NAME

        SV_RFC2181_4_2_port_selection - Port number selection

VERIFICATION POINTS

        Verify that a NUT selects the correct Port number.

Replies to all queries must be directed to the port from which they were sent. When queries are received via TCP this is an inherent part of the transport protocol. For queries received by UDP the server must take note of the source port and use that as the destination port in the response. Replies should always be sent from the port to which they were directed. Except in extraordinary circumstances, this will be the well known port assigned for DNS queries.

TARGET

        Authoritative Server

SYNOPSIS

	SV_RFC2181_4_2_port_selection.seq [-tooloption ...]: KOI tool option
	See also DNSConfig.pm

INITIALIZATION

Network Topology

        AP Server1 (TN)
          |3ffe:501:ffff:101::10
          |192.168.1.10
          |
Net-y   --+--------+-------------------------- 3ffe:501:ffff:101::/64 
                   |                           192.168.1/24
                   |
                   |
                 Router (TN)
                   |3ffe:501:ffff:100::1
                   |192.168.0.1
                   |
                   |
Net-z   --+--------+-----------------+-------- 3ffe:501:ffff:100::/64 
          |                          |          192.168.0/24
          |                          |
        DNS Server1 (NUT)            DNS Client1 (TN)
           3ffe:501:ffff:100::XXXX     3ffe:501:ffff:100::20 
           192.168.0.10                192.168.0.20
	

	XXXX: EUI64

Setup

Set the DNS Server1's (NUT) address as above mentioned Network Topology.

Configure the Server1's (NUT) zone file to response query from TN.

Example of example.com zone file:

$TTL    86400           ; TTL of 1 day
@ IN SOA NS1.example.com. root.example.com. (
	2005081600	; serial
	3600		; refresh every 1 hr
	900		; retry every 15 min
	604800		; expire after a week
	3600		; Minimum TTL of a 1 hr
)
;
	IN	NS	NS1.example.com.
NS1	IN	A	192.168.0.10
;
A	IN	A	192.168.1.10

TEST PROCEDURE

        This test sequence is following.

    DNS Client1 (TN)                       DNS Server1 (NUT)
        |                                      |
        |------------------------------------->|
        |   1. Send standard query             |
        |   *Source Port=2000                  |
        |       QNAME=A.example.com            |
        |       QTYPE=A                        |
        |                                      |
        |<-------------------------------------|
        |   2. Standard query response         |
        |   *Destination Port=2000             |
        |       A=192.168.1.10                 |
        |                                      |
        |------------------------------------->|
        |   3. Send standard query             |
        |   *Source Port=2001                  |
        |       QNAME=A.example.com            |
        |       QTYPE=A                        |
        |                                      |
        |<-------------------------------------|
        |   4. Standard query response         |
        |   *Destination Port=2001             |
        |       A=192.168.1.10                 |
        |                                      |
        |                                      |
        v                                      v

        1. TN send standard query QNAME=A.example.com, QTYPE=A to NUT that source port=2000.
        2. NUT reply query response w/ A=192.168.1.10 to TN that destination port=2000 (Judgment *2)
        3. TN send standard query QNAME=A.example.com, QTYPE=A to NUT that source port=2001.
        4. NUT reply query response w/ A=192.168.1.10 to TN that destination port=2001 (Judgment *4)

Packet Description

1st packet.

Standard query from DNS Client1 (TN) to Server1 (NUT)
IP Header	Source Address	CL1_NETZ
IP Header	Destination Address	NUT_NETZ
UDP Header	Src Port	2000
UDP Header	Dst Port	53
DNS Header	ID	0x1000
	QR	0
	OPCODE	0
	AA	0
	TC	0
	RD	1
	RA	0
	Z	0
	RCODE	0
	QDCOUNT	1
	ANCOUNT	0
	NSCOUNT	0
	ARCOUNT	0
DNS Question section	QNAME	A.example.com
	QTYPE	A (0x0001)
	QCLASS	IN (0x0001)

2nd packet.

