1. CIS 185 CCNP ROUTE Ch. 4 Manipulating Routing Updates Part 1 - Route Redistribution
Rick Graziani
Cabrillo College
Last Updated: Fall 2015

2. Objectives Using multiple IP routing protocols
Implementing route redistribution
Controlling routing update traffic

3. Multiple Routing Protocols on a Network

4. Why Run Multiple Routing Protocols?
When migrating from an older Interior Gateway Protocol (IGP) to a new IGP.
In mixed-router vendor environments, such as EIGRP and OSPF.
When the use of a new protocol is desired, but the old routing protocol is still being implemented.
When some departments do not want to change support a new routing protocol.

5. Selecting the Best Route in a Redistribution Environment
Cisco routers use the following two parameters to select the best path:
Administrative distance:
Trustworthiness of the routing source
Modifying the administrative distance to influence the route-selection process is discussed later
When using route redistribution, you might occasionally need to modify a protocol’s administrative distance so that it is preferred and to prevent routing loops. (later)
Routing metric:
Best path 1

6. Multiple Routing Protocols Solutions
Summarization
Redistribution between routing protocols
Route filtering

7. Route Redistribution

8. Routing protocols were not designed to interoperate with one another using different:
Metrics
Reactions to topology changes
Timers
Processes
Routers using different routing protocols can exchange routing information.
Route redistribution is the capability of boundary routers connecting different routing domains to exchange and advertise routing information between those routing domains.

9. One-way route redistribution - one protocol receives the routes from another)
Two-way route redistribution - both protocols receive routes from each other.
Boundary routers:
Routers that perform redistribution
Borders two or more ASs or routing domains.
Note: The term boundary router is also sometimes used to describe a router running a classful routing protocol (like RIP) that has interfaces in more than one classful network.

10. Redistribution is always performed outbound
The router doing redistribution does not change its routing table.
R1 (boundary router) participates in both:
OSPF
EIGRP
Two-way redistribution does not affect the routing table on R1
However:
R2 will learn about redistributed EIGRP networks (via OSPF)
R3 will learn about redistributed OSPF networks (via EIGRP)
Only networks in R1’s routing table can be redistributed.

11. Configuring Redistribution
My best path to is this way.
R2 and R3 are running both OSPF and EIGRP
Configuring Redistribution R3 R1
OSPF
Routing Loop!
EIGRP
Incompatible routing information
Each routing protocol uses different metrics.
EIGRP uses slowest BW and cumulative Delay
OSPF use cumulative BW
Metrics cannot be translated exactly into a different protocol
Path selection may not be optimal.
Potential Routing loops – Depending on how redistribution is used, routers can send routing information received from one AS back into the AS. (Route Feedback)
Inconsistent convergence times:
Different routing protocols converge at different rates.
These potential trouble spots can be avoided with careful planning and implementation. R2
My best path to is this way.

12. Concepts of Redistribution

13. Multiple Routing Processes
RTA#show running-config
router ospf 24
network area 0 !
router ospf 46
network area 2
router eigrp 53
network
network
router eigrp 141
network
network
Cisco routers support up to 30 dynamic routing processes on a single router.
Most routing protocols allow an administrator to configure multiple processes of the same routing algorithm
RIP and BGP are notable exceptions.
Not usually recommended
Not usually recommended

14. Route redistribution - The process of exchanging routing information between routing protocols.
EIGRP routing domain learns about networks in OSPF routing domain.
OSPF routing domain learns about networks in EIGRP routing domain.
Done by a boundary router which participates in both routing protocols.

15. Redistribution Concepts and Processes
I run both EIGRP and OSPF.
Router(config-router)# redistribute from-protocol [process-id]
Note: Other parameters may be required and will be discussed.
The redistribution command (“take routes from”)
Configured on the boundary router.
Participates in both routing protocols.
Independent of any one protocol
Various complexities depending on the routing protocols and the options.
The redistribution command
Available for all IP routing protocols,
Independent of any one protocol
Various complexities depending on the routing protocols and the options.
Route redistribution requires at least one router to do the following:
At least one “up/up” physical link with each routing domain
A working configured routing protocol for each routing domain
Redistribution configured for each routing protocol, (redistribute command),
Tells the routing protocol to take the routes learned by another source of routing information and then advertise those routes

16. Redistributing from OSPF into EIGRP

17. Our Topology OSPF 1 EIGRP 1 Boundary router R2-E-O is running:
EIGRP for subnets and network
OSPF for subnets and network
or not currently included in either routing protocol (more on this later)

18. Redistribution into EIGRP
redistribute protocol [process-id | as-number] [metric bw delay reliability load mtu ] [match {internal | nssa-external | external 1 | external 2}] [tag tag-value] [route-map name]
The syntax differs slightly depending on the routing protocol into which routes will be redistributed.

