OSPF
Introduction
- Attributes:
| Type | Link-State |
| Algorithm | Dijkstra |
| Metric | Cost (Bandwidth) |
| AD | 110 |
| Standard | RFC 2328, RFC 2740 |
| Protocols | IP |
| Transport | IP/89 |
| Authentication | Plaintext, MD5 |
| AllSPF Address | 224.0.0.5 |
| AllDR Address | 224.0.0.6 |
- OSPF Hello Packet has TTL=1. It cannot cross a hop.[1]
- Change AD in OSPF:
# router ospf 1 # distance 250 (useful in Protocol Migration) # distance 255 (invalid; do not use these routes)
- Metric Formula
This can be modifiable with cmd:
router ospf 1 auto-cost reference-bandwidth 1000
- All routers in an area have same Topology Table.
- ABR localizes updates to an Area.
- All Areas must connect to Area 0.
- Hello message is sent:
Every 10 sec on Broadcast/Point-to-point network. Every 30 sec on NBMA Network
- Dead Timer is 4 times Hello message
40 sec Broadcast/Point-to-point network. 120 sec NBMA Network
- On receiving a hello, If my Router-ID is already listed, reset Dead Timer, stop further processing, else start Neighbor relationship processing.
- EIGRP keeps a backup path in case primary path fails. OSPF does not keep backup path, so needs to re-run SPF again.
- Loopback interface is advertized as /32 address even if it is defined as /24, change this behavior:
int lo1 ip ospf network point-to-point
OSPF Databases and Tables
OSPF has 3 Databases used to create 3 Tables:
| Database | Table Name | Description |
|---|---|---|
| Adjacency Database | Neighbor Table |
|
| Link-State Database | Topology Table |
|
| Forwarding Database | Routing Table |
|
Packet types in OSPF
| Type | Packet Name | Description |
|---|---|---|
| 1 | Hello | Discovers Neighbors & builds adjacencies between them |
| 2 | Database Description(DBD) |
|
| 3 | Link-State request(LSR) | Requests specific link-state records from other router |
| 4 | LSU | Sends specifically requested link-state records(contain LSAs) |
| 5 | LSAck |
|
- Hello packet contains:
Router-ID Router Priority Neighbors Area ID Hello/Dead Timers DR/BDR IP Address Netmask Authentication Password
DR BDR
- 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, these routers listen only on 224.0.0.5 address.
- Neighbor Table shows:
Ethernet -> Full/DR, Full/BDR Serial -> Full/-
- DR preemption will not occur unless the current DR is reset
- DR/BDR is not Area/AS specific; There is a DR/BDR for every shared Segment.
- DROTHER is the name for other routers.
- Router will be in Full state with only DR & BDR; all other routers will be in 2-way state.
- Does not matter much which router becomes DR/BDR; except for Frame relay, where if Router with no access to full topology becomes DR, can cause serious issues.
- Election:
Default priority (0-255) is 1 Highest priority wins 0 cannot be elected In case of tie, Router with Highest Router ID wins election
- Set priority 0:
int eth0/0 ip ospf priority 0
Virtual Links
- Tunnel formed to join two areas across an intermediate Area.
- Not a permanent solution but a temporary fix in case no direct link exists, else it is a poor design.
- Depends on Router-ID. Needs to be hardcoded.
- We link ABR to ABR in a virtual Link.
- Forms a tunnel interface.
- Both end routers must share a common area
- At least one end must reside in area 0
- Cannot traverse stub areas
- Scenario
e0 e1
[R1]---------[R2}----------[R3]-----------[R4]
area0 area10 area 20
Here R3's e0 Interface is not having any issues e1 Interface is problematic as it lies in area 20; not connected to BB.
- Configuration:
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
Here:
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.
Verify:
show ip ospf virtual-link
Demand Circuit vs Flood Reduction
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 standardisation 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
Areas
- We divide into areas when SPF runs too often i.e. when networks become too large.
- ABR will have all information; Internal routers will have default routes.
- Standard areas
Contain LSAs of type 1, 2, 3, 4, and 5, and may contain an ASBR. The backbone is considered a standard area.
