Avaya G430 - Page 436

Prevention of 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 Branch Gateway 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 re-configured to eliminate the nested tunneling.
In addition to checking for nested tunneling, the Branch Gateway prevents loops in connection
with GRE tunnels by preventing the same packet from being encapsulated more than once in
the Branch Gateway.
Related topics:
Reasons for nested tunneling in a GRE tunnel on page 436
Nested tunneling example on page 437
Recommendations on avoiding nested tunneling on page 437
Reasons for nested tunneling in a GRE tunnel
• A static route exists on the source tunnel endpoint that tells the tunnel to route packets
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
endpoint via OSPF or RIP
• A combination of static routes via parallel tunnels lead to a situation in which each tunnel
is routing packets via another tunnel. For example:
Gxxx-001(super)# interface tunnel 1
Gxxx-001(super-if:Tunnel 1)# tunnel source x.x.x.x
Gxxx-001(super-if:Tunnel 1)# tunnel destination 1.0.0.1
Done!
Gxxx-001(super-if:Tunnel 1)# exit
Gxxx-001(super)# interface tunnel 2
Gxxx-001(super-if:Tunnel 2)# tunnel source x.x.x.x
Gxxx-001(super-if:Tunnel 2)# tunnel destination 2.0.0.1
Done!
Gxxx-001(super-if:Tunnel 2)# exit
Gxxx-001(super)# interface tunnel 3
Gxxx-001(super-if:Tunnel 3)# tunnel source x.x.x.x
Gxxx-001(super-if:Tunnel 3)# tunnel destination 3.0.0.1
Done!
Gxxx-001(super-if:Tunnel 3)# exit
Gxxx-001(super)# ip route 1.0.0.1 tunnel 2
Done!
Gxxx-001(super)# ip route 2.0.0.1 tunnel 3
Done!
Gxxx-001(super)# ip route 3.0.0.1 tunnel 1
Done!
Using the network shown in
Nested tunneling example on page 437 as an illustration, if Router
1 has an entry in its routing table regarding the tunnel’s receiving endpoint, this will cause an
The router
436 Administering Avaya G430 Branch Gateway October 2013
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