Bidirectional NAT+DNS_ALG

172.19.1.10

Host A

DNSe

private.com

external.com

Bidi-NAT

DNS_ALG

Internet

Router

DNSroot

reply

name lookup

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1. Name lookup from X.external.com for A.private.com
a. Name lookup for A.private.com crosses NAT (1-4)

b. Reply crosses NAT (5-6)
-- change A records private->private’ [assign]

-- assume private’ assignment is 131.108.1.1

2. Reverse name lookup from X.external.com for 131.108.1.1
a. Reverse name lookup crosses NAT (1-4)

-- change PTR in query private’->private

b. Reply crosses NAT (5-6)
-- change PTR in query private->private’

-- change A records private->private’ [assign]