[quagga-users 14436] Re: Redundant Service IP on loopback

Moacir Ferreira moacirferreira at hotmail.com
Tue Sep 27 13:43:22 BST 2016

Hey Dave,

You gave the whole answer on your question... You need to:

1 - Create a loopback interface making sure your services (DNS, FTP, HTTP, NTP, etc.) will also run in this IP address;

2 - Run a routing protocol (it can be BGP or OSPF, but I find it easier using OSPF unless facing the Internet for some reason); I would also recommend using Quagga that you can install via apt-get or yum install;

3 - Announce your /32 loopback IP address on the routing protocol that you are using;

4 - Manipulate the rounting protocol on each server (in BGP increase preference or AS path; in OSPF increase interface cost), so one of the servers will be preferred; the manipulation can also be done at the router/switch the servers are connected to;


By the way, this is becoming a very popular way for high availability. However, care must be taken should you need to synchronize data in between the two servers. If you need to keep them in sync, use the Ethernet IP address to do so (not the loopback address) and everything will go quite smooth.

As you need server redundancy, VRRP (HSRP) is not a solution for this. Unless you are willing to "complicate", anycast is really a bad choice.



From: Dave Hall <kdhall at binghamton.edu>
Sent: Tuesday, September 27, 2016 5:02 AM
To: quagga-users at lists.quagga.net
Subject: [quagga-users 14432] Redundant Service IP on loopback


I found a link about this a couple months ago but apparently I didn't
save it, so I'm going to have to ask...

The article I found described how to set up the IP for some service
(i.e. DNS) on the loopback interface of two identical servers and then
use BGP to distribute route advertisements with different metrics such
that if the server with the lower metric fails or is rebooted the
traffic will go to the other server.

My main goal here is services such as DNS and LDAP were the service is
primarily used by other hosts/servers on the same subnet.  I'm not sure
if the original scheme (above) assumed that there was a router involved,
but in this case there is no router.

Any guidance would be sincerely appreciated.



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