US20060159076A1 - Rapid response method for the failure of links between different routing domains - Google Patents

Rapid response method for the failure of links between different routing domains Download PDF

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US20060159076A1
US20060159076A1 US10/546,136 US54613605A US2006159076A1 US 20060159076 A1 US20060159076 A1 US 20060159076A1 US 54613605 A US54613605 A US 54613605A US 2006159076 A1 US2006159076 A1 US 2006159076A1
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route
routing
domain
router
alternative
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Roland Bless
Gotz Lichwald
Markus Schmidt
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Nokia Solutions and Networks GmbH and Co KG
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Siemens AG
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Assigned to SIEMENS AKTIENGESELLSCHAFT reassignment SIEMENS AKTIENGESELLSCHAFT ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: SCHMIDT, MARKUS, BLESS, ROLAND, LICHTWALD, GOTZ
Publication of US20060159076A1 publication Critical patent/US20060159076A1/en
Assigned to NOKIA SIEMENS NETWORKS GMBH & CO KG reassignment NOKIA SIEMENS NETWORKS GMBH & CO KG ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: SIEMENS AKTIENGESELLSCHAFT
Priority to US12/333,028 priority Critical patent/US7961598B2/en
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F03—MACHINES OR ENGINES FOR LIQUIDS; WIND, SPRING, OR WEIGHT MOTORS; PRODUCING MECHANICAL POWER OR A REACTIVE PROPULSIVE THRUST, NOT OTHERWISE PROVIDED FOR
    • F03B—MACHINES OR ENGINES FOR LIQUIDS
    • F03B17/00—Other machines or engines
    • F03B17/02—Other machines or engines using hydrostatic thrust
    • F03B17/04—Alleged perpetua mobilia
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L45/00—Routing or path finding of packets in data switching networks
    • H04L45/02—Topology update or discovery
    • H04L45/04—Interdomain routing, e.g. hierarchical routing
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L45/00—Routing or path finding of packets in data switching networks
    • H04L45/22—Alternate routing
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L45/00—Routing or path finding of packets in data switching networks
    • H04L45/28—Routing or path finding of packets in data switching networks using route fault recovery
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L45/00—Routing or path finding of packets in data switching networks
    • H04L45/24—Multipath
    • H04L45/247—Multipath using M:N active or standby paths

Definitions

  • the invention relates to a rapid response method for the failure of a link between two routing domains in a packet-oriented network.
  • the invention lies within the field of Internet technologies or, more specifically, in the field of routing methods in packet-oriented networks, and is directed at the transmission of data under real-time conditions.
  • Inter-domain routing is made more complicated by the fact, on the one hand, that the paths determined through the various domains to the destination should be the most optimal possible, but on the other hand the domain operators can use local strategies, which makes it more difficult to calculate paths which are globally optimal, according to objective criteria.
  • one strategy is to avoid the domains of network operators in a particular country for traffic from a particular source.
  • this strategy is not in general known to all the network operators with domains through which the traffic is routed, i.e. a network operator must make a local decision about the domain to which he forwards traffic, without full information being available about the optimal path as determined by some metric.
  • the strategies are also often referred to by the English term “policies”.
  • Border Gateway Protocol Version 4 border gateway protocol is often abbreviated to BGP
  • RFC Request For Comments 1771
  • the border gateway protocol is a so-called path-vector protocol.
  • a BGP instance (the term “BGP speaker” appears frequently in English-language literature) is informed by its BGP neighbors about possible routes to the destinations which can be reached via the BGP neighbor concerned. Using path attributes, details of which are supplied at the same time, the BGP instance contains for the reachable destinations what are, from its local point of view, the optimal routes in each case.
  • update message with which route data is propagated throughout the entire network, and which permits the network to be optimized for topology changes.
  • the emission of update messages usually leads to modification of the path data in all the network's BGP instances, for the purpose of optimizing the routings according to the data available locally.
  • keep-alive or status confirmation messages by which a BGP instance informs its BGP neighbors about its operability. In the absence of these messages, the BGP neighbors make the assumption that the link to the BGP instance is disrupted.
