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rfc2766.Network Address Translation - Protocol Translation (NAT-PT)

rfc2766.Network Address Translation - Protocol Translation (NAT-PT)
rfc2766.Network Address Translation - Protocol Translation (NAT-PT)

Network Working Group G. Tsirtsis Request for Comments: 2766 BT Category: Standards Track P. Srisuresh Campio Communications February 2000 Network Address Translation - Protocol Translation (NAT-PT)

Status of this Memo

This document specifies an Internet standards track protocol for the

Internet community, and requests discussion and suggestions for

improvements. Please refer to the current edition of the "Internet

Official Protocol Standards" (STD 1) for the standardization state

and status of this protocol. Distribution of this memo is unlimited.

Copyright Notice

Copyright (C) The Internet Society (2000). All Rights Reserved.

Abstract

This document specifies an IPv4-to-IPv6 transition mechanism, in

addition to those already specified in [TRANS]. This solution

attempts to provide transparent routing, as defined in [NAT-TERM], to end-nodes in V6 realm trying to communicate with end-nodes in V4

realm and vice versa. This is achieved using a combination of Network Address Translation and Protocol Translation. The scheme described

does not mandate dual-stacks (i.e., IPv4 as well as V6 protocol

support) or special purpose routing requirements (such as requiring

tunneling support) on end nodes. This scheme is based on a

combination of address translation theme as described in [NAT-TERM]

and V6/V4 protocol translation theme as described in [SIIT].

Acknowledgements

Special thanks to Pedro Marques for reviewing an earlier version of

this memo. Also, many thanks to Alan O’Neill and Martin Tatham, as

the mechanism described in this document was initially developed

through discussions with them.

Tsirtsis & Srisuresh Standards Track [Page 1]

Table of Contents

1. Introduction (2)

2. Terminology (3)

2.1 Network Address Translation (NAT) (4)

2.2 NAT-PT flavors (4)

2.2.1 Traditional-NAT-PT (4)

2.2.2 Bi-directional-NAT-PT (5)

2.3 Protocol Translation (PT) (5)

2.4 Application Level Gateway (ALG) (5)

2.5 Requirements (5)

3. Traditional-NAT-PT operation (V6 to V4) (6)

3.1 NAT-PT Outgoing Sessions (6)

3.2 NAPT-PT Outgoing Sessions (7)

4. Use of DNS-ALG for Address assignment (8)

4.1 V4 Address Assignment for Incoming Connections (V4 to V6). 9

4.2 V4 Address Assignment for Outgoing Connections (V6 to V4). 11

5. Protocol Translation Details (12)

5.1 Translating IPv4 Headers to IPv6 Headers (13)

5.2 Translating IPv6 Headers to IPv4 Headers (13)

5.3 TCP/UDP/ICMP Checksum Update (13)

6. FTP Application Level Gateway (FTP-ALG) Support (14)

6.1 Payload modifications for V4 originated FTP sessions (15)

6.2 Payload modifications for V6 originated FTP sessions (16)

6.3 Header updates for FTP control packets (16)

7. NAT-PT Limitations and Future Work (17)

7.1 Topology Limitations (17)

7.2 Protocol Translation Limitations (17)

7.3 Impact of Address Translation (18)

7.4 Lack of End-to-End Security (18)

7.5 DNS Translation and DNSSEC (18)

8. Applicability Statement (18)

9. Security Considerations (19)

10. References (19)

Authors’ Addresses (20)

Full Copyright Statement (21)

1. Introduction

IPv6 is a new version of the IP protocol designed to modernize IPv4

which was designed in the 1970s. IPv6 has a number of advantages over IPv4 that will allow for future Internet growth and will simplify IP configuration and administration. IPv6 has a larger address space

than IPv4, an addressing model that promotes aggressive route

aggregation and a powerful autoconfiguration mechanism. In time, it is expected that Internet growth and a need for a plug-and-play

solution will result in widespread adoption of IPv6.

Tsirtsis & Srisuresh Standards Track [Page 2]

There is expected to be a long transition period during which it will be necessary for IPv4 and IPv6 nodes to coexist and communicate. A

strong, flexible set of IPv4-to-IPv6 transition and coexistence

mechanisms will be required during this transition period.

The SIIT proposal [SIIT] describes a protocol translation mechanism

that allows communication between IPv6-only and IPv4-only nodes via

protocol independent translation of IPv4 and IPv6 datagrams,

requiring no state information for the session. The SIIT proposal

assumes that V6 nodes are assigned a V4 address for communicating

with V4 nodes, and does not specify a mechanism for the assignment of these addresses.

NAT-PT uses a pool of V4 addresses for assignment to V6 nodes on a

dynamic basis as sessions are initiated across V4-V6 boundaries. The V4 addresses are assumed to be globally unique. NAT-PT with private

V4 addresses is outside the scope of this document and for further

study. NAT-PT binds addresses in V6 network with addresses in V4

network and vice versa to provide transparent routing [NAT-TERM] for the datagrams traversing between address realms. This requires no

changes to end nodes and IP packet routing is completely transparent [NAT-TERM] to end nodes. It does, however, require NAT-PT to track

the sessions it supports and mandates that inbound and outbound

datagrams pertaining to a session traverse the same NAT-PT router.

You will note that the topology restrictions on NAT-PT are the same

with those described for V4 NATs in [NAT-TERM]. Protocol translation details specified in [SIIT] would be used to extend address

translation with protocol syntax/semantics translation. A detailed

applicability statement for NAT-PT may be found at the end of this

document in section 7.

By combining SIIT protocol translation with the dynamic address

translation capabilities of NAT and appropriate ALGs, NAT-PT provides a complete solution that would allow a large number of commonly used applications to interoperate between IPv6-only nodes and IPv4-only

A fundamental assumption for NAT-PT is only to be use when no other

native IPv6 or IPv6 over IPv4 tunneled means of communication is

possible. In other words the aim is to only use translation between

IPv6 only nodes and IPv4 only nodes, while translation between IPv6

only nodes and the IPv4 part of a dual stack node should be avoided

over other alternatives.

2. Terminology

The majority of terms used in this document are borrowed almost as is from [NAT-TERM]. The following lists terms specific to this document. Tsirtsis & Srisuresh Standards Track [Page 3]

2.1 Network Address Translation (NAT)

The term NAT in this document is very similar to the IPv4 NAT

described in [NAT-TERM], but is not identical. IPv4 NAT translates

one IPv4 address into another IPv4 address. In this document, NAT

refers to translation of an IPv4 address into an IPv6 address and

vice versa.

While the V4 NAT [NAT-TERM] provides routing between private V4 and

external V4 address realms, NAT in this document provides routing

between a V6 address realm and an external V4 address realm.

2.2 NAT-PT flavors

Just as there are various flavors identified with V4 NAT in [NAT-

TERM], the following NAT-PT variations may be identified in this

document.

2.2.1 Traditional NAT-PT

Traditional-NAT-PT would allow hosts within a V6 network to access

hosts in the V4 network. In a traditional-NAT-PT, sessions are uni-

directional, outbound from the V6 network. This is in contrast with Bi-directional-NAT-PT, which permits sessions in both inbound and

outbound directions.

Just as with V4 traditional-NAT, there are two variations to

traditional-NAT-PT, namely Basic-NAT-PT and NAPT-PT.

With Basic-NAT-PT, a block of V4 addresses are set aside for

translating addresses of V6 hosts as they originate sessions to the

V4 hosts in external domain. For packets outbound from the V6 domain, the source IP address and related fields such as IP, TCP, UDP and

ICMP header checksums are translated. For inbound packets, the

destination IP address and the checksums as listed above are

translated.

NAPT-PT extends the notion of translation one step further by also

translating transport identifier (e.g., TCP and UDP port numbers,

ICMP query identifiers). This allows the transport identifiers of a

number of V6 hosts to be multiplexed into the transport identifiers

of a single assigned V4 address. NAPT-PT allows a set of V6 hosts to share a single V4 address. Note that NAPT-PT can be combined with

Basic-NAT-PT so that a pool of external addresses are used in

conjunction with port translation.

Tsirtsis & Srisuresh Standards Track [Page 4]

For packets outbound from the V6 network, NAPT-PT would translate the source IP address, source transport identifier and related fields

such as IP, TCP, UDP and ICMP header checksums. Transport identifier can be one of TCP/UDP port or ICMP query ID. For inbound packets, the destination IP address, destination transport identifier and the IP

and transport header checksums are translated.

