Data Traffic Between Wlan And 3G Network; D-Ewag As First-Hop Router To Wlan Network; D-Ewag As Default Gateway; Apn Selection - Cisco ASR 5000 Administration Manual

DHCP-based Enhanced Wireless Access Gateway Overview
 DNS server address
 DHCP server address
After the WLAN attach procedure is completed as explained above, D-eWAG session for the UE becomes active and
ready for data transfer.
Note that if the WLC sends the Accounting-Start message to the D-eWAG (if it is configured as Accounting-Proxy at
WLC), it will proxy the Accounting-Start message to the 3GPP-AAA server and send the Accounting-Response
message back to the WLC.

Data Traffic between WLAN and 3G Network

As the D-eWAG acts as default-gateway for the UE, all uplink data packets are received by D-eWAG and sent to the
GGSN over GTP-U tunnel. When the downlink data packet is received from GGSN over the GTP-U tunnel, D-eWAG
throws the packet to WLC over the VLAN mapped for the UE session, and WLC delivers the packet to the UE.

D-eWAG as First-Hop Router to WLAN Network

The D-eWAG acts as the first-hop router to the WLAN network, which provides access to the 3G domain. This means
that D-eWAG has L2 connectivity with the Wireless LAN Controller (WLC) using VLANs and acts as first-hop router
to route traffic to the GGSN.
In a typical Wi-Fi network each SSID will have corresponding VLAN mapping at WLC node. Therefore, the network
setup should be in such a way that D-eWAG should also be the member of all VLANs as that of the WLC's VLAN
serving 3G-SSID. This ensures that all the traffic from UEs attaching to any 3G-SSID will reach the D-eWAG acting as
first-hop router through WLC.
Each VLAN interface at D-eWAG can be connected to one or more WLCs serving the same SSID, and each WLC acts
as RADIUS client and DHCP relay for that SSID. So, the RADIUS-client/DHCP-relay function at WLC will use the IP
address of VLAN interface mapped to that 3G-SSID, and D-eWAG is configured as corresponding RADIUS/DHCP
server.

D-eWAG as Default Gateway

D-eWAG operates as first-hop L3 router (default-gateway) for Wi-Fi clients (UE), it should be possible for all UEs to
send data traffic directly to the D-eWAG. This is achieved by sending the default-gateway DHCP option (or DHCP
ROUTER option-3) as described in the Requirements at GGSN section. Note that this default-gateway IP address should
be in the same subnet as that of IP address allocated by the GGSN.
Thus, when the UE wants to send traffic, it will first resolve the MAC address of the default-gateway using ARP-
Request. This ARP-Request gets forwarded by WLC over mapped VLAN and D-eWAG responds with ARP-
RESPONSE as it owns the IP address. This ensures that all the data packets from the UE reach D-eWAG.
When the default-gateway configuration is not available or does not match with subnet of the allocated IP address from
GGSN, the call will get dropped. This ensures that any consecutive DHCP packets from that UE get dropped at D-
eWAG.

APN Selection

APN for the D-eWAG session is selected in following way:
Cisco ASR 5000 Enhanced Wireless Access Gateway Administration Guide ▄
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