- Unlike EIGRP, OSPF creates LSAs to represent each external route, and OSPF must then apply some much different logic than EIGRP to calculate the best route to each external subnet.
General syntax:
redistribute protocol [process-id | as-number] [metric metric-value] [metric-type type-value] [match {internal | external 1 | external 2 | nssa-external}] [tag tag-value] [route-map map-tag] [subnets]
Parameters:
-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: Defines the cost metric assigned to routes redistributed by this command, unless overridden by a referenced route map.
-metric-type {1 | 2}: Defines the external metric type for the routes redistributed by this command: 1 (E1 routes) or 2 (E2 routes).
-match: If redistributing from another OSPF process, 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 routes redistributed by this command — a tag that 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 unique to the OSPF redistribute command.)
Note:
Redistribution into OSPF uses the following defaults:
- When taking from BGP, use a default metric of 1.
- When taking from another OSPF process, take the source route’s metric.
- When taking from all other sources, use a default metric of 20.
- Create a Type 5 LSA for each redistributed route (external) if not inside an NSSA area; create a Type 7 LSA if inside an NSSA area.
- Use external metric type 2.
- Redistribute only routes of classful (class A, B, and C) networks, and not routes for subnets.
Consider router R4, which is sitting between an EIGRP and an OSPF domain. Both protocols have been configured, but no redistribution yet:
R4#show run
...
!
router eigrp 1
network 172.16.0.2 0.0.0.0
network 172.16.0.12 0.0.0.3
network 192.168.44.0
no auto-summary
!
router ospf 1
router-id 4.4.4.4
log-adjacency-changes
network 192.168.0.12 0.0.0.3 area 0
!
R4#show run | i redistribute
R4#
Rule 1: By adding the redistribute eigrp 1 command in OSPF configuration mode, OSPF tries to redistribute routes from EIGRP – but with no success.
The reason is that by omitting the subnets parameter, OSPF will only redistribute routes for entire classful subnets, and only if such a route is listed in the IP routing table.
First, let's check the OSPF database on R4 and the routing table on a router inside the OSPF domain, like R1.
As expected, only directly connected and OSPF routes are in its table:
R4#show ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route
Gateway of last resort is not set
C 192.168.44.0/24 is directly connected, Loopback44
172.16.0.0/16 is variably subnetted, 5 subnets, 2 masks
C 172.16.0.12/30 is directly connected, Serial0/2
D 172.16.0.8/30 [90/2681856] via 172.16.0.1, 00:00:54, Serial0/0
D 172.16.0.4/30 [90/2195456] via 172.16.0.14, 00:00:56, Serial0/2
[90/2195456] via 172.16.0.1, 00:00:56, Serial0/0
C 172.16.0.0/30 is directly connected, Serial0/0
D 172.16.111.0/24 [90/2297856] via 172.16.0.1, 00:00:54, Serial0/0
D 192.168.55.0/24 [90/2297856] via 172.16.0.14, 00:00:55, Serial0/2
10.0.0.0/32 is subnetted, 3 subnets
O IA 10.0.1.3 [110/192] via 192.168.0.13, 00:00:00, Serial0/1
O IA 10.0.11.11 [110/193] via 192.168.0.13, 00:00:00, Serial0/1