2.2.2 Bi-Directional-NAT-PT

With Bi-directional-NAT-PT, sessions can be initiated from hosts in

V4 network as well as the V6 network. V6 network addresses are bound to V4 addresses, statically or dynamically as connections are

established in either direction. The name space (i.e., their Fully

Qualified Domain Names) between hosts in V4 and V6 networks is

assumed to be end-to-end unique. Hosts in V4 realm access V6-realm

hosts by using DNS for address resolution. A DNS-ALG [DNS-ALG] must

be employed in conjunction with Bi-Directional-NAT-PT to facilitate

name to address mapping. Specifically, the DNS-ALG must be capable

of translating V6 addresses in DNS Queries and responses into their

V4-address bindings, and vice versa, as DNS packets traverse between V6 and V4 realms.

2.3 Protocol Translation (PT)

PT in this document refers to the translation of an IPv4 packet into a semantically equivalent IPv6 packet and vice versa. Protocol

translation details are described in [SIIT].

2.4 Application Level Gateway (ALG)

Application Level Gateway (ALG) [NAT-TERM] is an application specific agent that allows a V6 node to communicate with a V4 node and vice

versa. Some applications carry network addresses in payloads. NAT-PT is application unaware and does not snoop the payload. ALG could work in conjunction with NAT-PT to provide support for many such

applications.

2.5 Requirements

The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD,

SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL, when they appear in this document, are to be interpreted as described in [KEYWORDS].

Tsirtsis & Srisuresh Standards Track [Page 5]

3. Traditional-NAT-PT Operation (V6 to V4)

NAT-PT offers a straight forward solution based on transparent

routing [NAT-TERM] and address/protocol translation, allowing a large number of applications in V6 and V4 realms to inter-operate without

requiring any changes to these applications.

In the following paragraphs we describe the operation of

traditional-NAT-PT and the way that connections can be initiated from a host in IPv6 domain to a host in IPv4 domain through a

traditional-NAT-PT

3.1 Basic-NAT-PT Operation

[IPv6-B]-+

| +==============+

[IPv6-A]-+-[NAT-PT]---------| IPv4 network |--[IPv4-C]

| +==============+

(pool of v4 addresses)

Figure 1: IPv6 to IPv4 communication

Node IPv6-A has an IPv6 address -> FEDC:BA98::7654:3210

Node IPv6-B has an IPv6 address -> FEDC:BA98::7654:3211

Node IPv4-C has an IPv4 address -> 132.146.243.30

NAT-PT has a pool of addresses including the IPv4 subnet

120.130.26/24

The V4 addresses in the address pool could be allocated one-to-one to the V6 addresses of the V6 end nodes in which case one needs as many V4 addresses as V6 end points. In this document we assume that the V6 network has less V4 addresses than V6 end nodes and thus dynamic

address allocation is required for at least some of them.

Say the IPv6 Node A wants to communicate with the IPv4 Node C. Node A creates a packet with:

Source Address, SA=FEDC:BA98::7654:3210 and Destination

Address, DA = PREFIX::132.146.243.30

NOTE: The prefix PREFIX::/96 is advertised in the stub domain by the NAT-PT, and packets addressed to this PREFIX will be routed to the

NAT-PT. The pre-configured PREFIX only needs to be routable within

the IPv6 stub domain and as such it can be any routable prefix that

the network administrator chooses.

The packet is routed via the NAT-PT gateway, where it is translated

to IPv4.

Tsirtsis & Srisuresh Standards Track [Page 6]

If the outgoing packet is not a session initialisation packet, the

NAT-PT SHOULD already have stored some state about the related

session, including assigned IPv4 address and other parameters for the translation. If this state does not exist, the packet SHOULD be

silently discarded.

If the packet is a session initialisation packet, the NAT-PT locally allocates an address (e.g: 120.130.26.10) from its pool of

addresses and the packet is translated to IPv4. The translation

parameters are cached for the duration of the session and the IPv6 to IPv4 mapping is retained by NAT-PT.

The resulting IPv4 packet has SA=120.130.26.10 and DA=132.146.243.30. Any returning traffic will be recognised as belonging to the same

session by NAT-PT. NAT-PT will use the state information to translate the packet, and the resulting addresses will be

SA=PREFIX::132.146.243.30, DA=FEDC:BA98::7654:3210. Note that this

packet can now be routed inside the IPv6-only stub network as normal.

3.2 NAPT-PT Operation

NAPT-PT, which stands for "Network Address Port Translation +

Protocol Translation", would allow V6 nodes to communicate with the

V4 nodes transparently using a single V4 address. The TCP/UDP ports

of the V6 nodes are translated into TCP/UDP ports of the registered

V4 address.

While NAT-PT support is limited to TCP, UDP and other port

multiplexing type of applications, NAPT-PT solves a problem that is

inherent with NAT-PT. That is, NAT-PT would fall flat when the pool

of V4 addresses assigned for translation purposes is exhausted. Once the address pool is exhausted, newer V6 nodes cannot establish

sessions with the outside world anymore. NAPT-PT, on the other hand, will allow for a maximum of 63K TCP and 63K UDP sessions per IPv4

address before having no TCP and UDP ports left to assign.

To modify the example sited in figure 1, we could have NAPT-PT on the border router (instead of NAT-PT) and all V6 addresses could be

mapped to a single v4 address 120.130.26.10.

IPv6 Node A would establish a TCP session with the IPv4 Node C as

follows:

Node A creates a packet with:

Source Address, SA=FEDC:BA98::7654:3210 , source TCP port = 3017 and Destination Address, DA = PREFIX::132.146.243.30, destination TCP

port = 23.

Tsirtsis & Srisuresh Standards Track [Page 7]

When the packet reaches the NAPT-PT box, NAPT-PT would assign one of the TCP ports from the assigned V4 address to translate the tuple of (Source Address, Source TCP port) as follows:

SA=120.130.26.10, source TCP port = 1025 and

DA=132.146.243.30, destination TCP port = 23.

The returning traffic from 132.146.243.30, TCP port 23 will be

recognised as belonging to the same session and will be translated

back to V6 as follows:

SA = PREFIX::132.146.243.30, source TCP port = 23;

DA = FEDC:BA98::7654:3210 , destination TCP port = 3017

Inbound NAPT-PT sessions are restricted to one server per service,

assigned via static TCP/UDP port mapping. For example, the Node

[IPv6-A] in figure 1 may be the only HTTP server (port 80) in the V6 domain. Node [IPv4-C] sends a packet:

SA=132.146.243.30, source TCP port = 1025 and

DA=120.130.26.10, destination TCP port = 80

NAPT-PT will translate this packet to:

SA=PREFIX::132.146.243.30, source TCP port = 1025

DA=FEDC:BA98::7654:3210, destination TCP port = 80

In the above example, note that all sessions which reach NAPT-PT with a destination port of 80 will be redirected to the same node [IPv6-

A].

4. Use of DNS-ALG for Address Assignment

An IPv4 address is assigned by NAT-PT to a V6 node when NAT-PT

identifies the start of session, inbound or outbound. Identification of the start of a new inbound session is performed differently than

for outbound sessions. However, the same V4 address pool is used for assignment to V6 nodes, irrespective of whether a session is

initiated outbound from a V6 node or initiated inbound from a V4

node.

Policies determining what type of sessions are allowed and in which

direction and from/to which nodes is out of the scope of this

document.

Tsirtsis & Srisuresh Standards Track [Page 8]

IPv4 name to address mappings are held in the DNS with "A" records.

IPv6 name to address mappings are at the moment held in the DNS with "AAAA" records. "A6" records have also been defined but at the time

of writing they are neither fully standardized nor deployed.

In any case, the DNS-ALG’s principle of operation described in this

section is the same with either "AAAA" or "A6" records. The only

difference is that a name resolution using "A6" records may require

more than one query - reply pairs. The DNS-ALG SHOULD, in that case, track all the replies in the transaction before translating an "A6"

record to an "A" record.

One of the aims of NAT-PT design is to only use translation when

there is no other means of communication, such as native IPv6 or some form of tunneling. For the following discussion NAT-PT, in addition

to the IPv4 connectivity that it has it may also have a native IPv6

and/or a tunneled IPv6 connection.

