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PDN Gateway Overview
GRE Protocol Interface Support
Use of GRE Interface Tunneling requires that a valid license key be installed. Contact your local Sales or Support
representative for information on how to obtain a license.
The P-GW supports GRE generic tunnel interfaces in accordance with RFC 2784, Generic Routing Encapsulation
(GRE). The GRE protocol allows mobile users to connect to their enterprise networks through GRE tunnels.
GRE tunnels can be used by the enterprise customers of a carrier 1) To transport AAA packets corresponding to an APN
over a GRE tunnel to the corporate AAA servers and, 2) To transport the enterprise subscriber packets over the GRE
tunnel to the corporation gateway.
The corporate servers may have private IP addresses and hence the addresses belonging to different enterprises may be
overlapping. Each enterprise needs to be in a unique virtual routing domain, known as VRF. To differentiate the tunnels
between same set of local and remote ends, GRE Key will be used as a differentiation.
GRE tunneling is a common technique to enable multi-protocol local networks over a single-protocol backbone, to
connect non-contiguous networks and allow virtual private networks across WANs. This mechanism encapsulates data
packets from one protocol inside a different protocol and transports the data packets unchanged across a foreign
network. It is important to note that GRE tunneling does not provide security to the encapsulated protocol, as there is no
encryption involved (like IPSec offers, for example).
GRE tunneling consists of three main components:
Passenger protocol-protocol being encapsulated. For example: CLNS, IPv4 and IPv6.
Carrier protocol-protocol that does the encapsulating. For example: GRE, IP-in-IP, L2TP, MPLS and IPSec.
Transport protocol-protocol used to carry the encapsulated protocol. The main transport protocol is IP.
Important:
appendix in this guide.
GTP Throttling
Use of GTP and Diameter Interface Throttling requires that a valid license key be installed. Contact your Cisco account
representative for information on how to obtain a license.
This feature will help control the rate of incoming/outgoing messages on P-GW/GGSN. This will help in ensuring P-
GW/GGSN doesn't get overwhelmed by the GTP control plan messages. In addition, it will help in ensuring the P-
GW/GGSN will not overwhelm the peer GTP-C peer with GTP Control plane messages.
This feature requires shaping/policing of GTP (v1 and v2) control messages over Gn/Gp and S5/S8 interfaces. Feature
will cover overload protection of P-GW/GGSN nodes and other external nodes with which it communicates. Throttling
would be done only for session level control messages. Path management messages would not be rate limited at all.
External node overload can happen in a scenario where P-GW/GGSN generates signaling requests at a higher rate than
other nodes can handle. Also, if the incoming rate is high at P-GW/GGSN node, we might flood any of the external
nodes; hence, throttling of both incoming and outgoing control messages is required.
For protecting external nodes from getting overloaded from P-GW/GGSN control signaling, a framework will be used
to handle shaping/policing of outbound control messages to external interfaces.
For more information on GRE protocol interface support, refer to the GRE Protocol Interface
Features and Functionality - Optional Enhanced Feature Software ▀
Cisco ASR 5x00 Packet Data Network Gateway Administration Guide ▄
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