19. redistribute protocol [process-id | as-number] [metric bw delay reliability load mtu ] [match {internal | nssa-external | external 1 | external 2}] [tag tag-value] [route-map name]
protocol - The source of routing information. Includes RIP, OSPF, EIGRP, IS-IS, BGP, connected, and static.
process-id, as-number - If redistributing a routing protocol that uses a process-id or ASN on the router global config command, use this parameter to refer to that process or ASN value.
metric - A keyword after which follows the four metric components (bandwidth, delay, reliability, link load), plus the MTU associated with the route.
match - If redistributing from OSPF, this keyword lets you match internal OSPF routes, external (by type), and NSSA external routes, essentially filtering which routes are redistributed.
tag - Assigns a unitless integer value to the route, which can be later matched by other routers using a route-map.
route-map - Apply the logic in the referenced route-map to filter routes, set metrics, and set route tags.

20. Current configurations
router eigrp 1
network
network
auto-summary
R2-E-O
router eigrp 1
network
auto-summary
router ospf 1
network area 0
R3-O
router ospf 1
network area 0
R4-O
router ospf 1
network area 0
network area 0

21. What networks do I know about and how did I learn about them?
What do you expect to see?
Directly Connected and any EIGRP networks – NO OSPF networks
R1-E# show ip route
C /16 is directly connected, Loopback31
/16 is variably subnetted, 6 subnets, 3 masks
C /24 is directly connected, FastEthernet0/1
C /24 is directly connected, Loopback0
C /30 is directly connected, Serial0/0
D /16 is a summary, 00:02:41, Null0
C /24 is directly connected, FastEthernet0/0
C /24 is directly connected, Loopback1
R1-E#

22. What do you expect to see? EIGRP and OSPF networks
What networks do I know about and how did I learn about them?
EIGRP and OSPF networks
R2-E-O# show ip route
O /16 [110/846] via , 00:02:32, Serial0/1
/16 is variably subnetted, 4 subnets, 2 masks
O /30 [110/845] via , 00:02:32, Serial0/1
C /30 is directly connected, Serial0/1
O /24 [110/782] via , 00:02:32, Serial0/1
O /24 [110/846] via , 00:02:32, Serial0/1
D /16 [90/ ] via , 00:03:46, Serial0/0
/16 is variably subnetted, 5 subnets, 2 masks
D /24 [90/ ] via , 01:22:36, Serial0/0
D /24 [90/ ] via , 01:22:36, Serial0/0
C /30 is directly connected, Serial0/0
D /24 [90/ ] via , 01:22:36, Serial0/0
D /24 [90/ ] via , 01:22:36, Serial0/0
/24 is subnetted, 1 subnets
C is directly connected, FastEthernet0/1
C /24 is directly connected, FastEthernet0/0
R2-E-O#

23. What do you expect to see?
What networks do I know about and how did I learn about them?
Only OSPF networks – NO EIGRP networks
R3-O# show ip route
O /16 [110/65] via , 00:09:06, Serial0/2
/16 is variably subnetted, 4 subnets, 2 masks
C /30 is directly connected, Serial0/2
C /30 is directly connected, Serial0/1
C /24 is directly connected, FastEthernet0/0
O /24 [110/65] via , 00:09:06, Serial0/2
R3-O#

24. What do you expect to see?
What networks do I know about and how did I learn about them?
Only OSPF networks – NO EIGRP networks
R4-O# show ip route
C /16 is directly connected, FastEthernet0/1
/16 is variably subnetted, 4 subnets, 2 masks
C /30 is directly connected, Serial0/0
O /30 [110/128] via , 00:09:52, Serial0/0
O /24 [110/65] via , 00:09:52, Serial0/0
C /24 is directly connected, FastEthernet0/0
R4-0#

25. Hey! I don’t see any of the networks in the OSPF domain! What happened?
No change for R1-E!
No OSPF networks
Let’s see what happened (or didn’t happen)…
I will redistribute my OSPF learned networks (and OSPF network command networks) into EIGRP, telling my EIGRP neighbors about these networks
R2-E-O(config)# router eigrp 1
R2-E-O(config-router)# redistribute ospf 1
R1-E# show ip route
C /16 is directly connected, Loopback31
/16 is variably subnetted, 6 subnets, 3 masks
C /24 is directly connected, FastEthernet0/1
C /24 is directly connected, Loopback0
C /30 is directly connected, Serial0/0
D /16 is a summary, 00:02:41, Null0
C /24 is directly connected, FastEthernet0/0
C /24 is directly connected, Loopback1
R1-E#