4.1 V4 Address assignment for incoming connections (V4 to V6)

[DNS]--+

| [DNS]------[DNS]-------[DNS]

[IPv6-B]-+ | |

| +==============+ |

[IPv6-A]-+----[NAT-PT]------| IPv4 network |--[IPv4-C]

| +==============+

(pool of v4 addresses)

Figure 2: IPv4 to IPv6 communication

Node IPv6-A has an IPv6 address -> FEDC:BA98::7654:3210

Node IPv6-B has an IPv6 address -> FEDC:BA98::7654:3211

Node IPv4-C has an IPv4 address -> 132.146.243.30

NAT-PT has a pool of addresses including the IPv4 subnet

120.130.26/24

In figure 2 above, when Node C’s name resolver sends a name look up

request for Node A, the lookup query is directed to the DNS server on the V6 network. Considering that NAT-PT is residing on the border

router between V4 and V6 networks, this request datagram would

traverse through the NAT-PT router. The DNS-ALG on the NAT-PT device would modify DNS Queries for A records going into the V6 domain as

follows: (Note that a TCP/UDP DNS packet is recognised by the fact

that its source or destination port number is 53)

a) For Node Name to Node Address Query requests: Change the Query type from "A" to "AAAA" or "A6".

Tsirtsis & Srisuresh Standards Track [Page 9]

b) For Node address to Node name query requests: Replace the

string "IN-ADDR.ARPA" with the string "IP6.INT". Replace the

V4 address octets (in reverse order) preceding the string "IN- ADDR.ARPA" with the corresponding V6 address (if there exists a map) octets in reverse order.

In the opposite direction, when a DNS response traverses from the DNS server on the V6 network to the V4 node, the DNS-ALG once again

intercepts the DNS packet and would:

a) Translate DNS responses for "AAAA" or "A6" records into "A"

records, (only translate "A6" records when the name has

completely been resolved)

b) Replace the V6 address resolved by the V6 DNS with the V4

address internally assigned by the NAT-PT router.

If a V4 address is not previously assigned to this V6 node, NAT-PT

would assign one at this time. As an example say IPv4-C attempts to

initialise a session with node IPv6-A by making a name lookup ("A"

record) for Node-A . The name query goes to the local DNS and from

there it is propagated to the DNS server of the IPv6 network. The

DNS-ALG intercepts and translates the "A" query to "AAAA" or "A6"

query and then forwards it to the DNS server in the IPv6 network

which replies as follows: (The example uses AAAA records for

convenience)

Node-A AAAA FEDC:BA98::7654:3210,

this is returned by the DNS server and gets intercepted and

translated by the DNS-ALG to:

Node-A A 120.130.26.1

The DNS-ALG also holds the mapping between FEDC:BA98::7654:3210 and

120.130.26.1 in NAT-PT. The "A" record is then returned to Node-C.

Node-C can now initiate a session as follows:

SA=132.146.243.30, source TCP port = 1025 and

DA=120.130.26.1, destination TCP port = 80

the packet will be routed to NAT-PT, which since it already holds a

mapping between FEDC:BA98::7654:3210 and 120.130.26.1 can translate the packet to:

SA=PREFIX::132.146.243.30, source TCP port = 1025

DA=FEDC:BA98::7654:3210, destination TCP port = 80

the communication can now proceed as normal.

Tsirtsis & Srisuresh Standards Track [Page 10]

The TTL values on all DNS resource records (RRs) passing through

NAT-PT SHOULD be set to 0 so that DNS servers/clients do not cache

temporarily assigned RRs. Note, however, that due to some buggy DNS

client implementations a value of 1 might in some cases work better. The TTL values should be left unchanged for statically mapped

addresses.

Address mappings for incoming sessions, as described above, are

subject to denial of service attacks since one can make multiple

queries for nodes residing in the V6 network causing the DNS-ALG to

map all V4 addresses in NAT-PT and thus block legitimate incoming

sessions. Thus, address mappings for incoming sessions should time

out to minimise the effect of denial of service attacks.

Additionally, one IPv4 address (using NAPT-PT, see 3.2) could be

reserved for outgoing sessions only to minimise the effect of such

attacks to outgoing sessions.

4.2 V4 Address assignment for outgoing connections (V6 to V4)

V6 nodes learn the address of V4 nodes from the DNS server in the V4 domain or from the DNS server internal to the V6 network. We

recommend that DNS servers internal to V6 domains maintain a mapping of names to IPv6 addresses for internal nodes and possibly cache

mappings for some external nodes. In the case where the DNS server in the v6 domain contains the mapping for external V4 nodes, the DNS

queries will not cross the V6 domain and that would obviate the need for DNS-ALG intervention. Otherwise, the queries will cross the V6

domain and are subject to DNS-ALG intervention. We recommend

external DNS servers in the V4 domain cache name mapping for external nodes (i.e., V4 nodes) only. Zone transfers across IPv4 - IPv6

boundaries are strongly discouraged.

In the case of NAPT-PT, a TCP/UDP source port is assigned from the

registered V4 address upon detection of each new outbound session.

We saw that a V6 node that needs to communicate with a V4 node needs to use a specific prefix (PREFIX::/96) in front of the IPv4 address

of the V4 node. The above technique allows the use of this PREFIX

without any configuration in the nodes.

To create another example from Figure 2 say Node-A wants to set up a session with Node-C. For this Node-A starts by making a name look-up ("AAAA" or "A6" record) for Node-C.

Since Node-C may have IPv6 and/or IPv4 addresses, the DNS-ALG on the NAT-PT device forwards the original AAAA/A6 query to the external DNS system unchanged, as well as an A query for the same node. If an

AAAA/A6 record exists for the destination, this will be returned to Tsirtsis & Srisuresh Standards Track [Page 11]

NAT-PT which will forward it, also unchanged, to the originating

host.

If there is an A record for Node-C the reply also returns to the

NAT-PT. The DNS-ALG then, translates the reply adding the appropriate PREFIX and forwards it to the originating device with any IPv6

addresses that might have learned. So, if the reply is

NodeC A 132.146.243.30, it is translated to

NodeC AAAA PREFIX::132.146.243.30 or to

NodeC A6 PREFIX::132.146.243.30

Now Node A can use this address like any other IPv6 address and the

V6 DNS server can even cache it as long as the PREFIX does not

change.

An issue here is how the V6 DNS server in the V6 stub domain talks to the V4 domain outside the V6 stub domain. Remember that there are no dual stack nodes here. The external V4 DNS server needs to point to a V4 address, part of the V4 pool of addresses, available to NAT-PT.

NAT-PT keeps a one-to-one mapping between this V4 address and the V6 address of the internal V6 DNS server. In the other direction, the V6 DNS server points to a V6 address formed by the IPv4 address of the

external V4 DNS servers and the prefix (PREFIX::/96) that indicates

non IPv6 nodes. This mechanism can easily be extended to accommodate secondary DNS servers.

Note that the scheme described in this section impacts DNSSEC. See

section 7.5 of this document for details.

5. Protocol Translation Details

The IPv4 and ICMPv4 headers are similar to their V6 counterparts but a number of field are either missing, have different meaning or

different length. NAT-PT SHOULD translate all IP/ICMP headers from v4 to v6 and vice versa in order to make end-to-end IPv6 to IPv4

communication possible. Due to the address translation function and

possible port multiplexing, NAT-PT SHOULD also make appropriate

adjustments to the upper layer protocol (TCP/UDP) headers. A separate section on FTP-ALG describes the changes FTP-ALG would make to FTP

payload as an FTP packet traverses from V4 to V6 realm or vice versa. Protocol Translation details are described in [SIIT], but there are

some modifications required to SIIT because of the fact that NAT-PT

also performs Network Address Translation.

Tsirtsis & Srisuresh Standards Track [Page 12]

5.1 Translating IPv4 headers to IPv6 headers

This is done exactly the same as in SIIT apart from the following

fields:

Source Address:

The low-order 32 bits is the IPv4 source address. The high-

order 96 bits is the designated PREFIX for all v4

communications. Addresses using this PREFIX will be routed

to the NAT-PT gateway (PREFIX::/96)

Destination Address:

NAT-PT retains a mapping between the IPv4 destination

address and the IPv6 address of the destination node. The

IPv4 destination address is replaced by the IPv6 address

retained in that mapping.

5.2 Translating IPv6 headers to IPv4 headers

This is done exactly the same as in SIIT apart from the Source

Address which should be determined as follows:

Source Address:

The NAT-PT retains a mapping between the IPv6 source address

and an IPv4 address from the pool of IPv4 addresses

available. The IPv6 source address is replaced by the IPv4

address retained in that mapping.

Destination Address:

IPv6 packets that are translated have a destination address

of the form PREFIX::IPv4/96. Thus the low-order 32 bits of

the IPv6 destination address is copied to the IPv4

destination address.

5.3 TCP/UDP/ICMP Checksum Update

NAT-PT retains mapping between IPv6 address and an IPv4 address from the pool of IPv4 addresses available. This mapping is used in the

translation of packets that go through NAT-PT.