  • the propagation of topology data by means of the BGP protocol has the disadvantage that, when there are frequent change reports, a substantial load occurs from the messages propagated through the network to report the changes, and that the network does not converge to a new state if the change messages follow one another too rapidly.
  • This problem that the network does not converge to a new state, or that the inter-domain routing does not become stable, has been tackled by the so-called route-flap damping approach.
  • the idea of this concept is to apply a sanction to the report of a change made by a BGP neighbor. On receipt of a change message, the damping parameter is increased and, if the damping parameter exceeds a threshold, change messages are ignored. In the absence of change notices, the value of the damping parameter is reduced.
  • the object of the invention is to specify a method which permits a rapid response to malfunctions during inter-domain routing and, at the same time, avoids the disadvantages of conventional methods.
  • a substitute route or substitute path is provided.
  • the inter-domain routing along this substitute route is set up in such a way that data packets which would normally be routed via the disrupted link are diverted along the substitute route to their destination.
  • link failure refers to any malfunction which interrupts the connection or connectivity between two routing domains.
  • a routing domain (the expressions “autonomous system” or “subnetwork” are also found in the literature) is characterized by unified routing within the domain. For example, within a domain packets may be routed using the OSPF (open shortest path first) protocol.
  • OSPF open shortest path first
  • inter-domain routing a measure for routing between domains—referred to below as inter-domain routing—which permits a rapid response to failures on links between domains. In this situation, the link failure is detected by one routing domain. This could be, for example, by a router in the routing domain, which is equipped with protocol software for inter-domain routing.
  • the BGP protocol we speak in such a case of a BGP speaker or a BGP instance.
  • the message about the link failure is propagated, but not throughout the entire network but only along one or more substitute routes.
  • Routers along the substitute route(s) adjust their inter-domain routing in such a way that packets can be routed along the substitute route(s). This is effected, for example, by changes to the routing tables for those routers belonging to the domains along the substitute route which have inter-domain protocol functionality.
  • Further propagation of a message about the link failure along the substitute route by an EGP routing instance can be omitted if the EGP routing instance already provides a routing, to the destination of the substitute route, which avoids the link which has failed. This can arise as a result of the topology of the network or alternatively due to the EGP routing instance having already had a notification from the opposite direction, e.g. originating from another EGP instance which has been informed of the link failure.
  • EGP Extra Gateway Protocol
  • BGP Border Gateway Protocol
  • the setting of the inter-domain routing for a domain on the substitute route can be effected in the following way: an EGP instance receives a notification of the link failure. At this point, the EGP instance selects an alternative route for a route which passes via the link which has failed.
  • the EGP instance provides alternative routes, for example, from update messages in the BGP protocol, which have been propagated in the network and used by the EGP instance for the purpose of determining multiple routes to different destinations.
  • the next routing domain on the alternative route can be identified by reference to the alternative route.
  • the substitute route is the route which is specified, on the basis of the method in accordance with the invention, for routing via a route which includes the link which has failed.
  • the alternative route refers to a local choice of route as an alternative to the route which has failed.
  • data can propagated about not only the link which has failed, but also about the selected alternative route.
  • this is not done but instead an alternative route is always selected by the routing domains lying on the substitute route, on the basis of the data about the link failure.
  • different strategies policies
  • a routing domain it is often only possible for a routing domain to make a decision which is locally valid, i.e. in relation to the routing, a decision about the next destination along an alternative route.
  • An alternative route which is locally selected can, but does not necessarily have to, coincide with the substitute route which is ultimately produced. It is thus possible for a routing domain to make a choice of alternative route which does not coincide with the choice by the routing domains which come before the substitute route.
  • the invention has the advantage that it is possible to react rapidly to a malfunction, without it being necessary to effect the propagation of messages throughout the entire network followed by convergence on a new state in terms of the topology. In particular, for malfunctions which are of limited duration, no resource-intensive fault response need take place.
  • the routing domains which are first informed of the malfunction or the routing domains which are, for example, at the two ends of a disrupted link, initiate the provision of substitute routes for all the routes which pass along the disrupted link.