26. Should R2’s routing table change? No
R2-E-O# show ip route
O /16 [110/846] via , 00:02:32, Serial0/1
/16 is variably subnetted, 4 subnets, 2 masks
O /30 [110/845] via , 00:02:32, Serial0/1
C /30 is directly connected, Serial0/1
O /24 [110/782] via , 00:02:32, Serial0/1
O /24 [110/846] via , 00:02:32, Serial0/1
D /16 [90/ ] via , 00:03:46, Serial0/0
/16 is variably subnetted, 5 subnets, 2 masks
D /24 [90/ ] via , 01:22:36, Serial0/0
D /24 [90/ ] via , 01:22:36, Serial0/0
C /30 is directly connected, Serial0/0
D /24 [90/ ] via , 01:22:36, Serial0/0
D /24 [90/ ] via , 01:22:36, Serial0/0
/24 is subnetted, 1 subnets
C is directly connected, FastEthernet0/1
C /24 is directly connected, FastEthernet0/0
R2-E-O#

27. Metric parameter with redistribute command
BW/DLY BW
redistribute protocol [process-id | as-number] [metric bw delay reliability load mtu ]
default-metric bw delay reliability load mtu
When redistributing into EIGRP from another routing protocol you must convert the other routing protocol’s metric (OSPF’s cost, bandwidth) into EIGRP’s metric (BW, DLY, Reliability and Load).
This metric, referred to as the seed or default metric, is defined during redistribution configuration.
Three methods:
Metric parameter with redistribute command
Sets the default for all redistribute commands
Default-metric command
Route-map
Sets different metrics for routes learned from a single source

28. metric parameter takes precedence over the default-metric command
OSPF 1
EIGRP 1
EIGRP 2
router eigrp 1
network
redistribute ospf 1
redistribute eigrp 2
default-metric
redistribute rip metric
RIP
default-metric command is used where the metric parameter is not being applied in the redistribute command.
metric parameter takes precedence over the default-metric command
Note: The metric will give all redistributed networks the same starting metric.
This is known as the seed metric

29.
R2-E-O(config)# router eigrp 1
R2-E-O(config-router)# redistribute ospf 1
R2-E-O(config-router)# default-metric
BW DLY RLY Load MTU OR
R2-E-O(config)# router eigrp 1
R2-E-O(config-router)# redistribute ospf 1 metric
BW DLY RLY Load MTU
Note:
MTU is NOT one of the EIGRP metrics (never has been, never will be)
MTU is included because it is tracked through the path to find the smallest MTU.

30. EX: External Route (redistributed)
Great! Now I see all the networks in the OSPF domain but as EIGRP routes.
R1-E# show ip route
D EX /16 [170/ ] via , 00:01:50, Serial0/0
/16 is variably subnetted, 4 subnets, 2 masks
D EX /30 [170/ ] via , 00:01:50, Serial0/0
D EX /30 [170/ ] via , 00:01:50, Serial0/0
D EX /24 [170/ ] via , 00:01:50, Serial0/0
D EX /24 [170/ ] via , 00:01:50, Serial0/0
C /16 is directly connected, Loopback31
/16 is variably subnetted, 6 subnets, 3 masks
C /24 is directly connected, FastEthernet0/1
C /24 is directly connected, Loopback0
C /30 is directly connected, Serial0/0
D /16 is a summary, 00:12:08, Null0
C /24 is directly connected, FastEthernet0/0
C /24 is directly connected, Loopback1
EX: External Route (redistributed)
170: Administrative distance (90 for EIGRP internal routes)
R1-E has the same metric ( ) for all external EIGRP networks (from the OSPF domain)

31. Redistribute command, redistributes the following:
R2-E-O# show ip eigrp top
P /30, 1 successors, FD is
via Redistributed ( /0)
R2 redistributed into EIGRP the routes learned via OSPF and its own directly connected network /30.
But not /24 and /8
This is because /30 is an OSPF enabled interface (network statement)
Redistribute command, redistributes the following:
All routes in the routing table learned by that routing protocol
All connected routes of interfaces on which that routing protocol is enabled
Otherwise must be redistributed another way (connected or static) – coming

32. Two ways to redistribute 10.0.0.0/24 network.
What about the /24 network? How can I redistribute it into EIGRP?
R2-E-O(config)# router ospf 1
R2-E-O(config-router)# network area 0
R2-E-O# show ip route
/24 is subnetted, 1 subnets
C is directly connected, FastEthernet0/1
No change to routing table
Two ways to redistribute /24 network.
Redistribute Connected
Add OSPF network command
Also propagates /24 throughout OSPF domain

33. The 10.0.0.0 network is now included as one of my EIGRP routes.
R1-E# show ip route
D EX [170/ ] via , 00:01:33, Serial0/0
R4-0# show ip route
O [110/129] via , 00:04:02, Serial0/0
is now redistributed into the EIGRP domain with the rest of the OSPF networks.

