04-14-2014 12:11 AM - edited 03-04-2019 10:47 PM
hi,
In this topology Rip and Ospf redistributing routes each other. R2 and R3 is ASBR and both routers doing mutual redistribution. Rip routes have tag 200 and Ospf 300. i use route filter tag to avoid routing loops in this topology but when R3 try to ping R1 loop it going via ospf domain to reach the destination.We can use distance cmd to solve this issue but i must use route tag to achieve the goal.
R2:-
router ospf 1
log-adjacency-changes
redistribute rip subnets route-map TAG200-DENY300
network 192.168.24.0 0.0.0.255 area 0
!
router rip
version 2
redistribute ospf 1 metric 5 route-map TAG300-DENY200
network 10.0.0.0
!
ip forward-protocol nd
!
!
no ip http server
no ip http secure-server
!
no cdp log mismatch duplex
!
route-map TAG200-DENY300 deny 10
match tag 300
!
route-map TAG200-DENY300 permit 20
set tag 200
!
route-map TAG300-DENY200 deny 10
match tag 200
!
route-map TAG300-DENY200 permit 20
set tag 300
------------------------------------------------------------------------------------------------
R3:-
router ospf 1
log-adjacency-changes
redistribute rip subnets route-map TAG300-DENY200
network 192.168.35.0 0.0.0.255 area 0
!
router rip
version 2
redistribute ospf 1 metric 5 route-map TAG300-DENY200
network 10.0.0.0
!
ip forward-protocol nd
!
!
no ip http server
no ip http secure-server
!
no cdp log mismatch duplex
!
route-map TAG200-DENY300 deny 10
match tag 300
!
route-map TAG200-DENY300 permit 20
set tag 200
!
route-map TAG300-DENY200 deny 10
match tag 200
!
route-map TAG300-DENY200 permit 20
set tag 300
--------------------------------------------------------------------------------------------------
R2#sh ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
Gateway of last resort is not set
O 192.168.45.0/24 [110/11] via 192.168.24.4, 00:59:53, FastEthernet1/0
C 192.168.24.0/24 is directly connected, FastEthernet1/0
10.0.0.0/24 is subnetted, 3 subnets
C 10.1.12.0 is directly connected, FastEthernet0/0
R 10.1.1.0 [120/1] via 10.1.12.1, 00:00:09, FastEthernet0/0
C 10.1.23.0 is directly connected, FastEthernet0/1
O 192.168.35.0/24 [110/21] via 192.168.24.4, 00:59:53, FastEthernet1/0
------------------------------------------------------------------------------------------------------------
R3#sh ip route
Gateway of last resort is not set
O 192.168.45.0/24 [110/20] via 192.168.35.5, 01:00:36, FastEthernet0/1
O 192.168.24.0/24 [110/30] via 192.168.35.5, 01:00:36, FastEthernet0/1
10.0.0.0/24 is subnetted, 3 subnets
O E2 10.1.12.0 [110/20] via 192.168.35.5, 00:58:47, FastEthernet0/1
O E2 10.1.1.0 [110/20] via 192.168.35.5, 00:58:33, FastEthernet0/1
C 10.1.23.0 is directly connected, FastEthernet0/0
C 192.168.35.0/24 is directly connected, FastEthernet0/1
R3#
Solved! Go to Solution.
04-17-2014 12:48 PM
Awesome!!! Understood well sir , am going to remake this lab again.
Thanks a lot to Milan, Jon and Yap Chin.
04-17-2014 12:34 PM
Hi Feroz thanks for this interesting network setup and questions.
I have recreated the network setup in Dynagen/Dynamips (https://db.tt/uz0xMBJp).
Below shows the IP routing tables on RT2 and RT3 upon the initial routers bootup.
Note that OSPF is not up yet due to the 40-second OSPF Wait timer for broadcast networks and DR/BDR election.
RT2#sh ip route Gateway of last resort is not set C 192.168.24.0/24 is directly connected, FastEthernet1/0 Gateway of last resort is not set R 192.168.24.0/24 [120/5] via 10.1.23.2, 00:00:16, FastEthernet0/0 |
Below shows the IP routing tables on RT2 and RT3 after OSPF is up and running.
RT2# Gateway of last resort is not set O 192.168.45.0/24 [110/11] via 192.168.24.4, 00:01:05, FastEthernet1/0 Gateway of last resort is not set O 192.168.45.0/24 [110/20] via 192.168.35.5, 00:01:12, FastEthernet0/1 |
There is a routing loop (RT3 > RT2 > RT4 > RT5 > RT3) as shown in the traceroute result below.
RT3#trace 10.1.1.1 Type escape sequence to abort. 1 10.1.23.2 36 msec 52 msec 28 msec |
The routing loop is resolved after modified the misconfiguration on RT3.
RT3#conf t Gateway of last resort is not set O 192.168.45.0/24 [110/20] via 192.168.35.5, 00:03:12, FastEthernet0/1 Gateway of last resort is not set O 192.168.45.0/24 [110/11] via 192.168.24.4, 00:04:07, FastEthernet1/0 Type escape sequence to abort. 1 192.168.35.5 48 msec 44 msec 24 msec |
After the routing loop is resolved, the suboptimal routing occurs, in which the routing path from RT3 towards RT1 is through the OSPF network (RT3 > RT5 > RT4 > RT2 > RT1), while the preferred routing path is through the RIP network (RT3 > RT2 > RT1).
I would say that this is a chicken-and-egg problem and is related to administrative distance.
Below shows how I solved the traffic engineering problem by tuning the AD for certain OSPF routes (using ACL for better granularity control) to make them less preferred over the RIP routes. I am unable to think of better solutions for the problem at the moment.
This is similar to the BGP Backdoor Route feature, which is to tune the AD for EBGP routes from 20 to 200, in order for other IGP routes (OSPF - 110, EIGRP - 90) to be preferred over the EBGP routes. More info about BGP Backdoor Routes at https://db.tt/hXs614n3.
RT2#conf t Gateway of last resort is not set O 192.168.45.0/24 [110/11] via 192.168.24.4, 00:00:06, FastEthernet1/0 Gateway of last resort is not set O 192.168.45.0/24 [110/20] via 192.168.35.5, 00:00:29, FastEthernet0/1 Type escape sequence to abort. 1 10.1.23.2 36 msec 40 msec 12 msec |
04-17-2014 12:50 PM
Awesome!!! Understood well sir , am going to remake this lab again.
Thanks a lot to Milan, Jon and Yap Chin.
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