Can an MX record point to BGP enabled IP address for Redundancy

[bbhattacharya]

Hello,

        I have an issue with mail redundancy for which I was hoping to get some guidance.

I have a multi-homed BGP setup and I am advertising a /24 group from my ASN (lets say xx.xx.xx.0/24). We use this primarily for incoming connection to fulfill a business need.
Multihoming is done via two routers and two separate ISPs.

for Mail - Our Exchange server is NATed to an external IP (NOT from the same group as above) and one of the two ISPs point the MX record to this IP address (yy.yy.yy.yy)

My question is - Can I ask the ISP to point the MXrecord to a BGP enabled IP address (from xx.xx.xx.0/24 pool) and create another NAT rule in the second router and achieve incoming mail redundancy in case of an outage?

OR should I create another MX record with the second ISP?
which method is more robust?

For outgoing, I am using HSRP.

It will be great if anyone here can point me in the right direction.

[Peter Paluch]

Hello,

Technically, the MX record does not point to an IP address but rather to a FQDN name, and only this name is further translated into an IP address. Putting an IP address into the MX record would be a violation of the correct MX RR usage.

I believe personally that it is more correct to create an additional MX record, in effect pointing to the another IP address. This will not require creating another NAT rule and thus relying on the NAT functionality (and all things that the NAT itself depends on). From the viewpoint of the SMTP protocol, it is more correct to propagate the information about several possibly usable MX servers along with their priority.

Of course, I suggest waiting for other friends here expressing their ideas about your query.

Best regards,

Peter

[Mohamed Sobair]

Hi,

I have implemented recently similar setup for a customer requirment when I worked for an ISP. The Actual case is that you can have 2 different MX records in the DNS servers pointing to two different IPs, its  possible, you can have two MX records , one is primary with highest priority and the Second configured in the Secondary ISP with lowest priority, However you cant have both working at the same time (TO Achieve loadbalancing).

Just tell both ISPs to configure two Different IP Addresses and create an MX record on thier DNS server pointing to your email with one Address being a primary for you and the Second is Secondary.

Now , with this setup, if your primary link fails, the Secondary ISP performs continous check on the presence of your Exchange server on its primary MX record (By the DNS Server), if its not reachable, then immediately the Secondary MX record is used and all outside emails comes through this connection.

HTH

Mohamed

[bbhattacharya]

Thank you very much for your reply fellows. Hope you guys had a great weekend.

I just wanted to make sure I understand it correctly. Please refer to the visio I have attached herewith.

1. create another MX record pointing to my FQDN to another IP addresss with lower priority.

2. Have another ISP host both MX records with the same priorities

3. Is there an agreed upon protocol by which the two ISPs can talk to one another to poll for availability?

My question is - can two ISPs host the same FQDN?

Will the final design look like how it is in the Visio.

[Mohamed Sobair · Accepted solution]

Hi,

Answers inline:

1- Correct.

2- Correct.

3- Normally yes, every ISP has International and National link, So they use the National links for other ISP's Networks , and they use the International Link for Internet.

The Two ISPs can indeed host different FQDN providing there is an existing reachability between both as I've described above.

So , you are good to go..

HTH

Mohamed

[bbhattacharya]

Thank you Mohammed for your help. It certainly aided my understanding.

[Mohamed Sobair]

You are Welcome,

Regards,

Mohamed