34. What about the 192.168.1.0 network? How can I redistribute it into EIGRP?
R2-E-O(config)# router eigrp 1
R2-E-O(config-router)# redistribute connected metric
R1-E# show ip route
/24 is subnetted, 1 subnets
D EX [170/ ] via , 00:01:57, Serial0/0
D EX /24 [170/ ] via , 00:01:57, Serial0/0
R1-E#
/24 is redistributed into EIGRP as a connected network.
metric option is not required for this command (default 0, but beyond the scope of this pres.)
/24 is redistributed into the EIGRP domain using the default metric but it is NOT propagated throughout OSPF domain

35. R2: Currently
router eigrp 1
network
auto-summary
redistribute ospf 1
default-metric
redistribute connected !
router ospf 1
network area 0
network area 0

36. Redistributing from EIGRP into OSPF

37. Several similarities and differences to redistributing into EIGRP.
BW/DLY BW
redistribute protocol [process-id | as-number] [metric {metric-value | transparent}] [metric-type type-value] [match {internal | external 1 | external 2 | nssa-external}] [tag tag-value] [route-map map-tag] [subnets]
Several similarities and differences to redistributing into EIGRP.
In this case we must convert the EIGRP metric to the Cisco OSPF metric of Bandwidth.

38. redistribute protocol [process-id | as-number] [metric {metric-value | transparent}] [metric-type type-value] [match {internal | external 1 | external 2 | nssa-external}] [tag tag-value] [route-map map-tag] [subnets]
Metric - Defines the cost metric assigned to the route in the Type 5 (or Type 7 if NSSA) LSA. metric transparent when taking from another OSPF process, pass through the metric with the route.
metric-type {1 | 2} - Defines the external metric type of 1 (E1 routes) or 2 (E2 routes).
Match - If redistributing from OSPF, this keyword lets you match internal OSPF routes, external (by type), and NSSA external routes, essentially filtering which routes are redistributed.
Tag - Assigns a unitless integer value to the route, which can be later matched by other routers using a route-map.
route-map - Apply the logic in the referenced route-map to filter routes, set metrics, and set route tags.
Subnets - Redistribute subnets of classful networks. Without this parameter, only routes for classful networks are redistributed. (This behavior is particular to the OSPF redistribute command.)

39. Defaults when redistributing into OSPF:
BW/DLY
BW=20
BW=20
redistribute protocol [process-id | as-number] [metric {metric-value | transparent}] [metric-type type-value] [match {internal | external 1 | external 2 | nssa-external}] [tag tag-value] [route-map map-tag] [subnets]
Defaults when redistributing into OSPF:
When redistributing networks from all other sources the default metric is 20.
External metric type 2 (metric does not change throughout OSPF routing domain)
Only redistributes routes of classful (Class A, B, and C) networks, and not for subnets

40. Where we left off… R2: Currently router eigrp 1 network 172.30.0.0
auto-summary
redistribute ospf 1
default-metric
redistribute connected !
router ospf 1
network area 0
network area 0
Where we left off…

41. What do you expect to see?
EIGRP and OSPF networks
What networks do I know about and how did I learn about them?
R2-E-O# show ip route
O /16 [110/846] via , 00:02:32, Serial0/1
/16 is variably subnetted, 4 subnets, 2 masks
O /30 [110/845] via , 00:02:32, Serial0/1
C /30 is directly connected, Serial0/1
O /24 [110/782] via , 00:02:32, Serial0/1
O /24 [110/846] via , 00:02:32, Serial0/1
D /16 [90/ ] via , 00:03:46, Serial0/0
/16 is variably subnetted, 5 subnets, 2 masks
D /24 [90/ ] via , 01:22:36, Serial0/0
D /24 [90/ ] via , 01:22:36, Serial0/0
C /30 is directly connected, Serial0/0
D /24 [90/ ] via , 01:22:36, Serial0/0
D /24 [90/ ] via , 01:22:36, Serial0/0
/24 is subnetted, 1 subnets
C is directly connected, FastEthernet0/1
C /24 is directly connected, FastEthernet0/0

42. No EIGRP networks being redistributed into OSPF
R2-E-O# show ip ospf data
OSPF Router with ID ( ) (Process ID 1)
Router Link States (Area 0)
Link ID ADV Router Age Seq# Checksum Link count
x x
x x006BB4 4
x x
R2-E-O#
No External Type 5 LSAs
No EIGRP networks being redistributed into OSPF

