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Configuring OSPF – Part 2 of 2. CIS 185 CCNP ROUTE Rick Graziani Cabrillo College [email protected] Last Updated: Fall 2010. OSPF Part 2. Review of Areas NSSA (Not-So-Stubby-Areas) Multiple ABRs Virtual Links Route Summarization Default Routes Authentication OSPF over Frame Relay - PowerPoint PPT Presentation
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Configuring OSPF – Part 2 of 2
CIS 185 CCNP ROUTE
Rick Graziani
Cabrillo College
Last Updated: Fall 2010
2
OSPF Part 2
Review of Areas NSSA (Not-So-Stubby-Areas) Multiple ABRs Virtual Links Route Summarization Default Routes Authentication OSPF over Frame Relay LSDB Overload Protection Passive Interface
3
Quick Review
4
LSA 1s – Router LSAs
show ip ospf database – Router Link States (LSA 1’s) Should display all the RouterIDs of routers in that area,
including its own. show ip route – “O” routes
Routes within that area
LSA 1’sLSA 1’s
LSA 1’s
5
LSA 2s – Network LSAs
show ip ospf database – Net Link States (LSA 2’s) Net Link States (LSA2’s) should display the RouterIDs of the
DRs on all multi-access networks in the area and their IP addresses.
show ip route – “O” routes Routes within that area
LSA 2’s
LSA 2’s
6
LSA 3 – Summary LSAs
LSA 3’sLSA 3’s
LSA 1’s
show ip ospf database – Summary Net Link States (LSA 3’s) Link ID = IP network addresses of networks in other areas ADV Router = ABR Router ID sending the LSA-3
show ip route – “IA” (Inter-Area Routes) Routes in other areas
7
LSA 4 – ASBR Summary Link States
show ip ospf database – Summary Net Link States (LSA 3’s) Link ID = IP network addresses of networks in other areas ADV Router = ABR Router ID sending the LSA-3
show ip route – “IA” (Inter-Area Routes) Routes in other areas
LSA 1’s ebit
LSA 4
LSA 4
8
“Redistribute” command creates an ASBR router. Originated by the ASBR. Describes destination networks external to the OSPF Routing Domain Flooded throughout the OSPF AS except to stub and totally stubby areas
R2 (ASBR)
router ospf 1
redistribute static
ip route 57.0.0.0 255.0.0.0 ser 0/3
LSA 5’sLSA 5
LSA 5
LSA 5 – External Link States
9
Stub Area
LSA 4 LSA 4 BlockedLSA 5 BlockedLSA 5
LSA 3 LSA 3
Default route to ABR injected
• Sent by ABR: LSA 3s (Inter-Area routes)• Blocked:
• LSA 4s (reachability to ASBR) • LSA 5s (External routes)
• The ABR injects a default route into the stub area, pointing to the ABR. • This does not mean the ABR has a default route of its own.
• Changes in External routes no longer affect Stub Area routing tables.
We only see routes in our area, other areas, and a default route.No external routes.
Stub Area LSA 1s still sent within each area.
10
Stub Area
LSA 4 LSA 4 BlockedLSA 5 BlockedLSA 5
LSA 3 LSA 3
Default route to ABR injected
• Blocked: • LSA 3s (Inter-Area routes)• LSA 4s (reachability to ASBR) • LSA 5s (External routes)
• The ABR injects a default route into the stub area, pointing to the ABR. • This does not mean the ABR has a default route of its own.
• Changes in other areas and external routes no longer affect Stub Area routing tables.
We only see routes in our area, other areas, and a default route.No external routes.
Totally Stubby Area
BlockedBlockedBlocked
Default route to ABR injected
We only see routes in our area and a default route.
No inter-area or external routes.
Totally Stubby Area LSA 1s still sent within each area.
NSSA (Not-So-Stubby-Areas)
12
NSSA (Not So Stubby Area)
NSSAArea 2
Backbone AreaArea 0
ASBR
ABR(Possible
ASBR)
RIP
RTARTB
RTC
RTD
RTE
RTF
RTG
RTH
13
Relatively new, standards based OSPF enhancement, RFC 1587. NSSA allows an area to remain a stub area, but carry external routing
information (Type 7 LSAs) from its stubby end back towards the OSPF backbone.
ASBR in NSSA injects external routing information into the backbone and the NSSA area, but rejects external routing information coming from the ABR.
The ABR does not inject a default route into the NSSA. This is true for a NSSA Stub, but a default route is injected for a NSSA
Totally Stubby area. Note: RFC 1587, “A default route must not be injected into the NSSA as a
summary (type-3) LSA as in the stub area case.” What??? Following scenario is only example of how NSSA works. For the purposes of
learning about NSSAs, don’t get hung up on the why’s and what if’s.
