2004-11-15 Paul Jakma <paul@dishone.st>

	* routeserver.texi: Strip ctrl-M from line endings, note by
	  sigma@smx.pair.com

1 files changed, 554 insertions, 554 deletions

diff --git a/doc/routeserver.texi b/doc/routeserver.texi
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-@c -*-texinfo-*-

-@c @value{COPYRIGHT_STR}

-@c See file quagga.texi for copying conditions.

-@c

-@c This file is a modified version of Jose Luis Rubio's TeX sources 

-@c of his RS-Manual document

-

-@node Configuring Quagga as a Route Server

-@chapter Configuring Quagga as a Route Server

-

-The purpose of a Route Server is to centralize the peerings between BGP

-speakers. For example if we have an exchange point scenario with four BGP

-speakers, each of which maintaining a BGP peering with the other three

-(@pxref{fig:full-mesh}), we can convert it into a centralized scenario where

-each of the four establishes a single BGP peering against the Route Server

-(@pxref{fig:route-server}).

-

-We will first describe briefly the Route Server model implemented by Quagga.

-We will explain the commands that have been added for configuring that

-model. And finally we will show a full example of Quagga configured as Route

-Server.

-

-@menu

-* Description of the Route Server model::

-* Commands for configuring a Route Server::

-* Example of Route Server Configuration::

-@end menu

-

-@node Description of the Route Server model

-@section Description of the Route Server model

-

-First we are going to describe the normal processing that BGP announcements

-suffer inside a standard BGP speaker, as shown in @ref{fig:normal-processing},

-it consists of three steps:

-

-@itemize

-@item When an announcement is received from some peer, the `In' filters

-configured for that peer are applied to the announcement. These filters can

-reject the announcement, accept it unmodified, or accept it with some of its

-attributes modified.

-

-@item The announcements that pass the `In' filters go into the

-Best Path Selection process, where they are compared to other

-announcements referred to the same destination that have been

-received from different peers (in case such other

-announcements exist). For each different destination, the announcement

-which is selected as the best is inserted into the BGP speaker's Loc-RIB.

-

-@item The routes which are inserted in the Loc-RIB are

-considered for announcement to all the peers (except the one

-from which the route came). This is done by passing the routes

-in the Loc-RIB through the `Out' filters corresponding to each

-peer. These filters can reject the route,

-accept it unmodified, or accept it with some of its attributes

-modified. Those routes which are accepted by the `Out' filters

-of a peer are announced to that peer.

-@end itemize

-

-@float Figure,fig:normal-processing

-@image{fig-normal-processing,500pt,,Normal announcement processing,eps}

-@caption{Announcement processing inside a ``normal'' BGP speaker}

-@end float

-

-@float Figure,fig:full-mesh

-@image{fig_topologies_full,,,Full Mesh BGP Topology,eps}

-@caption{Full Mesh}

-@end float

-

-@float Figure,fig:route-server

-@image{fig_topologies_rs,,,Route Server BGP Topology,eps}

-@caption{Route Server and clients} 

-@end float

-

-Of course we want that the routing tables obtained in each of the routers

-are the same when using the route server than when not. But as a consequence

-of having a single BGP peering (against the route server), the BGP speakers

-can no longer distinguish from/to which peer each announce comes/goes.

-@anchor{filter-delegation}This means that the routers connected to the route

-server are not able to apply by themselves the same input/output filters

-as in the full mesh scenario, so they have to delegate those functions to

-the route server.

-

-Even more, the ``best path'' selection must be also performed inside the route

-server on behalf of its clients. The reason is that if, after applying the

-filters of the announcer and the (potential) receiver, the route server

-decides to send to some client two or more different announcements referred

-to the same destination, the client will only retain the last one,

-considering it as an implicit withdrawal of the previous announcements for

-the same destination. This is the expected behavior of a BGP speaker as

-defined in @cite{RFC1771}, and even though there are some proposals of

-mechanisms that permit multiple paths for the same destination to be sent

-through a single BGP peering, none of them are currently supported by most

-of the existing BGP implementations.

-

-As a consequence a route server must maintain additional information and

-perform additional tasks for a RS-client that those necessary for common BGP

-peerings. Essentially a route server must:

-

-@anchor{Route Server tasks}

-@itemize

-@item Maintain a separated Routing Information Base (Loc-RIB)

-for each peer configured as RS-client, containing the routes

-selected as a result of the ``Best Path Selection'' process

-that is performed on behalf of that RS-client.

-

-@item Whenever it receives an announcement from a RS-client,

-it must consider it for the Loc-RIBs of the other RS-clients.

-

-@anchor{Route-server path filter process}

-@itemize

-@item

-This means that for each of them the route server must pass the

-announcement through the appropriate `Out' filter of the

-announcer.

-

-@item

-Then through the  appropriate `In' filter of

-the potential  receiver. 

-

-@item

-Only if the announcement is accepted by both filters it will be passed

-to the ``Best Path Selection'' process.

-

-@item

-Finally, it might go into the Loc-RIB of the receiver.

-@end itemize

-@c end of route-server best path process list

-@end itemize

-@c end of route-server tasks list

-

-When we talk about the ``appropriate'' filter, both the announcer and the

-receiver of the route must be taken into account. Suppose that the route

-server receives an announcement from client A, and the route server is

-considering it for the Loc-RIB of client B. The filters that should be

-applied are the same that would be used in the full mesh scenario, i.e.,

-first the `Out' filter of router A for announcements going to router B, and

-then the `In' filter of router B for announcements coming from router A.

-

-We call ``Export Policy'' of a RS-client to the set of `Out' filters that

-the client would use if there was no route server. The same applies for the

-``Import Policy'' of a RS-client and the set of `In' filters of the client

-if there was no route server.