- Stub areas
Contain type 1, 2, and 3 LSAs. Block Type 5 LSAs. A default route is substituted for external routes. Config: # router ospf 1 # area 2 stub
- Totally stubby area (Cisco propietary)
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. Config: # router ospf 1 # area 2 stub no-summary
- Not-So-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. Config: # router ospf 1 # area 2 nssa
- Not-So-Stubby Totally-Stubby areas
# router ospf 1 # area 2 nssa no-summary
Backbone Area
- Why do we use Backbone Area?
Source: stackexchange.com
The reason for this star-like topology is that OSPF inter-area routing uses the distance-vector approach and a strict area hierarchy permits avoidance of the "counting to infinity" problem. OSPF prevents inter-area routing loops by implementing a split-horizon mechanism, allowing ABRs to inject into the backbone only Summary-LSAs derived from the intra-area routes, and limiting ABRs' SPF calculation to consider only Summary-LSAs in the backbone area's link-state database.
- Simple example of OSPF's distance-vector behavior:
<-- Area 5 --><-- Area 0 --><-------------- Area 4 ----------->
R5-----------R1-----------R2------------R3---------------------R4
Cost 3 Cost 5 Cost 7 Cost 12
LSA--> LSA-->
Type3 LSA Type3 LSA
{From R1} {From R2}
R5 cost is 3 R5 cost is 8
- Consider what happens to a /32 Loopback route for R5:
R5 sends a Type1 LSA containing the /32 Loopback R1 (Area 5 ABR), is connected to Area 0; it translates the Type1 LSA into a Type3 LSA with a cost of 3. R2 (Area 4 ABR) receives R1's Type3 LSA (metric 3) and changes the metric to R5's Loopback, based on R2's cost to R1. Now R2's Type3 LSA for R5 has a cost of 8. This is the distance-vector behavior.
- Requiring all non-backbone routes to go through the backbone is a loop-prevention mechanism.
- Connecting non-backbone OSPF areas at an ABR:
If 2 areas aren't connected through area 0 (discontiguous), how does OSPF behaving as a link state protocol increase the possibility of routing loops? As we saw above, OSPF uses distance-vector behavior to send routes through the Area 0 backbone. Distance-vector protocols have well-known limits, such as the count-to-infinity problem. OSPF would be vulnerable to the same issues, if we didn't have boundaries on its behavior.
- Can we use OSPF without area 0?
There is only one way to use OSPF without an Area 0, and that is to use OSPF with a single area. If you only have one OSPF area, you can number it any way you like, but if you have even two areas, you must have an Area 0.
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
- Type 2 - Network LSAs
Generated by the DR on a multi access segment Represents the pseudonode(DR) for a multiaccess link. Provides similar information to an LSA type 1 for the multi access segment and subnet which it belongs
- Type 3 - Network Summary LSA / ABR Summary Route
Generated by ABRs Contain the subnets & costs Omit the topological data from all subnets in one area and sent to another area via the ABR
- Type 4 - ASBR summary LSA / ASBR Location
Same as summary LSA except the destination advertised by ABR is ASBR. ABR which is in the same area as the ASBR will originate the Type 4 LSA. The (assumed) presence of an ASBR is communicated from its immediate ABR via a type 1 LSA with the E flag set(which does not constitute a type 4 LSA) sent into backbone area 0. The only type 4 LSA generated in this example is sent from router C into area 2,
- Type 5 - AS external LSA / ASBR Summary Route
Generated by ASBRs Flooded throughout the AS to advertise a route external to OSPF
- Type 7 - NSSA External LSA
Generated by the ASBR in an NSSA area Used in stub areas in place of a type 5 LSA. Converted into a type 5 LSA by the ABR when leaving the area
- LSA as per Areas[2]:-
Adjacency
- OSPF neighbor requirements:
- Same area
- Same authentication config
- Same subnet
- Same Hello/Dead interval
- Matching stub flags
- Difference between Adjacency & Neighbor:
- Only Adjacent Routers can sync Link State DB
- Point-to-Point Links: If Neighbors, Adjcency automatically established
- Broadcast Link: Adjacency established with DR & BDR only, rest are in 2-way state[3]
- Point-to-Multipoint:_________
- Neighbor means Physical Connectivity(Direct)
- Adjacency means Database Syncronization
- Neighbor Requirements:
- Hello exchange => Subnet Mask, Subnet Number, Hello/Dead Interval, Area ID, Authentication must match.
