         Seq#       Checksum 172.30.0.1     1.1.1.1         98          0x80000004 0x0098B2

Summary Net Link States (Area 0)

Link ID        ADV Router      Age         Seq#       Checksum 10.10.0.0      2.2.2.2         1335        0x80000005 0x00A2F2 10.20.0.0      3.3.3.3         1442        0x80000003 0x001079 172.30.10.0    2.2.2.2         1335        0x80000004 0x0008CB 172.30.20.0    3.3.3.3         1442        0x8000000A 0x006F50

Router Link States (Area 10)

Link ID        ADV Router      Age         Seq#       Checksum Link count 2.2.2.2        2.2.2.2         1335        0x8000000B 0x0072C4 2 5.5.5.5        5.5.5.5         1323        0x8000000B 0x003F4C 6

Summary Net Link States (Area 10)

Link ID        ADV Router      Age         Seq#       Checksum 10.20.0.0      2.2.2.2         1337        0x80000004 0x001810 172.30.0.0     2.2.2.2         1337        0x80000004 0x0005FD 172.30.20.0    2.2.2.2         1337        0x80000005 0x0083E0

Summary ASB Link States (Area 10)

Link ID        ADV Router      Age         Seq#       Checksum 1.1.1.1        2.2.2.2         1337        0x80000004 0x00F6D1

Type-5 AS External Link States

Link ID        ADV Router      Age         Seq#       Checksum Tag 172.16.0.0     1.1.1.1         101         0x80000006 0x003AEE 0

R3#sh ip ospf database
 * R3:

OSPF Router with ID (3.3.3.3) (Process ID 1)

Router Link States (Area 0)

Link ID        ADV Router      Age         Seq#       Checksum Link count 1.1.1.1        1.1.1.1         1606        0x80000009 0x0029FC 1 2.2.2.2        2.2.2.2         1343        0x80000007 0x00EB34 1 3.3.3.3        3.3.3.3         1446        0x8000000E 0x009F70 1

Net Link States (Area 0)

Link ID        ADV Router      Age         Seq#       Checksum 172.30.0.1     1.1.1.1         105         0x80000004 0x0098B2

Summary Net Link States (Area 0)

Link ID        ADV Router      Age         Seq#       Checksum 10.10.0.0      2.2.2.2         1343        0x80000005 0x00A2F2 10.20.0.0      3.3.3.3         1446        0x80000003 0x001079 172.30.10.0    2.2.2.2         1343        0x80000004 0x0008CB 172.30.20.0    3.3.3.3         1446        0x8000000A 0x006F50

Router Link States (Area 20)

Link ID        ADV Router      Age         Seq#       Checksum Link count 3.3.3.3        3.3.3.3         1446        0x8000000D 0x0063B8 2 4.4.4.4        4.4.4.4         1325        0x8000000B 0x0070E2 6

Summary Net Link States (Area 20)

Link ID        ADV Router      Age         Seq#       Checksum 10.10.0.0      3.3.3.3         1447        0x80000007 0x006CBE 172.30.0.0     3.3.3.3         1447        0x8000000A 0x00DA1E 172.30.10.0    3.3.3.3         1447        0x80000005 0x00D396

Summary ASB Link States (Area 20)

Link ID        ADV Router      Age         Seq#       Checksum 1.1.1.1        3.3.3.3         1447        0x80000004 0x00D8EB

Type-5 AS External Link States

Link ID        ADV Router      Age         Seq#       Checksum Tag 172.16.0.0     1.1.1.1         106         0x80000006 0x003AEE 0

R4#sh ip ospf database
 * R4:

OSPF Router with ID (4.4.4.4) (Process ID 1)

Router Link States (Area 20)

Link ID        ADV Router      Age         Seq#       Checksum Link count 3.3.3.3        3.3.3.3         1453        0x8000000D 0x0063B8 2 4.4.4.4        4.4.4.4         1329        0x8000000B 0x0070E2 6

