Oracle RAC SCAN is not compatibile with NAT (and thus with PCI DSS)

Oracle Single Client Access Name (SCAN) – a single access point name for Oracle RAC instance VIPs – seems often to be problematic in environments that use NAT or have to be able with compliance regulations such as PCI DSS:

  1. section 1.3.3 – “Do not allow any direct connections inbound or outbound for traffic between the Internet and the cardholder data environment”
  2. section 1.3.8 – “Do not disclose private IP addresses and routing information to unauthorized parties. Note: Methods to obscure IP addressing may include, but are not limited to: Network Address Translation (NAT) [..]“

The problem with giving external/internal parties access to Oracle RAC database clusters basically could be defined as “Oracle SCAN incompatibility with Destination NAT/TCP proxies that are network brokers”, here’s simple successful connection example to TNS_ENTRY1 alias (served via single 1xSCAN raccluster-scan VIP and racnode1/racnode2 Oracle VIPs)

[someone@racnode1 ~]$ sqlplus doesnotexists@TNS_ENTRY1
[someone@racnode1 ~]$ grep -e nnftrne: -e niotns: -e nsc2addr: sqlnet_1696.trc
(1002018528) [06-AUG-2013 09:58:30:471] nnftrne: entry
(1002018528) [06-AUG-2013 09:58:30:471] nnftrne: Original name: TNS_ENTRY1
(1002018528) [06-AUG-2013 09:58:30:472] nnftrne: Using tnsnames.ora address (DESCRIPTION = (ADDRESS = (PROTOCOL = TCP)(HOST = raccluster-scan)(PORT = 1521)) (CONNECT_DATA = (SERVER = DEDICATED) (SERVICE_NAME = TNS_ENTRY1))) for name TNS_ENTRY1
(1002018528) [06-AUG-2013 09:58:30:472] nnftrne: exit
(1002018528) [06-AUG-2013 09:58:30:512] nnftrne: entry
(1002018528) [06-AUG-2013 09:58:30:512] nnftrne: Original name: TNS_ENTRY1
(1002018528) [06-AUG-2013 09:58:30:512] nnftrne: Using tnsnames.ora address (DESCRIPTION = (ADDRESS = (PROTOCOL = TCP)(HOST = raccluster-scan)(PORT = 1521)) (CONNECT_DATA = (SERVER = DEDICATED) (SERVICE_NAME = TNS_ENTRY1))) for name TNS_ENTRY1
(1002018528) [06-AUG-2013 09:58:30:512] nnftrne: exit
(1002018528) [06-AUG-2013 09:58:30:527] niotns: entry
(1002018528) [06-AUG-2013 09:58:30:527] niotns: niotns: setting up interrupt handler...
(1002018528) [06-AUG-2013 09:58:30:527] niotns: Not trying to enable dead connection detection.
(1002018528) [06-AUG-2013 09:58:30:528] niotns: Calling address: (DESCRIPTION=(ADDRESS=(PROTOCOL=TCP)(HOST=raccluster-scan)(PORT=1521))(CONNECT_DATA=(SERVER=DEDICATED)(SERVICE_NAME=TNS_ENTRY1)(CID=(PROGRAM=sqlplus)(HOST=racnode1)(USER=someone))))
(1002018528) [06-AUG-2013 09:58:30:529] nsc2addr: (DESCRIPTION=(CONNECT_DATA=(SERVER=DEDICATED)(SERVICE_NAME=TNS_ENTRY1)(CID=(PROGRAM=sqlplus)(HOST=racnode1)(USER=someone)))(ADDRESS=(PROTOCOL=TCP)(HOST=10.xx.yy.43)(PORT=1521)))
(1002018528) [06-AUG-2013 09:58:30:537] nsc2addr: (DESCRIPTION=(ADDRESS=(PROTOCOL=TCP)(HOST=10.xx.yy.42)(PORT=1521)))
(1002018528) [06-AUG-2013 09:58:30:572] niotns: niotns: passing ns handle back up...
(1002018528) [06-AUG-2013 09:58:30:572] niotns: exit
[someone@racnode1 ~]$

As you can see from the above example the following is happening:
a) client is connecting via TCP/1521 to raccluster-scan
b) SCAN listener on raccluster-scan redirects – via TCP data – to hostname of the least loaded Oracle VIP (!)
c) client spawns a new connection directly to the Oracle VIP on TCP/1521 (!!)

The main problem is that when you have DNAT defined with single TCP port redirection that looks like this some Oracle client –TCP port 33333 –> DNAT/proxy_redirection –> Oracle SCAN VIP, this is not going to work because Oracle SCAN listener will redirect “some Oracle client” to Oracle VIP TCP/1521. This will fail in 1 out of 3 ways:

  1. failure scenario1: client might fail to resolve hostname using it’s own DNS
  2. failure scenario2: client might succeed DNS hostname resolution of OracleVIPX resolution but is going to be unable to reach the private VIP address via IP routing because routers/default gateway won’t know how to route to the destination (e..g client is coming from different organization, internet, etc)
  3. failure scenario3: client might succeed DNS hostname resolution, might even be able to route to the the OracleVIPX IP is, but there is firewall somewhere in between (e.g. on the same box that is doing DNAT/TCP proxy) blocking “some client” to reach directly OracleVIPX on TCP/1521

There are several solutions to this problem:
1) don’t use Oracle SCAN simple name but provide long TNS conneciton string with a number of NAT-ted/proxied TCP ports defined (every Oracle RAC node VIP should have its own NATTed/proxied TCP port for failover purposes – Oracle client is responsible for load balancing and failovering Oracle connections)
- or -
2) implement some kind of highly available TCP proxy that intelligently routes Oracle traffic to healthy RAC instances (e.g. HAproxy if you really have clients that support only short Oracle hostnames)
- or -
3) do tricks on external-facing DNS name servers (or locally on clients by placing entries on /etc/hosts) by spoofing internal host names as proxy one, but you will need 1:1 ratio of external to internal IPs to meet this goal (remember each Oracle VIP serves connections on port 1521!)
- or -
4) THE SIMPLEST ONE: do not use NAT and allow direct traffic on firewall, as NAT is evil :)


One Response to “Oracle RAC SCAN is not compatibile with NAT (and thus with PCI DSS)”

  1. Mike says:

    Comments not working :-(

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