OSPF reverse path Issue

[deepak.nayak1]

Hi,

We have 2 wan links at branch end to reach the DC. When we are trying to access to DC applications outgoing traffic is going one link and return traffic is taking other link.

We want return traffic on same link.

Please suggest how we take fix the issue.

Regards,

Deepak

[Julio E. Moisa]

Hi,

Have you modified the OSPF cost under the interfaces, it should prefer the lowest value.

Also have you analyzed why it is preferring other link from the DC?

You can use a show ip ospf database and show ip route <branch source network>

[deepak.nayak1]

Hi,

Thanks for your reply.

Here I am sending output logs with entire router configuration at branch end. Please suggest.

[Julio E. Moisa]

Thank you Deepak,

Could you please share diagram (no a high level design) to know how it is connected?, The traffic from the branch to the DC is going to the correct path, right but it is not the same from the DC to the branch. 

I would like to see why the DC selects other patch. 

For example

Branch, source network send a packet to DC through link 1

DC: Reply a response to Branch through link 2.

Is possible to execute a show ip route <source network>  from the DC location? Probably the source is not being known through the link 1 just through the link 2, or there are different metrics. 

Thank you. 

[deepak.nayak1]

Hi,

Here is logs from DC  and attached configuration at DC end.

sh ip route 10.221.1.37
Routing entry for 10.221.1.37/32
  Known via "connected", distance 0, metric 0 (connected)
  Routing Descriptor Blocks:
  * directly connected, via GigabitEthernet0/0/0
      Route metric is 0, traffic share count is 1

[Julio E. Moisa]

Thank you, can you provide an output for other network not directly connected.

Thank you in advance. 

[deepak.nayak1]

Hi,

KGI-MPLS-CORE1#sh ip route
Codes: L - local, 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, H - NHRP, l - LISP
       a - application route
       + - replicated route, % - next hop override, p - overrides from PfR

