Two internals network ober GRE tunnel - how to

[comzkzg11]

Hello,

Hello,

We already have up and running a GRE tunnel within we route a one local network 172.20.20./24 The current configuration is:

interface Tunnel0
ip unnumbered FastEthernet0/0
ip mtu 1420
ip nat inside
ip virtual-reassembly
tunnel source FastEthernet0/0
tunnel destination xxx.x.xxx.xxx
tunnel path-mtu-discovery

and routing:

ip route 172.20.20.0 255.255.255.0 Tunnel0

The 172.20.20.0/24 is already exhausted - no more free ip addresses and due to this we need to route another network as well. I wonder in the below configuration is enough? The details:

ip route 172.20.21.0 255.255.255.0 Tunnel0

Of cource I will need to modify some access list as well.

Thank in you in advance for your any help.

regards,

Tomek

[Seb Rupik · Accepted solution]

Hi there,

Yes the addition of another static route would work. Why not summarise the two remote subnets:

!
ip route 172.20.20.0 255.255.254.0 Tunnel0
!

Better still, run a IGP like OSPF between two remote sites, using the GRE tunnel to form an adjacency between the two?

cheers,

Seb.

[comzkzg11]

Hi Seb,

Thank you very much for your help.

Summarizing them is much better way - thank you.

I am not familiar yet with the IGP and OSPF - also thank you for the suggestion. The GRE solution is imposed on our IC provider. Am I right that changing the GRE into a IGP like OSPF would imply the change as well on the IC site?

[Seb Rupik]

The tunnel would remain as you would run an IGP over the GRE tunnel. 

You would need to configure an IGP process at the remote end as well as your own router to allow communication between the two sites via the GRE tunnel.

cheers,

Seb.

[paul driver · Accepted solution]

Hello
Yes adding another static route to accomodate that addtional subnet would be applicable or you could amend the exisiting static route to include the new subnet.

no ip route 172.20.20.0 255.255.255.0 Tunnel0
ip route 172.20.20.0 255.255.254.0 Tunnel0 x.x.x.x (next hop ip)

[comzkzg11]

Hi Paul,

Thank you very much for your rapid help!

regards,

Tomek