Manual

Cisco Packet Data Serving Node (PDSN) Release 2.0

System Overview

12.3(11)T

5. Packets destined for the mobile station go through the HA; the HA tunnels them through the PDSN

to the mobile station using the care-of address.

6. When the PPP link is handed off to a new PDSN, the link is re-negotiated and the Mobile IP

registration is renewed.

7. The HA updates its binding table with the new care-of address.

Note For more information about Mobile IP, refer to the Cisco IOS Release 12.2 documentation modules

Cisco IOS IP Configuration Guide and Cisco IOS IP Command Reference. RFC2002 describes the

specification in detail. TIA/EIA/IS-835-B also defines how Mobile IP is implemented for PDSN.

PMTU Discovery by Mobile IP Client

FTP upload and ping from the end node may fail when PMTU Discovery (done by setting the DF bit) is

done by a MobileIP client (an end node) for packet sizes of about 1480. Due to failure of PMTUD

algorithm, the IP sender will never learn the smaller path MTU, but will continue unsuccessfully to

retransmit the too-large packet, until the retransmissions time out.

Please refer to http://www.cisco.com/warp/public/105/38.shtml#2000XP for disabling PMTUD for

windows 2000/XP platforms.

Cisco PDSN Proxy Mobile IP

Currently, there is a lack of commercially-available Mobile IP client software. Conversely, PPP, which

is widely used to connect to an Internet Service Provider (ISP), is ubiquitous in IP devices. As an

alternative to Mobile IP, you can use Cisco’s proxy Mobile IP feature. This capability of the Cisco

PDSN, which is integrated with PPP, enables a Mobile IP FA to provide mobility to authenticated PPP

users.

Note In Proxy Mobile IP, the MS can have only one IP flow per PPP Session.

The communication process occurs in the following order:

1. The Cisco PDSN (acting as an FA) collects and sends mobile station authentication information to

the AAA server.

2. If the mobile station is successfully authenticated to use Cisco PDSN Proxy Mobile IP service, the

AAA server returns the registration data and an HA address.

3. The FA uses this information, and other data, to generate a Registration Request (RRQ) on behalf

of the mobile station, and sends it to the HA.

4. If the registration is successful, the HA sends a registration reply (RRP) that contains an IP address

to the FA.

5. The FA assigns the IP address (received in the RRP) to the mobile station, using IPCP.

6. A tunnel is established between the HA and the FA/PDSN. The tunnel carries traffic to and from the

mobile station.