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.4 Atypical system entryin a Map after removing the comments looks like this.moriabert DAILY 2 ,swim WEEKLYThis entry says that moria has a link to bert, which it calls twice a day, and swim,which it calls weekly.We will come back to the Map le format in more detail below.Using the connectivity information provided in the maps, you can automatically generatethe full paths from your host to any destination site.This information is usually stored inthe paths le, also called pathalias database sometimes.Assume the Maps state that youcan reach bert through ernie, then a pathalias entry for moria generated from the Mapsnippet above may look like this:moria ernie! bert! moria! sIf you now give a destination address of janet@moria.uucp, your MTA will pickthe route shown above, and send the message to ernie with an envelope address ofbert!moria!janet.Building a paths le from the full Usenet maps is however not a very good idea.Theinformation provided in them is usually rather distorted, and occasionally out of date.Therefore, only a number of major hosts use the complete UUCP world maps to build theirpaths le.Most sites only maintain routing information for sites in their neighborhood,and send any mail to sites they don't nd in their databases to a smarter host with morecomplete routing information.This scheme is called smart-host routing.Hosts that haveonly one UUCP mail link so-called leaf sites don't do any routing of their own; they relyentirely on their smart-host.4Maps for sites registered with The UUCP Mapping Project are distributed through the newsgroupcomp.mail.maps; other organizations may publish separate maps for their network. 13.4.How does Mail Routing Work? 22113.4.3 Mixing UUCP and RFC 822The best cure against the problems of mail routing in UUCP networks so far is the adoptionof the domain name system in UUCP networks.Of course, you can't query a name serverover UUCP.Nevertheless, many UUCP sites have formed small domains that coordinatetheir routing internally.In the Maps, these domains announce one or two host as their mailgateways, so that there doesn't have to be a map entry for each host in the domain.Thegateways handle all mail that ows into and out of the domain.The routing scheme insidethe domain is completely invisible to the outside world.This works very well with the smart-host routing scheme described above.Global routinginformation is maintained by the gateways only; minor hosts within a domain will get alongwith only a small hand-written paths le that lists the routes inside their domain, and theroute to the mail hub.Even the mail gateways do not have to have routing information forevery single UUCP host in the world anymore.Beside the complete routing information forthe domain they serve, they only need to have routes to entire domains in their databasesnow.For instance, the pathalias entry shown below will route all mail for sites in thesub.org domain to smurf:.sub.org swim! smurf! sAny mail addressed to claire@jones.sub.org will be sent to swim with an envelopeaddress of smurf!jones!claire.The hierarchical organization of the domain name space allows mail servers to mix morespeci c routes with less speci c ones.For instance, a system in France may have speci croutes for subdomains of fr, but route any mail for hosts in the us domain toward somesystem in the U.S.In this way, domain-based routing as this technique is called greatlyreduces the size of routing datbases as well as te administrative overhead needed.The main bene t of using domain names in a UUCP environment, however, is that com-pliance with RFC 822 permits easy gatewaying between UUCP networks and the Internet.Many UUCP domains nowadays have a link with an Internet gateway that acts as theirsmart-host.Sending messages across the Internet is faster, and routing information is muchmore reliable because Internet hosts can use DNS instead of the Usenet Maps.In order to be reachable from the Internet, UUCP-based domains usually have theirInternet gateway announce an MX record for them MX records were described above.For instance, assume that moria belongs to the orcnet.org domain.gcc2.groucho.eduacts as their Internet gateway.moria would therefore use gcc2 as its smart-host, so thatall mail for foreign domains is delivered across the Internet.On the other hand, gcc2 wouldannounce an MX record for orcnet.org, and deliver all incoming mail for orcnet sites tomoria. 