O IA 10.0.1.1 [110/128] via 192.168.0.13, 00:00:00, Serial0/1
192.168.0.0/24 is variably subnetted, 4 subnets, 2 masks
C 192.168.0.12/30 is directly connected, Serial0/1
O 192.168.0.0/29 [110/74] via 192.168.0.13, 00:00:01, Serial0/1
O 192.168.0.16/30 [110/128] via 192.168.0.13, 00:00:01, Serial0/1
O 192.168.0.20/30 [110/128] via 192.168.0.13, 00:00:01, Serial0/1
192.168.100.0/32 is subnetted, 1 subnets
O 192.168.100.100 [110/65] via 192.168.0.13, 00:00:01, Serial0/1
192.168.3.0/30 is subnetted, 1 subnets
O IA 192.168.3.0 [110/138] via 192.168.0.13, 00:00:01, Serial0/1
R4#show ip ospf database
OSPF Router with ID (4.4.4.4) (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 75 0x80000004 0x00AE5F 8
2.2.2.2 2.2.2.2 76 0x80000002 0x00EB54 1
3.3.3.3 3.3.3.3 75 0x80000002 0x00455E 2
4.4.4.4 4.4.4.4 116 0x80000002 0x006035 2
5.5.5.5 5.5.5.5 117 0x80000002 0x00A4E0 2
9.9.9.9 9.9.9.9 110 0x80000001 0x000F4C 2
Net Link States (Area 0)
Link ID ADV Router Age Seq# Checksum
192.168.0.3 3.3.3.3 76 0x80000001 0x00703C
Summary Net Link States (Area 0)
Link ID ADV Router Age Seq# Checksum
10.0.1.1 9.9.9.9 50 0x80000001 0x00E22A
10.0.1.2 9.9.9.9 18 0x80000001 0x005B70
10.0.1.3 9.9.9.9 50 0x80000001 0x005179
10.0.10.10 9.9.9.9 20 0x80000001 0x00B108
10.0.11.11 9.9.9.9 52 0x80000001 0x009C1B
192.168.3.0 9.9.9.9 107 0x80000001 0x00F9AB
192.168.33.33 9.9.9.9 62 0x80000001 0x007FE2
192.168.168.0 2.2.2.2 118 0x80000001 0x00AE6D
192.168.169.170 2.2.2.2 63 0x80000001 0x001557
R1#show ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route
Gateway of last resort is not set
192.168.13.0/32 is subnetted, 1 subnets
O 192.168.13.13 [110/11] via 192.168.0.3, 00:24:15, FastEthernet0/0
10.0.0.0/32 is subnetted, 5 subnets
O IA 10.0.1.3 [110/128] via 192.168.0.22, 00:23:49, Serial0/0
O IA 10.0.1.2 [110/128] via 192.168.0.22, 00:23:19, Serial0/0
O IA 10.0.11.11 [110/129] via 192.168.0.22, 00:23:49, Serial0/0
O IA 10.0.10.10 [110/129] via 192.168.0.22, 00:23:19, Serial0/0
O IA 10.0.1.1 [110/64] via 192.168.0.22, 00:23:49, Serial0/0
192.168.0.0/24 is variably subnetted, 4 subnets, 2 masks
C 192.168.0.12/30 is directly connected, Serial0/1
C 192.168.0.0/29 is directly connected, FastEthernet0/0
C 192.168.0.16/30 is directly connected, Serial0/2
C 192.168.0.20/30 is directly connected, Serial0/0
192.168.168.0/30 is subnetted, 1 subnets
O IA 192.168.168.0 [110/20] via 192.168.0.2, 00:24:17, FastEthernet0/0
C 192.168.100.0/24 is directly connected, Loopback0
192.168.169.0/32 is subnetted, 1 subnets
O IA 192.168.169.170 [110/21] via 192.168.0.2, 00:24:04, FastEthernet0/0
192.168.3.0/30 is subnetted, 1 subnets
O IA 192.168.3.0 [110/74] via 192.168.0.22, 00:24:17, Serial0/0
192.168.33.0/32 is subnetted, 1 subnets
O IA 192.168.33.33 [110/75] via 192.168.0.22, 00:24:02, Serial0/0
Now, let's add the redistribute eigrp 1 command in OSPF configuration mode:
R4(config)#router ospf 1
R4(config-router)#redistribute eigrp 1
% Only classful networks will be redistributed
According to Rule 1 from above, not using the "subnets" keyword within the command redistributes only entire classful subnets listed in the routing table of R4.
