Preventing Nested Tunneling In Gre Tunnels - Avaya G250 Administration

Preventing nested tunneling in GRE tunnels

Nested tunneling occurs when the tunnel's next hop for its destination is another tunnel, or the
tunnel itself. When the next hop is the tunnel itself, a tunnel loop occurs. This is also known as
recursive routing.
When the G250/G350 recognizes nested tunneling, it brings down the tunnel interface and
produces a message that the interface is temporarily disabled due to nested tunneling. The
tunnel remains down until the tunnel is reconfigured to eliminate the nested tunneling.
In addition to checking for nested tunneling, the G250/G350 prevents loops in connection with
GRE tunnels by preventing the same packet from being encapsulated more than once in the
G250/G350.
Several things can lead to nested tunneling in a GRE tunnel:
A static route exists on the source tunnel endpoint that tells the tunnel to route packets
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addressed to the receiving tunnel endpoint via the tunnel itself.
The local endpoint of the tunnel learns the tunnel as a route to the tunnel's remote
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endpoint via OSPF or RIP.
A combination of static routes via parallel tunnels lead to a situation in which each tunnel is
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routing packets via another tunnel. For example:
G350-001(super)# interface tunnel 1
G350-001(super-if:Tunnel 1)# tunnel source x.x.x.x
G350-001(super-if:Tunnel 1)# tunnel destination 1.0.0.1
Done!
G350-001(super-if:Tunnel 1)# exit
G350-001(super)# interface tunnel 2
G350-001(super-if:Tunnel 2)# tunnel source x.x.x.x
G350-001(super-if:Tunnel 2)# tunnel destination 2.0.0.1
Done!
G350-001(super-if:Tunnel 2)# exit
G350-001(super)# interface tunnel 3
G350-001(super-if:Tunnel 3)# tunnel source x.x.x.x
G350-001(super-if:Tunnel 3)# tunnel destination 3.0.0.1
Done!
G350-001(super-if:Tunnel 3)# exit
G350-001(super)# ip route 1.0.0.1 tunnel 2
Done!
G350-001(super)# ip route 2.0.0.1 tunnel 3
Done!
G350-001(super)# ip route 3.0.0.1 tunnel 1
Done!
Using the network shown in
table regarding the tunnel's receiving endpoint, this will cause an internal route in which all
packets exiting the tunnel will be redirected back into the tunnel itself.
Figure 34 as an illustration, if Router 1 has an entry in its routing
Configuring GRE tunneling
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