The following sub-sections describe TCP/UDP/ICMP checksum update

procedure in NAT-PT, as packets are translated from V4 to V6 and vice versa.

Tsirtsis & Srisuresh Standards Track [Page 13]

5.3.1 TCP/UDP/ICMP Checksum Update from IPv4 to IPv6

UDP checksums, when set to a non-zero value, and TCP checksum SHOULD be recalculated to reflect the address change from v4 to v6. The

incremental checksum adjustment algorithm may be borrowed from [NAT]. In the case of NAPT-PT, TCP/UDP checksum should be adjusted to

account for the address and TCP/UDP port changes, going from V4 to V6 address.

When the checksum of a V4 UDP packet is set to zero, NAT-PT MUST

evaluate the checksum in its entirety for the V6-translated UDP

packet. If a V4 UDP packet with a checksum of zero arrives in

fragments, NAT-PT MUST await all the fragments until they can be

assembled into a single non-fragmented packet and evaluate the

checksum prior to forwarding the translated V6 UDP packet.

ICMPv6, unlike ICMPv4, uses a pseudo-header, just like UDP and TCP

during checksum computation. As a result, when the ICMPv6 header

checksum is computed [SIIT], the checksum needs to be adjusted to

account for the additional pseudo-header. Note, there may also be

adjustments required to the checksum due to changes in the source and destination addresses (and changes in TCP/UDP/ICMP identifiers in the case of NAPT-PT) of the payload carried within ICMP.

5.3.2 TCP/UDP/ICMP Checksum Update from IPv6 to IPv4

TCP and UDP checksums SHOULD be recalculated to reflect the address

change from v6 to v4. The incremental checksum adjustment algorithm

may be borrowed from [NAT]. In the case of NAPT-PT, TCP/UDP checksums should be adjusted to account for the address and TCP/UDP port

changes, going from V6 to V4 addresses. For UDP packets, optionally, the checksum may simply be changed to zero.

The checksum calculation for a V4 ICMP header needs to be derived

from the V6 ICMP header by running the checksum adjustment algorithm [NAT] to remove the V6 pseudo header from the computation. Note, the adjustment must additionally take into account changes to the

checksum as a result of updates to the source and destination

addresses (and transport ports in the case of NAPT-PT) made to the

payload carried within ICMP.

6. FTP Application Level Gateway (FTP-ALG) Support

Because an FTP control session carries, in its payload, the IP

address and TCP port information for the data session, an FTP-ALG is required to provide application level transparency for this popular

Internet application.

Tsirtsis & Srisuresh Standards Track [Page 14]

In the FTP application running on a legacy V4 node, arguments to the FTP PORT command and arguments in PASV response(successful) include

an IP V4 address and a TCP port, both represented in ASCII as

h1,h2,h3,h4,p1,p2. However, [FTP-IPV6] suggests EPRT and EPSV command extensions to FTP, with an intent to eventually retire the use of

PORT and PASV commands. These extensions may be used on a V4 or V6

node. FTP-ALG, facilitating transparent FTP between V4 and V6 nodes, works as follows.

6.1 Payload modifications for V4 originated FTP sessions

A V4 host may or may not have the EPRT and EPSV command extensions

implemented in its FTP application. If a V4 host originates the FTP

session and uses PORT or PASV command, the FTP-ALG will translate

these commands into EPRT and EPSV commands respectively prior to

forwarding to the V6 node. Likewise, EPSV response from V6 nodes will be translated into PASV response prior to forwarding to V4 nodes.

The format of EPRT and EPSV commands and EPSV response may be

specified as follows[FTP-IPV6].

EPRT

EPSV

(or)

EPSVALL

Format of EPSV response(Positive): 229

extended passive mode> ()

PORT command from a V4 node is translated into EPRT command, by

setting the protocol field to AF #2 (IPV6) and translating the V4 host Address (represented as h1,h2,h3,h4) into its NAT-PT

assigned V6 address in string notation, as defined in [V6ADDR] in the field. TCP port represented by p1,p2 in PORT command must be specified as a decimal in the EPRT command. Further,

translation may also be required in the case of NAPT-PT.

PASV command from a V4 node is be translated into a EPSV command with the argument set to AF #2. EPSV response from a V6 node is translated into PASV response prior to forwarding to the target V4

host.

If a V4 host originated the FTP session and was using EPRT and EPSV

commands, the FTP-ALG will simply translate the parameters to these

commands, without altering the commands themselves. The protocol

Number field will be translated from AF #1 to AF #2.

will be translated from the V4 address in ASCII to its

NAT-PT assigned V6 address in string notation as defined in [V6ADDR]. argument in EPSV response requires translation only in the case of NAPT-PT.

Tsirtsis & Srisuresh Standards Track [Page 15]

6.2 Payload modifications for V6 originated FTP sessions

If a V6 host originates the FTP session, however, the FTP-ALG has two approaches to pursue. In the first approach, the FTP-ALG will leave

the command strings "EPRT" and "EPSV" unaltered and simply translate the , and arguments from V6 to its

NAT-PT (or NAPT-PT) assigned V4 information. is translated only in the case of NAPT-PT. Same goes for EPSV response from V4

node. This is the approach we recommend to ensure forward support for RFC 2428. However, with this approach, the V4 hosts are mandated to have their FTP application upgraded to support EPRT and EPSV

extensions to allow access to V4 and V6 hosts, alike.

In the second approach, the FTP-ALG will translate the command

strings "EPRT" and "EPSV" and their parameters from the V6 node into their equivalent NAT-PT assigned V4 node info and attach to "PORT"

and "PASV" commands prior to forwarding to V4 node. Likewise, PASV

response from V4 nodes is translated into EPSV response prior to

forwarding to the target V6 nodes. However, the FTP-ALG would be

unable to translate the command "EPSVALL" issued by V6 nodes. In such a case, the V4 host, which receives the command, may return

an error code indicating unsupported function. This error response

may cause many RFC 2428 compliant FTP applications to simply fail,

because EPSV support is mandated by RFC 2428. The benefit of this

approach, however, is that is does not impose any FTP upgrade

requirements on V4 hosts.

6.3 Header updates for FTP control packets

All the payload translations considered in the previous sections are based on ASCII encoded data. As a result, these translations may

result in a change in the size of packet.

If the new size is the same as the previous, only the TCP checksum

needs adjustment as a result of the payload translation. If the new size is different from the previous, TCP sequence numbers should also be changed to reflect the change in the length of the FTP control

session payload. The IP packet length field in the V4 header or the

IP payload length field in the V6 header should also be changed to

reflect the new payload size. A table is used by the FTP-ALG to

correct the TCP sequence and acknowledgement numbers in the TCP

header for control packets in both directions.

The table entries should have the source address, source data port,

destination address and destination data port for V4 and V6 portions of the session, sequence number delta for outbound control packets

and sequence number delta for inbound control packets.

Tsirtsis & Srisuresh Standards Track [Page 16]

The sequence number for an outbound control packet is increased by

the outbound sequence number delta, and the acknowledgement number

for the same outbound packet is decreased by the inbound sequence

number delta. Likewise, the sequence number for an inbound packet is increased by the inbound sequence number delta and the

acknowledgement number for the same inbound packet is decreased by

the outbound sequence number delta.

7. NAT-PT Limitations and Future Work

All limitations associated to NAT [NAT-TERM] are also associated to

NAT-PT. Here are the most important of them in detail, as well as

some unique to NAT-PT.

7.1 Topology limitations

There are limitations to using the NAT-PT translation method. It is

mandatory that all requests and responses pertaining to a session be routed via the same NAT-PT router. One way to guarantee this would be to have NAT-PT based on a border router that is unique to a stub

domain, where all IP packets are either originated from the domain or destined to the domain. This is a generic problem with NAT and it is fully described in [NAT-TERM].

Note, this limitation does not apply to packets originating from or

directed to dual-stack nodes that do not require packet translation. This is because in a dual-stack set-up, IPv4 addresses implied in a

V6 address can be identified from the address format PREFIX::x.y.z.w and a dual-stack router can accordingly route a packet between v4 and dual-stack nodes without tracking state information.

This should also not affect IPv6 to IPv6 communication and in fact

only actually use translation when no other means of communication is possible. For example NAT-PT may also have a native IPv6 connection and/or some kind of tunneled IPv6 connection. Both of the above

connections should be preferred over translation when possible. The

above makes sure that NAT-PT is a tool only to be used to assist

transition to native IPv6 to IPv6 communication.