43. Subnets will not be redistributed
By default, only classful networks will be redistributed from EIGRP into OSPF.
Subnets will not be redistributed
Supernets will also be redistributed (such as /8)
R2-E-O(config)# router ospf 1
R2-E-O(config-router)# redistribute eigrp 1
% Only classful networks will be redistributed
R2-E-O(config-router)#
R2-E-O# show ip ospf data
<Router Link States omitted>
Type-5 AS External Link States
Link ID ADV Router Age Seq# Checksum Tag
x x0094D4 0
R2-E-O#

44. Remember, routes are only Redistributed if they are in the
Routing table
R2-E-O# show ip route
O /16 [110/846] via , 00:03:56, Serial0/1
/16 is variably subnetted, 4 subnets, 2 masks
O /30 [110/845] via , 00:03:56, Serial0/1
C /30 is directly connected, Serial0/1
O /24 [110/782] via , 00:03:56, Serial0/1
O /24 [110/846] via , 00:03:56, Serial0/1
D /16 [90/ ] via , 00:18:29, Serial0/0
/16 is variably subnetted, 5 subnets, 2 masks
D /24 [90/ ] via , 01:37:19, Serial0/0
D /24 [90/ ] via , 01:37:19, Serial0/0
C /30 is directly connected, Serial0/0
D /24 [90/ ] via , 01:37:19, Serial0/0
D /24 [90/ ] via , 01:37:19, Serial0/0
/24 is subnetted, 1 subnets
C is directly connected, FastEthernet0/1
C /24 is directly connected, FastEthernet0/0

45. Only the class B network 172.31.0.0/16 is redistributed into OSPF
I only see the class B /16 network in the EIGRP domain.
R3-O# show ip route
O /16 [110/65] via , 00:01:16, Serial0/2
/16 is variably subnetted, 4 subnets, 2 masks
C /30 is directly connected, Serial0/2
C /30 is directly connected, Serial0/1
C /24 is directly connected, FastEthernet0/0
O /24 [110/65] via , 00:01:16, Serial0/2
O E /16 [110/20] via , 00:01:16, Serial0/1
/24 is subnetted, 1 subnets
O [110/65] via , 00:01:17, Serial0/1
R3-O#
Only the class B network /16 is redistributed into OSPF

46. External Type 5 LSA R3-O# show ip ospf data
<Router Link States omitted>
Type-5 AS External Link States
Link ID ADV Router Age Seq# Checksum Tag
x x0094D4 0
R3-O#
External Type 5 LSA

47. Subnets – Subnets are now included in the redistribution.
I will add the subnets option.
R2-E-O(config)# router ospf 1
R2-E-O(config-router)# redistribute eigrp 1 subnets
No warning message “Only classful networks will be redistributed”
Subnets – Subnets are now included in the redistribution.

48. R2 now includes Type 5 LSAs for subnets
R2-E-O# show ip ospf data
Type-5 AS External Link States
Link ID ADV Router Age Seq# Checksum Tag
x x008EDE 0
x x0095D3 0
x x008ADD 0
x x007FE7 0
x x0074F1 0
x x0094D4 0
R2-E-O#
R2 now includes Type 5 LSAs for subnets

49. Now I see all networks and subnets from the EIGRP domain.
R3-O# show ip route
O /16 [110/65] via , 00:13:41, Serial0/2
/16 is variably subnetted, 4 subnets, 2 masks
C /30 is directly connected, Serial0/2
C /30 is directly connected, Serial0/1
C /24 is directly connected, FastEthernet0/0
O /24 [110/65] via , 00:13:41, Serial0/2
O E /16 [110/20] via , 00:13:41, Serial0/1
/16 is variably subnetted, 5 subnets, 2 masks
O E /24 [110/20] via , 00:00:12, Serial0/1
O E /24 [110/20] via , 00:00:12, Serial0/1
O E /30 [110/20] via , 00:00:12, Serial0/1
O E /24 [110/20] via , 00:00:14, Serial0/1
O E /24 [110/20] via , 00:00:14, Serial0/1
/24 is subnetted, 1 subnets
O [110/65] via , 00:00:14, Serial0/1
BW=20
Now I see all networks and subnets from the EIGRP domain.
External OSPF routes are E2 with a default cost of 20.
metric-type E2 - The cost of a type 2 route is always the external cost, irrespective of the interior cost to reach that route.

