10-21-2013 12:24 PM - edited 03-04-2019 09:22 PM
I'm not sure what I'm even looking to do can even be done but here's the scenario.
Router A advertises a default route to all ospf nodes with the "default-information-originate always" command
Router B connects to router A and to Router D
Router C connects to router A and to Router D
Router D has many networks advertised but we will say these are the pertinent ones:
Network 1 - 192.168.10.0/30
and
Network 2 - 192.168.11.0/30
And as previously mentioned, Router D has a connection to Router B and C on their own indivudual link.
All routers are part of the same area.
Is there a way to make it so that router A, see's Network 1 and prefers the path through Router B instead of Router C, and that Network 2 has a prefered path through Router C instead of B while also having default traffic take the same path it came from?
If this were EIGRP, I would easily make a distribute list for each of the interfaces on Router D that connect to B and C but distribute lists won't work in OSPF, is there an alternative?
Solved! Go to Solution.
10-22-2013 12:39 AM
Hello Ron,
Hope your doing well,
First i would like to tell you that OSPF doesn't support unequal load balancing like eigrp does so it is difficult to do prefix link load balancing with using cost.In your case if all of your link are having same bandwidth you might be having 2 equal cost for each network i.e for net1 and net2.rest of packet forwarding is done on data plane that is your cef is doing packet forwarding depending on per destination/per packet.
You can verify your packet forwarding for specific subnet using this command and check on which interface packets going
sh ip cef 192.168.1.0 255.255.255.252
sh ip cef exact-route
In your case you can use policy-base routing.
for net 1 you match in Access-list and set next hop of router B and for net 2 you can use normal routing.
Here is doc link for PBR
https://supportforums.cisco.com/docs/DOC-1634
Hope it helps
Regards,
Ashish
10-21-2013 04:48 PM
Hi,
May be this link will help:-
http://www.cisco.com/en/US/docs/ios/12_0s/feature/guide/routmap.html
Regards,
Alex.
Please rate useful posts.
10-22-2013 12:39 AM
Hello Ron,
Hope your doing well,
First i would like to tell you that OSPF doesn't support unequal load balancing like eigrp does so it is difficult to do prefix link load balancing with using cost.In your case if all of your link are having same bandwidth you might be having 2 equal cost for each network i.e for net1 and net2.rest of packet forwarding is done on data plane that is your cef is doing packet forwarding depending on per destination/per packet.
You can verify your packet forwarding for specific subnet using this command and check on which interface packets going
sh ip cef 192.168.1.0 255.255.255.252
sh ip cef exact-route
In your case you can use policy-base routing.
for net 1 you match in Access-list and set next hop of router B and for net 2 you can use normal routing.
Here is doc link for PBR
https://supportforums.cisco.com/docs/DOC-1634
Hope it helps
Regards,
Ashish
10-22-2013 01:08 AM
Hi,
One way is to go as Ashish suggest of PBR.
Another way is to use of Distribute list and Distribute list work very well with OSPF.
Distribute-list prevent route getting installed in routing table, they would be there in topology table.
Probably, you can share your config with distribute-list which you tried, so that we can figure out whats missing.
Regards,
Smitesh
10-22-2013 01:20 AM
Hi,
I tried simulating it in LAB..
Can you check below config and output to verify, is this what you wanted...
Route Table before Distribute-list
R1#sh ip ro ospf
2.0.0.0/24 is subnetted, 1 subnets
O 2.2.2.0 [110/2] via 10.10.12.2, 00:02:04, FastEthernet0/1
3.0.0.0/24 is subnetted, 1 subnets
O 3.3.3.0 [110/2] via 10.10.13.3, 00:01:35, FastEthernet0/0
192.168.10.0/30 is subnetted, 1 subnets
O 192.168.10.0 [110/3] via 10.10.13.3, 00:00:13, FastEthernet0/0
[110/3] via 10.10.12.2, 00:00:13, FastEthernet0/1
192.168.11.0/30 is subnetted, 1 subnets
O 192.168.11.0 [110/3] via 10.10.13.3, 00:00:03, FastEthernet0/0
[110/3] via 10.10.12.2, 00:00:03, FastEthernet0/1
10.0.0.0/24 is subnetted, 4 subnets
O 10.10.24.0 [110/2] via 10.10.12.2, 00:02:04, FastEthernet0/1
O 10.10.34.0 [110/2] via 10.10.13.3, 00:01:35, FastEthernet0/0
Now we will apply distribute list as below
R1#sh run | sec ospf
ip ospf network point-to-point
ip ospf 1 area 0
ip ospf 1 area 0
ip ospf 1 area 0
router ospf 1
log-adjacency-changes
default-information originate always
distribute-list prefix NET1 in FastEthernet0/0
distribute-list prefix NET2 in FastEthernet0/1
R1#
R1#sh ip prefix-list
ip prefix-list NET1: 2 entries
seq 5 deny 192.168.11.0/30
seq 10 permit 0.0.0.0/0 le 32
ip prefix-list NET2: 2 entries
seq 5 deny 192.168.10.0/30
seq 10 permit 0.0.0.0/0 le 32
R1#
R1#sh ip route ospf | i 192.168
192.168.10.0/30 is subnetted, 1 subnets
O 192.168.10.0 [110/3] via 10.10.13.3, 00:02:15, FastEthernet0/0
192.168.11.0/30 is subnetted, 1 subnets
O 192.168.11.0 [110/3] via 10.10.12.2, 00:02:15, FastEthernet0/1
Regards,
Smitesh Kharecha
PS: Please rate helpful posts
10-23-2013 12:05 PM
Smitesh, I forgot to add I cannot edit R1's OSPF config, it must stay as it is.
10-23-2013 12:06 PM
Ashish thank you, I did get this working with some PBR
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