7.2 Protocol Translation Limitations

A number of IPv4 fields have changed meaning in IPv6 and translation is not straightforward. For example, the option headers semantics and syntax have changed significantly in IPv6. Details of IPv4 to IPv6

Protocol Translation can be found in [SIIT].

Tsirtsis & Srisuresh Standards Track [Page 17]

7.3 Impact of Address Translation

Since NAT-PT performs address translation, applications that carry

the IP address in the higher layers will not work. In this case

Application Layer Gateways (ALG) need to be incorporated to provide

support for those applications. This is a generic problem with NAT

and it is fully described in [NAT-TERM].

7.4 Lack of end-to-end security

One of the most important limitations of the NAT-PT proposal is the

fact that end-to-end network layer security is not possible. Also

transport and application layer security may not be possible for

applications that carry IP addresses to the application layer. This

is an inherent limitation of the Network Address Translation

function.

Independent of NAT-PT, end-to-end IPSec security is not possible

across different address realms. The two end-nodes that seek IPSec

network level security must both support one of IPv4 or IPv6.

7.5 DNS Translation and DNSSEC

The scheme described in section 4.2 involves translation of DNS

messages. It is clear that this scheme can not be deployed in

combination with secure DNS. I.e., an authoritative DNS name server in the V6 domain cannot sign replies to queries that originate from

the V4 world. As a result, an V4 end-node that demands DNS replies

to be signed will reject replies that have been tampered with by

NAT-PT.

The good news, however, is that only servers in V6 domain that need

to be accessible from the V4 world pay the price for the above

limitation, as V4 end-nodes may not access V6 servers due to DNS

replies not being signed.

Also note that zone transfers between DNS-SEC servers within the same V6 network are not impacted.

Clearly, with DNS SEC deployment in DNS servers and end-host

resolvers, the scheme suggested in this document would not work.

8. Applicability Statement

NAT-PT can be a valuable transition tool at the border of a stub

network that has been deployed as an IPv6 only network when it is

connected to an Internet that is either V4-only or a combination of

V4 and V6.

Tsirtsis & Srisuresh Standards Track [Page 18]

NAT-PT, in its simplest form, without the support of DNS-ALG,

provides one way connectivity between an IPv6 stub domain and the

IPv4 world meaning that only sessions initialised by IPv6 nodes

internal to the IPv6 stub domain can be translated, while sessions

initiated by IPv4 nodes are dropped. This makes NAT-PT a useful

tool to IPv6 only stub networks that need to be able to maintain

connectivity with the IPv4 world without the need to deploy servers visible to the IPv4 world.

NAT-PT combined with a DNS-ALG provides bi-directional connectivity between the IPv6 stub domain and the IPv4 world allowing sessions to be initialised by IPv4 nodes outside the IPv6 stub domain. This makes NAT-PT useful for IPv6 only stub networks that need to deploy servers visible to the IPv4 world.

Some applications count on a certain degree of address stability for their operation. Dynamic address reuse by NAT-PT might not be

agreeable for these applications. For hosts running such address

critical applications, NAT-PT may be configured to provide static

address mapping between the host’s V6 address and a specific V4

address. This will ensure that address related changes by NAT-PT do

not become a significant source of operational failure.

9. Security Considerations

Section 7.4 of this document states that end-to-end network and

transport layer security are not possible when a session is

intercepted by a NAT-PT. Also application layer security may not be possible for applications that carry IP addresses in the application layer.

Section 7.5 of this document states that the DNS-ALG can not be

deployed in combination with secure DNS.

Finally, all of the security considerations described in [NAT-TERM]

are applicable to this document as well.

10. REFERENCES

[DNS-ALG] Srisuresh, P., Tsirtsis, G., Akkiraju, P. and A.

Heffernan, "DNS extensions to Network Address Translators (DNS_ALG)", RFC 2694, September 1999.

[DNSSEC] Eastlake, D., "Domain Name System Security Extensions",

RFC 2065, March 1999.

[FTP-IPV6] Allman, M., Ostermann, S. and C. Metz, "FTP Extensions for IPv6 and NATs", RFC 2428, September 1998.

Tsirtsis & Srisuresh Standards Track [Page 19]

[KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate

Requirement Levels", BCP 14, RFC 2119, March 1997.

[NAT] Egevang, K. and P. Francis, "The IP Network Address

Translator (NAT)", RFC 1631, May 1994.

[NAT-TERM] Srisuresh, P. and M. Holdrege, "IP Network Address

Translator (NAT) Terminology and Considerations", RFC

2663, August 1999.

[SIIT] Nordmark, E., "Stateless IP/ICMP Translator (SIIT)", RFC

2765, February 2000.

[TRANS] Gilligan, R. and E. Nordmark, "Transition Mechanisms for IPv6 Hosts and Routers", RFC 1933, April 1996.

[V6ADDR] Hinden, R. and S. Deering, "IP Version 6 Addressing

Architecture", RFC 2373, July 1998.

Authors’ Addresses

George Tsirtsis

Internet Futures

B29 Room 129

BT Adastral Park

IPSWICH IP5 3RE

England

Phone: +44 181 8260073

Fax: +44 181 8260073

EMail: george.tsirtsis@https://www.sodocs.net/doc/0111840570.html,

EMail (alternative): gtsirt@https://www.sodocs.net/doc/0111840570.html,

Pyda Srisuresh

630 Alder Drive

Milpitas, CA 95035

U.S.A.

Phone: (408) 519-3849

EMail: srisuresh@https://www.sodocs.net/doc/0111840570.html,

Tsirtsis & Srisuresh Standards Track [Page 20]

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No. 272, Bayi Road, Nanyang City Henan Prov. China 473000 528400广东中山市东区亨达花园7栋702 李有财 Li Youcai Room 702, 7th Building Hengda Garden, East District Zhongshan, China 528400 266042山东省青岛市开平路53号国棉四厂二宿舍1号楼2单元204户甲李有财Mr. Li Youcai NO. 204, A, Building NO. 1 The 2nd Dormitory of the NO. 4 State-owned Textile Factory 53 Kaiping Road, Qingdao, Shandong, China 266042 下面来介绍一下公司的译法: 1. line(s) (轮船、航空、航运等)公司 Atlantic Container Line大西洋集装箱海运公司 Hawaiian air Lines 夏威夷航空公司 2. agency 公司、代理行 The Austin advertising Agency 奥斯汀广告公司 China Ocean Shipping Agency 中国外轮代理公司 3. store(s) 百货公司 Great Universal Store 大世界百货公司(英) Tesco Stores (Holdings) 坦斯科百货公司(英) 4. associates(联合)公司

中文地址翻译成英文地址方法和技巧

中文地址翻译成英文地址的方法和技巧 中文地址的排列顺序是由大到小,如:X国X省X市X区X路X号,而英文地址则刚好相反,是由小到大。如上例写成英文就是:X号,X路,X区,X市,X省,X国。 1.各部分写法 ●X室:Room X ●X号:No. X ●X单元:Unit X ●X楼/层:X/F ●X号楼:Building No. X ●住宅区/小区:ResidentialQuater ●X街:XStreet ●X路:X Road East/Central/West东路 / 中路 / 西路 芙蓉西二路 / West 2nd Furong Road Central Dalian Rd. /大连中路 芙蓉中路的“中”可以用Central,也有用Middle的,一般用Mid比较简洁。 ●X区:X District ●X镇:X Town ●X县:X County ●X市:X City ●X省:X Province ●国家(State)中华人民共和国:The People’s Republic of China、P.R.China、 P.R.C.、China ●X信箱:Mailbox X 请注意:翻译人名、路名、街道名等,最好用拼音。 各地址单元间要加逗号隔开。

2.英文通信地址常用翻译 201室/房 Room 201 二单元 Unit 2 马塘村MatangVallage 一号楼/栋 Building 1

华为科技公司 Huawei Technologies Co., Ltd. xx公司 xx Corp. / xx Co., Ltd. 宿舍 Dormitory 厂 Factory 楼/层 Floor 酒楼/酒店 Hotel 住宅区/小区 Residential Quater 县 County 甲/乙/丙/丁 A/B/C/D 镇 Town 巷/弄 Lane 市 City 路 Road(也简写作Rd.,注意后面的点不能省略) 一环路 1st Ring Road 省 Province(也简写作Prov.) 花园 Garden 院 Yard 街 Street/Avenue 大学 College/University 信箱 Mailbox 区 District A座 Suite A 广场 Square 州 State 大厦/写字楼 Tower/Center/Plaza 胡同 Alley(北京地名中的条即是胡同的意思) 中国部分行政区划对照 自治区 Autonomous Region 直辖市 Municipality 特别行政区 Special Administration Region 简称SAR