50. External OSPF routes are E2 with a default cost of 20.
BW=20
BW=20
R4-0# show ip route
C /16 is directly connected, FastEthernet0/1
/16 is variably subnetted, 4 subnets, 2 masks
C /30 is directly connected, Serial0/0
O /30 [110/128] via , 00:04:02, Serial0/0
O /24 [110/65] via , 00:04:02, Serial0/0
C /24 is directly connected, FastEthernet0/0
O E /16 [110/20] via , 00:04:02, Serial0/0
/16 is variably subnetted, 5 subnets, 2 masks
O E /24 [110/20] via , 00:01:46, Serial0/0
O E /24 [110/20] via , 00:01:46, Serial0/0
O E /30 [110/20] via , 00:01:46, Serial0/0
O E /24 [110/20] via , 00:01:46, Serial0/0
O E /24 [110/20] via , 00:01:46, Serial0/0
/24 is subnetted, 1 subnets
O [110/129] via , 00:04:04, Serial0/0
External OSPF routes are E2 with a default cost of 20.
metric-type 2 - The cost of a type 2 route is always the external cost, irrespective of the interior cost to reach that route.

51. Redistribution into OSPF
R4-0# show ip ospf data
Type-5 AS External Link States
Link ID ADV Router Age Seq# Checksum Tag
x x008EDE 0
x x0095D3 0
x x008ADD 0
x x007FE7 0
x x0074F1 0
x x0094D4 0
R4-0#
R4 now includes Type 5 LSAs for subnets

52. This is okay because 192.168.1.0/24 is a Class C network.
R2-E-O(config)#router ospf 1
R2-E-O(config-router)#redistribute connected ?
metric Metric for redistributed routes
metric-type OSPF/IS-IS exterior metric type for redistributed routes
route-map Route map reference
subnets Consider subnets for redistribution into OSPF
tag Set tag for routes redistributed into OSPF
<cr>
R2-E-O(config-router)#redistribute connected
% Only classful networks will be redistributed
R2-E-O(config-router)#redistribute connected subnets
Let’s redistribute the /24 network into OSPF as a connected network.
This is okay because /24 is a Class C network.
If it was a subnet then…

53. Redistribution into OSPF
R4-0# show ip route
<other output omitted>
E /24 [110/20] via , 00:03:08, Serial0/0
R4-0# show ip ospf data
Type-5 AS External Link States
Link ID ADV Router Age Seq# Checksum Tag
<omitted>
x x0012B8 0
R4-0#

54. Summary so far… So far… OSPF learned networks are distributed
BW=20
BW=20
Summary so far…
R2 summary:
router eigrp 1
network
auto-summary
redistribute ospf 1
default-metric
redistribute connected metric !
router ospf 1
network area 0
network area 0
redistribute eigrp 1 subnets
redistribute connected
OSPF learned networks are distributed
into the EIGRP domain
Use the metrics for BW DLY RLY Load
Distribute any directly connected networks
and use these metrics for BW DLY RLY Load
So far…
EIGRP learned networks are distributed
into the OSPF domain, default metric of 20
Distribute any directly connected networks
and use default metric of 20

55. External OSPF routes are E2 with a default cost of 20.
R3-O#show ip route
O /16 [110/65] via , 00:13:41, Serial0/2
/16 is variably subnetted, 4 subnets, 2 masks
C /30 is directly connected, Serial0/2
C /30 is directly connected, Serial0/1
C /24 is directly connected, FastEthernet0/0
O /24 [110/65] via , 00:13:41, Serial0/2
O E /16 [110/20] via , 00:13:41, Serial0/1
/24 is subnetted, 4 subnets
O E [110/20] via , 00:11:25, Serial0/1
O E [110/20] via , 00:11:25, Serial0/1
O E [110/20] via , 00:11:25, Serial0/1
O E [110/20] via , 00:11:25, Serial0/1
/24 is subnetted, 1 subnets
O [110/65] via , 00:13:43, Serial0/1
O E /24 [110/20] via , 00:07:30, Serial0/1
External OSPF routes are E2 with a default cost of 20.
metric-type 2 - The cost of a type 2 route is always the external cost, irrespective of the interior cost to reach that route.

56. External OSPF routes are E2 with a default cost of 20
R4-0#show ip route
C /16 is directly connected, FastEthernet0/1
/16 is variably subnetted, 4 subnets, 2 masks
C /30 is directly connected, Serial0/0
O /30 [110/128] via , 00:14:05, Serial0/0
O /24 [110/65] via , 00:14:05, Serial0/0
C /24 is directly connected, FastEthernet0/0
O E /16 [110/20] via , 00:14:05, Serial0/0
/24 is subnetted, 4 subnets
O E [110/20] via , 00:11:49, Serial0/0
O E [110/20] via , 00:11:49, Serial0/0
O E [110/20] via , 00:11:49, Serial0/0
O E [110/20] via , 00:11:49, Serial0/0
/24 is subnetted, 1 subnets
O [110/129] via , 00:14:07, Serial0/0
O E /24 [110/20] via , 00:07:54, Serial0/0
External OSPF routes are E2 with a default cost of 20

