OAM

  1. Operations, administration, maintenance
    1. OAM functions
  2. Ethernet OAM
  3. MPLS OAM
  4. VXLAN OAM

Operations, administration, maintenance

  • tracks connectivity, delay, loss, throughput
  • defined for Ethernet and MPLS
  • entities:
    • maintenance entity (ME): logical and physical links
    • ME group (MEG): MEs under same administrative control
    • ME point (MEP): point where OAM packets are generated and accepted

OAM functions

  1. continuity check
    • unidirectional messages are sent
    • opcode = 1
    • timeout = 3.5 × period
  2. loopback (BFD)
    • opcode = 3
    • reply opcode = 2
  3. link trace
  4. alarm indication signal
  5. remote defect indication
  6. locked signal
  7. test signal
  8. automatic protection switching
  9. maintenance communications channel
  10. alarm loss management
  11. packet loss management
    • exchange number of Rx/Tx packets
    • opcode = 43
    • reply opcode = 42
  12. delay measurement
    • opcode = 47
    • reply opcode = 46
  13. throughput measurement

Ethernet OAM

  • IEEE 802.1ag, ITU-T Y.1731 (ITU ∈ IEEE ⇒ compatible)
  • EtherType 0x8902
  • down MEP:
    • OAM is sent to link (not processed by device)
    • OAM is received from link
  • up MEP:
    • OAM is sent towards switching plane (e.g., backplane)
    • OAM is received from switching plane
  • MEG integration point (MIP):
    • can process OAM packets
    • does not terminate or generate OAM packets
  • OAM can be sent OOB or with service level, assigned to customer
  • OAM destination:
    • unicast
      • MEG level within OAM packet
    • mcast
      • 0180.c200.003X
        • x[0]
          • 0 ≡ class 1, to all MEP in MEG
          • 1 ≡ class 2, to all MEP and MIP in MEG
        • x[1:3]: MEG level
Counter typeResponse NResponse N+1DeltaLoss
Query transmit100015005000
Response receive8001300500
Response transmit340038504505
Query receive21002545445

MPLS OAM

  • common ping/traceroute may not detect discontiguous LSP because of falling back to IP forwarding
  • OAM (RFC 6374): operation, administration and maintenance
  • MPLS ping/traceroute:
    1. UDP 3503
    2. src: sender IP (IP address of outgoing interface)
    3. dst: from 127.0.0.0/8 to mitigate IP forwarding
    4. TTL = 255
  • modes:
    1. default: return reply
    2. alert:
      • each LSR punts packet to CPU: pops label and sends as IP with Router Alert option
      • useful for detecting broken LSP
      • adds label = 1
      • can be used if no MPLS reply received
    3. no-reply
  • uses G-Ach + GAL
; enables MPLS ping and traceroute
(config)# mpls oam

; 3 = draft, 4 = RFC
(config)# mpls echo version 3|4

; includes Cisco TLV into request
(config)# mpls echo vendor-extension
# ping mpls ipv4 <dst IP>/<mask> [repeat <count>] [reply mode <mode>]
# ping mpls pseudowire <PE_IP> <VCID>
# traceroute mpls ipv4 <dst IP> <mask>

VXLAN OAM

  • shows path for specific UDP source port ⇒ excludes entropy in outer header for troubleshooting
  • can use NVO3 Tissa channel to get extra information: load, egress intf, …
# ping nve ip unknown [vrf <VRF>] payload ip <SRC> <DST> port <SRC> <DST> proto <N> payload-end vni <M>

; ICMP
# traceroute nve ip unknown [vrf <VRF>] payload ip <SRC> <DST> port <SRC> <DST> proto <N> payload-end vni <M>

; NVO3
# pathtrace nve ip unknown [vrf <VRF>] payload ip <SRC> <DST> port <SRC> <DST> proto <N> payload-end vni <M>