NSSA (Not So Stubby Area)
14
NSSAArea 2
Backbone AreaArea 0
ASBR
ABR(Possible
ASBR)
RIP
RTARTB
RTC
RTD
RTE
RTF
RTG
RTH
Default route via RTG
NSSA Stub Area Area 2 would like to be a stub network. RTH only supports RIP, so RTG will run RIP and redistribute those routes in OSPF. What type of OSPF router does this make RTG?
Unfortunately, this makes the area 2 router, RTG, an ASBR. Why is this a problem?
Stub areas cannot contain an ASBR. In this example RTH does not need to learn routes from OSPF, a default route to RTG is
all it needs. But all OSPF routers must know about the networks attached to the RIP router, RTH. to
route packets to it.
15
NSSA Stub Area (cont.) NSSA allow external routes to be advertised into the OSPF AS while retaining the
characteristics of a stub area to the rest of the OSPF AS. ASBR RTG will originate Type-7 LSAs to advertise the external destinations. These LSA 7s are flooded through the NSSA but are blocked by the NSSA ABR. The NSSA ABR translates LSA 7s into LSA 5s and flood other areas.
NSSAArea 2
Backbone AreaArea 0
ASBR
ABR(Possible
ASBR)
RIP
RTARTB
RTC
RTD
RTE
RTF
RTG
RTH
Default route via RTG
LSA 7LSA 7
LSA 7
LSA 7
LSA 7
LSA 7LSA 5
LSA 7s Blocked
16
Type 7 LSA NSSA External Link Entry Originated by an ASBR connected to an NSSA. Flooded throughout NSSAs and translated into LSA Type 5 messages by
ABRs. Routes learned via Type-7 LSAs are denoted by either a default “N1” or an
“N2” in the routing table. (Relative to E1 and E2).
NSSAArea 2
Backbone AreaArea 0
ASBR
ABR(Possible
ASBR)
RIP
RTARTB
RTC
RTD
RTE
RTF
RTG
RTH
Default route via RTG
LSA 7LSA 7
LSA 7
LSA 7
LSA 7
LSA 7LSA 5
LSA 7s Blocked
17
Configuring NSSA Stub AreaConfigured for all routers in Area 2:
router ospf 1
network 172.16.2.0 0.0.0.255 area 2
area 2 nssa
NSSAArea 2
Backbone AreaArea 0
ASBR
ABR(Possible
ASBR)
RIP
RTARTB
RTC
RTD
RTE
RTF
RTG
RTH
Default route via RTG
LSA 7LSA 7
LSA 7
LSA 7
LSA 7
LSA 7LSA 5
LSA 7s Blocked
NSSA Generic
18
NSSA Stub and NSSA Totally Stubby
There are two flavors in NSSA:
Stub
Totally Stubby
Area 2 routers may or may not receive Inter-area routes from RTA, depending upon NSSA configuration
NSSA areas have take on the same characteristics as stub and totally stubby areas, along with the characteristics of NSSA areas.
NSSA (Not So Stubby Area)
19
NSSA –Stub
NSSA stub areas:
NSSAs that block type 4 and 5, but allow type 3.
To make a stub area into an NSSA, use the following command under the OSPF configuration.
This command must be configured on all routers in area 2.
router ospf 1 area 2 nssa
20
NSSAArea 2
Backbone AreaArea 0
ASBR
ABR(Possible
ASBR)
RIP
RTARTB
RTC
RTD
RTE
RTF
RTG
RTH
LSA 7LSA 7
LSA 7
LSA 7
LSA 7
LSA 7LSA 5
LSA 7s Blocked
NSSA Stub Areas
0.0.0.0/0
LSA 3s
XRTH routes:E1/E2
RTH routes:N1/N2LSA 4s & LSA 5s
X
Default route via RTG
Internal NSSA routers have: All area 2 routes External routes from RTH (N1/N2) Inter-area routes from RTB
Area 0 routers have from area 2: All area 2 routes External routes from RTH (E1/E2)
21
Area 2 routers:
router ospf 1
network 172.16.2.0 0.0.0.255 area 2
area 2 nssa
NSSAArea 2
Backbone AreaArea 0
ASBR
ABR(Possible
ASBR)
RIP
RTARTB
RTC
RTD
RTE
RTF
RTG
RTH
Default route via RTG
LSA 7LSA 7
LSA 7
LSA 7
LSA 7
LSA 7LSA 5
LSA 7s Blocked
NSSA Stub Areas
0.0.0.0/0
LSA 3s
XRTH routes:E1/E2
RTH routes:N1/N2LSA 4s & LSA 5s
X
22
NSSA Totally Stubby Area
NSSA totally stub areas: Allow only summary default routes and filters everything else.
