GRE Hub-and-Spoke: one MainOffice router terminates tunnels to all branches. Branches reach each other via hub. As branch count grows, hub load increases — the limitation that DMVPN solves.
Topology
Configurations
MainOffice
enable
configure terminal
!
hostname MainOffice
no ip domain lookup
!
interface Tunnel0
ip address 172.20.20.1 255.255.255.0
no ip route-cache
keepalive 10 3
tunnel source Ethernet0/0
tunnel destination 12.12.12.12
tunnel key 3
tunnel sequence-datagrams
tunnel checksum
!
interface Tunnel1
ip address 172.20.21.1 255.255.255.0
no ip route-cache
keepalive 10 3
tunnel source Ethernet0/0
tunnel destination 13.13.13.14
tunnel key 3
tunnel sequence-datagrams
tunnel checksum
!
interface Ethernet0/0
ip address 25.25.25.25 255.255.255.0
ip nat outside
ip virtual-reassembly in
duplex auto
!
interface Ethernet0/1
ip address 192.168.1.1 255.255.255.0
ip nat inside
ip virtual-reassembly in
duplex auto
!
ip nat inside source list 1 interface Ethernet0/0 overload
ip route 0.0.0.0 0.0.0.0 25.25.25.24
ip route 192.168.2.0 255.255.255.0 Tunnel0
ip route 192.168.3.0 255.255.255.0 Tunnel1
!
access-list 1 permit 192.168.1.0 0.0.0.255
!
line con 0
exec-timeout 0 0
logging synchronous
end
!
wr
Branch
enable
configure terminal
!
hostname Branch
no ip domain lookup
!
interface Tunnel0
ip address 172.20.20.2 255.255.255.0
no ip route-cache
keepalive 10 3
tunnel source Ethernet0/0
tunnel destination 25.25.25.25
tunnel key 3
tunnel sequence-datagrams
tunnel checksum
!
interface Ethernet0/0
ip address 12.12.12.12 255.255.255.0
ip nat outside
ip virtual-reassembly in
duplex auto
!
interface Ethernet0/1
ip address 192.168.2.1 255.255.255.0
ip nat inside
ip virtual-reassembly in
duplex auto
!
ip nat inside source list 1 interface Ethernet0/0 overload
ip route 0.0.0.0 0.0.0.0 12.12.12.13
ip route 192.168.1.0 255.255.255.0 Tunnel0
ip route 192.168.3.0 255.255.255.0 Tunnel0
!
access-list 1 permit 192.168.2.0 0.0.0.255
!
line con 0
exec-timeout 0 0
logging synchronous
!
end
wr
Branch2
enable
configure terminal
!
hostname Branch2
no ip domain lookup
!
interface Tunnel0
ip address 172.20.21.2 255.255.255.0
no ip route-cache
keepalive 10 3
tunnel source Ethernet0/0
tunnel destination 25.25.25.25
tunnel key 3
tunnel sequence-datagrams
tunnel checksum
!
interface Ethernet0/0
ip address 13.13.13.14 255.255.255.0
ip nat outside
ip virtual-reassembly in
duplex auto
!
interface Ethernet0/1
ip address 192.168.3.1 255.255.255.0
ip nat inside
ip virtual-reassembly in
duplex auto
!
ip nat inside source list 1 interface Ethernet0/0 overload
ip route 0.0.0.0 0.0.0.0 Ethernet0/0
ip route 192.168.1.0 255.255.255.0 Tunnel0
ip route 192.168.2.0 255.255.255.0 Tunnel0
!
access-list 1 permit 192.168.3.0 0.0.0.255
!
line con 0
exec-timeout 0 0
logging synchronous
!
end
wr
Summary
Branch-to-branch traffic routes through MainOffice. Doesn’t fully solve scalability — hub load grows with each branch. Next step: DMVPN.