57. R2-E-O(config)#router ospf 1
R2-E-O(config-router)#redistribute eigrp 1 subnets metric 100
R2-E-O(config-router)#redistribute connected
R4-0#show ip route <external route>
O E /16 [110/100] via , 00:00:04, Serial0/0
/24 is subnetted, 4 subnets
O E [110/100] via , 00:00:05, Serial0/0
O E [110/100] via , 00:00:05, Serial0/0
O E [110/100] via , 00:00:05, Serial0/0
O E [110/100] via , 00:00:05, Serial0/0
O E /24 [110/20] via , 00:12:36, Serial0/0
/24 still has a cost of 20. Why?
It was redistributed with the redistribute connected command without the metric 100 parameter. <redistribute connected metric 100>

58. Notice that the previous metric 100 parameter is still included!
R2-E-O(config)# router ospf 1
R2-E-O(config-router)# redistribute eigrp 1 subnets metric-type 1
R2-E-O# show run
router ospf 1
log-adjacency-changes
redistribute connected
redistribute eigrp 1 metric 100 metric-type 1 subnets
network area 0
network area 0
Notice that the previous metric 100 parameter is still included!
metric-type {1 | 2} - Defines the external metric type of 1 (E1 routes) or 2 (E2 routes).
metric-type 1 - A type 1 cost is the addition of the external cost and the internal cost used to reach that route.
metric-type 2 - The cost of a type 2 route is always the external cost, irrespective of the interior cost to reach that route.

59. E1 routes, seed metric of 100 plus internal cost.
R3-O#show ip route
O E /16 [110/164] via , 00:00:23, Serial0/1
/24 is subnetted, 4 subnets
O E [110/164] via , 00:00:24, Serial0/1
O E [110/164] via , 00:00:24, Serial0/1
O E [110/164] via , 00:00:24, Serial0/1
O E [110/164] via , 00:00:24, Serial0/1
/24 is subnetted, 1 subnets
O [110/65] via , 00:21:45, Serial0/1
O E /24 [110/20] via , 00:15:32, Serial0/1
E1 routes, seed metric of 100 plus internal cost.
/24 still has a cost of 20.
It was redistributed with the redistribute connected command without the metric-type 1 parameter, E2 is the default <redistribute connected metric 100 metric-type 1>

60. FYI: More on OSPF and External Routes

61. Redistribution into OSPF
EIGRP
OSPF
Area 0
Area 1
New Topology

62. Redistribution into OSPF
redistribute protocol [process-id | as-number] [metric {metric-value | transparent}] [metric-type type-value] [match {internal | external 1 | external 2 | nssa-external}] [tag tag-value] [route-map map-tag] [subnets]
Default if no metric configuration exists
Cost 1 for routes learned from BGP
Cost 20 for all other route sources
default-metric cost OSPF subcommand
Setting the default for all redistribute commands
metric cost parameters on the redistribute command
Setting the metric for one route source
Metric transparent parameters on the redistribute command
When taking routes from another OSPF process, using the metrics used by that route source
Use the route-map parameter on the redistribute command
Setting different metrics for routes learned from a single source

63. Redistribution into OSPF
Router that performs redistribution becomes ASBR (Autonomous System Border Router).
Injects external routes into OSPF creating a Type 5 LSA for each network/subnet .
Type 5 LSA includes:
LSID: the subnet number
Mask: The subnet mask
Advertising router: The RID of the ASBR injecting the route
Metric: The metric as set by the ASBR
External Metric Type: The external metric type, either 1 or 2

64. Redistribution into OSPF
LSA 5
ASBR floods Type 5 LSAs throughout area.
If ABR is:
Normal (non-stubby) areas:
Flood Type 5 LSAs into area
Stub and Totally Stubby areas:
No Type 5 LSAs flooded
Default route injected by ABR

65. Redistributing External Type 2 Routes

66. Redistribution into OSPF
LSA 5
Metric = 20
Metric = 20
/23
E2 route’s metric is simply the metric in the Type 5 LSA.
Default = 20
metric parameter
R4 has two routes to /23:
Via R1
Via R8
To avoid loops, OSPF routers use two tiebreaker systems to allow a router to choose a best external route.
Router in question resides in the same area as the ASBR (intra-area)
Router in question resides in a different area (interarea) than the ASBR

67. Determining the Next-hop for Type 2 External Routes - Intra-area
Metric = 20
Metric = 20
/23
LSA 5
Router has multiple routes for same E2 destination network:
Selects the best route based on the lowest cost to reach any ASBR(s) that advertised the lowest E2 metric.
R4: Both routes use metric 20 in this case, so the routes tie.
Tiebreaker:
Find the advertising ASBR(s) as listed in the Type 5 LSA(s)
Using the intra-area LSDB topology calculate the best route to reach the ASBR(s). (This is the route that will be entered into the routing table.)
This determines the outgoing interface and next hop based address to to reach the ASBR
The route's metric is unchanged in the routing table as listed in theType 5 LSA