-

-It is also common to demand from a route server that it does not

-modify some BGP attributes (next-hop, as-path and MED) that are usually

-modified by standard BGP speakers before announcing a route.

-

-The announcement processing model implemented by Quagga is shown in

-@ref{fig:rs-processing}. The figure shows a mixture of RS-clients (B, C and D)

-with normal BGP peers (A). There are some details that worth additional

-comments:

-

-@itemize

-@item Announcements coming from a normal BGP peer are also

-considered for the Loc-RIBs of all the RS-clients. But

-logically they do not pass through any export policy.

-

-@item Those peers that are configured as RS-clients do not

-receive any announce from the `Main' Loc-RIB.

-

-@item Apart from import and export policies,

-`In' and `Out' filters can also be set for RS-clients. `In'

-filters might be useful when the route server has also normal

-BGP peers. On the other hand, `Out' filters for RS-clients are

-probably unnecessary, but we decided not to remove them as

-they do not hurt anybody (they can always be left empty).

-@end itemize

-

-@float Figure,fig:rs-processing

-@image{fig-rs-processing,500pt,,,eps}

-@caption{Announcement processing model implemented by the Route Server}

-@end float

-

-@node Commands for configuring a Route Server

-@section Commands for configuring a Route Server

-

-Now we will describe the commands that have been added to quagga

-in order to support the route server features.

-

-@deffn {Route-Server} {neighbor @var{peer-group} route-server-client} {}

-@deffnx {Route-Server} {neighbor @var{A.B.C.D} route-server-client} {}

-@deffnx {Route-Server} {neighbor @var{X:X::X:X} route-server-client} {}

-This command configures the peer given by @var{peer}, @var{A.B.C.D} or

-@var{X:X::X:X} as an RS-client.

-

-Actually this command is not new, it already existed in standard Quagga. It

-enables the transparent mode for the specified peer. This means that some

-BGP attributes (as-path, next-hop and MED) of the routes announced to that

-peer are not modified.

-

-With the route server patch, this command, apart from setting the

-transparent mode, creates a new Loc-RIB dedicated to the specified peer

-(those named `Loc-RIB for X' in @ref{fig:rs-processing}.). Starting from

-that moment, every announcement received by the route server will be also

-considered for the new Loc-RIB.

-@end deffn

-

-@deffn {Route-Server} {neigbor @{A.B.C.D|X.X::X.X|peer-group@} route-map WORD @{import|export@}} {}

-This set of commands can be used to specify the route-map that

-represents the Import or Export policy of a peer which is

-configured as a RS-client (with the previous command).

-@end deffn

-

-@deffn {Route-Server} {match peer @{A.B.C.D|X:X::X:X@}} {}

-This is a new @emph{match} statement for use in route-maps, enabling them to

-describe import/export policies. As we said before, an import/export policy

-represents a set of input/output filters of the RS-client. This statement

-makes possible that a single route-map represents the full set of filters

-that a BGP speaker would use for its different peers in a non-RS scenario.

-

-The @emph{match peer} statement has different semantics whether it is used

-inside an import or an export route-map. In the first case the statement

-matches if the address of the peer who sends the announce is the same that

-the address specified by @{A.B.C.D|X:X::X:X@}. For export route-maps it

-matches when @{A.B.C.D|X:X::X:X@} is the address of the RS-Client into whose

-Loc-RIB the announce is going to be inserted (how the same export policy is

-applied before different Loc-RIBs is shown in @ref{fig:rs-processing}.).

-@end deffn

-

-@deffn {Route-map Command} {call @var{WORD}} {}

-This command (also used inside a route-map) jumps into a different

-route-map, whose name is specified by @var{WORD}. When the called

-route-map finishes, depending on its result the original route-map

-continues or not. Apart from being useful for making import/export

-route-maps easier to write, this command can also be used inside

-any normal (in or out) route-map.

-@end deffn

-

-@node Example of Route Server Configuration

-@section Example of Route Server Configuration

-

-Finally we are going to show how to configure a Quagga daemon to act as a

-Route Server. For this purpose we are going to present a scenario without

-route server, and then we will show how to use the configurations of the BGP

-routers to generate the configuration of the route server.

-

-All the configuration files shown in this section have been taken

-from scenarios which were tested using the VNUML tool

-@uref{http://www.dit.upm.es/vnuml,VNUML}. 

-

-@menu

-* Configuration of the BGP routers without Route Server::

-* Configuration of the BGP routers with Route Server::

-* Configuration of the Route Server itself::

-* Further considerations about Import and Export route-maps::

-@end menu

-

-@node Configuration of the BGP routers without Route Server

-@subsection Configuration of the BGP routers without Route Server

-

-We will suppose that our initial scenario is an exchange point with three

-BGP capable routers, named RA, RB and RC. Each of the BGP speakers generates

-some routes (with the @var{network} command), and establishes BGP peerings

-against the other two routers. These peerings have In and Out route-maps

-configured, named like ``PEER-X-IN'' or ``PEER-X-OUT''. For example the

-configuration file for router RA could be the following:

-

-@example

-#Configuration for router 'RA'

-!

-hostname RA

-password ****

-!

-router bgp 65001

-  no bgp default ipv4-unicast

-  neighbor 2001:0DB8::B remote-as 65002

-  neighbor 2001:0DB8::C remote-as 65003

-!

-  address-family ipv6

-    network 2001:0DB8:AAAA:1::/64

-    network 2001:0DB8:AAAA:2::/64

-    network 2001:0DB8:0000:1::/64

-    network 2001:0DB8:0000:2::/64

-

-    neighbor 2001:0DB8::B activate

-    neighbor 2001:0DB8::B soft-reconfiguration inbound

-    neighbor 2001:0DB8::B route-map PEER-B-IN in

-    neighbor 2001:0DB8::B route-map PEER-B-OUT out

-

-    neighbor 2001:0DB8::C activate

-    neighbor 2001:0DB8::C soft-reconfiguration inbound

-    neighbor 2001:0DB8::C route-map PEER-C-IN in

-    neighbor 2001:0DB8::C route-map PEER-C-OUT out

-  exit-address-family

-!

-ipv6 prefix-list COMMON-PREFIXES seq  5 permit 2001:0DB8:0000::/48 ge 64 le 64

-ipv6 prefix-list COMMON-PREFIXES seq 10 deny any

-!

-ipv6 prefix-list PEER-A-PREFIXES seq  5 permit 2001:0DB8:AAAA::/48 ge 64 le 64

-ipv6 prefix-list PEER-A-PREFIXES seq 10 deny any

-!

-ipv6 prefix-list PEER-B-PREFIXES seq  5 permit 2001:0DB8:BBBB::/48 ge 64 le 64

-ipv6 prefix-list PEER-B-PREFIXES seq 10 deny any

-!

-ipv6 prefix-list PEER-C-PREFIXES seq  5 permit 2001:0DB8:CCCC::/48 ge 64 le 64

-ipv6 prefix-list PEER-C-PREFIXES seq 10 deny any

-!

-route-map PEER-B-IN permit 10

-  match ipv6 address prefix-list COMMON-PREFIXES

-  set metric 100

-route-map PEER-B-IN permit 20

-  match ipv6 address prefix-list PEER-B-PREFIXES

-  set community 65001:11111

-!

-route-map PEER-C-IN permit 10

-  match ipv6 address prefix-list COMMON-PREFIXES

-  set metric 200

-route-map PEER-C-IN permit 20

-  match ipv6 address prefix-list PEER-C-PREFIXES

-  set community 65001:22222

-!

-route-map PEER-B-OUT permit 10

-  match ipv6 address prefix-list PEER-A-PREFIXES

-!

-route-map PEER-C-OUT permit 10

-  match ipv6 address prefix-list PEER-A-PREFIXES

-!

-line vty

-!

-@end example

-

-@node Configuration of the BGP routers with Route Server

-@subsection Configuration of the BGP routers with Route Server

-

-To convert the initial scenario into one with route server, first we must

-modify the configuration of routers RA, RB and RC. Now they must not peer

-between them, but only with the route server. For example, RA's

-configuration would turn into:

-

-@example

-# Configuration for router 'RA'

-!

-hostname RA

-password ****

-!

-router bgp 65001

-  no bgp default ipv4-unicast

-  neighbor 2001:0DB8::FFFF remote-as 65000

-!

-  address-family ipv6

-    network 2001:0DB8:AAAA:1::/64

-    network 2001:0DB8:AAAA:2::/64

-    network 2001:0DB8:0000:1::/64

-    network 2001:0DB8:0000:2::/64

-

-    neighbor 2001:0DB8::FFFF activate

-    neighbor 2001:0DB8::FFFF soft-reconfiguration inbound

-  exit-address-family

-!

-line vty

-!

-@end example

-

-Which is logically much simpler than its initial configuration, as it now

-maintains only one BGP peering and all the filters (route-maps) have

-disappeared.

-

-@node Configuration of the Route Server itself

-@subsection Configuration of the Route Server itself

-

-As we said when we described the functions of a route server

-(@pxref{Description of the Route Server model}), it is in charge of all the

-route filtering. To achieve that, the In and Out filters from the RA, RB and

-RC configurations must be converted into Import and Export policies in the

-route server.

-

-This is a fragment of the route server configuration (we only show

-the policies for client RA):

-

-@example

-# Configuration for Route Server ('RS')

-!

-hostname RS

-password ix

-!

-bgp multiple-instance

-!

-router bgp 65000 view RS

-  no bgp default ipv4-unicast

-  neighbor 2001:0DB8::A  remote-as 65001

-  neighbor 2001:0DB8::B  remote-as 65002

-  neighbor 2001:0DB8::C  remote-as 65003

-!

-  address-family ipv6

-    neighbor 2001:0DB8::A activate

-    neighbor 2001:0DB8::A route-server-client

-    neighbor 2001:0DB8::A route-map RSCLIENT-A-IMPORT import

-    neighbor 2001:0DB8::A route-map RSCLIENT-A-EXPORT export

-    neighbor 2001:0DB8::A soft-reconfiguration inbound

-

-    neighbor 2001:0DB8::B activate

-    neighbor 2001:0DB8::B route-server-client

-    neighbor 2001:0DB8::B route-map RSCLIENT-B-IMPORT import

-    neighbor 2001:0DB8::B route-map RSCLIENT-B-EXPORT export

-    neighbor 2001:0DB8::B soft-reconfiguration inbound

-

-    neighbor 2001:0DB8::C activate

-    neighbor 2001:0DB8::C route-server-client

-    neighbor 2001:0DB8::C route-map RSCLIENT-C-IMPORT import

-    neighbor 2001:0DB8::C route-map RSCLIENT-C-EXPORT export

-    neighbor 2001:0DB8::C soft-reconfiguration inbound

-  exit-address-family

-!

-ipv6 prefix-list COMMON-PREFIXES seq  5 permit 2001:0DB8:0000::/48 ge 64 le 64

-ipv6 prefix-list COMMON-PREFIXES seq 10 deny any

-!

-ipv6 prefix-list PEER-A-PREFIXES seq  5 permit 2001:0DB8:AAAA::/48 ge 64 le 64

-ipv6 prefix-list PEER-A-PREFIXES seq 10 deny any

-!

-ipv6 prefix-list PEER-B-PREFIXES seq  5 permit 2001:0DB8:BBBB::/48 ge 64 le 64

-ipv6 prefix-list PEER-B-PREFIXES seq 10 deny any

-!