Gateway of last resort is 10.221.1.33 to network 0.0.0.0

S*    0.0.0.0/0 [1/0] via 10.221.1.33
      10.0.0.0/8 is variably subnetted, 69 subnets, 4 masks
C        10.221.1.32/27 is directly connected, GigabitEthernet0/0/0
L        10.221.1.37/32 is directly connected, GigabitEthernet0/0/0
C        10.221.2.1/32 is directly connected, Loopback0
O E2     10.221.2.2/32 [110/20] via 10.221.1.38, 7w0d, GigabitEthernet0/0/0
O E2     10.221.2.3/32 [110/1] via 10.221.1.38, 3d13h, GigabitEthernet0/0/0
O E2     10.221.2.4/32 [110/98] via 10.221.1.38, 1d06h, GigabitEthernet0/0/0
O IA     10.221.2.5/32 [110/11] via 10.221.1.38, 2w2d, GigabitEthernet0/0/0
O IA     10.221.2.6/32
           [110/11] via 10.221.1.38, 08:07:09, GigabitEthernet0/0/0
O IA     10.221.2.7/32 [110/11] via 10.221.3.2, 3d22h, GigabitEthernet0/1/0
                       [110/11] via 10.221.1.38, 3d22h, GigabitEthernet0/0/0
O IA     10.221.2.8/32 [110/206] via 10.221.1.38, 1w2d, GigabitEthernet0/0/0
O E2     10.221.2.9/32 [110/1] via 10.221.1.38, 2w0d, GigabitEthernet0/0/0
O        10.221.2.10/32 [110/15] via 10.221.3.2, 1w6d, GigabitEthernet0/1/0
S        10.221.2.11/32 [1/0] via 10.221.203.2
O E2     10.221.2.12/32
           [110/196] via 10.221.1.38, 05:17:32, GigabitEthernet0/0/0
O E2     10.221.2.14/32 [110/1] via 10.221.1.38, 1w2d, GigabitEthernet0/0/0
O E2     10.221.2.15/32
           [110/1] via 10.221.1.38, 11:22:06, GigabitEthernet0/0/0
O IA     10.221.2.16/32
           [110/11] via 10.221.3.2, 14:05:33, GigabitEthernet0/1/0
           [110/11] via 10.221.1.38, 14:05:33, GigabitEthernet0/0/0
C        10.221.3.0/30 is directly connected, GigabitEthernet0/1/0
L        10.221.3.1/32 is directly connected, GigabitEthernet0/1/0
O        10.221.3.4/30 [110/10] via 10.221.1.38, 6w6d, GigabitEthernet0/0/0
O        10.221.3.8/30 [110/14] via 10.221.3.2, 7w0d, GigabitEthernet0/1/0
O IA     10.221.3.12/30 [110/10] via 10.221.3.2, 3d22h, GigabitEthernet0/1/0
O E2     10.221.3.16/30 [110/1] via 10.221.3.2, 7w0d, GigabitEthernet0/1/0
O E2     10.221.3.20/30 [110/1] via 10.221.3.2, 1d07h, GigabitEthernet0/1/0
O E2     10.221.3.24/30 [110/1] via 10.221.3.2, 7w0d, GigabitEthernet0/1/0
O E2     10.221.3.28/30 [110/1] via 10.221.3.2, 7w0d, GigabitEthernet0/1/0
O E2     10.221.3.32/30 [110/1] via 10.221.3.2, 2w6d, GigabitEthernet0/1/0
O E2     10.221.3.36/30 [110/1] via 10.221.3.2, 4w5d, GigabitEthernet0/1/0
O E2     10.221.3.40/30 [110/1] via 10.221.3.2, 2w2d, GigabitEthernet0/1/0
C        10.221.5.0/30 is directly connected, GigabitEthernet0/1/1
L        10.221.5.1/32 is directly connected, GigabitEthernet0/1/1
O        10.221.5.4/30 [110/10] via 10.221.1.38, 7w0d, GigabitEthernet0/0/0
O E2     10.221.5.12/30
           [110/1] via 10.221.1.38, 00:12:57, GigabitEthernet0/0/0
O IA     10.221.5.16/30 [110/11] via 10.221.1.38, 1w1d, GigabitEthernet0/0/0
O IA     10.221.5.20/30
           [110/11] via 10.221.1.38, 08:07:10, GigabitEthernet0/0/0
O IA     10.221.5.28/30 [110/11] via 10.221.1.38, 4w2d, GigabitEthernet0/0/0
O IA     10.221.5.32/30 [110/11] via 10.221.1.38, 3w5d, GigabitEthernet0/0/0
O E2     10.221.5.36/30
           [110/1] via 10.221.1.38, 00:12:57, GigabitEthernet0/0/0
S        10.221.12.37/32 [1/0] via 10.221.1.33
S        10.221.12.65/32 [1/0] via 10.221.1.33
S        10.221.12.100/32 [1/0] via 10.221.1.33
S        10.221.12.101/32 [1/0] via 10.221.1.33
S        10.221.12.102/32 [1/0] via 10.221.1.33
S        10.221.16.22/32 [1/0] via 10.221.1.33
S        10.221.16.23/32 [1/0] via 10.221.1.33
S        10.221.16.24/32 [1/0] via 10.221.1.33
S        10.221.16.25/32 [1/0] via 10.221.1.33
S        10.221.16.26/32 [1/0] via 10.221.1.33
S        10.221.16.27/32 [1/0] via 10.221.1.33
S        10.221.16.30/32 [1/0] via 10.221.1.33
S        10.221.16.31/32 [1/0] via 10.221.1.33
S        10.221.16.32/32 [1/0] via 10.221.1.33
O E2     10.221.20.0/24 [110/1] via 10.221.1.38, 3d13h, GigabitEthernet0/0/0
O E2     10.221.21.0/24 [110/98] via 10.221.1.38, 1d06h, GigabitEthernet0/0/0
O IA     10.221.22.0/24 [110/11] via 10.221.1.38, 2w2d, GigabitEthernet0/0/0
O IA     10.221.23.0/24
           [110/11] via 10.221.1.38, 08:07:10, GigabitEthernet0/0/0
O IA     10.221.24.0/24 [110/11] via 10.221.3.2, 3d22h, GigabitEthernet0/1/0
                        [110/11] via 10.221.1.38, 3d22h, GigabitEthernet0/0/0
O IA     10.221.25.0/24 [110/206] via 10.221.1.38, 1w2d, GigabitEthernet0/0/0
O E2     10.221.26.0/24 [110/1] via 10.221.1.38, 2w0d, GigabitEthernet0/0/0
O        10.221.27.0/24 [110/15] via 10.221.3.2, 1w6d, GigabitEthernet0/1/0
O E2     10.221.28.0/24
           [110/196] via 10.221.1.38, 05:17:33, GigabitEthernet0/0/0
O E2     10.221.30.0/24 [110/1] via 10.221.1.38, 1w2d, GigabitEthernet0/0/0
O E2     10.221.31.0/24
           [110/1] via 10.221.1.38, 11:22:07, GigabitEthernet0/0/0
S        10.221.156.0/24 [1/0] via 10.221.203.2
C        10.221.203.0/30 is directly connected, GigabitEthernet0/2/0
L        10.221.203.1/32 is directly connected, GigabitEthernet0/2/0
C        10.221.203.4/30 is directly connected, GigabitEthernet0/2/1
L        10.221.203.5/32 is directly connected, GigabitEthernet0/2/1
S        10.221.204.0/24 [1/0] via 10.221.203.6
      152.102.0.0/28 is subnetted, 1 subnets
S        152.102.153.192 [1/0] via 10.221.1.33
      172.23.0.0/29 is subnetted, 1 subnets
O E2     172.23.4.32 [110/1] via 10.221.3.2, 7w0d, GigabitEthernet0/1/0
      172.34.0.0/16 is variably subnetted, 3 subnets, 2 masks
O E2     172.34.158.8/29
           [110/1] via 10.221.3.2, 07:36:09, GigabitEthernet0/1/0
O E2     172.34.158.16/29
           [110/1] via 10.221.3.2, 07:52:25, GigabitEthernet0/1/0
O E2     172.34.163.65/32
           [110/1] via 10.221.3.2, 08:05:24, GigabitEthernet0/1/0
      172.37.0.0/30 is subnetted, 1 subnets
O E2     172.37.84.192 [110/1] via 10.221.3.2, 08:05:24, GigabitEthernet0/1/0
      172.38.0.0/30 is subnetted, 1 subnets
O E2     172.38.34.0 [110/1] via 10.221.3.2, 08:05:24, GigabitEthernet0/1/0
      192.168.10.0/24 is variably subnetted, 2 subnets, 2 masks
C        192.168.10.0/30 is directly connected, Tunnel1
L        192.168.10.1/32 is directly connected, Tunnel1
      192.168.11.0/24 is variably subnetted, 2 subnets, 2 masks
C        192.168.11.0/30 is directly connected, Tunnel2
L        192.168.11.1/32 is directly connected, Tunnel2
      192.168.12.0/24 is variably subnetted, 2 subnets, 2 masks
C        192.168.12.0/30 is directly connected, Tunnel3
L        192.168.12.1/32 is directly connected, Tunnel3
      202.92.238.0/28 is subnetted, 1 subnets
O E2     202.92.238.208 [110/1] via 10.221.3.2, 08:05:25, GigabitEthernet0/1/0
      202.92.239.0/24 is variably subnetted, 7 subnets, 6 masks
O E2     202.92.239.0/26
           [110/1] via 10.221.3.2, 07:17:40, GigabitEthernet0/1/0
O E2     202.92.239.128/25
           [110/1] via 10.221.3.2, 08:05:25, GigabitEthernet0/1/0
O E2     202.92.239.176/28
           [110/1] via 10.221.3.2, 07:17:40, GigabitEthernet0/1/0
O E2     202.92.239.184/29
           [110/1] via 10.221.3.2, 08:04:11, GigabitEthernet0/1/0
O E2     202.92.239.192/26
           [110/1] via 10.221.3.2, 08:05:25, GigabitEthernet0/1/0
O E2     202.92.239.192/27
           [110/1] via 10.221.3.2, 08:05:25, GigabitEthernet0/1/0
O E2     202.92.239.233/32
           [110/1] via 10.221.3.2, 07:20:49, GigabitEthernet0/1/0
KGI-MPLS-CORE1#

