This feature adds support for selecting a subset of traffic from a host (via IP filter) for local forwarding, while tunneling the remaining traffic to GGSN/PGW. This allows selected traffic to bypass the mobile packet core. The IP address for the host still comes from the GGSN/PGW during GTP session setup. Therefore, the selected traffic for local breakout from SR OS requires NAT functionality to draw the return traffic back to the router. To support address overlap within GTP, the NAT functionality is L2-aware. The selection of traffic for local breakout (local forwarding and NAT) is based on a net action in an upstream Ip filter applied to the host.
Selective breakout can be enabled on a per-host basis via RADIUS VSA (Alc-GTP-Local-Breakout) in access-accept. It is not possible to change this during a host’s lifetime, such as via CoA. AA functionality is supported for local breakout traffic. Also, LI (after NAT) is supported for local breakout traffic, and is enabled via existing secure CLI, as stated in the OAM and Diagnostics Guide.
system>config>filter
ip-filter 10 create
entry 1 create
match protocol udp
dst-port eq 4000
exit
action gtp-local-breakout
exit
On traffic ingress from the host UE, normal ESM host lookup and CAM lookup with the ingress host filter is performed. If there is a match in the filter indicating ‟gtp-local-breakout”, the traffic is forwarded within the chassis to an ISA-BB, where is it subjected to L2-aware NAT function, and afterwards is forwarded using regular routing in the NAT outside VRF. The inside IP address is the address returned in GTP, and may not match a NAT L2-aware inside prefix. The outside IP is an address belonging to the NAT outside IP address range on the ISA. If the filter action results in a ‟forward” action (default), the traffic is GTP-tunneled without performing NAT functionality. The traffic received from the network can be a normal L3 packet or a GTP encapsulated packet. The normal Layer 3 packet is expected to be destined for the NAT outside IP and is normally routed to the NAT ISA.
By default, per-host accounting includes counters that are aggregated across GTP and local breakout traffic. Separate counters can be obtained by directing the GTP and local breakout traffic into different queues associated with the corresponding ESM host based on QoS IP classification. NAT information (outside IP and port range) associated with an ESM host subjected to selective breakout is included in accounting-updates.
Selective breakout is supported for IPv4 only.