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Community Member

OSPF and BGP network

Hi,

 

I have a query regarding the attached network. All the network protocols running are marked in the picture. Explaining about the network I have put the command default-information originate always on the OSPF configuration on the device iosvl2-3 and also on the router IOSv-3.

 

The far end server 2 IP is 50.50.50.50. 

 

When all the devices are up and working fine when i try to traceroute 50.50.50.50 from the switch iosvl2-7, it is taking the path iosvl2-2(HSRP master) >> iosvl2-3  >> iosv-1 >> iosvl2-8 and it reaches the destination Server -2.

 

when i try to traceroute 50.50.50.50 from the switch iosvl2-4, it is taking the path iosv-3 >> iosvl2-8 and it reaches the destination Server -2.

 

Now here lies the problem, if the switch iosvl2-3 is down , and when i try to traceroute 50.50.50.50 from the switch iosvl2-7, it is taking the path iosvl2-2(HSRP master) >> iosvl2-4  >> iosv-3 >> iosvl2-8  and it reaches the destination Server -2.

 

Now if the router iosv-1 is down , then there is problem . When i try to traceroute 50.50.50.50 from the switch iosvl2-7, it is traversing the path iosvl2-2(HSRP master) >> iosvl2-3 >> and then I am getting Destination host unreachable. How can i fix this. BGP needs to run on the left side of the diagram and OSPF needs to run on the Right side because of how the carriers are there in both locations.

 

 

 

8 REPLIES
VIP Gold

Re: OSPF and BGP network

Is the server 2 network being advertised in the OSPF domain or are you simply relying on the default route? If it is just the default route then the fact that iosv-1 is down does not change anything in the routing of the OSPF domain. Default information originate always means the 0.0.0.0 route gets propogated even if the route doesn't exist. Two options:

1- Allow the server 2 network to be propogated into the OSPF domain.

2- Allow BGP to advertise the 0.0.0.0 route into the OSPF domain and use only "default-information originate" without the "always" so that if iosv-1 goes down iosvl2-3 will no longer continue to advertise it.

Hope this makes sense and helps

Community Member

Re: OSPF and BGP network

Please find the answers to your two questions.

1> I will not be able to propagate the Server 2 network into the OSPF domain because in my real life        scenario there are multiple routes coming via the bgp from Service Provider and I wouldnt want all those routes in my ospf domain.

2>From my BGP , I am not getting any default route from my Service Provider (because only internal routes are being propagated via bgp, no internet access needed)

 

So is there any other solution. 

VIP Gold

Re: OSPF and BGP network

So my understanding is that to get to server 2 you must use the default route. Correct?

 

Is there a static default route configured in iosvl2-3 pointing to iosv-1?

 

If yes, if you configure "default information-originate" (without the always), if the connection to iosv-1 fails then the default route in OSPF from iosvl2-3 will be withdrawn and then use the route to iosvl2-4.

 

If no, you could configure conditional default route advertisement based on recieved routes from  iosv-1. See the link below.

https://supportforums.cisco.com/t5/network-infrastructure-documents/conditional-default-route-advertisement-in-ospf/ta-p/3145600

Hope this helps

Community Member

Re: OSPF and BGP network

The OSPF network terminates in the device iosvl2-3. Between iosvl2-3 and  iosv-1 and iosv-1 and iosvl2-8 we have bgp. 

 

So the device iosvl2-3 gets to know about the network of Server 2 via bgp.

 

OSPF area 0  runs between the device iosvl2-3 , iosvl2-1, iosvl2-2,iosvl2-7 and iosvl2-4.

 

The devices behind iosvl2-7 gets to know about reaching the network of Server 2 because of the default-information -originate always command being present in iosvl2-3. 

 

So if we try to ping the network of Server 2 from the device iosvl2-7, because of the default route in OSPF it reaches iosvl2-3 and from there because server-2 network is present in BGP it moves from there. 

 

My Question is this if iosv-1 fails , I want the traffic to flow between the link between iosvl2-2 and iosvl2-4 and reach Server 2 network via iosv-3 and viceversa.

 

At present it is not happening because evenif iosv-1 fails because all the traffic is reaching iosvl2-3 because of the default-information-originate-always in iosvl2-3.

 

I have tried putting a static route in iosvl2-3 pointing to the iosv-1 interface ip and then put default-information-originate in iosvl2-3. But even after shuttting down iosv-1 the traffic is still flowing to isovl2-3 and then dropping.

 

Can you please help me out. This is something urgent and I need to put a solution soon. 

VIP Gold

Re: OSPF and BGP network

In normal operation what is the output of "show ip route 50.50.50.50"in iosvls-3, iosvl2-2 (I assume the HSP master) and iosvl2-4?

If you could provide the same with the link to iosv-1 failed that would also help.

Post the configs of these three devices if you can too.

Community Member

Re: OSPF and BGP network

Please see the configurations attached

Community Member

Re: OSPF and BGP network

Please see the output of sh ip route 50.50.50.50

VIP Gold

Re: OSPF and BGP network

Just a point of clarification. When you said:

"I have tried putting a static route in iosvl2-3 pointing to the iosv-1 interface ip and then put default-information-originate in iosvl2-3. But even after shuttting down iosv-1 the traffic is still flowing to isovl2-3 and then dropping." Did the physical interface and associated VLAN 10 interface on iosvl2-3 to iosv-1 go down? If it didn't the default route would have still been advertised.

 

With the connection to iosv-1 one down, it would be helpful to see the output of "show ip route 0.0.0.0" in the same devices. Is that something you could do?

 

Aside from that, I'm not sure if you looked at the earlier post of conditional route advertisement. In the example below, we're telling iosvl2-3 to advertise the  default route as long as it has the 50.50.50.0/24 route in its routing table. In that way if the BGP session drops with iosv-1 and the route is flushed, the default advertisement ceases.

!
access-list standard DEFAULT_ROUTE
 permit 50.50.50.0 0.0.0.255
!
!
route-map ospf default permit 10
match ip address DEFAULT_ROUTE
!
!
router ospf 100
default-information originate always route-map DEFAULT_ROUTE
!
!

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