- Exchange hellos but not LSAs(2-Way State).
- Adjacency Requirements:
- Exchange LSAs
- Both routers are in Stable(Full) State.
- 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[4]
| State | Details |
|---|---|
| 1. Down |
|
| 2. Attempt |
|
| 3. Init |
|
| 4. 2-Way |
|
| 5. ExStart |
|
| 6. Exchange |
|
| 7. Loading |
|
| 8. Full |
|
Routing
Summarization
- Only ABR & ASBR can do Summarization in OSPF. In EIGRP Summarization can be done anywhere.
- Summarization at ABR:
area 20 range 10.20.0.0 255.255.252.0
- Summarization at ASBR:
summary-address 172.16.0.0 255.255.252.0
- Summarization:
10.10.0.0/24 => 10.10.0.0 - 10.10.3.255 10.10.1.0/24 10.10.2.0/24 10.10.3.0/24
- 1st method
3rd octet is:
128 64 32 16 8 4 2 1 1 1 1 1 1 1 0 0 => 6
10.10.0.0/24 8+8+6+0 = /22
- 2nd Method
3rd octet is:
0 0 0 0 0 0|0 0 0 0 0 0 0 0|0 1 0 0 0 0 0 0|1 0 0 0 0 0 0 0|1 1
6 bits remain same 8+8+6+0 = /22
So best summary route will be:
10.10.0.0/22
Route Types
- OSPF external type 1 - E1
- Metric Increments as they traverse through network.
- Used when multiple exit paths exist
[Ext network]---------[R1]-----------[R2]
200 10
Cost for E1 route in R2 will be 200 + 10 = 210
- OSPF external type 2 - E2 (Default)
- Cost does not increment in Network
- Used only when one Exit point exists.
- Bit easy for processor.
[Ext network]---------[R1]-----------[R2]
200 10
Cost for E2 route in R2 will be 200
- OSPF NSSA external type 1 - N1
 This section is under construction.
|
- OSPF NSSA external type 2 - N2
| This section is under construction.
|
- OSPF inter area - IA
| This section is under construction.
|
- OIA
| This section is under construction.
|
- Route Selection Hierarchy - E1, E2, N1, N2
| This section is under construction.
|
N1 N2 E1 E2
- Type 5 is E and Type 7 is N.
- An external route will be tagged as a Type 5 LSA (E route).
- This LSA is circulated throughout the OSPF domain except for Stub, Totally Stubby and NSSA.
- Stub areas are not allowed to have external routes there should be no ASBR in a Stub area, else configure it as NSSA.
- A route redistributed inside an NSSA area is a Type 7 LSA or N route.
- This LSA is circulated only within the NSSA area.
- E1 or E2 or N1 or N2 type routes are based upon cost of the route.
- E2 or N2 routes tell OSPF routers to set the metric as the metric at the point of redistribution.(At the ASBR)
- E1 or N1 routes tell OSPF routers to add the internal costs to reach the ASBR to the cost set at the point of redistrbution (At the ASBR)
1. N1 & E1 are preferred over N2 & E2 for the same route 2. When N1 & E1 have the same route to the destination, the one that have lower cost / Metric will win and get into the route table 3. If both N1 & E1 have the same cost, P-bit in N1 will be used to break the tide. 4. If P-bit is 0 (Then it would become E1) then we will have 2 E1 routes install into the routing table. (otherwise if maximum-path = 1, LSA with Higher Router-ID will get installed
Withdraw OSPF Routes
- Router LSA:
When a link fails, the connected OSPF routers send an updated LSA which omits the now shutdown link from it’s list of connected links. This new LSA has an incremented sequence number which replaces the old LSA in the LSDB of all routers in that area. OSPF will kick off a new SFP run, calculate a new topology and remove any routes associated with that link.
- Summary LSA
If no summarisation done on ABR, it will create a Type-3 Summary LSA for every Type-1 stub-network prefix. The ABR senda a new Summary LSA with updated sequence number flagged as unreachable by setting it’s 24-bit metric field to all Ones called LSInfinity with decimal value of 16777215. The LSA requests that it be flushed from the receiver’s LSDB by setting it’s LSAge to MaxAge (3600 seconds).
