GRE Overview
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941
Alcatel-Lucent
Beta Beta
OmniAccess 5740 Unified Services Gateway CLI Configuration Guide
GRE TUNNEL FEATURES
In addition to the above concepts, some important features should be highlighted:
T
OPOLOGY AND SCALABILITY FEATURES
Due to the flexible nature of GRE, tunnels can be established in different
topologies.
The use of different topologies also allows GRE tunnels to be scaled
appropriately. Specifically, a hierarchical structure allows a core to be constructed
by connecting core routers together with GRE tunnels. From that core, additional
tunnels can be provisioned to the provider edge routers.
S
EPARATION OF CUSTOMER AND PROVIDER ROUTING
In OmniAccess 5740 USG, OSPF protocol instances operate upon their own
instance of the routing table. Routes from one routing table instance are not
visible to the other routing table instance unless it is explicitly redistributed.
Therefore, even though customer routes are present in our routing table, they will
not be picked up by the provider OSPF instance.
Therefore, it is possible for us to have independent OSPF routing instances for
the VPN going over the tunnel, and the connectivity to the provider network.
In terms of BGP, it is possible to run BGP over the VPN by specifying a peer IP
address that is reachable over the tunnel. This will guarantee that all the BGP
messages to the peer will go over the tunnel.
F
ILTERS ON GRE TUNNELS
Filters are packet filters which determine whether packets are forwarded or
dropped. They are useful for security or policy purposes. The header in each
packet is examined and the relevant criteria include source and destination
address, source and destination port, or other information. Filters can be applied
to GRE tunnel interfaces, which means that packet filtering with its corresponding
benefits can be offered for GRE tunnels.
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