geoff molloy

TCP/IP procedures and application for the GTS

Geoff Molloy

Communications and Computing Branch

Bureau of Meteorology

Australia


Agenda• GTS Comms Evolution

• Network Topologies

• Overview of TCP/IP

• GTS IP Addressing

• Routing

• Data Transfer - TCP and FTP

• WMO standards – Sockets and FTP


GTS Comms Evolution• Asynchronous to X.25 to IP

• X.25 saw the introduction of error detection and correction.

• The advantages of TCP/IP include cost, simplicity and the ability to use a range of high level (application) protocols.– http (web) Remote machine logins (telnet,

rlogin, remsh) FTP (File Transfer Protocol) Smtp (e-mail) remote database access


Network Topology_pment Cabinet-1

_V 7,V _V 7,_V 7,_V

__V _V 7,

Head Office

_ Office_ Office_ Office

_ Office

Firewall

____wallce_wallce

_wallc

WEB FTP

_wallce

Message Switch

Internet

_rnetw

GTS

_rnet_rnetw

Regional

Public Addresses

Private or Public Addresses

Offices


IP Address format


IP Address format (cont.).

1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 --+-------------+------------------------------------------------ Class A |0| NET_ID | HOST_ID | |-+-+-----------+---------------+-------------------------------| Class B |1|0| NET_ID | HOST_ID | |-+-+-+-------------------------+---------------+---------------| Class C |1|1|0| NET_ID | HOST_ID | |-+-+-+-+---------------------------------------+---------------| Class D |1|1|1|0| MULTICAST_ID | |-+-+-+-+-------------------------------------------------------| Class E |1|1|1|1| EXPERIMENTAL_ID | --+-+-+-+--------------------------------------------------------FIGURE 5. IP Address Format.


IP Addresses• Must have public addresses for inter-agency

communications.

• Private addresses may be used within your organisation.

• Network Address Translation (NAT) is used to convert between private and public addresses

• WMO allocates public addresses for GTS: possible allocation for hosts, but cannot be used for Internet connection.


IP addresses (cont.)• GTS Allocation: 193.105.177.0 to

193.105.184.0

• Private address allocations:– 10.0.0.0 to 10.255.255.255– 172.16.0.0 to 172.16.255.255– 192.168.0.0 to 192.168.255.255

• Subnet Mask: 2 ways to refer top this– 192.168.1.1 255.255.255.0– 192.168.1.1/24

• /24 = 11111111 11111111 11111111 00000000


IP addresses (cont.)• Get IP address from ISP

• Possibly get IP address from WMO


GTS Connection with NAT_ÞmÞ_ÞmÞ_pment Cabinet-1

_ÞmÞ_Þm

_Þm

Firewall

___

_wall

10.1.1.1

_.1.1Þ__.1.1

BGP Routing

_.1.1_.1.1_.1.1

193.105.180.130193.105.180.129

_.1.1

Firewall

___

_wall

134.178.6.5

_178.6.

NAT

202.203.190.1 = 10.1.1.1

NAT Table:

TCP/IP procedures and application for the GTS How do you know which way to send ip packets – routing protocol

_pment Cabinet-1_V 7,V

_V 7,_V 7,_V

__V _V 7,

Head Office

_ Office_ Office_ Office

_ Office

Firewall

____wallce_wallce

_wallc

WEB FTP

_wallce

Message Switch

Internet

_rnetw

GTS

_rnet_rnetw

Regional

Public Addresses

Private or Public Addresses

Offices


Routing

• Two types of routing: Static and Dynamic• An internal routing protocol is used within

your network.• The GTS uses BGP for routing (static

routes can sometimes be used for stub networks)

• ATTACHMENT II-15Use of TCP/IP on the GTS give examples of setting up BGP Routing on a Cisco router – does not cover use of NAT.


Example of routing tablegatekeeper-gw#sh ip route

S 139.163.28.254/32 [1/0] via 139.163.79.1

B 202.245.39.0/24 [20/0] via 193.105.178.22, 2d23h

S 157.128.0.0/16 [1/0] via 202.12.61.9

B 203.10.243.192/27 [20/1] via 203.10.243.13, 05:46:25


BGP• Used by WMO on GTS

• Uses a tcp connection on port 179 between to routers to send updates.

• Each Network is given an Autonomous System (AS) number.

• WMO have allocated AS numbers out of the private AS address range for the GTS


GTS AS Numbers• Private range: 64512 through 65535• MTN Centres and reserve: 64512 to

64639• RA I: 64640 to 64767• RA II: 64768 to 64895• RA III: 64896 to 65023• RA IV: 65024 to 65151• RA V: 65152 to 65279• RA VI: 65280 to 65407• Antarctic and reserve:65408 to

65535


Local BGP links• Allocate AS numbers for private links out

of range: 65472 to 65535

• All GTS should not route this range.


