Transcript 00-03-0017-00-0000DNA-and-handoff

IEEE P802 Handoff ECSG
July 2003
Detection of Network Attachment
(DNA) and Handoff ECSG
Bernard Aboba
Microsoft
July 2003
Submission
Bernard Aboba, Microsoft
IEEE P802 Handoff ECSG
July 2003
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.
Submission
Bernard Aboba, Microsoft
IEEE P802 Handoff ECSG
July 2003
DNAv4 Model
• “Hints” – non-definitive indications whether the host has
connected to a previously encountered subnet
– L2 hints: 802.11 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
Submission
Bernard Aboba, Microsoft
IEEE P802 Handoff ECSG
July 2003
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?
Submission
Bernard Aboba, Microsoft
IEEE P802 Handoff ECSG
July 2003
Issues with IEEE 802.11 “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
•
•
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
–
–
•
STAs within the same SSID may not be assigned the same VLANID
Station may become alarmed by sharing of PMK between Virtual APs within the same physical AP
Need physical AP identifier
“Link up” confusion
–
IEEE 802.11i defines two Association protocols!
•
•
•
–
IEEE 802.11i and IEEE 802.11f have different definitions of Association
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•
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Secure association protocol: 4-way + group key handshake
Insecure Association Protocol: Association/Reassociation
Result: state machine complexity, DoS vulnerabilities
IEEE 802.11f triggered on insecure Association/Reassociation
IEEE 802.11i triggered on secure association
Observed Results
•
Submission
Hosts assigning IPv4LL address when DHCP server is available
Bernard Aboba, Microsoft
IEEE P802 Handoff ECSG
July 2003
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 802.11i: 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
Submission
Bernard Aboba, Microsoft
IEEE P802 Handoff ECSG
July 2003
Motion
• To straw poll on the proposed problem
statements
 - Problem Statement 1
 - Problem Statement 2
Submission
Bernard Aboba, Microsoft