© F5 Networks, Inc.

1

How Does DNS Work?

http://www.domain.com

A user browses to www.domain.com

LDNS

Root DNS Server(one of 16 from

root.hints)

Is there a record for www.domain.com?

Is there a record for www.domain.com?

Go ask .com

.com DNS Server

Is there a record for www.domain.com?

Go ask domain.com

The LDNS asks .com for www.domain.com, which returns

an NS record for domain.com

The LDNS asks domain.com for www.domain.com, which returns

an A record

Is there a record for www.domain.com?

66.163.171.129

domain.com DNS Server

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2

LDNS

Root DNS Server(one of 16 from

root.hints)

.com DNS Server domain.com

DNS Server

How Does DNS Work?

66.163.171.129

Web Server

http://www.domain.com

Is there a record for www.domain.com?

The browser opens a connection to address:80 and does a GET /…

… And the server returns the Web page response

66.163.171.129

The LDNS returns the A record to the client and

caches it locally

66.163.171.129

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3

General Use Cases for DNSDelegation

LDNS

www.company.comDNS Server

LDNS requests www.company.com

CNAME www.company.comto www.subzone.company.com

www.subzone.company.com DNS Server

www.subzone.company.com returns an A record with the IP address of the desired resource

LDNS requests www.subzone.company.com

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4

DNS Load Balancing with LTM (No GTM)

LDNS

Data Center

DNS Servers

company.com

LDNS requests www.company.com

LTM responds with the DNS A record

LTM passes the request to the DNS

server pool

The DNS server responds with an A record IP for

www.company.com BIG-IP

Local Traffic Manager

iA

DNS iRules*

IP Anycast*A

i

*Requires DNS Services Add-on

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5

Data Center

BIG-IPGlobal Traffic Manager

company.comDNS Serverwww.gtm.company.com

GSLB and Delegation Mode

LDNS

Root DNS Server

Is there a record for www.company.com?

Is there a record for www.company.com?

Go ask .com

.com DNS Server

Is there a record for www.company.com?

Go ask company.com

Is there a record for www.company.com?

Return CNAME www.gtm.company.com

http://www.company.com

© F5 Networks, Inc.

6

DNS Delegation Sample Configuration

Example database prior to delegation:

www.domain.com. IN A 200.10.10.10www.domain.com. IN A 150.10.10.10

Example database after delegation:

wip.domain.com. IN NS gtm1.wip.domain.com.wip.domain.com. IN NS gtm2.wip.domain.com.gtm1.wip.domain.com. IN A 200.10.10.53gtm2.wip.domain.com. IN A 150.10.10.54www.domain.com. IN CNAME www.wip.domain.com.

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7

GSLB and Delegation Mode

LDNS

Is there a record for www.gtm.company.com?

Is there a record for www.gtm.company.com?

Go ask .com

Is there a record for www.gtm.company.com?

Go ask company.com

Is there a record for www.gtm.company.com?

Root DNS Server

.com DNS Server

Data Center

BIG-IPGlobal Traffic Manager

company.comDNS Serverwww.gtm.company.com

http://www.company.com

© F5 Networks, Inc.

8

GLSB and Delegation Mode

http://www.company.com

LDNS

Is there a record for www.company.com?

Data Center

BIG-IPGlobal Traffic Manager

company.comDNS Serverwww.gtm.company.com66.163.171.12966.163.171.129

66.163.171.129

66.163.171.129

X72.68.171.103

Is there a record for www.gtm.company.com?

© F5 Networks, Inc.

9

BIG-IP DNS Authoritative Screen

LDNS

www.subzone.company.com DNS Server

Data Center

company.com

LDNS send a DNS query

BIG-IPGTM/LTM-DNS Services

Resolved DNS request

If GTM is enabled , check GTM Wide IPs and if matched, resolves

to the best IP

www.gtm.company.com

DNS Listener on the BIG-IP receives all DNS requests

Else, forward the query to external DNS

servers

If DNS Express is enabled, check against

DNS Express zones and then local BIND

© F5 Networks, Inc.

10

BIG-IP DNS Authoritative Screen

LDNS

www.subzone.company.com DNS Server

Data Center

company.comwww.gtm.company.com

Q Xi

DNS Express

DNSSEC

Geolocation

DNS iRules

X

Q

i

BIG-IPGTM/LTM-DNS Services

© F5 Networks, Inc.

11

GTM Pool

Wide IP (WIP) objects• Fully Qualified Domain Names (FQDNs) associated with one or more pools

Objects in the GTM Architecture

Primary DC Secondary DC Disaster Recovery DC

GTM GTM GTMLTM LTM LTM

Server Server

73.37.1.1:80

Virtual Server Virtual Server68.28.1.1:80

Pool objectsGroups of virtual servers to be load balanced

Virtual servers objects• IP address:port combinations on server objects

• Applications to load balance/resolve too • May represent multiple real servers (load balancers)• Or a single physical (standalone) server• Server objects often host multiple virtual servers

73.37.1.11:21

Virtual Server205.33.1.1:80

Virtual Server

Wide IP: www.f5.com = 73.37.1.1 or 68.28.1.1 or 205.33.1.1