To configure an NSSA totally stub area, use the following command under the OSPF configuration on the NSSA ABR:
router ospf 1 area 2 nssa no-summary
Configure this command on NSSA ABRs only.
All other routers in area 2 (internal area 2 routers):router ospf 1 area 2 nssa
After defining the NSSA totally stub area, area 2 has the following characteristics (in addition to the above NSSA characteristics):
No type 3 (except default), 4 or 5 LSAs are allowed in area 2.
A default route is injected into the NSSA totally stub area as a type 3 summary LSA by the ABR.
NSSA – Totally Stubby
23
NSSAArea 2
Backbone AreaArea 0
ASBR
ABR(Possible
ASBR)
RIP
RTARTB
RTC
RTD
RTE
RTF
RTG
RTH
Default route via RTG
LSA 7LSA 7
LSA 7
LSA 7
LSA 7
LSA 7LSA 5
LSA 7s Blocked
NSSA Totally Stubby Areas
0.0.0.0/0 (LSA 3)
LSA 3sX
RTH routes:E1/E2
RTH routes: N1/N2LSA 4s & LSA 5s
X
RTB (ABR):
router ospf 1
network 172.16.1.0 0.0.0.255 area 0
network 172.16.2.0 0.0.0.255 area 2 ...
area 2 nssa no-summary
Area 2 routers:
router ospf 1
network 172.16.2.0 0.0.0.255 area 2
area 2 nssa
24
NSSA Totally Stubby Areas
Internal NSSA routers have: All area 2 routes External routes from RTH (N1/N2) Default route from RTB
Area 0 routers have from area 2: All area 2 routes External routes from RTH (E1/E2)
NSSAArea 2
Backbone AreaArea 0
ASBR
ABR(Possible
ASBR)
RIP
RTARTB
RTC
RTD
RTE
RTF
RTG
RTH
Default route via RTG
LSA 7LSA 7
LSA 7
LSA 7
LSA 7
LSA 7LSA 5
LSA 7s Blocked
0.0.0.0/0 (LSA 3)
LSA 3sX
RTH routes:E1/E2
RTH routes: N1/N2LSA 4s & LSA 5s
X
Multiple ABRs
26
Multiple ABRs – If you want to experiment…
Used with “normal” areas. Routers choose best path to other areas. Can be used with Stub and Totally Stubby but inefficient routing
may occur due to multiple default routes injected by ABR.
OSPF-MultiArea-Advanced.pkt
27
Multiple ABRs
Intra-area routes, OSPF uses pure Link State logic. All routers inside the area have an identical copy of the LSDB for
that area.
ABR1
ABR2
RTA
RTB
RTC
Network XLSA 1’s
LSDB
SPF
Distribute List
Routing Table
Area 51 Area 0
28
Multiple ABRs
Best route to reach each ABR is an intra-area SPF calculation. Interarea routes (LSA 3s) use Distance Vector logic. ABR advertises Type 3 Summary LSAs (metric but not topology
information). Total cost to Network X = Cost to ABR + ABR’s cost to Network X. RTB selects best route to Network X via ABR1 and/or ABR2.
ABR1
ABR2
RTA
RTB
RTC
Network X
Link State Logic
LSDB
SPF
Distribute List
Routing Table
To ABR
Area 51 Area 0
LSA 3’s
Distance Vector Logic
LSA 3’s
29
Multiple ABRs
Total cost to Network X = Cost to ABR + ABR’s cost to Network X. RTB selects best route to Network X via ABR1 and/or ABR2.
With stub and totally stubby areas this may not be the most optimum route!
ABR1
ABR2
RTA
RTB
RTC
Network X
Area 51 Area 0
LSA 3’s
Normal Area
My cost to network X
is 10
My cost to network X
is 200
The best path to Network X is via
ABR1 with a total cost of 20.
Cost = 20
Cost = 205
30
Multiple ABRs – Stub Networks
Stub and totally stubby area ABRs inject a default route into the area. Stub ABRs block LSA 4’s and 5’s (external networks) Totally Stubby ABRs block LSA 3’s (interarea networks), 4’s and
5’s (external networks) In both cases internal routers can only determine the best route to
an ABR, which may not be the best route to the destination network.
ABR1
ABR2
RTA
RTB
RTC
Network X
Area 51 Area 0
LSA 3’s
Default Route
Totally Stubby Area
My cost to network X
is 10
My cost to network X
is 200
ABR2 is “closer” a lesser metric, so I will use ABR2 for all routes outside my area even if its
not the most optimum path.
