On 7/20/2011 1:15 AM, AMANI M. BIN SUWAIF wrote:
Hi,
The problem is that fail-over between A records is not standard and
might/might not work with various SIP clients. On the other hand SRV
in my opinion has been designed with that in mind, that's why the
additional complexity with 2 SRV records.
Thanks & Regards,
*Amani*
On 7/20/2011 2:50 AM, Kevin Darcy wrote:
On 7/18/2011 11:42 PM, AMANI MOHAMED BIN SUWAIF wrote:
Hi,
I have the below scenario
_TCP.EXAMPLE.COM IN SRV 10 0 5060
primary-sbg.example.com
_TCP.EXAMPLE.COM IN SRV 20 0 5060
secondary-sbg.example.com
I have 2 IP ranges and 2 SBGs host, my intention is
for client in IP range1
primary-sbg IN A 1.1.1.1
secondary-sbg IN A 2.2.2.2
for client in IP range2
primary-sbg IN A 2.2.2.2
secondary-sbg IN A 1.1.1.1
can this be achieved without using a views?
I thought this can be solved just by a sortlist, where
primary-sbg IN A 1.1.1.1
primary-sbg IN A 2.2.2.2
secondary-sbg IN A 2.2.2.2
secondary-sbg IN A 1.1.1.1
and then introduce the sortlist, which sorts the position of IP
addresses based on the IP range client comes from?
something like,
sortlist {
{
IPRANGE1; // 1st client IP selection matches any of these
{1.1.1.1; // return any of these response IPs as 1st preference
};
{
IPRANGE2; // 1st client IP selection matches any of these
{2.2.2.2; // return any of these response IPs as 1st preference
};
};
but in this case,
client from IPRANGE1 receive 1.1.1.1 as a first choice for both
primary-sbg and secondary-sbg
and
client from IPRANGE2 receive 2.2.2.2 as a first choice for both
primary-sbg and secondary-sbg
which is not the intention. sortlist doesn't not consider domain name.
The intention is to have primary SBG for first iprange act as a
secondary SBG for the second ip range and vice verse and in similar
manner for multiple IP ranges and SBGs. Problem with views is that
anytime this setup gets bigger and we will have additional ip ranges
and additional SBGs, it will require additional views...
(LOC)RANGE PRIMARY(LOC) SECONDARY(LOC)
(L1)IPRANGE1 SBG1(L1) SBG6(L2)
(L1)IPRANGE2 SBG2(L1) SBG7(L2)
(L1)IPRANGE3 SBG3(L1) SBG8(L2)
(L1)IPRANGE4 SBG4(L1) SBG9(L2)
(L1)IPRANGE5 SBG5(L1) SBG10(L2)
(L2)IPRANGE6 SBG6(L2) SBG1(L1)
(L2)IPRANGE7 SBG7(L2) SBG2(L1)
(L2)IPRANGE8 SBG8(L2) SBG3(L1)
(L2)IPRANGE9 SBG9(L2) SBG4(L1)
(L2)IPRANGE10 SBG10(L2) SBG5(L1)
half of the SBGs is in one location (L1) and half in other (L2),
that's why it is important that for clients from ranges in one
location, first half of SBGs is preferred, and for other clients
from second location other half of SBGs is preferred. Client
configuration should be uniformed (same SRV) regardless the location.
Are you over-engineering this? If the A-record failover by your
client is fast enough you might only need 1 SRV record, and then
sortlisting will work fine (subject to the usual caveats: as long as
you can control the sortlist config of every resolver your clients
will use, and keep them in sync).
- Kevin
Well, you could always stand up some virtual IPs on the same servers (or
possibly NAT it upstream) and then perform some *fancy* sortlisting, e.g.
for clients in IP range1
primary-sbg 1.1.1.1, 2.2.2.3
secondary-sbg 2.2.2.2, 1.1.1.2
for clients in IP range2
primary-sbg 2.2.2.3, 1.1.1.1
secondary-sbg 1.1.1.2, 2.2.2.2
That way range1 clients would always fail over -- via SRV failover or
A-record failover -- from the 1.1.1.x server to the 2.2.2.x server and
range2 clients would always fail over from the 2.2.2.x server to the
1.1.1.x server.
Bear in mind that "view"s, i.e. giving different answers to the same DNS
query, depending on the client, is not something which is (as far as I'm
aware) sanctioned by the Internet Standards, but A-record failover was
specified as far back as RFC 1123 (1989):
"2.3 Applications on Multihomed hosts
When the remote host is multihomed, the name-to-address translation will
return a list of alternative IP addresses. As specified in Section
6.1.3.4, this list should be in order of decreasing preference.
Application protocol implementations SHOULD be prepared to try multiple
addresses from the list until success is obtained. More specific
requirements for SMTP are given in Section 5.3.4. "
2.3 Applications on Multihomed hosts
When the remote host is multihomed, the name-to-address
translation will return a list of alternative IP addresses. As
specified in Section 6.1.3.4, this list should be in order of
decreasing preference. Application protocol implementations
SHOULD be prepared to try multiple addresses from the list until
success is obtained. More specific requirements for SMTP are
given in Section 5.3.4.
So if you're worried about what is "standard" and what isn't, you should
cast your lot with A-record failover and *not* any "view" trickery.
- Kevin
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