  • the routing domains which are, for example, at the two ends of a disrupted link initiate the provision of substitute routes for all the routes which pass along the disrupted link.
  • the additional substitute routes which are provided can be used as a backup or for the implementation of policies.
  • the additional alternative path(s) can then be used as a substitute for the preferred path or for a routing which depends on the routing strategies. For example, a decision may be made about which alternative path should be used by reference to data in the packet header.
  • a protocol is specified, to provide for a network-wide propagation of messages for the calculation of optimal routes, for example the BGP protocol.
  • the BGP protocol for example, the BGP process, on the router to which the link malfunction has been reported, is restrained from sending update messages to other BGP instances.
  • the router which is neighboring to the link malfunction can act as a proxy for EGP instances which can no longer be reached, and can send keep-alive messages to mimic the orderly functioning of the link which has failed to the BGP processes of other BGP instances.
  • This function of suppressing messages, can be disabled after the period of time, so that a second propagation of messages takes place for the purpose of determining optimal routes.
  • This development has the advantage that it is possible to distinguish between short-term and longer lasting (“persistent”) malfunctions, whereby the response to short-term malfunctions is the provision of substitute routes and for longer-term malfunctions an appropriate modification of the topology within the overall network is initiated.
  • FIG. 1 shows a conventional response when a link fails, using BGP inter-domain rerouting
  • FIG. 2 shows a response in accordance with the invention to the failure of a link
  • FIG. 3 shows a flow diagram of the protocol
  • FIG. 4 shows a use of routing arrays for the purpose of taking into account routing strategies.
  • FIG. 1 shows eleven autonomous systems or routing domains AS- 1 to AS- 11 together with links which connect these autonomous systems to each other.
  • the autonomous systems communicate with each other with the help of the BGP protocol, whereby individual routers in the autonomous systems are equipped with appropriate protocol capabilities.
  • BGP speakers or BGP instances we use the terms BGP speakers or BGP instances.
  • the autonomous systems exchange messages with each other, either confirming the stored state or giving information about changes which should be taken into account in routing.
  • FIG. 1 indicates how the system responds to a link failure, under the control of the BGP protocol. In this case the link between the autonomous systems AS- 6 and AS- 8 is disrupted.
  • update messages are propagated through the whole network, or the eleven autonomous systems AS- 1 , . . . , AS- 11 receive update messages, as applicable, prompting them to recalculate routes which are optimal in terms of a local metric.
  • FIG. 2 shows the same network of autonomous systems as in FIG. 1 .
  • FIG. 2 shows a rapid response in accordance with the invention to the failure of the link between the autonomous systems AS- 6 and AS- 8 .
  • messages are sent to autonomous systems which lie on substitute routes for routes which pass along the failed link.
  • the autonomous system AS- 8 sends messages about the link failure to the autonomous system AS- 7 , and this in turn to the autonomous system AS- 5 . Since the autonomous system AS- 8 can reach all the autonomous systems in the right-hand half of the figure, i.e.
  • the autonomous system AS- 5 does not need to propagated further the message about the-link failure which it received from AS- 8 .
  • the autonomous system AS- 6 sends a message to the autonomous system AS- 5 .
  • the latter then informs the autonomous system AS- 7 .
  • the autonomous systems AS- 5 to AS- 8 which are affected by the link failure, and which provide or identify, as applicable, substitute routes for the routes which pass along the failed link.
  • no messages need to be propagated over the whole network.
  • the autonomous systems AS- 1 to AS- 4 and AS- 9 to AS- 11 receive no messages about the link failure, and do not need to make any modifications.
  • FIG. 3 shows three different phases of the method in accordance with the invention, namely the phase (Fail) in which the link failure is recognized, the phase (Recv) in which a recovery of the link is signaled if this takes place within the time period, and a phase (Pererr) which shows the procedure if the fault concerned is a longer lasting one.