Cost = 10
Cost = 5
Virtual Links
32
Virtual Links
33
All areas in an OSPF autonomous system must be physically connected to the backbone area (area 0).
This is not always possible, you can use a virtual link to connect to the backbone through a non-backbone area.
Transit area - The area through which you configure the virtual link and must have full routing information.
Must be configured between two ABRs.
The transit area cannot be a stub area.
Virtual Links
34
A virtual link has the following two requirements: It must be established between two routers that share a common area
and are both ABRs. One of these two routers must be connected to the backbone.
Doyle, “should be used only as a temporary fix to an unavoidable topology problem.”
Virtual Links
35
Virtual Links
Routers do not have to be directly connected.
36
The command to configure a virtual link is as follows:
area <area-id> virtual-link <remote-router-id>
RTA(config)#router ospf 1
RTA(config-router)#network 192.168.0.0 0.0.0.255 area 51
RTA(config-router)#network 192.168.1.0 0.0.0.255 area 3
RTA(config-router)#area 3 virtual-link 10.0.0.1
...
RTB(config)#router ospf 1
RTB(config-router)#network 192.168.1.0 0.0.0.255 area 3
RTB(config-router)#network 192.168.2.0 0.0.0.255 area 0
RTB(config-router)#area 3 virtual-link 10.0.0.2
37
OSPF allows for linking discontinuous parts of the backbone using a virtual link.
OSPF messages between virtual link routers sent as unicast.
Virtual Links
router ospf 1
area 1 virtual-link 4.4.4.4
interface loopback 1
ip address 1.1.1.1 255.255.255.0
router ospf 4
area 1 virtual-link 1.1.1.1
interface loopback 1
ip address 4.4.4.4 255.255.255.0
C1
C2
38
C1# show ip ospf virtual-links
Virtual Link OSPF_VL0 to router 4.4.4.4 is up
Run as demand circuit
DoNotAge LSA allowed.
Transit area 1, via interface FastEthernet0/1, Cost of using 3
Transmit Delay is 1 sec, State POINT_TO_POINT,
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Hello due in 00:00:02
Adjacency State FULL (Hello suppressed)
Routers use of the Do Not Age (DNA) bit, so periodic reflooding (every 30 minutes) will not occur over this virtual link.
OSPF Note: Router IDs do not have to be advertised and therefore may not be pingable.
39
C1# show ip ospf neighbor
Neighbor ID Pri State Dead Time Address Interface4.4.4.4 0 FULL/ - - 10.24.1.1 OSPF_VL02.2.2.2 1 FULL/DR 00:00:35 10.21.1.2 FastEthernet0/1
C1# show ip ospf neighbor detail 4.4.4.4 Neighbor 4.4.4.4, interface address 10.24.1.1 In the area 0 via interface OSPF_VL0
"In the area 0 via interface OSPF VL0" – confirming that the neighbor relationship does indeed exist in area 0.
Route Summarization
41
Route Summarization
Inter-Area Route Summarization - Area Range By default ABRs do not summarize routes between areas.
In OSPF, an ABR will advertise networks in one area into another area.
If at least one component subnet exists (subnets that sit inside the range), then the ABR advertises the summary route as a Type 3 LSA.
If no component subnets exist, the ABR does not advertise the summary. The ABR assigns a metric for the summary route's Type 3 LSA, by default, to
match the best (lowest) metric amongst all component subnets.
The area range command can also explicitly set the cost of the summary.
On the ABR (Summarizes routes before injecting them into different area)Router(config-router)# area area-id range network-
address subnet-mask
area-id - Identifier of the area about which routes are to be summarized. (From area)
42
Summarize Area 1 172.17.0.0 routes on Area 1 ABRs .