- External LSA
When the link goes down the ASBR will send an updated Type-5 LSA for the prefix with an updated sequence number with link cost of LSIninity and LSAge to MaxAge. Type-5 prefix withdrawal is simpler as Type-5 LSAs have domain-wide flooding scope. As such the poisoned LSA will immediately be flooded to all routers in the OSPF domain, regarded as unreachable and flushed from the receivers LSDB and routing tables.
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).
OSPF Notes 2
- OSPF Packet type -Hello ,DBD ,LSR ,LSU ,LSA
- Each interface participate in OSPF send hello at 224.0.0.5
- Two router to form neighborship-same area ,samehello and dead interval,same subnetmask ,authentication must same .
- OSPF States - Down, Init, Two way, Exstart (DR, BDR selection), Exchange (DBD contains entry of link or net type having following info link type,adv router,seq number,costoflink),if router donot have update info for link type it send LSR (loading state), Neirouter send updated LSU again LSR router adds new entry in lSDB once all the routers have identical LSDB -routers are in full state .
- To send request to DR and BDR - 224.0.0.6
- For broadcast n/w type each ospf speaking router will be form full adjancey b/w DR, BDR and two way state b/w DR other routers.
- sh ip ospf database summary ( prefix ) will give information for type 3 inter area routes learned via ABR.
- Type 3 LSA called summary LSA doesnot mean network prefixes are summarised while propagated by ABR means topolgy information is summarised.
- EACH LSA in LSDB contains seq number, EACH LSA is flooded after 30 minutes, each time LSA is flooded it is incremnted by one ) - 195
- Point to point - T1,E1,neighbors are discovered automatically,hellos send at M.A 224.0.0.5, NO DR BDR election as there are only two routers.
- Multiaccess - DR, BDR election DR failes BDR becomes DR and new BDR is elected.
- If new router added with highest priorty it will not preemt existing DR and BDR election, if DR or BDR goes down then only selection starts.
- DR/BDR-ip ospf priority =0 for DR other
- STUB Area- All the routers in Area must agree on stub flag, does not allow type 5 and type 4 LSA and ABR generates default route in stub area to reach external destination.
to cofigure stub area - area x stub
- Tottaly Stub area - removes type 3,4,5 LSA and ABR genrates inter area default route, total stubby area configured on ABR of the area.
- To configure totally stubby - on ABR area x stub no summary and other routers need to configued wth area x stub command.
- NSSA area - was desgined to keep stub feature attribute and also allowed external routes, ASBR will genrate type 7 LSA in NSSA and se the P bit 1 and ABR will translate type 7 to type 5 propagate in ospf domain and all routers should agree on NSSA area. ABR does not genrate default route automatically. So in case if we other external AS connected to other areas NSSA area will not have information for that external routes, so in that case we need to genrate defaul route mannually.
- NOSo-total stubby area - remove type 3 ,4 ,5 lsa , genrates type 7 LSA and ABR genrates default route. Note it is not necessary for ABR to be part of total stubby NSSA it can still run NSSA for that area in ospf process.
- Order of preference of OSPF routes- O,OIA,E1,E2,N1,N2.
- When ABR does LSA translation from Type 7 to Type 5, if we look for external network in an area using sh ip os database external. There are field, Advertising router and Forwading address, Advertising address will be address of ABR which is doing the translation and Forwading address is address of ASBR.
- Also if the forwading address field is 0.0.0.0, then traffic will be forwading to who is orginating the route.
- If we have mutliple ABR in NSSA the ABR with highest router id will genrate type 5 LSA. This does not mean all the traffic will follow the ABR with highest router id because the forwading address field contains the information for the ASBR to reach external destination.
- In case if we want to change the forwading address on ABR while tranlating from type 7 to type 5 we can use the command
area i nssa no summary translate type 7 suppress forwading address.
Note - in the LSA lookup if the forwading address is 0.0.0.0 so the router which is advertising the lsa and is announcing it self to use himself to reach destination.
- E1 and E2 routes - E1 routes external cost is added to cost of link packet traverse, if we have multiple ASBR then we should use marked external routes as type E1
- If we have muliple ASBR, then default metric to reach external network would be same propagated by both of them, in that case each ospf speaking router will use forward metric to reach ASBR as best path.In case the forward metric is same then decision will be based on router id of ASBR.
- That can be verified by:
sh ip ospf database external XXXX.
- E2 -External cost only, if we have single ASBR
Note- ABR has information for all the connected area's so when genrating the type 3 SLA topogy information is summarised and propagated from one area to other area.
- Loop prevnetion mechanism in OSPF-Its ABR only that accespts and process the type 3 LSA if it is from backbone area.
area X filter-list prefix {in|out}
- Good news here - this command applies after all summarization has been done and filters the routing information from being used for type-3 LSA generation. It applies to all three type of prefixes: intra-area routes, inter-area routes, and summaries generated as a result of the area X range command. All information is being learned from the router's RIB. used to filter specific prefix in Type 3 LSA.
- LSA Type 5 filerting -This LSA is originated by an ASBR (router redistributing external routes) and flooded through the whole OSPF autonomous system, Important - You may filter the redistributed routes by using the command distribute - list out configured under the protocol, which is the source of redistribution or simply applying filtering with your redistribution.
- The key thing you should remember is that non-local route filtering for OSPF is only available at ABRs and ASBRs
- Distribute list out on ABR and ASBR will filter the type 5 LSA while propagting
- We can verify using:
sh ip ospf database external x.x.x.x
- Distribute list in - Will filter the information from routing table but lSA will still be propagating to neighbor routers.
- If we have NSSA area we want to filer type 5 SLA on ABR we can filter the forwading address using ditribute list on ABR. (As the forwading address is copied from type 7 SLA when ABR regenrates the type 5 SLA out of it.
- OSPF Network Types
1. Point to point - Supports broadcast like T1, E1, there are only two routers no DR/BDR election ,hello and dead are 10/40. 2. Brodacast - Like ethernet, broadacst capabilty, There is DR and BDR election, 10 and 40. 3. Point to multipoint brodacast - have broadcast capabilty, NO DR and BDr election , hello/dead are 40 /130, In case of hub and spoke topology hub will form adjancy.
with the spokes ,other spokes will not form adjancy as there is not direct layer connection so when hub receive the update from spoke it changes its next hop self while propagating the updates.
4. Point to multipoint non brodcast - No broadcast capabilty, hello will be send as unicast, will not be send if neighbors are not defined manually. As there is no brodcast capabilty hellos are send as unicast and there is no DR /BDR election. hello/dead are 40 /130, Special next hope processing. Non-Broadcast is the default network type on multipoint frame-relay interface, eg a main interface. 5. Non broadcast n/w - Default network type is nonbroadcast for frame-relay network , there is no broadcast capabilty , hello are send as unicast ,neibors need to define mannualy .hello /dead 30-40 ,DR and BDR election, NBMAN-(Non broadcast)-Nei needs to define mannualy ,there is slection of DR and BDR ,full mesh or partail mesh,IN NBMAN if there is DR ,BDR selction all routers should be fully meshed or DR BDR can be staticly configured on router that should have full adjancies to all routers. Make sure the for non-broadcastn/w make sure hub is chossen as DR and need to define nei mannaulay to send ospf updates as unicast.
Note - Broadcast and non broadcast n/w , DR on receiveing the LSA's didnot change the next hop while propagating the LSA to other DR-other routers so in case of broadcast segment its fine while for non broadcaset frame relay network we need to mannualy define the layer 3 to layer 2 resoltuion to reach that neibour. While in case of point-point, HDLC there is only one device at other end so layer 3 to layer 2 mapping is not required.
6. In OSPF loopbacks are advertised as stub host and network type loopback.if the mask of loopback is /24 and we want to advertise as /24 to ospf domain we need to change the network type
- By adjusting the hello/dead timers you can make non-compatible OSPF network types appear as neighbors via the - show ip ospf neighbor - but they won't become adjacent with each other. OSPF network types that use a DR (broadcast and non-broadcast) can neighbor with each other and function properly. Likewise OSPF network types (point-to-point and point-to-multipoint) that do not use a DR can neighbor with each other and function properly. But if you mix DR types with non-DR types they will not function properly (i.e. not fully adjacent). You should see in the OSPF database Adv Router is not-reachable messages when you've mixed DR and non-DR types.