-ipv6 prefix-list PEER-C-PREFIXES seq  5 permit 2001:0DB8:CCCC::/48 ge 64 le 64

-ipv6 prefix-list PEER-C-PREFIXES seq 10 deny any

-!

-route-map RSCLIENT-A-IMPORT permit 10

-  match peer 2001:0DB8::B

-  call A-IMPORT-FROM-B

-route-map RSCLIENT-A-IMPORT permit 20

-  match peer 2001:0DB8::C

-  call A-IMPORT-FROM-C

-!

-route-map A-IMPORT-FROM-B permit 10

-  match ipv6 address prefix-list COMMON-PREFIXES

-  set metric 100

-route-map A-IMPORT-FROM-B permit 20

-  match ipv6 address prefix-list PEER-B-PREFIXES

-  set community 65001:11111

-!

-route-map A-IMPORT-FROM-C permit 10

-  match ipv6 address prefix-list COMMON-PREFIXES

-  set metric 200

-route-map A-IMPORT-FROM-C permit 20

-  match ipv6 address prefix-list PEER-C-PREFIXES

-  set community 65001:22222

-!

-route-map RSCLIENT-A-EXPORT permit 10

-  match peer 2001:0DB8::B

-  match ipv6 address prefix-list PEER-A-PREFIXES

-route-map RSCLIENT-A-EXPORT permit 20

-  match peer 2001:0DB8::C

-  match ipv6 address prefix-list PEER-A-PREFIXES

-!

-...

-...

-...

-@end example

-

-If you compare the initial configuration of RA with the route server

-configuration above, you can see how easy it is to generate the Import and

-Export policies for RA from the In and Out route-maps of RA's original

-configuration.

-

-When there was no route server, RA maintained two peerings, one with RB and

-another with RC. Each of this peerings had an In route-map configured. To

-build the Import route-map for client RA in the route server, simply add

-route-map entries following this scheme:

-

-@example

-route-map <NAME> permit 10

-    match peer <Peer Address>

-    call <In Route-Map for this Peer>

-route-map <NAME> permit 20

-    match peer <Another Peer Address>

-    call <In Route-Map for this Peer>

-@end example

-

-This is exactly the process that has been followed to generate the route-map

-RSCLIENT-A-IMPORT. The route-maps that are called inside it (A-IMPORT-FROM-B

-and A-IMPORT-FROM-C) are exactly the same than the In route-maps from the

-original configuration of RA (PEER-B-IN and PEER-C-IN), only the name is

-different.

-

-The same could have been done to create the Export policy for RA (route-map

-RSCLIENT-A-EXPORT), but in this case the original Out route-maps where so

-simple that we decided not to use the @var{call WORD} commands, and we

-integrated all in a single route-map (RSCLIENT-A-EXPORT).

-

-The Import and Export policies for RB and RC are not shown, but

-the process would be identical.

-

-@node Further considerations about Import and Export route-maps

-@subsection Further considerations about Import and Export route-maps

-

-The current version of the route server patch only allows to specify a

-route-map for import and export policies, while in a standard BGP speaker

-apart from route-maps there are other tools for performing input and output

-filtering (access-lists, community-lists, ...). But this does not represent

-any limitation, as all kinds of filters can be included in import/export

-route-maps. For example suppose that in the non-route-server scenario peer

-RA had the following filters configured for input from peer B:

-

-@example

-    neighbor 2001:0DB8::B prefix-list LIST-1 in

-    neighbor 2001:0DB8::B filter-list LIST-2 in

-    neighbor 2001:0DB8::B route-map PEER-B-IN in

-    ...

-    ...

-route-map PEER-B-IN permit 10

-  match ipv6 address prefix-list COMMON-PREFIXES

-  set local-preference 100

-route-map PEER-B-IN permit 20

-  match ipv6 address prefix-list PEER-B-PREFIXES

-  set community 65001:11111

-@end example

-

-It is posible to write a single route-map which is equivalent to

-the three filters (the community-list, the prefix-list and the

-route-map). That route-map can then be used inside the Import

-policy in the route server. Lets see how to do it:

-

-@example

-    neighbor 2001:0DB8::A route-map RSCLIENT-A-IMPORT import

-    ...

-!

-...

-route-map RSCLIENT-A-IMPORT permit 10

-  match peer 2001:0DB8::B

-  call A-IMPORT-FROM-B

-...

-...

-!

-route-map A-IMPORT-FROM-B permit 1

-  match ipv6 address prefix-list LIST-1

-  match as-path LIST-2

-  on-match goto 10

-route-map A-IMPORT-FROM-B deny 2

-route-map A-IMPORT-FROM-B permit 10

-  match ipv6 address prefix-list COMMON-PREFIXES

-  set local-preference 100

-route-map A-IMPORT-FROM-B permit 20

-  match ipv6 address prefix-list PEER-B-PREFIXES

-  set community 65001:11111

-!

-...

-...

-@end example

-

-The route-map A-IMPORT-FROM-B is equivalent to the three filters

-(LIST-1, LIST-2 and PEER-B-IN). The first entry of route-map

-A-IMPORT-FROM-B (sequence number 1) matches if and only if both

-the prefix-list LIST-1 and the filter-list LIST-2 match. If that

-happens, due to the ``on-match goto 10'' statement the next

-route-map entry to be processed will be number 10, and as of that

-point route-map A-IMPORT-FROM-B is identical to PEER-B-IN. If

-the first entry does not match, `on-match goto 10'' will be

-ignored and the next processed entry will be number 2, which will

-deny the route.

-

-Thus, the result is the same that with the three original filters,

-i.e., if either LIST-1 or LIST-2 rejects the route, it does not

-reach the route-map PEER-B-IN. In case both LIST-1 and LIST-2

-accept the route, it passes to PEER-B-IN, which can reject, accept

-or modify the route.