172.17.1.0/24 172.17.2.0/24 172.17.3.0/24 172.17.4.0/24 172.17.5.0/24 172.17.6.0/24 172.17.7.0/24
43
172.17. 0000 0001 . 0000 0000
172.17. 0000 0010 . 0000 0000
172.17. 0000 0011 . 0000 0000
172.17. 0000 0100 . 0000 0000
172.17. 0000 0101 . 0000 0000
172.17. 0000 0110 . 0000 0000
172.17. 0000 0111 . 0000 0000
172.17.1.0/24 172.17.2.0/24 172.17.3.0/24 172.17.4.0/24 172.17.5.0/24 172.17.6.0/24 172.17.7.0/24
44
172.17.0.0 255.255.248.0 (/21)172.17. 0000 0001 . 0000 0000
172.17. 0000 0010 . 0000 0000
172.17. 0000 0011 . 0000 0000
172.17. 0000 0100 . 0000 0000
172.17. 0000 0101 . 0000 0000
172.17. 0000 0110 . 0000 0000
172.17. 0000 0111 . 0000 0000
172.17.1.0/24 172.17.2.0/24 172.17.3.0/24 172.17.4.0/24 172.17.5.0/24 172.17.6.0/24 172.17.7.0/24
45
router ospf 1
area 1 range 172.17.0.0 255.255.248.0
172.17.1.0/24 172.17.2.0/24 172.17.3.0/24 172.17.4.0/24 172.17.5.0/24 172.17.6.0/24 172.17.7.0/24
46
Inter-Area Route Summarization - Area Range
R2# show ip route
172.17.0.0/24 is subnetted, 7 subnets
O IA 172.17.1.1 [110/66] via 10.0.0.1, 00:02:19, Serial0/0
O IA 172.17.2.1 [110/66] via 10.0.0.1, 00:02:19, Serial0/0
O IA 172.17.3.1 [110/66] via 10.0.0.1, 00:02:19, Serial0/0
O IA 172.17.4.1 [110/66] via 10.0.0.1, 00:02:19, Serial0/0
O IA 172.17.5.1 [110/66] via 10.0.0.1, 00:02:19, Serial0/0
O IA 172.17.6.1 [110/66] via 10.0.0.1, 00:02:19, Serial0/0
O IA 172.17.7.1 [110/66] via 10.0.0.1, 00:02:19, Serial0/0
R2# show ip route
O IA 172.17.0.0/21 [110/66] via 10.0.0.1, 00:10:17, Serial0/0
Before
After
47
External Route Summarization - summary-address
When redistributing routes from other protocols into OSPF (later), each route is advertised individually in an external link state advertisement (LSA).
However, you can configure the Cisco IOS software to advertise a single route for all the redistributed routes that are covered by a specified network address and mask.
Doing so helps decrease the size of the OSPF link state database.
On the ASBR only (Summarizes external routes before injecting them into the OSPF domain.)
Router(config-router)# summary-address network-address subnet-mask
128.213.64.0 /24 … 128.213.95.0 /24
48
ASBR router ospf 1 summary-address 128.213.64.0 255.255.224.0 redistribute bgp 50 metric 1000 subnets (later)
Route Summarization128.213.64.0 /24 … 128.213.95.0 /24
Default Routes
50
Injecting Default Routes into OSPF
By default, 0.0.0.0/0 route is not propagated from the ASBR to other routers.
An autonomous system boundary router (ASBR) can be forced to generate a default route into the OSPF domain.
As discussed earlier, a router becomes an ASBR whenever routes are redistributed into an OSPF domain.
However, an ASBR does not, by default, generate a default route into the OSPF routing domain.
51
The way that OSPF generates default routes (0.0.0.0) varies depending on the type of area the default route is being injected into.
Stub and Totally Stubby Areas
For stub and totally stubby areas, the area border router (ABR) to the stub area generates a summary link-state advertisement (LSA) with the link-state ID 0.0.0.0.
This is true even if the ABR doesn't have a default route.
In this scenario, you don't need to use the default-information originate
command.
Injecting Default Routes into OSPF
52
Stub Area
LSA 4 LSA 4 BlockedLSA 5 BlockedLSA 5
LSA 3 LSA 3
Default route to ABR injected
• Sent by ABR: LSA 3s (Inter-Area routes)• Blocked:
• LSA 4s (reachability to ASBR) • LSA 5s (External routes)
• The ABR injects a default route into the stub area, pointing to the ABR. • This does not mean the ABR has a default route of its own.
• Changes in External routes no longer affect Stub Area routing tables.
We only see routes in our area, other areas, and a default route.No external routes.
Stub Area LSA 1s still sent within each area.
53
Stub Area
LSA 4 LSA 4 BlockedLSA 5 BlockedLSA 5
LSA 3 LSA 3
Default route to ABR injected
• Blocked: • LSA 3s (Inter-Area routes)• LSA 4s (reachability to ASBR) • LSA 5s (External routes)
• The ABR injects a default route into the stub area, pointing to the ABR. • This does not mean the ABR has a default route of its own.
• Changes in other areas and external routes no longer affect Stub Area routing tables.
We only see routes in our area, other areas, and a default route.No external routes.
Totally Stubby Area
BlockedBlockedBlocked
Default route to ABR injected
We only see routes in our area and a default route.
No inter-area or external routes.