[Predrag Jovic]

There is a lot of information missing here. It is not clear what is exactly current design.
Possibilities with OSPF are design dependent (generally summarization and manipulation with route types are preferred with OSPF design traffic engineering (if design allows it)).
1. If you are trying to use the same traffic path for all networks advertise different network types to ISPs (in both directions). For example you can advertise external routes E1 type from DC and Branch to ISP1 for specific set of routes (or all routes) and advertise external routes E2 type from DC and Branch to ISP2 for all routes (or for load balancing some portion of routes can be advertised as E1 to ISP2).
2. Route summarization (or route leaking) to one ISP1 for traffic engineering and send unsumarized routes to ISP2 that is preferred for specific routes.
Since you have area 0 and area 4 I guess at least one of the scenarios should be available (I guess scenario 2 would seem to be preferred).
- Problem with changing interface cost value is that cost is affecting all route calculations.
- Problem with changing interface bandwidth value will influence QoS and all route calculations.

But, once again, it is OSPF design dependent...

[Julio E. Moisa]

there are many subnets learned through these interfaces: 

GigabitEthernet0/0/0

GigabitEthernet0/1/0

Im assumming this device is located into the DC location, could you indicate what interface should be used to have symmetric traffic?

[Joseph W. Doherty]

We want return traffic on same link.

While using both links or just one of the two links?

If you only desire to direct all you traffic across one link, both directions, as Paul and Julio have noted, insuring one link is preferred over the other, would be the way to accomplish it.

However, if you're looking to use both links, concurrently, and have individual application flows use the same path for both inbound and outbound, that's much more difficult to accomplish.

If that's also what you're trying to accomplish, may I ask why?

[paul driver]

Hello

In this case the options you could use for basic path manipulation would be:

• decreasing/increasing the interface Bandwidth or Cost to the less preferred link
• Policy Base route (PBR)
• Assign least preferred path interfaces to a non backbone ospf area

Between those options, Applying a higher opsf interface interface cost is less disruptive and most simplistic

either side of the peering--
in x/x
ip ospf cost xxx

res
Paul