User's Manual

Configuring GRE Tunnels
308625-14.00 Rev 00
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The disadvantage of using an announce policy is that it prevents the advertisement
of other subnets within the blocked range. Depending on the network topology,
this configuration may not be desirable.
Accept Policies
An accept policy governs the addition of new routes to the routing tables. For
GRE tunneling, you can configure an accept policy for each routing protocol (RIP,
OSPF, BGP) configured on the logical tunnel interface to block the receipt of
advertisements from a range of network addresses that contains the tunnel’s
remote physical interface address. For information about configuring RIP and
OSPF accept policies, see Configuring IP, ARP, RARP, RIP, and OSPF Services.
For information about configuring BGP accept policies, see Configuring IP
Exterior Gateway Protocols (BGP and EGP).
The disadvantage of using an accept policy is that it prevents the receipt of
advertisements of subnets contained in the blocked range. Depending on the
network topology, this configuration may not be desirable.
Static Routes
A static route is a route configuration that designates a specific router within the
intervening network cloud as the next hop to the remote physical tunnel end point.
Because static routes take precedence over routes that the router learns
dynamically from routing protocols, this configuration forces the router to direct
packets through the cloud to reach the tunnel’s remote physical address.
The disadvantage of using a static route is that it is fixed. If the path through the
chosen next hop to the remote tunnel end point goes down, the tunnel goes down
as well until you manually reconfigure the static route. Similarly, even if the path
through the chosen next hop becomes more costly than the path through some
other attached router, the tunnel continues to use the costlier path unless you
manually intervene.
Note:
When configuring a static route, be careful not to inadvertently create a
loop.