Totally Stubby Area LSA 1s still sent within each area.
54
Normal Areas
By default, in normal areas routers don't generate default routes.
To have an OSPF router generate a default route, use the default-information originate command.
This generates an external type-2 link with link-state ID 0.0.0.0 and network mask 0.0.0.0.
This command should only be used on the ASBR.
Some documentation states this command works only on an ASBR while other documentation states this command turns a router into an ASBR.
Injecting Default Routes into OSPF
55
To have OSPF generate a default route use the following:
router ospf 10default-information originate [always] [metric metric-value]
[metric-type type-value] [route-map map-name]
Injecting Default Routes into OSPF
56
There are two ways to generate a default.
1) default-information originate
Conditional: If the ASBR already has the default route (ip route 0.0.0.0 0.0.0.0), you can advertise 0.0.0.0 into the area.
2) default-information originate always
Unconditional: If the ASBR doesn't have the route (ip route 0.0.0.0 0.0.0.0), you can add the keyword always to the default-information
originate command, and then advertise 0.0.0.0. You should be careful when using the always keyword. If your router
advertises a default (0.0.0.0) inside the domain and does not have a default itself or a path to reach the destinations, routing will be broken.
Injecting Default Routes into OSPF
57
ASBRrouter ospf 1
network 172.16.1.0 0.0.0.255 area 0
default-information originate
ip route 0.0.0.0 0.0.0.0 10.0.0.2
Injecting Default Routes into OSPF
58
ASBRrouter ospf 1
network 172.16.1.0 0.0.0.255 area 0
default-information originate always
Injecting Default Routes into OSPF
No 0.0.0.0/0 route, but propagated anyway or “always”
59
E1 vs. E2 External Routes
External routes fall under two categories:
External type 1
External type 2.
The difference between the two is in the way the cost (metric) of the route is being calculated.
A type 1 (E1) cost is the addition of the external cost and the internal cost used to reach that route.
The cost of a type 2 (E2) route is always the external cost, irrespective of the interior cost to reach that route.
Type 2 (E2) is the default!
Redistributing External Routes
60
router ospf 1
redistribute routing-protocol metric-type [1|2] subnets
metric-type 1 - A type 1 cost is the addition of the external cost and the internal cost used to reach that route.
redistribute rip [metric value] metric-type 1
metric-type 2 - The cost of a type 2 route is always the external cost, irrespective of the interior cost to reach that route.
redistribute rip [metric value] metric-type 2 The subnets keyword redistributes subnet details.
Without it subnetted networks would not be redistributed. Only classful network addresses (non-subnets) would be distributed.
(more later)
We will look at this command, along with internal/external costs, later in the chapter discussion route redistribution.
Redistributing External Routes (FYI for now)
61
Redistributing External Routes (FYI for now)
metric-type 2 - The cost of a type 2 route is always the external cost, irrespective of the interior cost to reach that route.
redistribute rip [metric value] metric-type 2 subnets
More later, but here is a taste of the metric value option … If a value is not specified for the metric value option, and no value is
specified using the default-metric command, the default metric value is 0, except for OSPF where the default cost is 20.
0 is only understood by IS-IS and not by RIP, IGRP and EIGRP. RIP, IGRP and EIGRP must have the appropriate metrics assigned to any
redistributed routes, or redistribution will not work. Use a value consistent with the destination protocol. More later!
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ASBRrouter ospf 1
redistribute rip metric 500 metric-type 1
network 206.202.0.0 0.0.0.255 area 0
Redistributing External RoutesRIP routes redistributed with a metric (cost) of 500 plus the outgoing cost of the interface and a metric-type 1
metric-type 1
564 564
565
566
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ASBRrouter ospf 1
redistribute rip metric 500 metric-type 2
network 206.202.0.0 0.0.0.255 area 0
Redistributing External Routes metric-type 2
500 500
500
500
RIP routes redistributed with a metric (cost) of 500 and a metric-type 2 (default)
Authentication
Configuring Simple or Plain Text Authentication
configure a password for the interface using the ip ospf authentication-key command.
Rtr(config-if)# ip ospf authentication-key passwd
password = Clear text unless message-digest is used (next) Maximum 8 characters Passwords do not have to be the same throughout an area, but they must be same
between neighbors.
For simple password authentication, use the ip ospf authentication command without any parameters.
Rtr(config-if)# ip ospf authentication
Configuring Plain Text Authentication
Verify67
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The debug ip ospf adj command is used to display OSPF adjacency-related events and is useful when troubleshooting authentication.
Will show any unsuccessful authentication information (such as authentication type).
