RE: Question re IP address mapping in a RAC environment
- From: "William Wagman" <wjwagman@xxxxxxxxxxx>
- To: "K Gopalakrishnan" <kaygopal@xxxxxxxxx>
- Date: Fri, 22 Feb 2008 14:28:47 -0800
Exactly, thank you.
Bill Wagman
Univ. of California at Davis
IET Campus Data Center
wjwagman@xxxxxxxxxxx
(530) 754-6208
-----Original Message-----
From: K Gopalakrishnan [mailto:kaygopal@xxxxxxxxx]
Sent: Friday, February 22, 2008 11:45 AM
To: William Wagman
Cc: finn.oracledba@xxxxxxxxx; oracle-l@xxxxxxxxxxxxx
Subject: Re: Question re IP address mapping in a RAC environment
Bill,
Quoting from my 'Oracle Database 10g RAC Handbook'...Hope this is what
you are looking...
Virtual IP is required to ensure that applications can be designed to
be highly available. To design this, system needs to eliminate single
point of failures. In oracle we need to ensure that clients connected
to a RAC database, survives a node failure. Client applications
connect to the oracle instance and access the database through the
instance. So a node failure will bring down the instance to which the
client might have connected.
The first design available from Oracle was Transparent Application
Failover (TAF). With TAF a session can failover to the surviving
instances and continue processing. Various limitations existed with
TAF; only query failover is supported. Also to achieve less latency in
failing over to the surviving node, we had to tweak the tcp timeout
(platform dependent, defaults to 10 minutes in most UNIX ports). It
wouldn't be a good idea to design a system where a client takes 10
mins to detect that there is no response from the node to which it has
connected.
To address this, 10g introduced a new feature called cluster virtual
IPs (VIPs). VIP is cluster virtual IP address, which would be used by
outside world to connect to the database and this IP address needs to
be different from the set of IP addresses, within the cluster.
Traditionally listeners would be listening on the public IP of the
box. and clients would contact the listener on this IP. If the node
dies, then the client would take the tcp timeout value to detect the
death of the node. In 10g each node of the cluster has a VIP
configured in the same subnet of the public IP. Virtual IP name and
addresses must be registered in the DNS in addition to the standard
static IP information. Listeners would be configured to listen on VIPs
instead of the public IP.
When a node is down, the VIP is automatically failed over to the one
of the other nodes. During the failover, the node, which gets the
VIP, will re-arp to the world indicating the new MAC address of the
VIP. Clients who have connected to this VIP will immediately get a
reset packet sent. This results in clients getting errors immediately
rather than waiting for the tcp timeout value. When one node goes down
in cluster and client is connecting to same node, in this case client
connection will be refused by down node and client application will
chose next available node from tns descriptor list to get connection.
Applications need to be written such that they catch the reset errors
and handle them. Typically for queries, they should see ORA-3113
error.
In computer networking the Address Resolution Protocol (ARP) is the
method of finding the host's hardware address (MAC address) when only
IP address is known. ARP is used by the hosts when they want to
communicate each other in the same network. It also used by routers to
forward a packet from one host through another router. In cluster
Virtual IP failovers, the new node which gets the VIP advertises the
new ARP Address to the world. This is typically known as gracious-arp
and during this operation, the old hardware address is invalidated in
the ARP cache and all the new connections will get the new hardware
address.
On Fri, Feb 22, 2008 at 10:19 AM, William Wagman <wjwagman@xxxxxxxxxxx>
wrote:
>
> Finn,
>
> I believe that is in fact what it is. I am just looking for a
discussion or
> documentation on the architecture of this process. I sort of
understand how
> it works but I'm not sure and am looking for an explanation.
>
> Thanks.
>
>
> Bill Wagman
> Univ. of California at Davis
> IET Campus Data Center
> wjwagman@xxxxxxxxxxx
> (530) 754-6208
>
> ________________________________
> From: oracle-l-bounce@xxxxxxxxxxxxx
[mailto:oracle-l-bounce@xxxxxxxxxxxxx]
> On Behalf Of Finn Jorgensen
> Sent: Thursday, February 21, 2008 5:28 PM
> To: William Wagman
> Cc: oracle-l@xxxxxxxxxxxxx
> Subject: Re: Question re IP address mapping in a RAC environment
>
>
>
> Wouldn't that be the VIP of node 2 that's migrated to node 1?
>
> Finn
>
--
Best Regards,
K Gopalakrishnan
Co-Author: Oracle Wait Interface, Oracle Press 2004
http://www.amazon.com/exec/obidos/tg/detail/-/007222729X/
Author: Oracle Database 10g RAC Handbook, Oracle Press 2006
http://www.amazon.com/gp/product/007146509X/
--
//www.freelists.org/webpage/oracle-l
Other related posts:
