From 0c3368a8da771423da4c59a9ccd65d9eb4f7af6a Mon Sep 17 00:00:00 2001 From: paul Date: Sun, 7 Nov 2004 19:00:16 +0000 Subject: 2004-11-07 Paul Jakma * Add the route server docs. * routeserver.texi: new file, texinfo'fied and slightly modified version of the original TeX from James Luis Rubio. * fig-*.eps: new files, diagrammes. --- doc/routeserver.texi | 554 +++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 554 insertions(+) create mode 100644 doc/routeserver.texi (limited to 'doc/routeserver.texi') diff --git a/doc/routeserver.texi b/doc/routeserver.texi new file mode 100644 index 00000000..96de1de5 --- /dev/null +++ b/doc/routeserver.texi @@ -0,0 +1,554 @@ +@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 permit 10 + match peer + call +route-map permit 20 + match peer + call +@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. -- cgit v1.2.1