Cisco IOS XE Intelligent Services

Configuring ISG Access for IP Subscriber Sessions
Information About ISG Access for IP Subscriber Sessions
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Figure 2 Routed Access Network
IP Subscriber Session Initiation
ISG can be configured to allow one or more of the following events to signal the start of an IP session
or IP subnet session on an interface:
• DHCP DISCOVER packet
If the following conditions are met, receipt of a DHCP DISCOVER packet will trigger the creation
of an IP session:
– The ISG serves as a DHCP relay or server for new IP address assignments.
– Subscribers are configured for DHCP.
– The DHCP DISCOVER packet is the first DHCP request received from the subscriber.
• Unclassified source IP address
For routed IP subscribers, a new IP session is triggered by the appearance of an IP packet with an
unclassified source IP address (which means that an IP session does not yet exist for that IP address).
• Unclassified source MAC address
For Layer 2 connected IP subscribers, a new IP session is triggered by the appearance of an IP packet
with an unclassified source MAC address (which means that an IP session does not yet exist for that
MAC address).
• RADIUS Access-Request packet
For routed or Layer 2 connected access, a new IP session is triggered by the appearance of a
RADIUS Access-Request packet when ISG is serving as a RADIUS proxy.
IP Subscriber Addressing
The following sections provide information about how ISG handles IP addressing for IP subscribers:
• Methods of ISG Subscriber IP Address Assignment
• Public and Private IP Addresses
• Overlapping IP Addresses
• ISG Subscriber IP Address Assignment Using DHCP
Routed
access network
Core network
ISG
IP subscriber
IP subscriber
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