R1# debug ip ospf adjacency
Configuring MD5 Authentication
Assign a key ID and key to be used with neighboring routers that are using the OSPF MD5 authentication:
Rtr(config-if)# ip ospf message-digest-key key-id md5 password
Key-id = 1 to 255, must match on each router to authenticate. md5 = Encryption-type password = encrypted
Passwords do not have to be the same throughout an area, but they must be same between neighbors.
Maximum 16 characters
Specify the authentication type using the interface configuration command:Rtr(config-if)# ip ospf authentication [message-digest | null]
Configuring MD 5Authentication
Verify 71
Verify 72
Verify73
Verfy
74
Troubleshooting (Different Key IDs)75
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MD5 Authentication (FYI) http://www.cisco.com/en/US/tech/tk713/tk507/technologies_tech_note09186a00800b4131.shtml
1 2
3 4
5 6
Simple Authentication over Virtual Link
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On router R1, simple password authentication is configured for the whole area 0, with the:
area 0 authentication
The virtual link, connecting area 2 to area 0, is created via transit area 1 with plain text authentication and the authentication key cisco, with:
area 1 virtual-link 3.3.3.3 authentication-key cisco
The configuration of router R3 is similar to router R1.
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MPLS and Frame Relay
79
Adjacency over Layer 2 MPLS VPN
EoMPLS is also known as a type of MetroEthernet R1 and R2 exchange Ethernet frames transparently across the MPLS
backbone They are connected to Provider Edge (PE) routers. The PE1 router:
Takes encapsulates the Ethernet frame into an MPLS packet and forwards it across the backbone to the PE2 router
The PE2 router: Decapsulates the MPLS packet Reproduces the Ethernet frame on its Ethernet link to router R2
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When deploying OSPF over EoMPLS, there are no changes to the OSPF configuration from the customer perspective. The PE1 and PE2 routers are not visible. A neighbor relationship is established directly between routers R1 and
R2 (just like any Ethernet broadcast network). The OSPF network type is a multiaccess broadcast network so DR and
BDR routers are elected.
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Adjacency over Layer 3 MPLS VPN
To the customer routers running OSPF (routers R1 and R2), the Layer 3 MPLS VPN backbone looks like a standard corporate backbone.
The CE routers form adjacencies with the PE routers. The OSPF network type of the CE-PE link can be point-to-point, broadcast
or NBMA.
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OSPF over Frame Relay
Frame Relay is a multiaccess network similar to Ethernet LAN. A single access circuit provides access to multiple neighboring routers
(networks). Unlike Ethernet:
Each virtual circuit between routers needs to be created, managed and maintained by the frame relay service provider.
Broadcast and multicast packets must be sent as individual packets for each router. (Non-Broadcast)
By default, OSPF cannot build adjacencies with neighbor routers over NBMA interfaces
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Full-mesh All routers have virtual circuits (VCs) to all other destinations. Although costly, provides direct connections from each site to all
other sites and allows for redundancy. As the number of nodes in the full-mesh topology increases, the
topology becomes increasingly expensive. n(n – 1)/2, where n is the number of nodes in the network.
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Partial-mesh Not all sites have direct access to a central site. This method reduces the cost compared to implementing a full-
mesh topology.
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Hub-and-Spoke or Star Most common Frame Relay network topology. Remote sites connect to a central site that generally provides a service or
application. The least expensive topology because it requires the fewest PVCs. The central router provides a multipoint connection because it typically
uses a single physical interface to interconnect multiple PVCs Each connection between central site and remote sites is a separate PVC
86
There are many ways to implement OSPF over Frame Relay.
In most cases there is more than one way to do it. Decisions:
One subnet or individual subnets? Are multicasts and broadcasts supported by the
network? Do I want the neighbor adjacencies to be discovered
automatically or should I configure them manually? Are all my routers Cisco routers? Do I want the use of a DR/BDR to be the central point of
LSA distribution? 87
ip ospf network To configure the OSPF network type to a type other than the default for
a given medium, use the ip ospf network command in interface configuration mode.
The default depends upon the type of medium
88
Broadcast (cisco)
Topologies: Full-mesh or Partial-mesh Note: Makes the WAN interface look like a LAN Subnet: One subnet Adjacency: Automatically discovered by OSPF multicasts DR/BDR: Elected RFC or Cisco: Cisco
Notes: Workaround for statically listing all existing neighboring routers Take special care to ensure either a full-mesh topology or a static election of the DR
based on the interface priority. 89
Router(config-router)#ip ospf network broadcast
Non- Broadcast (RFC)
Topologies: Full-mesh or Partial-mesh or Star Note: OSPF emulates operation over a broadcast network. Subnet: One subnet Adjacency: Must be manually configured using the neighbor command (non-broadcast
mode) neighbor statements required only on the DR and BDR
DR/BDR: Elected DR and BDR must have full connectivity to all other routers (DROTHERs) DR must be the Hub in Hub-and-Spoke topology
RFC or Cisco: RFC
Notes: Routers B and C could be configured with the ip ospf priority 0 command and/or
Router A includes the priority 0 option in its neighbor command to ensure Router A becomes the DR.