Summary Net Link States (Area 20)

Link ID        ADV Router      Age         Seq#       Checksum 10.10.0.0      3.3.3.3         1453        0x80000007 0x006CBE 172.30.0.0     3.3.3.3         1453        0x8000000A 0x00DA1E 172.30.10.0    3.3.3.3         1453        0x80000005 0x00D396

Summary ASB Link States (Area 20)

Link ID        ADV Router      Age         Seq#       Checksum 1.1.1.1        3.3.3.3         1453        0x80000004 0x00D8EB

Type-5 AS External Link States

Link ID        ADV Router      Age         Seq#       Checksum Tag 172.16.0.0     1.1.1.1         112         0x80000006 0x003AEE 0

R5#sh ip ospf database
 * R5:

OSPF Router with ID (5.5.5.5) (Process ID 1)

Router Link States (Area 10)

Link ID        ADV Router      Age         Seq#       Checksum Link count 2.2.2.2        2.2.2.2         1353        0x8000000B 0x0072C4 2 5.5.5.5        5.5.5.5         1338        0x8000000B 0x003F4C 6

Summary Net Link States (Area 10)

Link ID        ADV Router      Age         Seq#       Checksum 10.20.0.0      2.2.2.2         1353        0x80000004 0x001810 172.30.0.0     2.2.2.2         1353        0x80000004 0x0005FD 172.30.20.0    2.2.2.2         1353        0x80000005 0x0083E0

Summary ASB Link States (Area 10)

Link ID        ADV Router      Age         Seq#       Checksum 1.1.1.1        2.2.2.2         1353        0x80000004 0x00F6D1

Type-5 AS External Link States

Link ID        ADV Router      Age         Seq#       Checksum Tag 172.16.0.0     1.1.1.1         117         0x80000006 0x003AEE 0


 * Neighbor Table

R1#show ip ospf neighbor
 * R1:

Neighbor ID    Pri   State           Dead Time   Address         Interface 2.2.2.2          0   FULL/DROTHER    00:00:30    172.30.0.2      Ethernet0/0 3.3.3.3          0   FULL/DROTHER    00:00:34    172.30.0.3      Ethernet0/0

R2#show ip ospf neighbor
 * R2:

Neighbor ID    Pri   State           Dead Time   Address         Interface 1.1.1.1          1   FULL/DR         00:00:32    172.30.0.1      Ethernet0/0 3.3.3.3          0   2WAY/DROTHER    00:00:35    172.30.0.3      Ethernet0/0 5.5.5.5          0   FULL/  -        00:00:39    172.30.10.5     Serial1/0

R3#show ip ospf neighbor
 * R3:

Neighbor ID    Pri   State           Dead Time   Address         Interface 1.1.1.1          1   FULL/DR         00:00:39    172.30.0.1      Ethernet0/0 2.2.2.2          0   2WAY/DROTHER    00:00:39    172.30.0.2      Ethernet0/0 4.4.4.4          0   FULL/  -        00:00:39    172.30.20.4     Serial1/0

R4#show ip ospf neighbor
 * R4:

Neighbor ID    Pri   State           Dead Time   Address         Interface 3.3.3.3          0   FULL/  -        00:00:36    172.30.20.3     Serial1/0

R5#show ip ospf neighbor
 * R5:

Neighbor ID    Pri   State           Dead Time   Address         Interface 2.2.2.2          0   FULL/  -        00:00:34    172.30.10.2     Serial1/0


 * Show ip ospf interface

R1#show ip ospf interface Ethernet0/0 is up, line protocol is up  Internet Address 172.30.0.1/24, Area 0 Process ID 1, Router ID 1.1.1.1, Network Type BROADCAST, Cost: 100 Transmit Delay is 1 sec, State DR, Priority 1 Designated Router (ID) 1.1.1.1, Interface address 172.30.0.1 No backup designated router on this network Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5 oob-resync timeout 40 Hello due in 00:00:09 Supports Link-local Signaling (LLS) Index 1/1, flood queue length 0 Next 0x0(0)/0x0(0) Last flood scan length is 1, maximum is 4 Last flood scan time is 0 msec, maximum is 4 msec Neighbor Count is 2, Adjacent neighbor count is 2 Adjacent with neighbor 2.2.2.2 Adjacent with neighbor 3.3.3.3 Suppress hello for 0 neighbor(s)
 * R1:

R2#show ip ospf interface Ethernet0/0 is up, line protocol is up  Internet Address 172.30.0.2/24, Area 0 Process ID 1, Router ID 2.2.2.2, Network Type BROADCAST, Cost: 100 Transmit Delay is 1 sec, State DROTHER, Priority 0 Designated Router (ID) 1.1.1.1, Interface address 172.30.0.1 No backup designated router on this network Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5 oob-resync timeout 40 Hello due in 00:00:06 Supports Link-local Signaling (LLS) Index 1/1, flood queue length 0 Next 0x0(0)/0x0(0) Last flood scan length is 2, maximum is 6 Last flood scan time is 0 msec, maximum is 4 msec Neighbor Count is 2, Adjacent neighbor count is 1 Adjacent with neighbor 1.1.1.1 (Designated Router) Suppress hello for 0 neighbor(s) Serial1/0 is up, line protocol is up  Internet Address 172.30.10.2/24, Area 10 Process ID 1, Router ID 2.2.2.2, Network Type POINT_TO_POINT, Cost: 647 Transmit Delay is 1 sec, State POINT_TO_POINT, Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5 oob-resync timeout 40 Hello due in 00:00:04 Supports Link-local Signaling (LLS) Index 1/2, flood queue length 0 Next 0x0(0)/0x0(0) Last flood scan length is 1, maximum is 7 Last flood scan time is 4 msec, maximum is 4 msec Neighbor Count is 1, Adjacent neighbor count is 1 Adjacent with neighbor 5.5.5.5 Suppress hello for 0 neighbor(s)
 * R2:

R3#show ip ospf interface Ethernet0/0 is up, line protocol is up  Internet Address 172.30.0.3/24, Area 0 Process ID 1, Router ID 3.3.3.3, Network Type BROADCAST, Cost: 100 Transmit Delay is 1 sec, State DROTHER, Priority 0 Designated Router (ID) 1.1.1.1, Interface address 172.30.0.1 No backup designated router on this network Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5 oob-resync timeout 40 Hello due in 00:00:05 Supports Link-local Signaling (LLS) Index 1/1, flood queue length 0 Next 0x0(0)/0x0(0) Last flood scan length is 2, maximum is 4 Last flood scan time is 0 msec, maximum is 4 msec Neighbor Count is 2, Adjacent neighbor count is 1 Adjacent with neighbor 1.1.1.1 (Designated Router) Suppress hello for 0 neighbor(s) Serial1/0 is up, line protocol is up  Internet Address 172.30.20.3/24, Area 20 Process ID 1, Router ID 3.3.3.3, Network Type POINT_TO_POINT, Cost: 647 Transmit Delay is 1 sec, State POINT_TO_POINT, Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5 oob-resync timeout 40 Hello due in 00:00:08 Supports Link-local Signaling (LLS) Index 1/2, flood queue length 0 Next 0x0(0)/0x0(0) Last flood scan length is 1, maximum is 4 Last flood scan time is 0 msec, maximum is 4 msec Neighbor Count is 1, Adjacent neighbor count is 1 Adjacent with neighbor 4.4.4.4 Suppress hello for 0 neighbor(s)
 * R3:

R4#show ip ospf interface Loopback4 is up, line protocol is up  Internet Address 10.20.3.1/24, Area 20 Process ID 1, Router ID 4.4.4.4, Network Type LOOPBACK, Cost: 1 Loopback interface is treated as a stub Host Loopback3 is up, line protocol is up  Internet Address 10.20.2.1/24, Area 20 Process ID 1, Router ID 4.4.4.4, Network Type LOOPBACK, Cost: 1 Loopback interface is treated as a stub Host Loopback2 is up, line protocol is up  Internet Address 10.20.1.1/24, Area 20 Process ID 1, Router ID 4.4.4.4, Network Type LOOPBACK, Cost: 1 Loopback interface is treated as a stub Host Loopback1 is up, line protocol is up  Internet Address 10.20.0.1/24, Area 20 Process ID 1, Router ID 4.4.4.4, Network Type LOOPBACK, Cost: 1 Loopback interface is treated as a stub Host Serial1/0 is up, line protocol is up  Internet Address 172.30.20.4/24, Area 20 Process ID 1, Router ID 4.4.4.4, Network Type POINT_TO_POINT, Cost: 647 Transmit Delay is 1 sec, State POINT_TO_POINT, Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5 oob-resync timeout 40 Hello due in 00:00:05 Supports Link-local Signaling (LLS) 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 1, Adjacent neighbor count is 1 Adjacent with neighbor 3.3.3.3 Suppress hello for 0 neighbor(s)
 * R4:

R5#show ip ospf interface Loopback1 is up, line protocol is up  Internet Address 10.10.0.1/24, Area 10 Process ID 1, Router ID 5.5.5.5, Network Type POINT_TO_POINT, Cost: 1 Transmit Delay is 1 sec, State POINT_TO_POINT, Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5 oob-resync timeout 40 Supports Link-local Signaling (LLS) Index 1/1, flood queue length 0 Next 0x0(0)/0x0(0) Last flood scan length is 0, maximum is 0 Last flood scan time is 0 msec, maximum is 0 msec Neighbor Count is 0, Adjacent neighbor count is 0 Suppress hello for 0 neighbor(s) Serial1/0 is up, line protocol is up  Internet Address 172.30.10.5/24, Area 10 Process ID 1, Router ID 5.5.5.5, Network Type POINT_TO_POINT, Cost: 647 Transmit Delay is 1 sec, State POINT_TO_POINT, Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5 oob-resync timeout 40 Hello due in 00:00:08 Supports Link-local Signaling (LLS) Index 5/5, 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 1, Adjacent neighbor count is 1 Adjacent with neighbor 2.2.2.2 Suppress hello for 0 neighbor(s) Loopback4 is up, line protocol is up  Internet Address 10.10.3.1/24, Area 10 Process ID 1, Router ID 5.5.5.5, Network Type LOOPBACK, Cost: 1 Loopback interface is treated as a stub Host Loopback3 is up, line protocol is up  Internet Address 10.10.2.1/24, Area 10 Process ID 1, Router ID 5.5.5.5, Network Type LOOPBACK, Cost: 1 Loopback interface is treated as a stub Host Loopback2 is up, line protocol is up  Internet Address 10.10.1.1/24, Area 10 Process ID 1, Router ID 5.5.5.5, Network Type LOOPBACK, Cost: 1 Loopback interface is treated as a stub Host
 * R5:

OSPF Areas Lab


GNS3 Project:

Objectives
Advertize all networks attached. On R1 redistribute static routes to inject external routes. These routes should be marked as type E1. These routes should reach external network using default route which cannot be statically configured. They should reach external network using a default route with initial OSPF cost of 100.
 * Configure basic OSPF:
 * R1 should never form neighbor relation on any interface where OSPF router is not connected.
 * All routers in Area 0 should use MD5 auth with password cisco.
 * Area 23 should use clear-text authentication.
 * Routers in Area 45 are weak, should never receive external to OSPF routes(config Stub area).
 * Routers in Area 23 should not receive Type 3,4,5 LSAs.
 * You should be able to ping every router in OSPF Routing Table (configure virtual link for area 78)

Configurations
! interface Ethernet0/0 ip address 10.100.1.1 255.255.255.0 ip ospf authentication message-digest ip ospf message-digest-key 1 md5 cisco half-duplex ! ! router ospf 1 router-id 1.1.1.1 log-adjacency-changes redistribute static metric 50 metric-type 1 subnets passive-interface default no passive-interface Ethernet0/0 network 10.100.1.1 0.0.0.0 area 0 ! ip route 172.31.0.0 255.255.255.0 Null0 ip route 172.31.1.0 255.255.255.0 Null0 ip route 172.31.2.0 255.255.255.0 Null0 ip route 172.31.3.0 255.255.255.0 Null0 !
 * R1 config:

! interface Ethernet0/0 ip address 10.100.1.2 255.255.255.0 ip ospf authentication message-digest ip ospf message-digest-key 1 md5 cisco half-duplex ! interface Serial1/0 ip address 10.23.1.2 255.255.255.0 ip ospf authentication ip ospf authentication-key cisco serial restart-delay 0 ! router ospf 1 router-id 2.2.2.2 log-adjacency-changes area 23 stub no-summary area 23 default-cost 100 network 10.23.1.2 0.0.0.0 area 23 network 10.100.1.2 0.0.0.0 area 0 !
 * R2 config:

! interface Loopback0 ip address 172.30.0.1 255.255.255.0 ! interface Loopback1 ip address 172.30.1.1 255.255.255.0 ! interface Loopback2 ip address 172.30.2.1 255.255.255.0 ! interface Loopback3 ip address 172.30.3.1 255.255.255.0 ! ! interface Serial1/0 ip address 10.23.1.3 255.255.255.0 ip ospf authentication ip ospf authentication-key cisco serial restart-delay 0 ! ! router ospf 1 router-id 3.3.3.3 log-adjacency-changes area 23 stub network 10.23.1.3 0.0.0.0 area 23 network 172.30.0.0 0.0.255.255 area 23 !
 * R3 config:

! interface Ethernet0/0 ip address 10.100.1.4 255.255.255.0 ip ospf authentication message-digest ip ospf message-digest-key 1 md5 cisco half-duplex ! ! interface Serial1/0 ip address 10.45.1.4 255.255.255.0 serial restart-delay 0 ! router ospf 1 router-id 4.4.4.4 log-adjacency-changes area 45 stub network 10.45.1.4 0.0.0.0 area 45 network 10.100.1.4 0.0.0.0 area 0 !
 * R4 config:

! interface Serial1/0 ip address 10.45.1.5 255.255.255.0 serial restart-delay 0 ! ! router ospf 1 router-id 5.5.5.5 log-adjacency-changes area 45 stub network 10.45.1.5 0.0.0.0 area 45 !
 * R5 config:


 * R6 config:

! interface Ethernet0/0 ip address 10.100.1.6 255.255.255.0 ip ospf authentication message-digest ip ospf message-digest-key 1 md5 cisco half-duplex ! ! interface Serial1/0 ip address 10.67.1.6 255.255.255.0 serial restart-delay 0 ! router ospf 1 router-id 6.6.6.6 log-adjacency-changes area 67 virtual-link 7.7.7.7 network 10.67.1.6 0.0.0.0 area 67 network 10.100.1.6 0.0.0.0 area 0 !

! interface Serial1/0 ip address 10.67.1.7 255.255.255.0 serial restart-delay 0 ! interface Serial1/1 ip address 10.78.1.7 255.255.255.0 serial restart-delay 0 ! ! router ospf 1 router-id 7.7.7.7 log-adjacency-changes area 67 virtual-link 6.6.6.6 network 10.67.1.7 0.0.0.0 area 67 network 10.78.1.7 0.0.0.0 area 78 !
 * R7 config:

! interface Serial1/1 ip address 10.78.1.8 255.255.255.0 serial restart-delay 0 ! ! router ospf 1 router-id 8.8.8.8 log-adjacency-changes network 10.78.1.8 0.0.0.0 area 78 !
 * R8 config:

Command Line Outputs
=References=