Example of BGP routing

gatekeeper-gw#sh ip bgp neigh 193.105.178.22 route

BGP table version is 205, local router ID is 134.178.31.9

Status codes: s suppressed, d damped, h history, * valid, > best, i - internal

Origin codes: i - IGP, e - EGP, ? - incomplete

Network Next Hop Metric LocPrf Weight Path

*> 140.90.88.0/24 193.105.178.22 0 64520 64513 i

*> 202.245.36.0 193.105.178.22 0 64520 ?

*> 202.245.39.0 193.105.178.22 0 0 64520 i

*> 205.156.51.96/27 193.105.178.22 0 64520 64513 i

Total number of prefixes 4

gatekeeper-gw#


BGP Conifigurationrouter bgp 64512 no synchronization network 134.178.0.0 redistribute ospf 101 metric 20 match internal neighbor 193.105.178.22 remote-as 64520 neighbor 193.105.178.22 distribute-list 10 out neighbor 193.105.178.22 filter-list 4 in neighbor 193.105.178.22 filter-list 1 out!ip as-path access-list 1 permit ^$ip as-path access-list 4 permit ^64520$ip as-path access-list 4 permit _64520$ip as-path access-list 4 permit _64513$!access-list 10 permit 134.178.6.0 0.0.0.255access-list 10 deny any


Useful cisco BGP commands• Sh tcp

• Sh ip route

• Sh ip bgp neighbor 1.1.1.1 route

• Sh ip bgp neighbor 1.1.1.1 advert


NAT• Static and Dynamic

• Static needed for GTS so that hosts inside the network can be contacted and for security.

• NAT addresses must appear in BGP routing table.


TCP overview• Connection oriented and reliable.

• TCP uses a port number to define connections

• Connection defined by source IP address/source port and destination IP address and destination port

• Can have multiple connections to the same TCP port number


TCP Packet format


Common TCP ports• ftp-data 20/tcp # File Transfer Protocol (Data)• ftp 21/tcp # File Transfer Protocol

(Control)• telnet 23/tcp # Virtual Terminal Protocol• smtp 25/tcp # Simple Mail Transfer Protocol• http 80/tcp # World Wide Web HTTP• pop3 110/tcp # Post Office Protocol - V 3• GTS ports >10000


UDP• Connectionless not reliable

• Not used for GTS transfers

• Examples: used for network management (SNMP), voice data


FTP• Uses 2 TCP connections: Control (port 21)

and data (port 20)

• Two modes: normal and passive.

• Used for transferring files.


FTP OperationNormal

Client host - connects to port 21

Client host “give me file on port 2345

Client/2345 host/20 –connects to port 2345

Passive

Client host - connects to port 21

Client host “give me file on port 2345

Client host/2345 –connects to port 2345


FTP Commandsget Retrieve a fileput send a filebinary send or retrieve a file in raw binary

format (no processing) cd Change directories on the

remote systemrename Rename a file on the remote

systemHash display a ‘hash’ symbol which

indicates how much data has been sent.Ls List the directory on the

remote system.


FTP ExampleC:\>ftp gorgon.ho.bom.gov.auConnected to gorgon.ho.bom.gov.au.220 gorgon FTP server (Version 1.7.212.5 Wed May 30 12:19:42 GMT 2001) ready.User (gorgon.ho.bom.gov.au:(none)): anonymous331 Password required for anonymous.Password:230 User gvm logged in.ftp> cd temp250 CWD command successful.ftp> binary200 Type set to I.ftp> put info.txt200 PORT command successful.150 Opening BINARY mode data connection for INFO.TXT.226 Transfer complete.ftp: 833 bytes sent in 0.01Seconds 83.30Kbytes/sec.ftp> rename info.txt to final.txt550 info.txt: No such file or directory.ftp> rename INFO.TXT final.txt350 File exists, ready for destination name.250 RNTO command successful.ftp> ls200 PORT command successful.150 Opening ASCII mode data connection for file list.test.zipfinal.txt226 Transfer complete.ftp: 62 bytes received in 0.00Seconds 62000.00Kbytes/sec.ftp>


WMO Standards• FTP transfer

• Socket Connections


WMO Socket Connections• WMO Use TCP ports > 10000

– Suggest that use ports > 30000

• Use separate sockets for ASCII and Binary data and separate sockets for transmit and receive.

• Maintain socket connection

• Old sockets should be closed when a new connection to the same port from the same host occurs – avoids problems with connection loss.