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Router(config-router)#ip ospf network non-broadcast
Point-to-Multipoint (broadcast)(RFC)
Topologies: Partial-mesh or Star Note: Used when VCs support multicast and broadcast
OSPF treats all router-to-router connections over the nonbroadcast network as if they are point-to-point links.
Subnet: One subnet Adjacency: Automatically discovered by OSPF multicasts DR/BDR: None RFC or Cisco: RFC
Notes: Multicasts and broadcasts must be enabled on the VCs for RFC compliant point-to-
multipoint to be used. If not routers cannot dynamically discover neighbors - Cisco mode should be used (next)
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Router(config-router)#ip ospf network point-to-multipoint
Point-to-Multipointnon-broadcast (cisco)
Topologies: Partial-mesh or Star Note: Used when VCs cannot support multicast and broadcast Subnet: One subnet Adjacency: Must be manually configured using the neighbor command (like in non-
broadcast mode)
RouterA(config-router)# neighbor 192.168.1.2
RouterA(config-router)# neighbor 192.168.1.3 DR/BDR: None RFC or Cisco: cisco
Notes: Used when multicasts and broadcasts cannot be enabled on the VCs, so RFC compliant
point-to-multipoint cannot be used because routers cannot dynamically discover neighbors. 92
Router(config-router)#ip ospf network point-to-multipoint non-broadcast
Point-to-Pointnon-broadcast (cisco)
Topologies: Partial-mesh or Star Note: Used when only two routers need on form an adjacency on a pair of interfaces Subnet: Different IP subnet on each interface Adjacency: Automatically discovered by OSPF multicasts DR/BDR: none RFC or Cisco: cisco
Notes: Cisco point-to-point can also be used with Ethernet interfaces.
ip ospf network point-to-point on an Ethernet interface means no DR or BDR will be elected.
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192.168.2.2
192.168.1.1
192.168.2.1
Router(config-router)#ip ospf network point-to-point
OSPF LSDB Overload Protection
94
Router keeps count of the number of received (non-self-generated) LSAs that it keeps in its LSDB.
If other routers are misconfigured, causing, for example, a redistribution of a large number of prefixes, large numbers of LSAs can be generated.
These excessive LSAs can drain local CPU and memory resources. OSPF LSDB overload protection can be configured to protect against this
Cisco IOS Software Release 12.3(7)T and later (and some specific earlier releases)
OSPF command: max-lsa maximum-number [threshold-percentage] [warning-only] [ignore-time minutes] [ignore-count count-number] [reset-time minutes] 95
Router keeps count of the number of received (non-self-generated) LSAs that it keeps in its LSDB.
When this number reaches a configured threshold number: An error message is logged A notification is sent when it exceeds the threshold number
If the LSA count still exceeds the threshold after one minute: OSPF goes into the ignore state OSPF process takes down all adjacencies Clears the OSPF database No OSPF packets are sent or received by interfaces that belong to that OSPF
process. OSPF process remains in the ignore state for the time defined by the ignore-time
parameter. ignore-count parameter defines the maximum number of times that the OSPF
process can consecutively enter the ignore state before remaining permanently down and requiring manual intervention.
reset-time parameter defines the time the OSPF process remains normal and then the ignore state counter is reset to 0. 96
Error Message
Notification Message
OSPF Passive-Interface
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passive-interface type number [default] router configuration command
Prevents OSPF routing updates from being sent through the specified router interface.
This command can be used with all IP-based routing protocols except BGP OSPF’s behavior with this command is different than other routing protocols With OSPF the specified interface appears as a stub network (not a stub
area) in OSPF domain. OSPF routing information is neither sent nor received through the
interface. As long as the appropriate network command is still used the router will
still advertise the network to its OSPF neighbors.98
Router R1 has three interfaces that act as stub networks. LSAs are not sent or received through these interfaces The only interface that should participate in the OSPF process is
interface Serial0/0/1. For Router R2, only one interface is a stub interface, where the propagation
of LSAs should be stopped, interface Ethernet0.
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Configuring OSPF – Part 2 of 2
CIS 185 CCNP ROUTE
Rick Graziani
Cabrillo College