Now, we can check again the OSPF database on R4 and routing table on R1:
R4#show ip ospf database
OSPF Router with ID (4.4.4.4) (Process ID 1)
Router Link States (Area 0)
Link ID ADV Router Age Seq# Checksum Link count
1.1.1.1 1.1.1.1 481 0x80000004 0x00AE5F 8
2.2.2.2 2.2.2.2 482 0x80000002 0x00EB54 1
3.3.3.3 3.3.3.3 481 0x80000002 0x00455E 2
4.4.4.4 4.4.4.4 351 0x80000003 0x00642E 2
5.5.5.5 5.5.5.5 523 0x80000002 0x00A4E0 2
9.9.9.9 9.9.9.9 516 0x80000001 0x000F4C 2
Net Link States (Area 0)
Link ID ADV Router Age Seq# Checksum
192.168.0.3 3.3.3.3 482 0x80000001 0x00703C
Summary Net Link States (Area 0)
Link ID ADV Router Age Seq# Checksum
10.0.1.1 9.9.9.9 456 0x80000001 0x00E22A
10.0.1.2 9.9.9.9 425 0x80000001 0x005B70
10.0.1.3 9.9.9.9 456 0x80000001 0x005179
10.0.10.10 9.9.9.9 426 0x80000001 0x00B108
10.0.11.11 9.9.9.9 458 0x80000001 0x009C1B
192.168.3.0 9.9.9.9 513 0x80000001 0x00F9AB
192.168.33.33 9.9.9.9 468 0x80000001 0x007FE2
192.168.168.0 2.2.2.2 524 0x80000001 0x00AE6D
192.168.169.170 2.2.2.2 469 0x80000001 0x001557
Type-5 AS External Link States
Link ID ADV Router Age Seq# Checksum Tag
192.168.44.0 4.4.4.4 352 0x80000001 0x00D723 0
192.168.55.0 4.4.4.4 352 0x80000001 0x005E91 0
R1#show ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route
Gateway of last resort is not set
192.168.13.0/32 is subnetted, 1 subnets
O 192.168.13.13 [110/11] via 192.168.0.3, 00:06:03, FastEthernet0/0
O E2 192.168.44.0/24 [110/20] via 192.168.0.14, 00:06:03, Serial0/1
O E2 192.168.55.0/24 [110/20] via 192.168.0.14, 00:06:03, Serial0/1
10.0.0.0/32 is subnetted, 5 subnets
O IA 10.0.1.3 [110/128] via 192.168.0.22, 00:06:03, Serial0/0
O IA 10.0.1.2 [110/128] via 192.168.0.22, 00:06:03, Serial0/0
O IA 10.0.11.11 [110/129] via 192.168.0.22, 00:06:03, Serial0/0
O IA 10.0.10.10 [110/129] via 192.168.0.22, 00:06:05, Serial0/0
O IA 10.0.1.1 [110/64] via 192.168.0.22, 00:06:05, Serial0/0
192.168.0.0/24 is variably subnetted, 4 subnets, 2 masks
C 192.168.0.12/30 is directly connected, Serial0/1
C 192.168.0.0/29 is directly connected, FastEthernet0/0
C 192.168.0.16/30 is directly connected, Serial0/2
C 192.168.0.20/30 is directly connected, Serial0/0
192.168.168.0/30 is subnetted, 1 subnets
O IA 192.168.168.0 [110/20] via 192.168.0.2, 00:06:06, FastEthernet0/0
C 192.168.100.0/24 is directly connected, Loopback0
192.168.169.0/32 is subnetted, 1 subnets
O IA 192.168.169.170 [110/21] via 192.168.0.2, 00:06:06, FastEthernet0/0
192.168.3.0/30 is subnetted, 1 subnets
O IA 192.168.3.0 [110/74] via 192.168.0.22, 00:06:06, Serial0/0
192.168.33.0/32 is subnetted, 1 subnets
O IA 192.168.33.33 [110/75] via 192.168.0.22, 00:06:06, Serial0/0
As seen above, the only external OSPF routes on R1 are the ones which represent classful subnets in R4's routing table.
