HP VPN Firewall Appliances High Availability Configuration Guide

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• A DNS MX record defines the mapping between a domain name and mail server name. When an
Internet user sends an Email, the local mail server typically sends a DNS request to the LB device first
to query the MX record of the mail recipient address.
Inbound link load balancing operates in the following way:
1. Upon receiving a DNS request sent by the local server (local DNS server or local mail server), if the
request is an MX record query request, the LB device searches a match, resolve the domain name
suffix of the recipient address to a mail server name, and goes to the following step to search an
A record by using the mail server name as the requested domain name. If the request is an A
record query request, it goes to the following step.
To reduce packet exchanges, the LB device uses the MX query result to query A records, and adds
the A record query result as an appended record into the MX response to send to the local server.
When querying MX records, if finding multiple matches, the LB device returns at most 10 matches
to the local server, which selects one according to the priority of the MX records.
2. The LB device uses the requested domain name to search the inbound link load balancing DNS A
record for a match. If the source IP address of the DNS request matches the ACL in the DNS record,
the LB device responds with the IP address in the DNS record. Otherwise, it goes to the following
step.
3. The LB device matches the source IP address of the DNS request against the best performing link
entry, uses the physical link in the matched best performing link entry, and responds with the IP
address in the corresponding DNS A record. If no match is found, the LB device performs best
performing link detection on all the physical links corresponding to the DNS A records that match
the domain name to generate a best performing link entry, and goes to the following step.
4. If ISP routing is enabled, the LB device matches the source IP address of the DNS request against
the ISP entry, uses the physical link in the matched ISP entry, and responds with the IP address in
the corresponding DNS A record. If ISP routing is not enabled or no match is found, the LB device
does not add the search result of the A record when the request is an MX record query request. The
LB device uses the physical link that corresponds with the first DNS record that matches the
requested domain name, and responds with the IP address of the DNS record if the request is an
A record query request.
Recommended configuration procedure
Configuring outbound link load balancing
Ste
p
Remarks
1. Saving of the last hop
information
Optional.
For more information, see "Configuring public parameters."
2. Configuring a health monitoring
method
Optional.
3. Creating a physical link
Required.
4. Configuring the best performing
link function
Optional.
Configure dynamic best performing link parameters and static best
performing link entries.
For outbound link load balancing, this function is available only when
enabling of best performing link is configured for a virtual service.