- Here is what will work:
Broadcast to Broadcast Non-Broadcast to Non-Broadcast Point-to-Point to Point-to-Point Point-to-Multipoint to Point-to-Multipoint Broadcast to Non-Broadcast (adjust hello/dead timers) Point-to-Point to Point-to-Multipoint (adjust hello/dead timers)
- Command lines:
1. sh ip os inter brief 2. sh ip route ospf 3. sh ip os boarder routers 4. sh ip os da summary x.x.x - type 3 5. sh ip os da external x.x.x.x-type 5 6. sh ip os data router .x..x.x.x- type 1
- Sumarisation can occur on ABR and ASBR
- ABR uses area range command
- when ABR /ASBR does sumarization it genrates null route for the summary , in case spefic prefix went unreachable for some reason and ABR has received traffic for that preifx it wll drop the traffic , if we want to avoid it use default route to forward the traffic we can use command ( no discard route internal / external) to drop the null route from routing table .
ASBR- Summary address x.x.x.x mask
- RFC 2328 - to learn the ospf
- Virtual links
- All areas in an Open Shortest Path First (OSPF) autonomous system must be physically connected to the backbone area (Area 0). In some cases, where this is not possible, you can use a virtual link to connect to the backbone through a non-backbone area. You can also use virtual links to connect two parts of a partitioned backbone through a non-backbone area. The area through which you configure the virtual link, known as a transit area, must have full routing information. The transit area cannot be a stub area.
- The transit area cannot be a stub area, because routers in the stub area do not have routes for external destinations. Because data is sent natively, if a packet destined for an external destination is sent into a stub area which is also a transit area, then the packet is not routed correctly. The routers in the stub area do not have routes for specific external destinations.
- We can also use GRE link between nonbackbone area and backbone area ,run area 0 over tunneled interface but there is GRE overhead. In case of virtul only OSPF packets are send as tunneled packet and data traffic is send as it is normal area connected to backbone area.
LAB
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.[5]
- If OSPF is stuck in ExStart State, MTU mismatch may be the cause, as it is requirement to successfully pass DBD Packets. Matching MTU is not a Adjacency Requirement, but is required to successfully pass Database Descriptor Packets
- In OSPF, MTU Mismatch causes neighbors swinging between ExStart state to Down state
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
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:
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
- R2:
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
- R3:
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
- R4:
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
- R5:
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
- Routing Tables
- R1:
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
- R2:
172.16.0.0/22 is subnetted, 1 subnets
O E2 172.16.0.0 [110/200] via 172.30.0.1, 00:53:15, 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
- R3:
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
- R4:
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
- R5:
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
- Topology Tables
- R1:
R1#sh ip ospf database
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:
R2#sh ip ospf database
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:
R3#sh ip ospf database
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:
R4#sh ip ospf database
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:
R5#sh ip ospf database
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:
R1#show ip ospf neighbor 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:
R2#show ip ospf neighbor 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:
R3#show ip ospf neighbor 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:
R4#show ip ospf neighbor Neighbor ID Pri State Dead Time Address Interface 3.3.3.3 0 FULL/ - 00:00:36 172.30.20.3 Serial1/0
- R5:
R5#show ip ospf neighbor 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:
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)
- R2:
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)
- R3:
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)
- R4:
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)
- R5:
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
OSPF Areas Lab
GNS3 Project: File:Cbt nuggets ospf areas lab.zip
Objectives
- Configure basic OSPF:
Advertize all networks attached. On R1 redistribute static routes to inject external routes. These routes should be marked as type E1.
- 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).
These routes should reach external network using default route which cannot be statically configured.
- Routers in Area 23 should not receive Type 3,4,5 LSAs.
They should reach external network using a default route with initial OSPF cost of 100.
- You should be able to ping every router in OSPF Routing Table (configure virtual link for area 78)
Configurations
- R1 config
! 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 !
- R2 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 !
- R3 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 !
- R4 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 !
- R5 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 !
- 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 !
- R7 config
! 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 !
- R8 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 !
Command Line Outputs
References
{{#widget:DISQUS |id=networkm |uniqid=OSPF |url=https://aman.awiki.org/wiki/OSPF }}