中国地址的英文翻译

英语中对地址得翻译 例句 Chinese Guangdong Province Maoming city oil city 4 group new lake 7 street 3rd yard 6 102 至于方法就就是: 翻译原则:先小后大。 中国人喜欢先说大得后说小得,如**区**路**号 而外国人喜欢先说小得后说大得,如**号**路**区,因此您在翻译时就应该先写小得后写大得。 例如:中国山东省青岛市四方区洛阳路34号3号楼4单元402户,您就要从房开始写起,Room 402, Unit 4, Building 3, No、34、Luoyang Road, sifang District, Qingdao City, Shandong Prov, China (逗号后面有空格)。注意其中路名、公司名、村名等均不用翻译成同意得英文,只要照写拼音就行了。因为您得支票就是中国得邮递员送过来,关键就是要她们明白。技术大厦您写成Technology Building,她们可能更迷糊呢。 现在每个城市得中国邮政信件分拣中心都有专人负责将外国来信地址翻译成中文地址,并写在信封上交下面邮递员送过来、 重要: 您得邮政编码一定要写正确,因为外国信件中间得几道邮政环节都就是*邮政编码区域投递得。 常见中英文对照 ***室/房Room *** ***村*** Vallage ***号No、*** ***号宿舍*** Dormitory ***楼/层***/F ***住宅区/小区*** Residential Quater 甲/乙/丙/丁A/B/C/D ***巷/ 弄Lane *** ***单元Unit *** ***号楼/ 栋*** Building ***公司***、 *** Crop ***LTD、CO ***厂*** Factory ***酒楼/酒店*** Hotel ***路*** Road ***花园*** Garden ***街*** Street ***信箱Mailbox *** ***区*** District ***县*** County ***镇*** Town ***市*** City ***省*** Prov、 ***院***Yard ***大学***College **表示序数词,比如1st、2nd、3rd、4th……如果不会,就用No、***代替,或者直接填数字吧! 另外有一些***里之类难翻译得东西,就直接写拼音*** Li。而***东(南、西、北)路,直接用拼音也行,写*** East(South、West、North)Road也行。还有,如果地方不够可以将7栋3012室写成:73012。 201室: Room 201 12号: No、12 2单元: Unit 2

netscreen网络地址翻译nat方法总结和实验

网络地址翻译方法总结和实验 一、前言................................................................................................... 错误!未定义书签。 二、源网络地址转换(NAT-Src) .............................................................. 错误!未定义书签。 一.不带DIP .............................................................................................. 错误!未定义书签。 二.带DIP .................................................................................................. 错误!未定义书签。 一). 1对1映射 ................................................................................ 错误!未定义书签。 二). 1对多映射 ............................................................................... 错误!未定义书签。 三).多对1 映射 ............................................................................ 错误!未定义书签。 四).多对多映射 ............................................................................. 错误!未定义书签。 三、Netscreen防火墙各种地址翻译方法的特点总结.......................... 错误!未定义书签。 四、地址翻译方法实验........................................................................... 错误!未定义书签。 1. Netscreen防火墙的地址翻译实验环境...................................... 错误!未定义书签。 2. Netscreen防火墙的策略地址翻译实验...................................... 错误!未定义书签。 3.1 由外向内的地址翻译........................................................... 错误!未定义书签。 3.2 由内向外的地址翻译........................................................... 错误!未定义书签。 3. Netscreen防火墙的接口地址翻译实验...................................... 错误!未定义书签。 4.1 MIP地址翻译.......................................................................... 错误!未定义书签。 4.2 VIP地址翻译 .......................................................................... 错误!未定义书签。 4. 将MIP和VIP用策略地址翻译替代实验 ................................. 错误!未定义书签。 5.1 MIP地址翻译的替代.............................................................. 错误!未定义书签。 5.2 VIP地址翻译的替代 .............................................................. 错误!未定义书签。 一、前言 Juniper防火墙的几种常用功能主要是指基于策略的NAT的实现,包括:MIP、VIP和DIP,这三种常用功能主要应用于防火墙所保护服务器提供对外服务。MIP MIP是“一对一”的双向地址翻译(转换)过程。通常的情况是:当你有若干个公网IP地址,又存在若干的对外提供网络服务的服务器(服务器使用私有IP地址),为了实现互联网用户访问这些服务器,可在Internet出口的防火墙上建立公网IP地址与服务器私有IP地址之间的一对一映射(MIP),并通过策略实现对服务器所提供服务进行访问控制。 VIP MIP是一个公网IP地址对应一个私有IP地址,是一对一的映射关系;而VIP 是一个公网IP地址的不同端口(协议端口如:21、25、110等)与内部多个私有IP地址的不同服务端口的映射关系。通常应用在只有很少的公网IP地址,却拥有多个私有IP地址的服务器,并且,这些服务器是需要对外提供各种服务的。

中文地址的翻译

英文地址的写法 中国MPA在线的英文地址:Rome1232,Youth building,No.34 West Beisanhuan Road, Beijing,China 一、寄达城市名的批译: 我国城市有用英文等书写的,也有用汉语拼音书写的。例如“北京”英文写为“Peking”,汉语拼音写为 “Beijing”二者虽然都是用拉丁字母,但拼读方法不同,前者是以音标相拼,而后者则是用声母和韵母相拼的, 批译时要注意识别,以免错译。 二、街道地址及单位名称的批译: 常见有英文书写、汉语拼音书写、英文和汉语拼音混合书写三种。 1、英文书写的,例如:Address:6 East Changan Avenue PeKing译为北京市东长安街6号; 2、汉语拼音书写的,例如:105 niujie Beijing译为北京市牛街105号; 3、英文、汉语拼音混合书写的,例如:NO.70 dong feng dong Rd.Guangzhou译为广州东风东路70号。 三、机关、企业等单位的批译: 收件人为机关、企业等单位的,应先译收件人地址,再译单位名称。批译方法为: 1、按中文语序书写的要顺译。 例如:SHANGHAI FOODSTUFFS IMP AND EXP CO. 译为:上海食品进出口公司; 2、以英文介词短语充当定语,一般位于被修饰的名词之后,译在该名词之前。 例如:Civil Aviation Administration Of China 译为:中国民航局; 3、机关、企业单位的分支机构一般用英文“branch”(分部、分公司等)表示。 例如:Beijing Electron Co. Ltd Xian branch 译为:北京电子有限公司西安分公司。 四、姓名方面:

教你怎么写英文地址(住址标准英文翻译)

很多人不知道自己家的标准英文地址怎么写,这里给大家介绍一下。 英文地址与中文的顺序是完全相反的. 一定在"中国"前写好当地的邮政编码! 中文地址的排列顺序是由大到小,如:X国X省X市X区X路X号,而英文地址则刚好相反,是由小到大。如上例写成英文就是:X号,X路,X区,X市,X省,X国。掌握了这个原则,翻译起来就容易多了! X室Room X X号No. X X单元Unit X X号楼Building No. X X小区X Residential quarters X街X Street X路X Road X区X District X县X County X镇X Town X市X City X省X Province 请注意:翻译人名、路名、街道名等,最好用拼音。 中文地址翻译范例: 宝山区示范新村37号403室 Room 403, No. 37, SiFang Residential Quarter, BaoShan District 虹口区西康南路125弄34号201室 Room 201, No. 34, Lane 125, XiKang Road(South), HongKou District 473004河南省南阳市中州路42号李有财 Li Youcai Room 42 Zhongzhou Road, Nanyang City Henan Prov. China 473004 434000湖北省荆州市红苑大酒店李有财 Li Youcai Hongyuan Hotel Jingzhou city Hubei Prov. China 434000 473000河南南阳市八一路272号特钢公司李有财 Li Youcai Special Steel Corp. No. 272, Bayi Road, Nanyang City Henan Prov. China 473000 528400广东中山市东区亨达花园7栋702 李有财 Li Youcai

