Dean Cheng ([e-mail])

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NAT State Synchronization using
SCSPdraft-xu-nat-state-sync-00

• Dean Cheng (chengd_at_huawei.com)
• Xiaohu Xu (xuxh_at_huawei.com)
• Joel Halpern (Joel.Halpern_at_ericsson.com)
• Mohamed Boucadair (mohamed.boucadair_at_orange-ftgrou
  p.com)
• IETF76, Hiroshima

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SCSP A Protocol for Data Cache Synchronization

• Server Cache Synchronization Protocol (SCSP -
  RFC2334) solves a general server
  synchronization/cache-replication problem for
  distributed databases.
• SCSP uses link-state based algorithm to reliably
  flood database entries among participating
  servers.
• SCSP defines application-independent protocol
  mechanisms and requires applications to define
  their own formats for cache records, called Cache
  State Advertisement (CSA).
• This document specifies a method of using SCSP to
  achieve NAT state synchronization among NAT
  devices in a redundancy group including
  associated CSA format.

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Requirements for NAT Devices Deployed
with Redundancy

• Achieve hot-standby and load balancing, data
  synchronization is a MUST.
• Reliability and robustness are very much desired
  during data synchronization process.
• Stateful contents in data cache maintained by NAT
  MUST be replicated and synchronized on all
  participating NAT devices in a redundancy group.
• When a NAT device in a redundancy group fails,
  all existing NAT sessions must survive without
  any perceived impact on traffic (e.g., severe
  delay, loss, etc.)

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Use SCSP to Sync NAT Database

• Multiple NAT devices deployed on the border
  between two IP domains form a redundancy group
  which, possibly along with
• other redundancy groups, belong to a SCSP
  Server Group (SG), identified by SGID.
• Within a redundancy group, there is a primary and
  one or more backup devices. When the primary NAT
  device fails, a new
• primary NAT device is elected.
• For each NAT type, a separate SCSP Protocol ID
  (PID) is
• assigned by IANA.
• Currently NAT type includes NAT44, NAT64, and
  NAT46.
• The method described is applicable to stateful
  NAT devices only.

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NAT State Refreshment Mechanism

• Only primary NAT device can create new cache
  entries.
• NAT database entries are aged. The primary device
  is responsible to re-originate and re-flood them
  before aging out for active entries.
• After a switchover, the newly elected primary NAT
  device MUST re-originate all cache entries that
  were originated by the previous primary NAT
  device, with NAT contents remain the same
  followed by a reliable flooding defined by SCSP.

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SCSP Message Mandatory Common Part

• 0 1 2
  3 0 1 2 3 4 5 6 7 8 9 0 1 2 3
  4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  -------------------------
  ------- Protocol ID
  Server Group ID
  -------------------------
  ------- Unused
  Flags
  -------------------------
  ------- Sender ID Len Recvr ID Len
  Number of Records
  
  ------------------------
  -------- /
  / /
  Sender ID (Variable Length)
  / /
  / -----------
  --------------------- /
  
  / / Receiver ID
  (Variable Length) / /
  
  / ---------------------
  -----------

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Values for the SCSP Mandatory Common Part

• Protocol ID TBD
• There is a separate Protocol ID for NAT44, NAT64,
  and NAT46, assigned by IANA.
• Server Group ID NAT device redundancy group ID
• Sender ID Len
• 4, if IPv4 address is used
• 16, if IPv6 address is used.
• Per RFC2334, an identifier assigned to a server
  (in this case, a NAT device), might be the
  protocol address of the sending server.
• Recvr ID Len
• 4, if IPv4 address is used
• 16, if IPv6 address is used.
• Per RFC2334, an identifier assigned to a server
  (in this case, a NAT device), might be the
  protocol address of the receiving server.

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Values for the SCSP CSAS Record

• Cache Key Len 4
• This 4-byte opaque string is generated by the NAT
  device that originates the CSAS.
• Originator ID Len
• 4, if IPv4 address is used
• 16, if IPv6 address is used.
• Per RFC2334, an identifier assigned to a server
  (in this case, a NAT device) might be the
  protocol address of the server.

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NAT Specific CSA

• 0 1 2
  3 0 1 2 3 4 5 6 7 8 9 0 1 2 3
  4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  -------------------------
  ------- Protocol Option
  Length Unused
  -------------------------
  ------- Port Mapped from
  Port Mapped to
  -------------------------
  ------- /
  / /
  Address Mapped from (Specific to NAT type)
  / /
  / -----------
  --------------------- /
  
  / / Address Mapped to
  (Specific to NAT type) / /
  
  / ---------------------
  ----------- /
  / /
  TLV Options (Variable Length)
  / /
  /
  -------------------------
  -------

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The Next

• Authors would like to solicit comments with
  discussion on mailing list at this time
• If there is enough interest, well propose to
  move this I-D as a working group document