By changing the configuration to use the redistribute eigrp 1 subnets command, OSPF indeed redistributes the expected routes:
R4(config)#router ospf 1
R4(config-router)#redistribute eigrp 1 subnets
Now, let's check the tables again and see if the EIGRP subnets have been redistributed into the OSPF domain - and indeed they have been:
R4#show ip ospf database
OSPF Router with ID (4.4.4.4) (Process ID 1)
Router Link States (Area 0)
Link ID ADV Router Age Seq# Checksum Link count
1.1.1.1 1.1.1.1 732 0x80000004 0x00AE5F 8
2.2.2.2 2.2.2.2 733 0x80000002 0x00EB54 1
3.3.3.3 3.3.3.3 732 0x80000002 0x00455E 2
4.4.4.4 4.4.4.4 602 0x80000003 0x00642E 2
5.5.5.5 5.5.5.5 774 0x80000002 0x00A4E0 2
9.9.9.9 9.9.9.9 767 0x80000001 0x000F4C 2
Net Link States (Area 0)
Link ID ADV Router Age Seq# Checksum
192.168.0.3 3.3.3.3 733 0x80000001 0x00703C
Summary Net Link States (Area 0)
Link ID ADV Router Age Seq# Checksum
10.0.1.1 9.9.9.9 707 0x80000001 0x00E22A
10.0.1.2 9.9.9.9 675 0x80000001 0x005B70
10.0.1.3 9.9.9.9 707 0x80000001 0x005179
10.0.10.10 9.9.9.9 677 0x80000001 0x00B108
10.0.11.11 9.9.9.9 709 0x80000001 0x009C1B
192.168.3.0 9.9.9.9 764 0x80000001 0x00F9AB
192.168.33.33 9.9.9.9 719 0x80000001 0x007FE2
192.168.168.0 2.2.2.2 775 0x80000001 0x00AE6D
192.168.169.170 2.2.2.2 720 0x80000001 0x001557
Type-5 AS External Link States
Link ID ADV Router Age Seq# Checksum Tag
172.16.0.0 4.4.4.4 78 0x80000001 0x00D7FE 0
172.16.0.4 4.4.4.4 78 0x80000001 0x00AF23 0
172.16.0.8 4.4.4.4 78 0x80000001 0x008747 0
172.16.0.12 4.4.4.4 78 0x80000001 0x005F6B 0
172.16.111.0 4.4.4.4 78 0x80000001 0x002044 0
192.168.44.0 4.4.4.4 603 0x80000001 0x00D723 0
192.168.55.0 4.4.4.4 603 0x80000001 0x005E91 0
R1#show ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route
Gateway of last resort is not set
192.168.13.0/32 is subnetted, 1 subnets
O 192.168.13.13 [110/11] via 192.168.0.3, 00:10:58, FastEthernet0/0
O E2 192.168.44.0/24 [110/20] via 192.168.0.14, 00:10:58, Serial0/1
172.16.0.0/16 is variably subnetted, 5 subnets, 2 masks
O E2 172.16.0.12/30 [110/20] via 192.168.0.14, 00:02:16, Serial0/1
O E2 172.16.0.8/30 [110/20] via 192.168.0.14, 00:02:16, Serial0/1
O E2 172.16.0.4/30 [110/20] via 192.168.0.14, 00:02:16, Serial0/1
O E2 172.16.0.0/30 [110/20] via 192.168.0.14, 00:02:16, Serial0/1
O E2 172.16.111.0/24 [110/20] via 192.168.0.14, 00:02:18, Serial0/1
O E2 192.168.55.0/24 [110/20] via 192.168.0.14, 00:10:59, Serial0/1
10.0.0.0/32 is subnetted, 5 subnets
O IA 10.0.1.3 [110/128] via 192.168.0.22, 00:10:59, Serial0/0
O IA 10.0.1.2 [110/128] via 192.168.0.22, 00:10:59, Serial0/0
O IA 10.0.11.11 [110/129] via 192.168.0.22, 00:11:00, Serial0/0
O IA 10.0.10.10 [110/129] via 192.168.0.22, 00:11:00, Serial0/0
O IA 10.0.1.1 [110/64] via 192.168.0.22, 00:11:00, Serial0/0
192.168.0.0/24 is variably subnetted, 4 subnets, 2 masks
C 192.168.0.12/30 is directly connected, Serial0/1
C 192.168.0.0/29 is directly connected, FastEthernet0/0
C 192.168.0.16/30 is directly connected, Serial0/2
C 192.168.0.20/30 is directly connected, Serial0/0
192.168.168.0/30 is subnetted, 1 subnets
O IA 192.168.168.0 [110/20] via 192.168.0.2, 00:11:00, FastEthernet0/0
C 192.168.100.0/24 is directly connected, Loopback0
192.168.169.0/32 is subnetted, 1 subnets
O IA 192.168.169.170 [110/21] via 192.168.0.2, 00:11:00, FastEthernet0/0
192.168.3.0/30 is subnetted, 1 subnets
O IA 192.168.3.0 [110/74] via 192.168.0.22, 00:11:00, Serial0/0
192.168.33.0/32 is subnetted, 1 subnets
O IA 192.168.33.33 [110/75] via 192.168.0.22, 00:11:02, Serial0/0
Notes:
- According to show ip ospf database, we can see that indeed R4 is the advertising router of the new Type 5 LSAs: 4.4.4.4
- Looking at R1's routing table, we confirm that the default external metric type is E2 and the default metric for each route coming from EIGRP is 20. Each route being an E2 route, internal OSPF costs are not added to the cost of the route.
No comments:
Post a Comment