Ben Mack-Crane
Apr 10, 2023 1
bp-sajassi-cfm-0711-v01.pdf Flow-Level CFM:
◦ CFM functions performed on the user flows.
Network-Level CFM:◦ CFM functions performed on a test “VLAN” that covers the
network. Test flows are chosen to exercise all ECMPs for the Test VLAN.
Service-Level CFM:◦ CFM functions performed on a service VLAN. Test flows are
chosen to exercise all ECMPs for that VLAN. It can be considered as a special case of Network Level CFM.
Apr 10, 2023 2
bp-sajassi-cfm-0711-v01.pdf Test Flow Discovery Path Trace Path Verification Fault Monitoring Fault Isolation
Apr 10, 2023 3
Test Flow Discovery◦ Computed set of (SA, DA, Flow Hash) for Network or Service
Path Trace◦ Link Trace
Path Verification◦ Loopback
Fault monitoring◦ CCM, infer Flow Hash from RDI
Fault Isolation◦ Loopback◦ DDCFM
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LTM sent to individual DA with specific Flow Hash Each hop sends back LTR (if LTM TTL is not 0) Forwards LTM to ECMP selected hop (if LTM TTL is >1) LTR frames identify path for DA+Flow Hash
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LTM to individual address w/ flow
hash LTR may take any path
LBMs sent to individual DA with Flow Hash to select path LBM MIP TLV contains MIP address MIP responds with LBR LBR may take different path from LBM
◦ Could add Flow Hash TLV to LBM to attempt to make LBR symmetric…◦ But there is no guarantee that LBR is symmetric if network is misbehaving!
Apr 10, 2023 6
LBM to Individual DA,
MIP address in TLV LBR to LBM SA
CCMs sent from B-VLAN endpoint (CBP) use a source specific tree* Each endpoint expects to receive CCMs from all other endpoints Detects unreachable endpoint Does not test all paths
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CCM to Group Address
Cs-ss-ss-00-00-FF
*Or a shared tree using group address 80-1E-83-00-00-FF
CCMs sent from a CBP MEP within a TESI mux (specific to VID, SA, DA) using a specific Flow Hash
Multiple paths can be tested using a list of Flow Hash values, each sent at least three consecutive times
Detects broken path (but not rerouted path)
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CCM to Individual Address*
Flow Hash A
Flow Hash B
Flow Hash C
*Option to use flow-specificgroup address?
MEP location in baggy pant leg◦ “Support for Flow Filtering” shim with 6.11 (or
6.9)◦ MEP/MIP locations unchanged◦ Use TESI mux (6.19) for path test MEPs
PNP only supports ECMP MIPs◦ Partial paths ECMP VLAN are not interesting
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Placing Flow Filtering shim with CBP shim:-Keeps all tag processing together
CFM :-MEP generates CCM frames with group address for default I-SID.
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Placing Flow Filtering shim with CBP shim:-Keeps all tag processing together
CFM :-MEP generates CCM frames with individual address-Flow Hash value(s) selected to test desired path(s)
Apr 10, 2023 12
Placing Flow Filtering shim with VLAN tag shim:-Keeps all tag processing together-Could have used one tag to carry all info
Only MIPs supported on PNP for ECMP VLANs-ECMP makes MEPs less useful here
Path verification◦ Determine expected path via computation or LTM◦ Use Loopback to verify each hop in path
Fault isolation◦ Use Loopback to find “broken” hop◦ DDCFM supports special diagnostics, i.e.
reflecting specific frames or injecting test frames
Apr 10, 2023 13