+@c -*-texinfo-*-
+@c @value{COPYRIGHT_STR}
+@c See file quagga.texi for copying conditions.
+@c
+@c This file is a modified version of Jose Luis Rubio's TeX sources 
+@c of his RS-Manual document
+
+@node Configuring Quagga as a Route Server
+@chapter Configuring Quagga as a Route Server
+
+The purpose of a Route Server is to centralize the peerings between BGP
+speakers. For example if we have an exchange point scenario with four BGP
+speakers, each of which maintaining a BGP peering with the other three
+(@pxref{fig:full-mesh}), we can convert it into a centralized scenario where
+each of the four establishes a single BGP peering against the Route Server
+(@pxref{fig:route-server}).
+
+We will first describe briefly the Route Server model implemented by Quagga.
+We will explain the commands that have been added for configuring that
+model. And finally we will show a full example of Quagga configured as Route
+Server.
+
+@menu
+* Description of the Route Server model::
+* Commands for configuring a Route Server::
+* Example of Route Server Configuration::
+@end menu
+
+@node Description of the Route Server model
+@section Description of the Route Server model
+
+First we are going to describe the normal processing that BGP announcements
+suffer inside a standard BGP speaker, as shown in @ref{fig:normal-processing},
+it consists of three steps:
+
+@itemize
+@item When an announcement is received from some peer, the `In' filters
+configured for that peer are applied to the announcement. These filters can
+reject the announcement, accept it unmodified, or accept it with some of its
+attributes modified.
+
+@item The announcements that pass the `In' filters go into the
+Best Path Selection process, where they are compared to other
+announcements referred to the same destination that have been
+received from different peers (in case such other
+announcements exist). For each different destination, the announcement
+which is selected as the best is inserted into the BGP speaker's Loc-RIB.
+
+@item The routes which are inserted in the Loc-RIB are
+considered for announcement to all the peers (except the one
+from which the route came). This is done by passing the routes
+in the Loc-RIB through the `Out' filters corresponding to each
+peer. These filters can reject the route,
+accept it unmodified, or accept it with some of its attributes
+modified. Those routes which are accepted by the `Out' filters
+of a peer are announced to that peer.
+@end itemize
+
+@float Figure,fig:normal-processing
+@image{fig-normal-processing,500pt,,Normal announcement processing,eps}
+@caption{Announcement processing inside a ``normal'' BGP speaker}
+@end float
+
+@float Figure,fig:full-mesh
+@image{fig_topologies_full,,,Full Mesh BGP Topology,eps}
+@caption{Full Mesh}
+@end float
+
+@float Figure,fig:route-server
+@image{fig_topologies_rs,,,Route Server BGP Topology,eps}
+@caption{Route Server and clients} 
+@end float
+
+Of course we want that the routing tables obtained in each of the routers
+are the same when using the route server than when not. But as a consequence
+of having a single BGP peering (against the route server), the BGP speakers
+can no longer distinguish from/to which peer each announce comes/goes.
+@anchor{filter-delegation}This means that the routers connected to the route
+server are not able to apply by themselves the same input/output filters
+as in the full mesh scenario, so they have to delegate those functions to
+the route server.
+
+Even more, the ``best path'' selection must be also performed inside the route
+server on behalf of its clients. The reason is that if, after applying the
+filters of the announcer and the (potential) receiver, the route server
+decides to send to some client two or more different announcements referred
+to the same destination, the client will only retain the last one,
+considering it as an implicit withdrawal of the previous announcements for
+the same destination. This is the expected behavior of a BGP speaker as
+defined in @cite{RFC1771}, and even though there are some proposals of
+mechanisms that permit multiple paths for the same destination to be sent
+through a single BGP peering, none of them are currently supported by most
+of the existing BGP implementations.
+
+As a consequence a route server must maintain additional information and
+perform additional tasks for a RS-client that those necessary for common BGP
+peerings. Essentially a route server must:
+
+@anchor{Route Server tasks}
+@itemize
+@item Maintain a separated Routing Information Base (Loc-RIB)
+for each peer configured as RS-client, containing the routes
+selected as a result of the ``Best Path Selection'' process
+that is performed on behalf of that RS-client.
+
+@item Whenever it receives an announcement from a RS-client,
+it must consider it for the Loc-RIBs of the other RS-clients.
+
+@anchor{Route-server path filter process}
+@itemize
+@item
+This means that for each of them the route server must pass the
+announcement through the appropriate `Out' filter of the
+announcer.
+
+@item
+Then through the  appropriate `In' filter of
+the potential  receiver. 
+
+@item
+Only if the announcement is accepted by both filters it will be passed
+to the ``Best Path Selection'' process.
+
+@item
+Finally, it might go into the Loc-RIB of the receiver.
+@end itemize
+@c end of route-server best path process list
+@end itemize
+@c end of route-server tasks list
+
+When we talk about the ``appropriate'' filter, both the announcer and the
