ssh through GRE tunel

[sir_ulrick]

Hi,

I have a teorical question about GRE performance. Suppose that we have 5 routers connected (A->B->C-D->E) with a GRE tunnel between A and E routers. Would be possible to do a ssh between A and C routers? This ssh connection will use GRE tunnel or phisical interface? more traffic could flow correctly before to E router?

Thanks in advance

[luis_cordova · Accepted solution]

Hi @sir_ulrick 

As far as I know, it will depend on which interface the route to the SSH destination ip was learned.
If the route to that IP was learned through the tunnel interface, then the connection will be achieved by the GRE.
If the route was learned through the physical interface, then the SSH connection will be made through that interface.

Regards

[sir_ulrick]

Ok, so if I want to reach a different device of final node (E) I would need to create a new tunnel where I want to connected, right? for instance A -> C and execute ssh to tunnel ip, right?

[luis_cordova]

Hi @sir_ulrick ,

Not necessarily, since the GRE tunnel connects you to the entire destination network.
The first step is to verify if the source device has a route to the network where the device is located.

If you already have a route, it's just a matter of trying the SSH.
If you don't have a route, you can evaluate how to learn that network, either through a tunnel interface or through a physical interface.

Regards

[sir_ulrick · Accepted solution]

Ok, If I understood, exist 3 different ways to reach a destination out tunnel GRE between A -> E devices. 

1) If 2 devices are connected directly with a physical interface (A->B)

2) Routing between them outside gre tunnel, I mean, routing between devices (A->C, for instance) where them ip's are knowed using either static or dinamic routing

3) New gre tunnel between them (A->D)

Thanks a lot for your reply Luis

[Deepak Kumar · Accepted solution]

Hi,

I am not sure that I got your question correctly or not but I have a suggestion as:

As you have few routers in a series as A---B---C

You are setting on router A and trying to SSH router C. Is it correct? If it is correct then you must have to complete a few requirements as:

1. Tunnel to Tunnel reachability. This may as Router A have tunnel to router B and Router B have a tunnel to router C or Router A may have tunnels for Router B and C (mGRE or Two different Tunnels).

2. Routing reachability from router A to C using the static or dynamic routing.

3. SSH configuration.

Let me know if you need more information as a configuration or query. 

[paul driver · Accepted solution]

Hello

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@sir_ulrick wrote:

Hi,

I have a teorical question about GRE performance. Suppose that we have 5 routers connected (A->B->C-D->E) with a GRE tunnel between A and E routers. Would be possible to do a ssh between A and C routers? This ssh connection will use GRE tunnel or phisical interface? more traffic could flow correctly before to E router?

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By default NO it wont unless your pushing all traffic from A to E through the tunnel otherwise it should go by the default routing path which would be the physical routing path underpinning your tunnels

[sir_ulrick]

Thanks everybody for your replies!