Roaming & OperationsL2

Roaming Reference

Roaming Design Troubleshooting

ROAMING LATENCY REFERENCE -- All methods compared | For Roaming Analyzer, Fast Roaming Advisor, FILS Analyser tools | IEEE 802.11r/k/v + 802.11ai FILS + RFC 6696 ERP8 rows#

Roaming Method	Total Latency	Scan Time	Auth+Assoc	4-Way HS	Notes / Requirements
Full EAP (no optimization)	300-600 ms	200-400 ms	50-100 ms	50-100 ms	Baseline. Full 802.1X EAP exchange. No caching. DHCP adds another 50-200 ms on top. VoIP call drops guaranteed.
PMKSA Cache (same AP return)	30-100 ms	N/A	20-50 ms	30-60 ms	STA returns to same AP. PMK cached. Skip full EAP. 4-way HS still required. dot11RSNAConfigPMKLifetime=43200s.
OKC (roam to new AP, same WLC)	80-150 ms	50-100 ms	20-40 ms	30-60 ms	PMK shared to all APs by WLC. PMKID computed with target AP MAC. 4-way HS still needed. No 802.11r required.
802.11r FT over-Air	20-60 ms	10-30 ms	10-20 ms	0 ms (keys pre-derived)	FT: PMK-R0 stored at R0KH. PMK-R1 pushed to target AP. PTK derived in Reassoc. No separate 4-way HS.
802.11r FT over-DS	15-50 ms	0-10 ms (pre-scan)	10-20 ms	0 ms	STA requests roam via current AP. Faster than over-Air if current AP cooperates. Requires AP-to-AP communication.
FILS (FILS-SK with ERP)	30-80 ms	10-30 ms	10-20 ms (combined in 2 frames)	0 ms (keys in Auth frames)	802.11ai FILS. Auth+Assoc+Keys in 2 frames. rMSK from ERP -> PMK. GTK delivered in Auth Resp Wrapped Data IE.
FILS with IP assignment	30-80 ms (no DHCP)	10-30 ms	10-20 ms	0 ms	FILS delivers IP config inside encrypted Auth Response. Total connection time < 100ms including IP ready.
802.11be MLO link switch	< 10 ms	0 ms (other link already up)	0 ms (no re-assoc)	0 ms	Not a roam -- link switching between bands within same MLO session. Target <1ms for latency-sensitive apps.

ROAMING STEP BREAKDOWN -- What happens during each roam type9 rows#

Step	Full EAP	PMKSA/OKC	802.11r FT	FILS	Description
1. Trigger	RSSI < -70 dBm for 3s	RSSI < -70 dBm for 3s	RSSI < -70 dBm for 3s	RSSI < -70 dBm for 3s	Threshold varies by vendor. 802.11k neighbor report helps find target AP without full scan.
2. Channel Scan	100-400 ms (all channels)	100-400 ms	Reduced by 802.11k neighbor list	Reduced by 802.11k	802.11k: AP sends neighbor report with BSSID, channel, RSSI -> STA only scans known candidates.
3. Probe Req/Resp	5-10 ms per channel	5-10 ms	5-10 ms (directed)	5-10 ms	Directed probe to specific BSSID is faster than broadcast probe. Neighbor report enables directed probe.
4. Authentication	50-300 ms (full EAP)	~2 ms (Open auth)	~5 ms (FT Auth alg=2)	~10 ms (SAE or Open+FILS)	802.11r FT: Auth=2 frame exchange with FT IEs. FILS: Auth=1 frame exchange (FILS-SK).
5. Association / Reassociation	5-20 ms	5-20 ms	5-10 ms (FT Reassoc)	5-10 ms (FILS Assoc)	FT Reassoc: carries PMK-R1 / FT IEs. AP derives PTK immediately. FILS: AP derives keys in Auth Resp.
6. 4-Way Handshake	30-80 ms	30-80 ms	0 ms (done in Reassoc)	0 ms (done in Auth/Assoc)	4-WHS: 4 EAPOL frames + 3x SIFS + processing. FT and FILS eliminate this step.
7. DHCP	50-200 ms (full DHCP)	50-200 ms	50-200 ms (unless FILS IP)	0 ms (FILS IP assignment)	DHCP is often the largest delay. FILS IP assignment eliminates DHCP. Cached DHCP lease renewal is faster.
Total (no DHCP)	200-500 ms	100-150 ms	25-50 ms	20-40 ms	DHCP adds 50-200ms to all except FILS with IP assignment.
Total (with DHCP)	300-700 ms	150-350 ms	75-250 ms	20-40 ms	FILS is the only method that can achieve <100ms with IP assignment.

802.11k/r/v CAPABILITY FLAGS -- What to check in beacon/probe/assoc frames5 rows#

Protocol	Beacon/Probe IE	Assoc Req IE	Required From STA	Effect When Present	Notes
802.11k (RRM)	Extended Caps IE bit 52: RRM Enabled AP announces: RRM Enabled Capabilities IE (tag 70)	Extended Caps IE bit 52 set by STA to indicate RRM support	STA must set bit 52 in Extended Caps to request/receive neighbor reports	AP can send Neighbor Report Response with BSSID, RSSI, channel, capabilities of neighboring APs. STA uses this to direct probe scan instead of full channel scan. Reduces scan time from 400ms to 50ms.	If not present: STA scans all channels. Always enable 802.11k on APs and clients.
802.11r (FT)	Mobility Domain IE (tag 54): MDID + FT Policy (key use + resource req protocol) AP announces it supports FT	FT Action in RSN IE AKM: type=3 (FT/802.1X) or type=4 (FT/PSK) STA includes MDE (Mobility Domain Element)	STA RSN IE must have FT AKM type. STA must include MDE in Assoc Req.	Enables fast BSS transition with pre-derived PTK. Eliminates 4-way HS on roam. Target: <50ms total roam. over-Air or over-DS modes.	Compatibility: Some clients (older Android) fail FT. Always test before deploying. Transition mode: mix of FT and non-FT clients.
802.11v (BSS TM)	Extended Caps IE bit 19: BSS Transition set by AP	Extended Caps IE bit 19 set by STA	STA should set bit 19 in Extended Caps. If not: AP cannot send BTM Request.	AP can send BSS Transition Management Request (Action Cat=10, code=7) to STA with target BSSID, disassoc timer, and candidate list. STA should roam to suggested AP.	'Sticky client' problem: STA ignores BTM Request. AP can set Disassociation Imminent bit + force disassoc as last resort. Monitor BTM Accept rate to quantify steering success.
802.11v DTIM Broadcast	Extended Caps IE bit 18	N/A	N/A	TIM Broadcast Request: STA requests alternate DTIM delivery	Less common. Used for power save optimization.
802.11w (PMF)	RSN Caps bits 6-7 in RSN IE: MFPC (capable), MFPR (required)	STA RSN Caps must match AP requirement	If MFPR=1: STA must support PMF. Connection fails if STA doesn't support PMF.	Deauth, Disassoc, Action frames encrypted and integrity-protected. Prevents deauth attacks. Mandatory for WPA3.	Common interop issue: older clients (pre-2014) don't support PMF. Deploy MFPC (capable but not required) for mixed networks.