13.5.Pathalias and Map File Format 222The only remaining problem is that the UUCP transport programs can't deal with fullyquali ed domain names.Most UUCP suites were designed to cope with site names of upto eight characters, some even less, and using non-alphanumeric characters such as dots iscompletely out of the question for most.Therefore, some mapping between RFC 822 names and UUCP hostnames is needed.The way this mapping is done is completely implementation-dependent.One common wayof mapping FQDNs to UUCP names is to use the pathalias le for this:moria.orcnet.org ernie! bert! moria! sThis will produce a pure UUCP-style bang path from an address that speci es a fullyquali ed domain name.Some mailers provide a special les for this; sendmail, for instance,uses the uucpxtable for this.The reverse transformation colloquially called domainizing is sometimes required whensending mail from a UUCP network to the Internet.As long as the mail sender uses thefully quali ed domain name in the destination address, this problem can be avoided by notremoving the domain name from the envelope address when forwarding the message to thesmart-host.However, there are still some UUCP sites that are not part of any domain.They are usually domainized by appending the pseudo-domain uucp.13.5 Pathalias and Map File FormatThe pathalias database provides the main routing information in UUCP-based networks.Atypical entry looks like this site name and path are separated by TABs :moria.orcnet.org ernie! bert! moria! smoria ernie! bert! moria! sThis makes any message to moria be delivered via ernie and bert.Both moria's fullyquali ed name and its UUCP name have to be given if the mailer does not have a separateway to map between these name spaces.If you want to direct all messages to hosts inside some domain to its mail relay, you mayalso specify a path in the pathalias database, giving the domain name as target, precededby a dot.For example, if all hosts in the sub.org may be reached through swim!smurf,the pathalias entry might look like this:.sub.org swim! smurf! s 13.5.Pathalias and Map File Format 223Writing a pathalias le is acceptable only when you are running a site that does not haveto do much routing.If you have to do routing for a large number of hosts, a better way isto use the pathalias command to create the le from map les.Maps can be maintainedmuch easier, because you may simply add or remove a system by editing the system's mapentry, and re-create the map le.Although the maps published by the Usenet MappingProject aren't used for routing very much anymore, smaller UUCP networks may providerouting information in their own set of maps.A map le mainly consists of a list of sites, listing the sites each system polls or is polledby.The system name begins in column one, and is followed by a comma-separated list oflinks.The list may be continued across newlines if the next line begins with a tab.Eachlink consists of the name of the site, followed by a cost given in brackets.The cost is anarithmetic expression, made up of numbers and symbolic costs.Lines beginning with ahash sign are ignored.As an example, consider moria, which polls swim.twobirds.com twice a day, andbert.sesame [ Pobierz całość w formacie PDF ]
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.4 Atypical system entryin a Map after removing the comments looks like this.moriabert DAILY 2 ,swim WEEKLYThis entry says that moria has a link to bert, which it calls twice a day, and swim,which it calls weekly.We will come back to the Map le format in more detail below.Using the connectivity information provided in the maps, you can automatically generatethe full paths from your host to any destination site.This information is usually stored inthe paths le, also called pathalias database sometimes.Assume the Maps state that youcan reach bert through ernie, then a pathalias entry for moria generated from the Mapsnippet above may look like this:moria ernie! bert! moria! sIf you now give a destination address of janet@moria.uucp, your MTA will pickthe route shown above, and send the message to ernie with an envelope address ofbert!moria!janet.Building a paths le from the full Usenet maps is however not a very good idea.Theinformation provided in them is usually rather distorted, and occasionally out of date.Therefore, only a number of major hosts use the complete UUCP world maps to build theirpaths le.Most sites only maintain routing information for sites in their neighborhood,and send any mail to sites they don't nd in their databases to a smarter host with morecomplete routing information.This scheme is called smart-host routing.Hosts that haveonly one UUCP mail link so-called leaf sites don't do any routing of their own; they relyentirely on their smart-host.4Maps for sites registered with The UUCP Mapping Project are distributed through the newsgroupcomp.mail.maps; other organizations may publish separate maps for their network. 13.4.How does Mail Routing Work? 22113.4.3 Mixing UUCP and RFC 822The best cure against the problems of mail routing in UUCP networks so far is the adoptionof the domain name system in UUCP networks.Of course, you can't query a name serverover UUCP.Nevertheless, many UUCP sites have formed small domains that coordinatetheir routing internally.In the Maps, these domains announce one or two host as their mailgateways, so that there doesn't have to be a map entry for each host in the domain.Thegateways handle all mail that ows into and out of the domain.The routing scheme insidethe domain is completely invisible to the outside world.This works very well with the smart-host routing scheme described above.Global routinginformation is maintained by the gateways only; minor hosts within a domain will get alongwith only a small hand-written paths le that lists