中文地址翻译规则

中文地址的排列顺序是由大到小,如:X国X省X市X区X路X号,而英文地址则刚好相反,是由小到大。如上例写成英文就是:X号,X路,X区,X市,X省,X国。掌握了这个原则,翻译起来就容易多了。 请注意:翻译人名、路名、街道名等,最好用拼音。 例如:虹口区西康南路125弄34号201室 Room 201, No. 34, Lane 125, XiKang Road(South), HongKou District 473004河南省南阳市中州路42号李有财 Li Youcai No. 42,Zhongzhou Road, Nanyang City,Henan Prov. China 473004 用汉语拼音字母拼写中国地名,不仅是中国的统一标准,而且是国际标准,全世界都要遵照使用。 一、专名是单音节的英译法 专名是单音节,通名也是单音节,这时通名应视作专名的组成部分,先音译并与专名连写,后重复意译,分写(汉字带点的字是通名,英语的画线部分是音译;括号内为该地所在省、市、地区或县,下同)例如: 1、恒山 Hengshan Mountain (山西) 2、淮河 the Huaihe River (河南、安徽、江苏) 二、通名专名化的英译法 通名专名化主要指单音节的通名,如山、河、江、湖、海、港、峡、关、岛等,按专名处理,与专名连写,构成专名整体。例如: 1、都江堰市 Dujiangyan City (比较: the Dujiang Weir)(四川) 2、绥芬河市 Suifenhe City (比较:the Suifen River)(黑龙江)

三、通名是同一个汉字的多种英译法 通名是单音节的同一个汉字,根据意义有多种不同英译法,在大多数情况下,这些英译词不能互相代换。例如: 1、mount:峨眉山 Mount Emei(四川峨眉) 2、sea:邛海 the Qionghai Lake(四川西昌) 在某些情况下,根据通名意义,不同的汉字可英译为同一个单词。例如:“江、河、川、水、溪”英译为river。 四、专名是同一个汉字的不同英译法 专名中同一个汉字有不同的读音和拼写,据笔者不完全统计,地名中这样的汉字有七八十个之多,每个字在地名中的读音和拼写是固定的,英译者不能一见汉字就按语言词典的读音和拼写翻译,而只能按中国地名词典的读音和拼写进行翻译。例如: 1、陕西省 Shaanxi Province 陕县Shanxian County(河南) 2、洞庭湖the Dong Lake(湖南)洪洞县Hongtong County(山西) 五、专名是同样汉字的多种英译法 专名中的汉字是相同的,但表示不同的地点,每个地点的读音和拼写是固定的,应按“名从主人”的原则译写,不能按普通语言词典,而必须按中国地名词典英译。例如: 1、浍河 1)the Huihe River (河南、安徽) 2)the Kuaihe River(山西) 2、阿克乔克山 1)Akqoka Mountain (新疆昭苏县) 2)Akxoki Mountain (新疆塔城市) 3、色拉寺 1)the Sera Monastery(拉萨市) the Sula Temple(四川色达) 六、中国各民族名称的罗马字母拼写法

NAT———网络地址翻译

随着Internet的飞速发展,网上丰富的资源产生着巨大的吸引力。接入Internet、访问Internet成为当今信息业最为迫切的需求。 但这受到IP地址的许多限制。首先,许多局域网在未联入Internet之前,就已经运行许多年了,局域网上有了许多现成的资源和应用程序,但它的IP地址分配不符合Internet 的国际标准,因而需要重新分配局域网的IP地址,这无疑是劳神费时的工作;其二,随着Internet的膨胀式发展,其可用的IP地址越来越少,要想在ISP处申请一个新的IP地址已不是很容易的事了。这不仅仅是费用的问题,而是IP地址的现行标准IPv4决定的。当然,随着IPv6的出台,这个问题应当能够得到解决。但从IPv4到IPv6的升级不是一两天就能完成的。 NAT(网络地址翻译)能解决不少令人头疼的问题。它解决问题的办法是:在内部网络中使用内部地址,通过NAT把内部地址翻译成合法的IP地址,在Internet上使用。其具体的做法是把IP包内的地址域用合法的IP地址来替换。 NAT功能通常被集成到路由器、防火墙、ISDN路由器或者单独的NAT设备中。NAT设备维护一个状态表,用来把非法的IP地址映射到合法的IP地址上去。每个包在NAT设备中都被翻译成正确的IP地址发往下一级,这意味着给处理器带来了一定的负担。但这对于一般的网络来说是微不足道的,除非是有许多主机的大型网络。 需要注意的是,NAT并不是一种有安全保证的方案,它不能提供类似防火墙、包过滤、隧道等技术的安全性,仅仅在包的最外层改变IP地址。这使得黑客可以很容易地窃取网络信息,危及网络安全。 NAT有三种类型:静态NAT(staticNAT)、NAT池(pooledNAT)和端口NAT(PAT)。其中静态NAT设置起来最为简单,内部网络中的每个主机都被永久映射成外部网络中的某个合法的地址。而NAT池则是在外部网络中定义了一系列的合法地址,采用动态分配的方法映射到内部网络。PAT则是把内部地址映射到外部网络的一个IP地址的不同端口上。根据不同的需要,各种NAT方案都是有利有弊。 ■使用NAT池 使用NAT池,可以从未注册的地址空间中提供被外部访问的服务,也可以从内部网络访问外部网络,而不需要重新配置内部网络中的每台机器的IP地址。例如,建立在NT+IIS 服务器上的内部试验子网192.168.0.0,其网络地址属于B类保留地址。作为企业网的一个子网,其IP地址不分配给企业网上的设备而仅仅局限在试验子网的设备上。为了使企业网能访问到这个内部网,在网络上增加一条静态路径,使信息能回传给Cisco4700路由器。其中的路由器可以把内部网和企业网连接起来,使之能相互访问。在内部网中不要使用RIP 协议,因为使用RIP后,内部网络相对外部来说变得不可见了。 这样,本地信息可以相互访问了,但由于192.168.0.0属于保留地址,故不能直接访问Internet。所以在路由器中设置一个NAT池,用来翻译来自内部网络的IP包,把它的IP地址映射成地址池(pooledaddresses)中的合法IP地址。那么,内部网可以访问Internet上的任何服务器,Internet上的任何主机也能通过TCP或UDP访问到内部网。

网络专业词汇 英语翻译

网络专业词汇英语翻译 account(帐号):一个有指定的用户名和口令的用于访问计算机或网络的表格,它通常带有一个主目录,一个e-mail信箱和一系列访问权限。 address(地址):1、某台计算机(也称网上主机或Intermet节点)的地址,格式为host.Subdomain.domain。2、一个e-mail地址,格式为username@host.subdomain.domain。3、一个Web地址(URL)格式为:http://host.subdomain.domain/option...-filename.ext。 address book(地址簿):在有些e-mail程序中,address book是e-mail地址的简要列表。 anonymous FTP(匿名FTP):FTP(Internet文件传输协议)最常见的使用方法。允许匿名FTP访问的FTP的FTP节点,不要求在访问时输入口令——登录时用户只需输入Anonymous 作为用户名,将自己的e-mail地址作为口令以备记录。 *.answers:用于邮寄FAQ公告的调制新闻组。在“*.answers”中,“*”代表任何名称。“*.answers”新闻组包括news.answers、alt.answers、rec.answers,misc.answers等等。 article(文章):一个Usenet邮件。 attachment(附件):与用户e-mail消息一起发送的任何格式的数据文件。 .avi:Windows平台提供的电影格式。 back(返回):1、一个Web浏览器命令,通常是一个用于返回用户先前看过的页面或链路的快捷键。2、在Unix页面程序中,这个命令可以返回到前一个屏幕。 bandwidth(带宽):1、在一定时间间隔内通过传输线所能传输的信息量。2、竭尽全力不想在网络中浪费时间的人常常提起的一个字眼。 baud(波特率):这个词经常与bps(每秒钟的位数)相混淆。baud是一个技术词汇,指的是用户的调制解调器每秒钟通过电话线改变信号的次数。 BBS(公告牌):一个布告栏系统,有许多BBS都连接到Internet上。 Bcc line:是e-mail信息头的一部分,在那儿可以列出要将信息盲拷贝发送到的接收者名单。这就意味着最初的以及Cc:接受者将不会看到接受盲拷贝者的姓名。 bookmark(书签):Web或Gopher浏览器中的目标记录,用户可以在任何时候立即返回到bookmark中的目标(在一些浏览器和其它Hotlist的项目中,bookmark也叫做Favorites Place)。

(实验四)网络地址翻译nat与pat实验

一、实验目的 本实验验证NA T,PAT的地址转换,实现了内网地址的转换。 二、设备需求 路由器一台,交换机两台,PC机四台,直连线六条,电源线。 三、拓扑结构及接口IP配置 实验拓扑如下图所示(三个实验IP地址有所不同,但设备连接状况是一样的): 实验的拓扑结构 四、实验配置文档 1.静态NAT配置: 网络拓扑如上图所示,内部端口fa0/0的IP为:192.168.10.1/255.255.255.0,内网IP为192.168.10.2——192.168.10.4,外部端口fa0/1的IP为:11.11.11.129/29,用作转换的IP为11.11.11.30——11.11.11.32,外网主机PC4的IP为:11.11.11.134/29,命令配置如下: 1)配置外部端口IP: Router(config)#int fa0/0 Router(config-if)#ip addr 192.168.10.1 255.255.255.0 Router(config-if)#no shut

