IEEE P802 Handoff ECSG Submission July 2003 Bernard Aboba, Microsoft Detection of Network Attachment (DNA) and Handoff ECSG Bernard Aboba Microsoft July 2003

IEEE P802 Handoff ECSG Submission July 2003 Bernard Aboba, Microsoft Problem Statement Statement 1: –There is a need to develop a handoff standard that allows a mobile terminal to optimize detection of network attachment (DNA) at Layer 3. Statement 2: –There is a need to develop a handoff standard that permits a mobile terminal to switch between one point of attachment and another with minimal latency.

IEEE P802 Handoff ECSG Submission July 2003 Bernard Aboba, Microsoft DNAv4 Model Hints – non-definitive indications whether the host has connected to a previously encountered subnet –L2 hints: SSID, Infrastructure/Adhoc, IEEE 802 LLDP traffic –L3 hints: IRDP Most Likely point of attachment (POA) –Best guess, based on hints –By default: previous point of attachment Reachability detection –ARP Request sent to most likely default gateway Address re-acquisition –Used only if client retains a valid lease –DHCPREQUEST sent in INIT-REBOOT state

IEEE P802 Handoff ECSG Submission July 2003 Bernard Aboba, Microsoft DNAv4 Strawman Proposal Formulate most likely point of attachment –Is IPv4 LL ever most likely ? Probably not May wish to test reachability to all networks with valid IP leases prior to configuring an IPv4 LL address Check for valid IP address lease (<T1) –If valid, perform reachability detection on default gateway of most likely network If reachability succeeds, reuse address –Note: To handle movement between private networks, need to match *both* IP address and MAC address of default gateway If reachability fails send DHCPREQUEST in INIT-REBOOT state If no valid IP address lease, or no response to DHCPREQUEST after retransmission, go to INIT state If DHCP fails, do we allocate IPv4 LL address? –Empirical evidence is that this is invalid much of the time, but it could be required. –If IPv4LL is allocated, how often do we attempt to obtain a routable IP address?

IEEE P802 Handoff ECSG Submission July 2003 Bernard Aboba, Microsoft Issues with IEEE Hints SSID not a reliable indicator of subnet change –Lots of APs advertising default SSID SSID -> subnet mapping not unique –IEEE 802.1X-2001 supports dynamic VLAN assignment STAs within the same SSID may not be assigned the same VLANID AP discovery mechanisms limited to coverage area –Since Beacon/Probe Responses not audible outside the coverage area, not possible to discover APs outside of the coverage area –Result: Handoff needs to be completed within the coverage overlap area Virtual AP confusion –Station may become alarmed by sharing of PMK between Virtual APs within the same physical AP –Need physical AP identifier Link up confusion –IEEE i defines two Association protocols! Secure association protocol: 4-way + group key handshake Insecure Association Protocol: Association/Reassociation Result: state machine complexity, DoS vulnerabilities –IEEE i and IEEE f have different definitions of Association IEEE f triggered on insecure Association/Reassociation IEEE i triggered on secure association –Observed Results Hosts assigning IPv4LL address when DHCP server is available

IEEE P802 Handoff ECSG Submission July 2003 Bernard Aboba, Microsoft Potential Solutions Subnet change indications –Subnet provided in last message of secure association protocol Allows subnet to be learned prior to DNA Allows for dynamic VLAN assignment Virtual AP confusion –Physical AP identifier independent of BSSID Discovery outside the coverage area –Addition of Neighbor IE to the Beacon/Probe Response Provides BSSID of neighboring APs –Allows pre-authentication to be initiated outside coverage overlap area Link up Confusion –Define a single Link up trigger in IEEE i: 4-way + group key handshake Add Association/Reassociation fields to 4-way handshake to allow secure verification Add delete message to 4-way handshake to allow for secure Disassociation/Deauthentication Rename 4-way handshake + group key handshake to secure association –Treat insecure Association/Reassociation as vestigial if it cannot be removed

IEEE P802 Handoff ECSG Submission July 2003 Bernard Aboba, Microsoft Motion To straw poll on the proposed problem statements - Problem Statement 1 - Problem Statement 2