Packet Handling On Subscriber Interfaces - Cisco ASR 9000 Series Configuration Manual

Packet Handling on Subscriber Interfaces

• Server Identifier Override Sub-option—This sub-option value is copied in the reply packet from the
The VPN Identifier, Subnet Selection, and Server Identifier Override sub-options are used by DHCP
Note
relay/proxy for supporting MPLS VPNs.
Packet Handling on Subscriber Interfaces
This section describes how subscriber interfaces are supported in certain special cases. These special cases
include L3 forwarded interfaces. As a result, this support is applicable only to PPP over Ethernet PPP
Termination and Aggregation (PPPoE PTA) and IPoE sessions.
Most subscriber data packets are forwarded directly by the network processing unit (NPU). There are certain
special cases where the NPU does not completely handle the data packet. These special cases are handled by
the CPU, and go through an internal interface created for this purpose. This internal interface is named the
Subscriber Interface or SINT. SINT is an aggregate interface, which is used by all packets punted on subscriber
interfaces. There is one SINT for each node. When the BNG package is installed, by default the SINT is
created. The SINT interfaces are needed for punt-inject of packets on subscriber interfaces.
These special cases are supported for both IPoE and PPPoE PTA:
These special cases do not apply to PPPoE L2TP, because it is an L2 service.
Note
• Ping to and from subscriber
• Option Handling
Cisco ASR 9000 Series Aggregation Services Router Broadband Network Gateway Configuration Guide,
Release 4.2.x
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DHCP server, instead of the normal server ID address. This sub-option contains the incoming interface
IP address, which is the IP address on the relay agent that is accessible from the client. Using this
information, the DHCP client sends all renew and release packets to the relay agent, which in turn adds
all of the VPN sub-options and forwards the renew and release packets to the original DHCP server.
BNG allows the receiving of a ping request from both IPoE and PPPoE PTA subscriber interfaces; this
is consistent with other non-BNG interface types as well. Similarly, BNG also allows the sending of a
ping request to both IPoE and PPPoE PTA subscriber interfaces. This includes:
• various lengths of ping packets including lengths exceeding the subscribers MTU size
• subscriber in the default and private VRFs
• various ping options such as type of service, DF set, and verbose
BNG also supports receiving a ping request from both IPv4 subscribers.
Excessive Punt Flow Trap feature should be disabled when sending a high rate of pings
Note
to, or from subscriber interfaces.
Establishing Subscriber Sessions
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