Cisco IOS XE, Руководство по настройке

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Configuring ISG Access for IP Subscriber Sessions
Information About ISG Access for IP Subscriber Sessions
10
DHCP Lease Query Support
The DHCP Lease Query message is a DHCP message type transmitted from a DHCP relay agent to a
DHCP server. A DHCP Lease Query aware relay agent sends the location of an IP endpoint to the DHCP
Lease Query message.
The DHCP Lease Query transaction is a DHCP transaction with special message types that enable clients
to query DHCP servers regarding the owner and the lease expiration time of an IP address. For
information about configuring DHCP server for Lease Query, see the
“Configuring a DHCP Server IP
Address” section on page 28 .
Layer 2 Connected IP Subscriber Identity
A Layer 2 connected access network is capable of providing IP connectivity to IP subscribers with
foreign and overlapping IP addresses, in addition to IP subscribers with native IP addresses. Because
subscriber IP addresses might not be unique in such an access network, ISG uses the subscriber MAC
address to identify Layer 2 connected IP subscribers, regardless of what kind of IP address a subscriber
has.
Traffic that comes from IP subscribers with private or overlapping IP addresses and that is destined to
the Internet is subject to NAT.
For Layer 2 connected IP subscribers, both the subscriber MAC address (unique within a VLAN) and
the IP address serve as the keys for the IP session, but they are used in different directions:
• In the upstream direction, the VLAN ID and source MAC address of an IP packet are used to identify
the IP session.
•
In the downstream direction, both the destination IP address and the VLAN ID of an IP packet are
used to identify the IP subscriber context.
VPN Connectivity and Services for IP Subscribers
The following sections provide information about VPN connectivity and services for ISG IP subscribers:
•
Subscriber VPN Membership
• VPN Addressing
•
VPN IP Subscriber Identity
• Service Model for VRF Transfers
•
Benefits of Dynamic VPN Selection
Subscriber VPN Membership
Depending on deployment requirements, an IP subscriber may or may not have VPN service. If an IP
subscriber does have VPN service, the subscriber may belong to only one VPN domain at any time. An
IP subscriber is associated with a VPN domain in one of the following ways:
• Static VPN assignment—The VPN IP subscriber belongs to a static VPN domain. Whenever the IP
subscriber connects to ISG, the IP subscriber is placed in the preassigned VPN domain.
• Dynamic VPN selection—The VPN IP subscriber can choose and switch among different VPN
domains through dynamic service logon. Whenever a new VPN domain is selected, VPN services
of the current VPN domain must be removed before VPN services of the new VPN domain can be
applied to the IP subscriber.