68. Determining the Next-hop for Type 2 External Routes - Intra-area
Metric = 20
Metric = 20
/23
LSA 5
Best path
R4 looks in the Type 5 LSA, and sees RID (R1) is the advertising ASBR.
R4 then looks at its area 0 LSDB entries, including the Type 1 LSA for RID , and calculates all possible area 0 routes to reach
R4's best route to reach RID happens to be through its S0/0/0 interface, to next-hop RD1 ( ), so R4's route to /23 uses these details.
The route lists metric 20, as listed in the Type 5 LSA.

69. Determining the Next-hop for Type 2 External Routes - Interarea
/23
LSA 5
Metric = 20
Metric = 20
When router is in a different area same issues remain.
Different tiebreaker to reach ASBR.
Calculation requires more information that previous Intra-area example.
To calculate their best route to reach the ASBR, a router in another area:
Adds the cost to reach an ABR between the areas
Plus that ABR's cost to reach the ASBR

70. Determining the Next-hop for Type 2 External Routes - Interarea
/23 64 1 64 64
Best path
R5 has two possible routes to reach ASBR:
Via R3
Via R4
Although the metric is 20, R5 will use the cost to the ABR PLUS the ABR’s cost to the ASBR to determine the best path.
Via R3: = 65
Via R4: = 128
R5 chooses the route via R3 because it is a better path (65).
The router’s process for doing this is:
Calculate the cost to reach the ABR, based on the area's topology database
Add the cost from the ABR to the ASBR, as listed in a Type 4 LSA
Let’s talk about that Type 4 LSA!

71. Determining the Next-hop for Type 2 External Routes - Interarea
LSA 4: I am ABR R4, I can reach ASBR R1 and my cost to the ASBR is 64.
Determining the Next-hop for Type 2 External Routes - Interarea
/23
LSA 4: I am ABR R3, I can reach ASBR R1 and my cost to the ASBR is 1.
LSA 4
The following slides provide additional information on LSA 4s if you are interested...
Otherwise
The End 

72. Determining the Next-hop for Type 2 External Routes - Interarea
LSA 4: I am ABR R4, I can reach ASBR R1 and my cost to the ASBR is 64.
Determining the Next-hop for Type 2 External Routes - Interarea
/23
LSA 4: I am ABR R3, I can reach ASBR R1 and my cost to the ASBR is 1.
LSA 4
Type 4 Summary ASBR LSA:
RID of the ASBR
RID of the ABR that created and flooded the LSA 4
ABR's cost to reach the ASBR
ABRs create Type 4 LSAs after receiving an external Type 5 LSA from an ASBR.
ABR forwards a Type 5 LSA into an area
ABR looks at the RID of the ASBR that created the Type 5 LSA..
ABR creates a Type 4 LSA listing that ASBR, and the cost to reach that ASBR, flooding that LSA into the neighboring areas.

73. Determining the Next-hop for Type 2 External Routes - Interarea
LSA 4: I am ABR R4, I can reach ASBR R1 and my cost to the ASBR is 64.
Determining the Next-hop for Type 2 External Routes - Interarea
/23
LSA 4: I am ABR R3, I can reach ASBR R1 and my cost to the ASBR is 1.
LSA 4
Best path
ABR R3 creates and floods Type 4 Summary ASBR LSA into area 1.
ASBR (R1), ABR (R3), and cost 1 (R3's cost to reach ASBR).
ABR R4 creates and floods Type 4 Summary ASBR LSA into area 1.
ASBR (R1), ABR (R4), and lists cost 64 (R4's cost to reach ASBR).
When R5 finds two routes for subnet /23, and finds both have a metric of 20
Break the tie.
For each route: Add intra-area cost to reach the ABR PLUS the ABR's cost to reach the ASBR (as listed in the Type 4 LSA).
R5 determines best route is through R3 has the lower cost (65).

74. Determining the Next-hop for Type 2 External Routes - Interarea
LSA 4: I am ABR R4, I can reach ASBR R1 and my cost to the ASBR is 64.
Determining the Next-hop for Type 2 External Routes - Interarea
/23
LSA 4: I am ABR R3, I can reach ASBR R1 and my cost to the ASBR is 1.
Best path
R5# show ip route
O E /23 [110/20] via , 05:48:42, Serial0/0

75. CIS 185 CCNP ROUTE Ch. 4 Manipulating Routing Updates
Rick Graziani
Cabrillo College