When doing a redistribute connected, One consideration in using a redistribute connected is the effect of the command in an existing IGP routes.
On this lab, I’m going to present the issue when redistributing a specified interface or connected route and the solution to remediation that issue.
Pre-Configured Lab in IOU-Web Format
Obtain IOU-WEB VM from : www.routereflector.com/cisco/cisco-iou-web-interface
Redistribute Connected LAB - IOU-Web Format
Pre-Configured Lab in GNS3 Format
Redistribute Connected LAB - GNS3 Format
Router R1 Initial Configuration
interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface Ethernet0/0
ip address 12.12.12.1 255.255.255.0
!
router eigrp 12
network 1.1.1.1 0.0.0.0
network 12.12.12.1 0.0.0.0
Router R2 Initial Configuration
interface Loopback0
des eigrp loopback
ip address 2.2.2.2 255.255.255.255
!
interface Loopback1
des ospf loopback
ip address 2.2.2.22 255.255.255.255
!
interface Ethernet0/0
des eigrp connected interface
ip address 12.12.12.2 255.255.255.0
!
interface Ethernet0/1
des ospf connected interface
ip address 23.23.23.2 255.255.255.0
!
interface Ethernet0/2
des connected interface
ip address 24.24.24.2 255.255.255.0
router eigrp 12
network 2.2.2.2 0.0.0.0
network 12.12.12.2 0.0.0.0
redistribute ospf 23 metric 1 1 1 1 1
!
router ospf 23
redistribute eigrp 12 subnets
network 2.2.2.22 0.0.0.0 area 0
network 23.23.23.2 0.0.0.0 area 0
Router R3 Initial Configuration
interface Loopback0
ip address 3.3.3.3 255.255.255.255
!
interface Ethernet0/0
no ip address
shutdown
!
interface Ethernet0/1
ip address 23.23.23.3 255.255.255.0
!
router ospf 23
network 3.3.3.3 0.0.0.0 area 0
network 23.23.23.3 0.0.0.0 area 0
Routing Table before introducing redistribute connected on R2
R1>show ip route eigrp
2.0.0.0/32 is subnetted, 2 subnets
D 2.2.2.2 [90/409600] via 12.12.12.2, 00:20:25, Ethernet0/0
D EX 2.2.2.22 [170/2560025856] via 12.12.12.2, 00:12:17, Ethernet0/0
3.0.0.0/32 is subnetted, 1 subnets
D EX 3.3.3.3 [170/2560025856] via 12.12.12.2, 00:20:25, Ethernet0/0
23.0.0.0/24 is subnetted, 1 subnets
D EX 23.23.23.0 [170/2560025856] via 12.12.12.2, 00:12:17, Ethernet0/0
R3>show ip route ospf 1.0.0.0/32 is subnetted, 1 subnets O E2 1.1.1.1 [110/20] via 23.23.23.2, 00:22:43, Ethernet0/1 2.0.0.0/32 is subnetted, 2 subnets O E2 2.2.2.2 [110/20] via 23.23.23.2, 00:04:08, Ethernet0/1 O 2.2.2.22 [110/11] via 23.23.23.2, 00:26:10, Ethernet0/1 12.0.0.0/24 is subnetted, 1 subnets O E2 12.12.12.0 [110/20] via 23.23.23.2, 00:04:08, Ethernet0/1 R3#
Introducing redistribute connected on R2
! R2
router ospf 23
redistribute connected route-map LAN subnet
!