+receiver of the route must be taken into account. Suppose that the route
+server receives an announcement from client A, and the route server is
+considering it for the Loc-RIB of client B. The filters that should be
+applied are the same that would be used in the full mesh scenario, i.e.,
+first the `Out' filter of router A for announcements going to router B, and
+then the `In' filter of router B for announcements coming from router A.
+
+We call ``Export Policy'' of a RS-client to the set of `Out' filters that
+the client would use if there was no route server. The same applies for the
+``Import Policy'' of a RS-client and the set of `In' filters of the client
+if there was no route server.
+
+It is also common to demand from a route server that it does not
+modify some BGP attributes (next-hop, as-path and MED) that are usually
+modified by standard BGP speakers before announcing a route.
+
+The announcement processing model implemented by Quagga is shown in
+@ref{fig:rs-processing}. The figure shows a mixture of RS-clients (B, C and D)
+with normal BGP peers (A). There are some details that worth additional
+comments:
+
+@itemize
+@item Announcements coming from a normal BGP peer are also
+considered for the Loc-RIBs of all the RS-clients. But
+logically they do not pass through any export policy.
+
+@item Those peers that are configured as RS-clients do not
+receive any announce from the `Main' Loc-RIB.
+
+@item Apart from import and export policies,
+`In' and `Out' filters can also be set for RS-clients. `In'
+filters might be useful when the route server has also normal
+BGP peers. On the other hand, `Out' filters for RS-clients are
+probably unnecessary, but we decided not to remove them as
+they do not hurt anybody (they can always be left empty).
+@end itemize
+
+@float Figure,fig:rs-processing
+@image{fig-rs-processing,500pt,,,eps}
+@caption{Announcement processing model implemented by the Route Server}
+@end float
+
+@node Commands for configuring a Route Server
+@section Commands for configuring a Route Server
+
+Now we will describe the commands that have been added to quagga
+in order to support the route server features.
+
+@deffn {Route-Server} {neighbor @var{peer-group} route-server-client} {}
+@deffnx {Route-Server} {neighbor @var{A.B.C.D} route-server-client} {}
+@deffnx {Route-Server} {neighbor @var{X:X::X:X} route-server-client} {}
+This command configures the peer given by @var{peer}, @var{A.B.C.D} or
+@var{X:X::X:X} as an RS-client.
+
+Actually this command is not new, it already existed in standard Quagga. It
+enables the transparent mode for the specified peer. This means that some
+BGP attributes (as-path, next-hop and MED) of the routes announced to that
+peer are not modified.
+
+With the route server patch, this command, apart from setting the
+transparent mode, creates a new Loc-RIB dedicated to the specified peer
+(those named `Loc-RIB for X' in @ref{fig:rs-processing}.). Starting from
+that moment, every announcement received by the route server will be also
+considered for the new Loc-RIB.
+@end deffn
+
+@deffn {Route-Server} {neigbor @{A.B.C.D|X.X::X.X|peer-group@} route-map WORD @{import|export@}} {}
+This set of commands can be used to specify the route-map that
+represents the Import or Export policy of a peer which is
+configured as a RS-client (with the previous command).
+@end deffn
+
+@deffn {Route-Server} {match peer @{A.B.C.D|X:X::X:X@}} {}
+This is a new @emph{match} statement for use in route-maps, enabling them to
+describe import/export policies. As we said before, an import/export policy
+represents a set of input/output filters of the RS-client. This statement
+makes possible that a single route-map represents the full set of filters
+that a BGP speaker would use for its different peers in a non-RS scenario.
+
+The @emph{match peer} statement has different semantics whether it is used
+inside an import or an export route-map. In the first case the statement
+matches if the address of the peer who sends the announce is the same that
+the address specified by @{A.B.C.D|X:X::X:X@}. For export route-maps it
+matches when @{A.B.C.D|X:X::X:X@} is the address of the RS-Client into whose
+Loc-RIB the announce is going to be inserted (how the same export policy is
+applied before different Loc-RIBs is shown in @ref{fig:rs-processing}.).
+@end deffn
+
+@deffn {Route-map Command} {call @var{WORD}} {}
+This command (also used inside a route-map) jumps into a different
+route-map, whose name is specified by @var{WORD}. When the called
+route-map finishes, depending on its result the original route-map
+continues or not. Apart from being useful for making import/export
+route-maps easier to write, this command can also be used inside
+any normal (in or out) route-map.
+@end deffn
+
+@node Example of Route Server Configuration
+@section Example of Route Server Configuration
+
+Finally we are going to show how to configure a Quagga daemon to act as a
+Route Server. For this purpose we are going to present a scenario without
+route server, and then we will show how to use the configurations of the BGP
+routers to generate the configuration of the route server.
+
+All the configuration files shown in this section have been taken
+from scenarios which were tested using the VNUML tool
+@uref{http://www.dit.upm.es/vnuml,VNUML}. 
+
+@menu
+* Configuration of the BGP routers without Route Server::
+* Configuration of the BGP routers with Route Server::
