Enabling Dhcp Proxy - Cisco ASR 9000 Series Configuration Manual

Establishing Subscriber Sessions
For the subscriber access interface, DHCP uses the policy-plane to determine whether the IP subscriber session
should be created for a client binding. This is determined based on whether a valid control policy is applied
to the access-interface on which the client binding is created. If a subscriber session is created, then a route
is added for the subscriber interface, but no ARP requests are sent out from that subscriber interface.
BNG can be configured to either act as DHCP proxy in the DHCP network.
DHCP relay is not supported for BNG.
Note

Enabling DHCP Proxy

As the DHCP proxy, BNG performs all the functions of a relay and also provides some additional functions.
In the proxy mode, BNG conceals DHCP server details from DHCP clients. BNG modifies the DHCP replies
such that the client considers the proxy to be the server. In this state the client interacts with BNG as if it is
the DHCP server.
BNG procures IP leases from the DHCP server and keeps it in its pool. When the client needs to renew its
lease, it unicasts the lease renewal request directly to the BNG, assuming it to be the server. BNG renews the
lease by allocating the lease from its lease pool.
This way the DHCP proxy splits the lease management process into two phases:
• Server to Proxy (Proxy Lease)
• Proxy to Client (Client lease)
The two phase lease management has these features:
• Shorter client lease times and longer proxy lease times.
• High frequency lease management (renews) at network edge.
• Low frequency lease management (renews) at centralized server.
The benefits of DHCP proxy are:
• Reduced traffic between BNG and DHCP server.
• Quicker client response to network outages.
Configuring DHCP proxy on BNG involves these phases:
• Creating a proxy profile. The profile contains various proxy settings. These settings are applied when
OL-28375-03
the profile is attached to an interface. To create a proxy profile, see
Proxy Class, on page 126
◦ Specifying client lease period. The client should renew the lease before the completion of this time
period, otherwise the lease expires. To specify the client lease period within a proxy profile, see
Configuring the Client Lease Time, on page
◦ Specifying remote-ID. The remote-ID is used by the proxy to identify the host that had sent the
DHCP request. To define a remote-id within a proxy profile, see
page 128.
Cisco ASR 9000 Series Aggregation Services Router Broadband Network Gateway Configuration Guide, Release
Enabling DHCP Proxy
Configuring DHCP IPv4 Profile
130.
Configuring a Remote-ID, on
4.3.x
125