Which two ways can you prevent recursive routing in a tunneled environment?

In which two ways can you prevent recursive routing in a tunneled environment? (Choose two)
A. Configure routes through the tunnel with a lower metric than other routes.
B. Configure route filtering to prevent the tunnel endpoints from learning each other through the tunnel.
C. Enable QoS on the link.
D. Configure routes through the tunnel with a higher metric than other routes.
E. configure GRE keepalives on the tunnel interface.

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2 thoughts on “Which two ways can you prevent recursive routing in a tunneled environment?

  1. Correct answer : B & D

    In order to prevent recursive routing with tunnels, the key point we need to take away is to make sure that the route to the tunnel destination in the RIB does not point to the tunnel interface itself as the exit interface. For this we need to make sure that the tunnel destination is not learned via the tunnel. Depending on the implementation, a few possible solutions include:

    Separate IGPs can be used for the underlay and the overlay while ensuring the tunnel destination is never advertised in the overlay protocol.
    In case a single IGP is being utilized:
    The metric of the route learned through the tunnel should be higher than the path through the underlying network. For routing protocols like OSPF and EIGRP, this is taken care of automatically because the tunnel interface bandwidth and delay are set artificially high, resulting in routes learned through the tunnel having a higher metric by default.
    Route filtering could be used to filter the tunnel endpoints from being learned over the tunnel. This is useful for a routing protocol like RIP that uses hop count as a metric.

    https://packetpushers.net/anatomy-of-gre-tunnels/

  2. B and D are correct
    Make sure the administrative distance of the tunnel destination IP address through the tunnel is higher (worse) than what you have in the routing table now.

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