+* Configuration of the Route Server itself::
+* Further considerations about Import and Export route-maps::
+@end menu
+
+@node Configuration of the BGP routers without Route Server
+@subsection Configuration of the BGP routers without Route Server
+
+We will suppose that our initial scenario is an exchange point with three
+BGP capable routers, named RA, RB and RC. Each of the BGP speakers generates
+some routes (with the @var{network} command), and establishes BGP peerings
+against the other two routers. These peerings have In and Out route-maps
+configured, named like ``PEER-X-IN'' or ``PEER-X-OUT''. For example the
+configuration file for router RA could be the following:
+
+@example
+#Configuration for router 'RA'
+!
+hostname RA
+password ****
+!
+router bgp 65001
+  no bgp default ipv4-unicast
+  neighbor 2001:0DB8::B remote-as 65002
+  neighbor 2001:0DB8::C remote-as 65003
+!
+  address-family ipv6
+    network 2001:0DB8:AAAA:1::/64
+    network 2001:0DB8:AAAA:2::/64
+    network 2001:0DB8:0000:1::/64
+    network 2001:0DB8:0000:2::/64
+
+    neighbor 2001:0DB8::B activate
+    neighbor 2001:0DB8::B soft-reconfiguration inbound
+    neighbor 2001:0DB8::B route-map PEER-B-IN in
+    neighbor 2001:0DB8::B route-map PEER-B-OUT out
+
+    neighbor 2001:0DB8::C activate
+    neighbor 2001:0DB8::C soft-reconfiguration inbound
+    neighbor 2001:0DB8::C route-map PEER-C-IN in
+    neighbor 2001:0DB8::C route-map PEER-C-OUT out
+  exit-address-family
+!
+ipv6 prefix-list COMMON-PREFIXES seq  5 permit 2001:0DB8:0000::/48 ge 64 le 64
+ipv6 prefix-list COMMON-PREFIXES seq 10 deny any
+!
+ipv6 prefix-list PEER-A-PREFIXES seq  5 permit 2001:0DB8:AAAA::/48 ge 64 le 64
+ipv6 prefix-list PEER-A-PREFIXES seq 10 deny any
+!
+ipv6 prefix-list PEER-B-PREFIXES seq  5 permit 2001:0DB8:BBBB::/48 ge 64 le 64
+ipv6 prefix-list PEER-B-PREFIXES seq 10 deny any
+!
+ipv6 prefix-list PEER-C-PREFIXES seq  5 permit 2001:0DB8:CCCC::/48 ge 64 le 64
+ipv6 prefix-list PEER-C-PREFIXES seq 10 deny any
+!
+route-map PEER-B-IN permit 10
+  match ipv6 address prefix-list COMMON-PREFIXES
+  set metric 100
+route-map PEER-B-IN permit 20
+  match ipv6 address prefix-list PEER-B-PREFIXES
+  set community 65001:11111
+!
+route-map PEER-C-IN permit 10
+  match ipv6 address prefix-list COMMON-PREFIXES
+  set metric 200
+route-map PEER-C-IN permit 20
+  match ipv6 address prefix-list PEER-C-PREFIXES
+  set community 65001:22222
+!
+route-map PEER-B-OUT permit 10
+  match ipv6 address prefix-list PEER-A-PREFIXES
+!
+route-map PEER-C-OUT permit 10
+  match ipv6 address prefix-list PEER-A-PREFIXES
+!
+line vty
+!
+@end example
+
+@node Configuration of the BGP routers with Route Server
+@subsection Configuration of the BGP routers with Route Server
+
+To convert the initial scenario into one with route server, first we must
+modify the configuration of routers RA, RB and RC. Now they must not peer
+between them, but only with the route server. For example, RA's
+configuration would turn into:
+
+@example
+# Configuration for router 'RA'
+!
+hostname RA
+password ****
+!
+router bgp 65001
+  no bgp default ipv4-unicast
+  neighbor 2001:0DB8::FFFF remote-as 65000
+!
+  address-family ipv6
+    network 2001:0DB8:AAAA:1::/64
+    network 2001:0DB8:AAAA:2::/64
+    network 2001:0DB8:0000:1::/64
+    network 2001:0DB8:0000:2::/64
+
+    neighbor 2001:0DB8::FFFF activate
+    neighbor 2001:0DB8::FFFF soft-reconfiguration inbound
+  exit-address-family
+!
+line vty
+!
+@end example
+
+Which is logically much simpler than its initial configuration, as it now
+maintains only one BGP peering and all the filters (route-maps) have
+disappeared.
+
+@node Configuration of the Route Server itself
+@subsection Configuration of the Route Server itself
+
+As we said when we described the functions of a route server
+(@pxref{Description of the Route Server model}), it is in charge of all the
+route filtering. To achieve that, the In and Out filters from the RA, RB and
+RC configurations must be converted into Import and Export policies in the
+route server.
+
+This is a fragment of the route server configuration (we only show
+the policies for client RA):
+
+@example
+# Configuration for Route Server ('RS')
+!
+hostname RS
+password ix
+!
+bgp multiple-instance
+!
+router bgp 65000 view RS
+  no bgp default ipv4-unicast
+  neighbor 2001:0DB8::A  remote-as 65001
+  neighbor 2001:0DB8::B  remote-as 65002
+  neighbor 2001:0DB8::C  remote-as 65003
+!
+  address-family ipv6
+    neighbor 2001:0DB8::A activate
+    neighbor 2001:0DB8::A route-server-client
+    neighbor 2001:0DB8::A route-map RSCLIENT-A-IMPORT import
+    neighbor 2001:0DB8::A route-map RSCLIENT-A-EXPORT export
+    neighbor 2001:0DB8::A soft-reconfiguration inbound
+
+    neighbor 2001:0DB8::B activate
+    neighbor 2001:0DB8::B route-server-client
+    neighbor 2001:0DB8::B route-map RSCLIENT-B-IMPORT import
+    neighbor 2001:0DB8::B route-map RSCLIENT-B-EXPORT export
+    neighbor 2001:0DB8::B soft-reconfiguration inbound
+
+    neighbor 2001:0DB8::C activate
+    neighbor 2001:0DB8::C route-server-client
+    neighbor 2001:0DB8::C route-map RSCLIENT-C-IMPORT import
+    neighbor 2001:0DB8::C route-map RSCLIENT-C-EXPORT export
+    neighbor 2001:0DB8::C soft-reconfiguration inbound
+  exit-address-family
+!
+ipv6 prefix-list COMMON-PREFIXES seq  5 permit 2001:0DB8:0000::/48 ge 64 le 64
+ipv6 prefix-list COMMON-PREFIXES seq 10 deny any
+!