第10章实验指导213 2)配置内部端口IP: Router(config-if)#int fa0/1 Router(config-if)#ip addr 11.11.11.129 255.255.255.248 Router(config-if)#no shut 3)NAT内外之间的转换 Router(config)#ip nat inside source static 192.168.10.2 11.11.11.130 Router(config)#ip nat inside source static 192.168.10.3 11.11.11.131 Router(config)#ip nat inside source static 192.168.10.4 11.11.11.132 4)应用到接口 Router(config)#int fa0/0 Router(config-if)#ip nat inside Router(config-if)#int fa0/1 Router(config-if)#ip nat outside 2.动态NAT配置: 与之前的静态NA T相比,网络拓扑是一样的,知识改变了IP地址。内部端口IP为192.168.10.1/255.255.255.0,外端IP为11.11.11.112/16,IP地址池为129.129.129.1——129.129.129.100/16,配置命令如下: 1)配置内部端口IP: Router(config)#int fa0/0 Router(config-if)#ip addr 192.168.10.1 255.255.255.0 Router(config-if)#no shut 2)配置外部端口IP: Router(config-if)#int fa0/1 Router(config-if)#ip addr 11.11.11.112 255.255.0.0 Router(config-if)#no shut 3)定义内部网络中允许访问外部网络的访问控制列表: Router(config)#access-list 10 permit 192.168.10.0 0.0.0.255 4)定义合法的IP地址池: Router(config)#ip nat pool cuit 129.129.129.1 129.129.129.100 netmask 255.255.0.0 5)实现IP地址转换: Router(config)#ip nat inside source list 10 pool cuit 6)在端口上启用NAT: Router(config)#int fa0/0 Router(config-if)#ip nat inside Router(config-if)#int fa0/1 Router(config-if)#ip nat outside

中国地址的英文书写格式

中国地址英文书写格式 英文地址书写格式 室/房---Room 单元---Unit 村---Village 号楼/栋---Building 号---No. 公司---Com.或Crop 或LTD.CO 号宿舍---Dormitory 厂---Factory 楼/层---/F 酒楼/酒店---Hotel 住宅区/小区---ResidentialQuater 县---County 甲/乙/丙/丁----A/B/C/D 镇---Town 巷/弄---Lane 市---City 路---Road 省---Prov. 花园---Garden 院---Yard 街---Street 大学---College 信箱---Mailbox 区---District 表示序数词,比如1st 、2nd 、3rd 、4th ……如果不会,就用No.***代替,或者直接填数字! 另外有一些***里之类难翻译的东西,就直接写拼音***Li 。而***东(南、西、北)路,直接用拼音也行,写*** East (South 、West 、North )Road 也行。还有,如果地方不够可以将7栋3012室写成:7-3012。 201室Room201 12号No.12 2单元Unit2 长安街ChangAnstreet 3号楼BuildingNo.3 长安公司ChangAnCompany 南京路Nanjingroad 宝山区BaoShanDistrict 赵家酒店ZhaoJiahotel 钱家花园:Qianjiagarden 孙家县Sunjiacounty 李家镇Lijiatown 广州市Guangzhoucity 广东省Guangdongprovince 中国China 地址翻译实例: 宝山区南京路12号3号楼201室 room201,buildingNo.3,No.12,nanjingroad ,BaoShanDistrict 如果地方不够可以将3号楼201室写成:3-201 宝山区示范新村37号403室 Room403,No.37,SiFanResidentialQuarter,BaoShanDistrict 中华人民共和国民政部政策研究中心北京河沿大街147号 No.147#HeiYianStreetthepolicycenterofciviladministration departmentthePeople ’RepublicofChina 虹口区西康南路125弄34号201室 Room201,No.34,Lane125,XiKangRoad(South),HongKouDistrict 北京市崇文区天坛南里西区20楼3单元101 Room3-101buildingNo.20,TianTan-NanXiLiResidentialChongWenDistrict BeiJingCity 江苏省扬州市宝应县泰山东村102栋204室 Room204buildingNo.102,EastTaiShanResidentialBaoYinCountyJiangSu Province 473004河南省南阳市中州路42号王坤 WangKun Room42,ZhongzhouRoad ,NanyangCity ,HenanProv.China473004 中国四川省江油市川西北矿区采气一队 1TeamCaiQiChuanXiBeiMiningAreaJiangYouCitySiChuanProvinceChina 中国河北省邢台市群众艺术馆 TheMassesArtCentreXinTaiCityHeBeiProv.China 江苏省吴江市平望镇联北村七组 7GroupLiBeiVillagePingWangTownWeJiangCityJiangSuProvince 434000湖北省荆州市红苑大酒店王坤 WangKun HongyuanHotel,Jingzhoucity,HubeiProv.China434000 473000河南南阳市八一路272号特钢公司王坤 WangKun SpecialSteelCorp ,No.272,Bayi Road ,NanyangCity , HenanProv.China473000 528400广东中山市东区亨达花园7栋702王坤 WangKun Room702,7thBuilding,HengdaGarden,EastDistrict,Zhongshan,China 528400 361012福建省厦门市莲花五村龙昌里34号601室王坤 WangKun Room601,No.34LongChangLi,Xiamen,Fujian,China361012 361004厦门公交总公司承诺办王坤 Mr.WangKun ChengNuoBan,GongJiaoZongGongSiXiamen,Fujian,China361004 266042山东省青岛市开平路53号国棉四厂二宿舍1号楼2单元204户甲王坤 Mr.ZhouWangcai NO.204,A,BuildingNO.1,The2ndDormitoryoftheNO.4State-owned TextileFactory, 53KaipingRoad,Qingdao,Shandong,China266042 英文地址的写法 [英文地址] 中国MPA 在线的英文地址: Rome1232,Youthbuilding,No.34WestBeisanhuanRoad, Beijing,China 一、寄达城市名的批译: 我国城市有用英文等书写的,也有用汉语拼音书写的。例如“北京”英文写为“Peking ”,汉语拼音写为“Beijing ”二者虽然都是用拉丁字母,但拼读方法不同,前者是以音 标相拼,而后者则是用声母和韵母相拼的,批译时要注意识别,以免错译。 二、街道地址及单位名称的批译: 常见有英文书写、汉语拼音书写、英文和汉语拼音混合书写三种。 1、英文书写的,例如Address :6EastChanganAvenuePeKing 译为北京市东长安街6号; 2、汉语拼音书写的,例如:105niujieBeijing 译为北京市牛街105号; 3、英文、汉语拼音混合书写的,例如:NO.70dongfengdongRd.Guangzhou 译为广州东风东路70号。 三、机关、企业等单位的批译: 收件人为机关、企业等单位的,应先译收件人地址,再译单位名称。批译方法为: 1、按中文语序书写的要顺译。 例如:SHANGHAIFOODSTUFFSIMPANDEXPCO. 译为:上海食品进出口公司; 2、以英文介词短语充当定语,一般位于被修饰的名词之后,译在该名词之前。 例如:CivilAviationAdministrationOfChina 译为:中国民航局; 3、机关、企业单位的分支机构一般用英文“branch ”(分部、分公司等)表示。 例如:BeijingElectronCo.LtdXianbranch 译为:北京电子有限公司西安分公司。 四、姓名方面: 外国人习惯是名(Firstname )在前,姓(Lastname)在后。若碰到让您一起填的,最好要注意一 下顺序,不过你要是填反了,也没关系。中国银行收支票时是都承认的。 例如:刘刚,可写成GangLiu ,也可写成LiuGang 。 五、地址翻译——翻译原则:先小后大。 1、中国人喜欢先说大的后说小的,如**区**路**号。 而外国人喜欢先说小的后说大的,如 :**号**路**区,因此您在翻译时就应该先写小的后写大的。例如:中国山东省青岛市四方区洛阳路34号3号楼4单元402户,就要从房开始写 起: Prov,China (逗号后面有空格)。 注意:其中路名、公司名、村名等均不用翻译成同意的英文,只要照写拼音就行了。 因为您的支票是中国的邮递员送过来,关键是要他们明白。技术大厦您写成TechnologyBuilding ,他们可能更迷糊。

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