Standard query response from DNS Server1 (NUT) to Client1 (TN)
IP Header	Source Address	NUT_NETZ
IP Header	Destination Address	CL1_NETZ
UDP Header	Src Port	53
UDP Header	Dst Port	2000
DNS Header	ID	0x1000
	QR	1
	OPCODE	0
	AA	1
	TC	0
	RD	1
	RA	ANY
	Z	0
	RCODE	0
	QDCOUNT	1
	ANCOUNT	1
	NSCOUNT	1
	ARCOUNT	1
DNS Question section	QNAME	A.example.com
	QTYPE	A (0x0001)
	QCLASS	IN (0x0001)
DNS Answer section	NAME	A.example.com (Pointer 0xC00C)
	TYPE	A (0x0001)
	CLASS	IN (0x0001)
	TTL	1 day (86400)
	RDLENGTH	4
	ADDRESS	192.168.1.10
DNS Authority section	NAME	example.com (Pointer 0xC00E)
	TYPE	NS (0x0002)
	CLASS	IN (0x0001)
	TTL	1 day (86400)
	RDLENGTH	6
	NSDNAME	NS1.example.com (NS1 + Pointer 0xC00E)
DNS Additional section	NAME	NS1.example.com (Pointer 0xC03B)
	TYPE	A (0x0001)
	CLASS	IN (0x0001)
	TTL	1 day (86400)
	RDLENGTH	4
	ADDRESS	192.168.0.10

3rd packet.

Standard query from DNS Client1 (TN) to Server1 (NUT)
IP Header	Source Address	CL1_NET
IP Header	Destination Address	NUT_NETZ
UDP Header	Src Port	2001
UDP Header	Dst Port	53
DNS Header	ID	0x1001
	QR	0
	OPCODE	0
	AA	0
	TC	0
	RD	1
	RA	0
	Z	0
	RCODE	0
	QDCOUNT	1
	ANCOUNT	0
	NSCOUNT	0
	ARCOUNT	0
DNS Question section	QNAME	A.example.com
	QTYPE	A (0x0001)
	QCLASS	IN (0x0001)

4th packet.

Standard query response from DNS Server1 (NUT) to Client1 (TN)
IP Header	Source Address	NUT_NETZ
IP Header	Destination Address	CL1_NETZ
UDP Header	Src Port	53
UDP Header	Dst Port	2001
DNS Header	ID	0x1001
	QR	1
	OPCODE	0
	AA	1
	TC	0
	RD	1
	RA	ANY
	Z	0
	RCODE	0
	QDCOUNT	1
	ANCOUNT	1
	NSCOUNT	1
	ARCOUNT	1
DNS Question section	QNAME	A.example.com
	QTYPE	A (0x0001)
	QCLASS	IN (0x0001)
DNS Answer section	NAME	A.example.com (Pointer 0xC00C)
	TYPE	A (0x0001)
	CLASS	IN (0x0001)
	TTL	1 day (86400)
	RDLENGTH	4
	ADDRESS	192.168.1.10
DNS Authority section	NAME	example.com (Pointer 0xC00E)
	TYPE	NS (0x0002)
	CLASS	IN (0x0001)
	TTL	1 day (86400)
	RDLENGTH	6
	NSDNAME	NS1.example.com (NS1 + Pointer 0xC00E)
DNS Additional section	NAME	NS1.example.com (Pointer 0xC03B)
	TYPE	A (0x0001)
	CLASS	IN (0x0001)
	TTL	1 day (86400)
	RDLENGTH	4
	ADDRESS	192.168.0.10

Exp.

NUT_NETZ	DNS Server1's (NUT) Net-z address
CL1_NETZ	DNS Client1's (TN) Net-z address

JUDGMENT

        2. Received standard query response w/ A=192.168.1.10 that destination port=2000.
        3. Received standard query response w/ A=192.168.1.10 that destination port=2001.

TERMINATION

        None

REFERENCE

        RFC2181 Clarifications to the DNS Specification
        4.2. Port Number Selection