the routes inside their domain, and theroute to the mail hub.Even the mail gateways do not have to have routing information forevery single UUCP host in the world anymore.Beside the complete routing information forthe domain they serve, they only need to have routes to entire domains in their databasesnow.For instance, the pathalias entry shown below will route all mail for sites in thesub.org domain to smurf:.sub.org swim! smurf! sAny mail addressed to claire@jones.sub.org will be sent to swim with an envelopeaddress of smurf!jones!claire.The hierarchical organization of the domain name space allows mail servers to mix morespeci c routes with less speci c ones.For instance, a system in France may have speci croutes for subdomains of fr, but route any mail for hosts in the us domain toward somesystem in the U.S.In this way, domain-based routing as this technique is called greatlyreduces the size of routing datbases as well as te administrative overhead needed.The main bene t of using domain names in a UUCP environment, however, is that com-pliance with RFC 822 permits easy gatewaying between UUCP networks and the Internet.Many UUCP domains nowadays have a link with an Internet gateway that acts as theirsmart-host.Sending messages across the Internet is faster, and routing information is muchmore reliable because Internet hosts can use DNS instead of the Usenet Maps.In order to be reachable from the Internet, UUCP-based domains usually have theirInternet gateway announce an MX record for them MX records were described above.For instance, assume that moria belongs to the orcnet.org domain.gcc2.groucho.eduacts as their Internet gateway.moria would therefore use gcc2 as its smart-host, so thatall mail for foreign domains is delivered across the Internet.On the other hand, gcc2 wouldannounce an MX record for orcnet.org, and deliver all incoming mail for orcnet sites tomoria. 13.5.Pathalias and Map File Format 222The only remaining problem is that the UUCP transport programs can't deal with fullyquali ed domain names.Most UUCP suites were designed to cope with site names of upto eight characters, some even less, and using non-alphanumeric characters such as dots iscompletely out of the question for most.Therefore, some mapping between RFC 822 names and UUCP hostnames is needed.The way this mapping is done is completely implementation-dependent.One common wayof mapping FQDNs to UUCP names is to use the pathalias le for this:moria.orcnet.org ernie! bert! moria! sThis will produce a pure UUCP-style bang path from an address that speci es a fullyquali ed domain name.Some mailers provide a special les for this; sendmail, for instance,uses the uucpxtable for this.The reverse transformation colloquially called domainizing is sometimes required whensending mail from a UUCP network to the Internet.As long as the mail sender uses thefully quali ed domain name in the destination address, this problem can be avoided by notremoving the domain name from the envelope address when forwarding the message to thesmart-host.However, there are still some UUCP sites that are not part of any domain.They are usually domainized by appending the pseudo-domain uucp.13.5 Pathalias and Map File FormatThe pathalias database provides the main routing information in UUCP-based networks.Atypical entry looks like this site name and path are separated by TABs :moria.orcnet.org ernie! bert! moria! smoria ernie! bert! moria! sThis makes any message to moria be delivered via ernie and bert.Both moria's fullyquali ed name and its UUCP name have to be given if the mailer does not have a separateway to map between these name spaces.If you want to direct all messages to hosts inside some domain to its mail relay, you mayalso specify a path in the pathalias database, giving the domain name as target, precededby a dot.For example, if all hosts in the sub.org may be reached through swim!smurf,the pathalias entry might look like this:.sub.org swim! smurf! s 13.5.Pathalias and Map File Format 223Writing a pathalias le is acceptable only when you are running a site that does not haveto do much routing.If you have to do routing for a large number of hosts, a better way isto use the pathalias command to create the le from map les.Maps can be maintainedmuch easier, because you may simply add or remove a system by editing the system's mapentry, and re-create the map le.Although the maps published by the Usenet MappingProject aren't used for routing very much anymore, smaller UUCP networks may providerouting information in their own set of maps.A map le mainly consists of a list of sites, listing the sites each system polls or is polledby.The system name begins in column one, and is followed by a comma-separated list oflinks.The list may be continued across newlines if the next line begins with a tab.Eachlink consists of the name of the site, followed by a cost given in brackets.The cost is anarithmetic expression, made up of numbers and symbolic costs.Lines beginning with ahash sign are ignored.As an example, consider moria, which polls swim.twobirds.com twice a day, andbert.sesame [ Pobierz całość w formacie PDF ]