WMO Sockets Continued• Use CSN (channel sequence numbers)

manditory – recommend 5 character CSN

• Each message is preceded by a message length field of eight ASCII characters and a message type field of two ASCII characters.– BI for binary, AN for alphanumeric or FX for

facsimile


Socket Data Format

Message Message nnnlength type SOH CR CR LF or CR CR LF Heading CR CR LF ETX

(8 characters) (2 characters) nnnnn

Message length

Message length : Length from SOH to ETX (e.g. 00001826 = 1826bytes) M essage type AN: Alphanumeric, B I: B inary, FX: facsimile


Socket Programming• See ATTACHMENT II-15

Use of TCP/IP on the GTS


WMO FTP Procedures • Procedures for accumulating messages into files

so as to minimise FTP overheads with short messages (applies only to existing message types);

• file naming conventions for existing message types (existing AHL);

• file renaming;• use of directories;• account names and passwords;• FTP sessions;• Local FTP requirements


Accumulating messages into files• Multiple messages in the one file

• Messages should be accumulated in files thus:– length indicator, message 1 (8 characters);– format identifier (2 characters);– message 1;– length indicator, message 2 (8 characters);– format identifier (2 characters);– message 2;– and so on, until the last message;


FTP message format

M e s s a g e 2l e n g t h( 8 c h a c s )

M e s s a g e 1 F o r m a tI d e n t i f i e r

n n nl e n g t h S O H C R C R L F o r C R C R L F H e a d i n g T e x t C R C R L F E T X

( 8 c h a r a c t e r s ) 0 0 n n n n n

M e s s a g e l e n g t h

O p t i o n 1 . S t a r t i n g L i n e a n d E n d o f M e s s a g e p r e s e n tM e s s a g e l e n g t h : L e n g t h f r o m S O H t o E T X ( e . g . 0 0 0 0 1 8 2 6 = 1 8 2 6 b y t e s )

M e s s a g e 2 l e n g t h( 8 c h a r a c t e r s )

M e s s a g e 1 l e n g t h( 8 c h a r a c t e r s )

F o r m a tI d e n t i f i e r 0 1

F o r m a tI d e n t i f i e r 0 1

C R C R L F H e a d i n g T e x t

M e s s a g e l e n g t h

O p t i o n 2 . S t a r t i n g L i n e a n d E n d o f M e s s a g e a b s e n tM e s s a g e l e n g t h : L e n g t h f r o m f i r s t C R t o e n d o f T e x t ( e . g . 0 0 0 0 1 8 2 6 = 1 8 2 6 b y t e s )


File naming conventions• CCCCNNNNNNNN.ext where:

– CCCC is the international four letter location identifier of the sending Centre, as defined in WMO publication No. 9, Volume C;

– NNNNNNNN is a sequential number from 0 to 99999999 generated by the sending Centre;

– ext is

– ‘ua’ for urgent alpha numeric information

– ‘ub’ for urgent binary information

– ‘a’ for normal alpha numeric information

– ‘b’ for normal binary information

– ‘f’ for facsimile information


File renaming• most centres detect the presence of a new file by

scanning a directory.• To avoid problems with the receiving centre

processing a file before it has completely arrived, all sending centres must be able to remotely rename the files they send

• The file shall be sent with the extent ‘.tmp’ and then renamed

• Recommended that a separate directory be used for each host system which is initiating FTP sessions to avoid the possibility of filename duplication


General FTP “Rules”• Anonymous FTP may be used, but not on

servers accessible from the Internet

• To Limit load, only one ftp session per centre per file type

• receiving Centres to delete files after they have been processed

• Do not use compression of files.


FTP suggestions• Use format identifier “00”

– This allows the WMO request/repeat service to recover missing data.

• Use filename of *.b to exchange alphanumeric or binary messages– CCCCNNNNNNNN.b - for alpha numeric and binary

– CCCCNNNNNNNN.f - for facsimile (FAX T.4)

• Send one T4 chart in each file• Send up to 100 messages in a file but do not delay

sending a message for more than 60 seconds.• Read incoming files at least every minute.


Socket/FTP Comparison• Sockets:

– Quick, low overhead– Requires programming– Request/Repeat system can be slow

• FTP– More Delays– Standard clients (less programming)– Easy to see failures and repeat transmission.


Checklist for GTS link• Link requirements:

– 1. Get link addresses and private AS numbers from WMO

– 2. Agree whether to use BGP or not– 3. Establish connectivity between routers.


Checklist for GTS link cont.• Use only official IP addresses • Exchange details on host names.• Declare which IP addresses in your Centre are

eligible to use the GTS.• Establish an IP connection with one or more

Centres.• Configure dynamic routing with BGP (or static

routing)• Obtain an autonomous-system number • Check the barrier between Internet and the GTS• Filter incoming and outgoing traffic in accordance

with the requirements described above


Checklist for GTS link cont.• WMO socket requirements:

– Define socket/port numbers to receive on – Agree on 3 or 5 digit sequence numbers

• FTP requirements:– Exchange user-id and password of receive accounts– Exchange directory names– Agree on format identifier – preferably “00” (include

WMO header/trailer)– Agree on filenames. Suggest:– Exchange information on maximum messages to be in

a file and delays before sending a file and delays before reading a file (not essential but is useful information)

– Agree on 3 or 5 digit sequence numbers


Email Standard• Proposed standard in documentation.


END

geoff molloy

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