router eigrp 12
redistribute connected route-map LAN metric 1 1 1 1 1
route-map LAN
match interface e0/2
Has resulted on the removal of external route from both IGP
R1 debug ip routing logs R1# *Mar 29 20:20:45.989: RT: delete route to 2.2.2.22 via 12.12.12.2, eigrp metric [170/2560025856] *Mar 29 20:20:45.989: RT: no routes to 2.2.2.22, delayed flush *Mar 29 20:20:45.989: RT: delete subnet route to 2.2.2.22/32 *Mar 29 20:20:45.989: RT: updating eigrp 2.2.2.22/32 (0x0) : via 12.12.12.2 Et0/0 0 1048578 *Mar 29 20:20:45.989: RT: rib update return code: 5 *Mar 29 20:20:45.989: RT: delete route to 23.23.23.0 via 12.12.12.2, eigrp metric [170/2560025856] *Mar 29 20:20:45.989: RT: no routes to 23.23.23.0, delayed flush *Mar 29 20:20:45.989: RT: delete subnet route to 23.23.23.0/24 *Mar 29 20:20:45.989: RT: updating eigrp 23.23.23.0/24 (0x0) : R1# via 12.12.12.2 Et0/0 0 1048578 *Mar 29 20:20:45.989: RT: rib update return code: 5 *Mar 29 20:20:46.005: RT: updating eigrp 24.24.24.0/24 (0x0) : via 12.12.12.2 Et0/0 0 1048578 *Mar 29 20:20:46.005: RT: add 24.24.24.0/24 via 12.12.12.2, eigrp metric [170/2560025856] R1#
R3 debug ip routing logs R3# *Mar 29 20:20:46.967: RT: del 2.2.2.2 via 23.23.23.2, ospf metric [110/20] *Mar 29 20:20:46.967: RT: delete subnet route to 2.2.2.2/32 *Mar 29 20:20:47.004: RT: del 12.12.12.0 via 23.23.23.2, ospf metric [110/20] *Mar 29 20:20:47.004: RT: delete subnet route to 12.12.12.0/24 *Mar 29 20:20:47.004: RT: updating ospf 24.24.24.0/24 (0x0) : via 23.23.23.2 Et0/1 0 1048578 *Mar 29 20:20:47.004: RT: add 24.24.24.0/24 via 23.23.23.2, ospf metric [110/20] R3#
If you have noticed, the route being removed are the route from the redistributed IGP’s
Example the route 2.2.2.2/32 which is a loopback IP address native to OSPF is being removed after the redistribution on the EIGRP process.
to correct this issue we need to update the route-map for the connected route to include the connected interface within the R2 to allow have the correct route to be installed.
Modified route-map for R2
route-map CON-EIGRP permit 10
match interface Ethernet0/2
route-map CON-EIGRP permit 20
description OSPF Connected Interface
match interface Ethernet0/1 Loopback1
route-map CON-OSPF permit 10
description EIGRP Connected Interface
match interface Ethernet0/0 Loopback0
router eigrp 12
redistribute connected metric 1 1 1 1 1 route-map CON-EIGRP
router ospf 23
redistribute connected subnets route-map CON-OSPF
Resulting Routes which include the missing external route for both IGP’s
R1#show ip route eigrp
2.0.0.0/32 is subnetted, 2 subnets
D 2.2.2.2 [90/409600] via 12.12.12.2, 00:45:53, Ethernet0/0
D EX 2.2.2.22 [170/2560025856] via 12.12.12.2, 00:00:31, Ethernet0/0
3.0.0.0/32 is subnetted, 1 subnets
D EX 3.3.3.3 [170/2560025856] via 12.12.12.2, 00:45:53, Ethernet0/0
23.0.0.0/24 is subnetted, 1 subnets
D EX 23.23.23.0 [170/2560025856] via 12.12.12.2, 00:00:31, Ethernet0/0
24.0.0.0/24 is subnetted, 1 subnets
D EX 24.24.24.0 [170/2560025856] via 12.12.12.2, 00:18:04, Ethernet0/0
R1#
R3#show ip ro ospf
1.0.0.0/32 is subnetted, 1 subnets
O E2 1.1.1.1 [110/20] via 23.23.23.2, 00:55:15, Ethernet0/1
2.0.0.0/32 is subnetted, 2 subnets
O E2 2.2.2.2 [110/20] via 23.23.23.2, 00:09:53, Ethernet0/1
O 2.2.2.22 [110/11] via 23.23.23.2, 00:58:42, Ethernet0/1
12.0.0.0/24 is subnetted, 1 subnets
O E2 12.12.12.0 [110/20] via 23.23.23.2, 00:09:53, Ethernet0/1
24.0.0.0/24 is subnetted, 1 subnets
O E2 24.24.24.0 [110/20] via 23.23.23.2, 00:27:28, Ethernet0/1
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