Dynamic routing and GRE

[Groto145]

Hi,

I just started learning about GRE. Now, I understand the concept and implementation, but I don't know how to send/force send traffic through the tunnel. I watched the following video: https://www.youtube.com/watch?v=FyQSOAevcyk and in it, traffic is sent through the tunnel using static IP route from PC-A to PC-C and R2, because of it, doesn't know their LAN network addresses and the network address of the tunnel. Now, the problem with that is that now you can not ping R2. Also, let's say that I connect to all routers more routers and to all of them more LAN networks- the static routers begin to be a big problem.

Now, if I take that kind of networks topology- my steps of configuration are as following:

1. use dynamic routing protocol as for example OSPF to advertise all the network so that I archive all-round connectivity

2. implement GRE

3. advertise GRE tunnel network using OSPF which results in forming OSPF neighbor over the tunnel

Now, the result of this that while I can still accomplish all-round ping, only pinging from the tunnel gateway to tunnel gateway will result in traffic going through the tunnel and the rest of traffic will go normally to intermediate routers.     

Now, my question is- how to force traffic, with the usage of dynamic routing protocol, to go through the tunnel if it needs to go from router to router which forms the GRE tunnel and not normally thought intermediate router(s) and the rest of traffic to go normally.

The following image shows my intent- ping from PC-0 to PC-1 did not go through the tunnel even though the tunnel is up and there is formed OSPF neighbor over it (when pinging from Zagreb to Dubrovnik ( and vice-versa) ping goes through the tunnel)     

[Richard Burts]

I have looked at your diagram. I do not understand from the diagram where is the GRE tunnel. We do not have any details of the configurations and so are not able to give good advice about this issue. I will say that in general if you are running a dynamic routing protocol over the GRE tunnels and also running they dynamic routing protocol over other physical interfaces that you should be able to change the OSPF cost (manipulate the configured bandwidth or directly configure the OSPF cost of the interface) to make the GRE tunnel more attractive than the physical interfaces.

HTH

Rick

[Groto145]

GRE tunnel is between routers Zagreb and Dubrovnik. I changed topology to better show the problem and I am putting packet tracer file so you can see entire configurations but the main steps in order are:

1. connecting and configuration of interfaces

2. ospf advertise all networks to achieve all-round ping 

3. creating GRE between R1 and R2

4. ospf advertise GRE network

Problem is that if I ping from PC-1/3 to PC-2/4 (and vice-versa) ping will not go through GRE tunnel.

I tried your solution but it didn't work and I believe I found out the why- in show IP route table, the route is learned to go through the physical interface only- there is no learned route that goes through the tunnel?! Is this correct and if it is, how to fix it?

[Deepak Kumar · Accepted solution]

Hi,

This is a PT Lab and very limited functions are available for the configuration. You can't do anything with Route-map, OSPF Metric-change, etc. it is advised to use the two different routing protocol  Underlying is OSPF and for the overlay is EIGRP routing protocol. 

Means for the Tunnel routing protocol you can use the EIGRP routing protocol for archive desired goal. 

[Groto145]

But how to achieve that? I have tried to advertise only GRE tunnel network address in EIGRP and the rest in OSPF- didn't work.

Tried to advertise only GRE tunnel network address in OSPF and the rest in EIGRP- didn't work. 

Tried to advertise all address in both OSPF AND EIGRP- didn't work.

Could you, PLEASE, implement that for me in following PT file? - the network is already connected and interfaces are configurated including tunnel interfaces, but there is no dynamic routing what so ever.