+ipv6 prefix-list PEER-A-PREFIXES seq  5 permit 2001:0DB8:AAAA::/48 ge 64 le 64
+ipv6 prefix-list PEER-A-PREFIXES seq 10 deny any
+!
+ipv6 prefix-list PEER-B-PREFIXES seq  5 permit 2001:0DB8:BBBB::/48 ge 64 le 64
+ipv6 prefix-list PEER-B-PREFIXES seq 10 deny any
+!
+ipv6 prefix-list PEER-C-PREFIXES seq  5 permit 2001:0DB8:CCCC::/48 ge 64 le 64
+ipv6 prefix-list PEER-C-PREFIXES seq 10 deny any
+!
+route-map RSCLIENT-A-IMPORT permit 10
+  match peer 2001:0DB8::B
+  call A-IMPORT-FROM-B
+route-map RSCLIENT-A-IMPORT permit 20
+  match peer 2001:0DB8::C
+  call A-IMPORT-FROM-C
+!
+route-map A-IMPORT-FROM-B permit 10
+  match ipv6 address prefix-list COMMON-PREFIXES
+  set metric 100
+route-map A-IMPORT-FROM-B permit 20
+  match ipv6 address prefix-list PEER-B-PREFIXES
+  set community 65001:11111
+!
+route-map A-IMPORT-FROM-C permit 10
+  match ipv6 address prefix-list COMMON-PREFIXES
+  set metric 200
+route-map A-IMPORT-FROM-C permit 20
+  match ipv6 address prefix-list PEER-C-PREFIXES
+  set community 65001:22222
+!
+route-map RSCLIENT-A-EXPORT permit 10
+  match peer 2001:0DB8::B
+  match ipv6 address prefix-list PEER-A-PREFIXES
+route-map RSCLIENT-A-EXPORT permit 20
+  match peer 2001:0DB8::C
+  match ipv6 address prefix-list PEER-A-PREFIXES
+!
+...
+...
+...
+@end example
+
+If you compare the initial configuration of RA with the route server
+configuration above, you can see how easy it is to generate the Import and
+Export policies for RA from the In and Out route-maps of RA's original
+configuration.
+
+When there was no route server, RA maintained two peerings, one with RB and
+another with RC. Each of this peerings had an In route-map configured. To
+build the Import route-map for client RA in the route server, simply add
+route-map entries following this scheme:
+
+@example
+route-map <NAME> permit 10
+    match peer <Peer Address>
+    call <In Route-Map for this Peer>
+route-map <NAME> permit 20
+    match peer <Another Peer Address>
+    call <In Route-Map for this Peer>
+@end example
+
+This is exactly the process that has been followed to generate the route-map
+RSCLIENT-A-IMPORT. The route-maps that are called inside it (A-IMPORT-FROM-B
+and A-IMPORT-FROM-C) are exactly the same than the In route-maps from the
+original configuration of RA (PEER-B-IN and PEER-C-IN), only the name is
+different.
+
+The same could have been done to create the Export policy for RA (route-map
+RSCLIENT-A-EXPORT), but in this case the original Out route-maps where so
+simple that we decided not to use the @var{call WORD} commands, and we
+integrated all in a single route-map (RSCLIENT-A-EXPORT).
+
+The Import and Export policies for RB and RC are not shown, but
+the process would be identical.
+
+@node Further considerations about Import and Export route-maps
+@subsection Further considerations about Import and Export route-maps
+
+The current version of the route server patch only allows to specify a
+route-map for import and export policies, while in a standard BGP speaker
+apart from route-maps there are other tools for performing input and output
+filtering (access-lists, community-lists, ...). But this does not represent
+any limitation, as all kinds of filters can be included in import/export
+route-maps. For example suppose that in the non-route-server scenario peer
+RA had the following filters configured for input from peer B:
+
+@example
+    neighbor 2001:0DB8::B prefix-list LIST-1 in
+    neighbor 2001:0DB8::B filter-list LIST-2 in
+    neighbor 2001:0DB8::B route-map PEER-B-IN in
+    ...
+    ...
+route-map PEER-B-IN permit 10
+  match ipv6 address prefix-list COMMON-PREFIXES
+  set local-preference 100
+route-map PEER-B-IN permit 20
+  match ipv6 address prefix-list PEER-B-PREFIXES
+  set community 65001:11111
+@end example
+
+It is posible to write a single route-map which is equivalent to
+the three filters (the community-list, the prefix-list and the
+route-map). That route-map can then be used inside the Import
+policy in the route server. Lets see how to do it:
+
+@example
+    neighbor 2001:0DB8::A route-map RSCLIENT-A-IMPORT import
+    ...
+!
+...
+route-map RSCLIENT-A-IMPORT permit 10
+  match peer 2001:0DB8::B
+  call A-IMPORT-FROM-B
+...
+...
+!
+route-map A-IMPORT-FROM-B permit 1
+  match ipv6 address prefix-list LIST-1
+  match as-path LIST-2
+  on-match goto 10
+route-map A-IMPORT-FROM-B deny 2
+route-map A-IMPORT-FROM-B permit 10
+  match ipv6 address prefix-list COMMON-PREFIXES
+  set local-preference 100
+route-map A-IMPORT-FROM-B permit 20
+  match ipv6 address prefix-list PEER-B-PREFIXES
+  set community 65001:11111
+!
+...
+...
+@end example
+
+The route-map A-IMPORT-FROM-B is equivalent to the three filters
+(LIST-1, LIST-2 and PEER-B-IN). The first entry of route-map
+A-IMPORT-FROM-B (sequence number 1) matches if and only if both
+the prefix-list LIST-1 and the filter-list LIST-2 match. If that
+happens, due to the ``on-match goto 10'' statement the next
+route-map entry to be processed will be number 10, and as of that
+point route-map A-IMPORT-FROM-B is identical to PEER-B-IN. If
+the first entry does not match, `on-match goto 10'' will be
+ignored and the next processed entry will be number 2, which will
+deny the route.
+
+Thus, the result is the same that with the three original filters,
+i.e., if either LIST-1 or LIST-2 rejects the route, it does not
+reach the route-map PEER-B-IN. In case both LIST-1 and LIST-2
+accept the route, it passes to PEER-B-IN, which can reject, accept
+or modify the route.