  • BGPspk 1 On the horizontal axis are shown two BGP speakers or BGP instances, namely BGPspk 1 , a BGP instance to which the fault is directly signaled, that is it belongs to the autonomous system which is adjacent to the failed link, and the BGP instance BGPspk 2 , which belongs to an autonomous system which is informed of the link failure by the BGP instance BGPspk.
  • BGPspk 1 Three software or protocol modules, as applicable, of the first instance BGPspk 1 are shown, namely DCT (detection), a module which detects the link failure, the module FSR (fast scope rerouting) which deals with the response in accordance with the invention or the emission of messages, as applicable, and BGP, the corresponding BGP protocol software (in this connection, one refers also to a BGP routing engine).
  • DCT detection
  • FSR fast scope rerouting
  • the time axes run from above to below, i.e. messages or events, as applicable, which appear further down are later in time.
  • BGP Keepalive
  • BGPspk 1 the BGP protocol
  • BGPspk 1 the BGP protocol
  • the malfunction is detected, for example by the absence of keepalive messages, BGP (Keepalive) (in FIG. 3 , the detection of the link failure corresponds to the Linkfail message).
  • the FSR software is informed of link failure (the corresponding message in FIG. 3 is called ‘notify’).
  • the FSR software in BGP instance 1 , BGPspk 1 sends a message, FSRlinkdown, to the FSR software in BGP instance 2 , BGPspk 2 , which in turn sends a corresponding message, FSRlinkdown, along a substitute route or numerous substitute routes, as applicable.
  • the message FSRlinkdown notifies the receiver instance concerned about the link failure, and at the receiver initiates a rapid response to the link failure, in accordance with the invention. During the rapid response to the link failure, regular functioning of the link which has failed is simulated at the BGP protocol level.
  • the FSR software FSR in the first BGP instance BGPspk 1 , sends BGP keepalive messages, BGP(Keepalive), to the BGP software BGP.
  • BGP(Keepalive) BGP(Keepalive)
  • the FSR software FSR acts, so-to-speak, as a proxy for the BGP instance at the other end of the failed link, to block any recalculation of routes in the network by the BGP protocol.
  • the FSR software FSR in the first BGP instance, BGPspk 1 uses the message FSRrecv to inform the second BGP instance, BGPspk 2 , that the link has gone back into service.
  • This FSRrecv message is propagated along the substitute route. After receiving the message about the failure of the link, the BGP instances which lie along the substitute route will have replaced the routes which pass via the failed link by other routes, and will have identified the substituted routes as temporarily unavailable.
  • the routes identified in this way can be put back into service again after the message about the recovery of the link is received.
  • the first BGP instance, BGPspk 1 will again receive BGP keepalive messages, BGP(Keepalive) via the link which has gone back into service.
  • the third period Pererr shows the response in the case of longer-lasting link failures.
  • BGPspk 1 sends a message FSRpererr (standing for ‘FSR persistent error’) to the second BGP instance BGPspk 2 , by which it signals that the fault is a longer lasting one.
  • the routes which are marked as temporarily unavailable can now be removed from the routing table(s).
  • the FSR software FSR of the first BGP speaker, BGPspk 1 now no longer simulates to the BGP software the operability of the link which has failed, but instead sends a notification BGPlinkdown which informs the BGP software BGP about the failure of the link.
  • BGP update messages (Update) are propagated throughout the entire network, and initiate a recalculation of the routes.
  • the selection of alternative routes through the routing domains or BGP instances, as applicable, along the substitute routes is made by reference to two criteria, namely first that the substitute route does not pass along the link which has failed and (the substitute route must satisfy the condition that it represents a REAL substitute for the failed link) secondly that the substitute route is optimal according to some metric which is used locally.
  • the substitute route provides for the routing of data packets a substitution for the link which has failed.
  • One metric for determining the best alternative route when there are several options for determining an alternative route could, for example, take into account such criteria as the number of hops to a destination.
  • the metric used in each case is local insofar as the routing strategies of other routing domains, which are not known to the routing domain concerned, are not taken into consideration. It is to be recommended, above all in respect of the different routing strategies or policies, that several alternative routes are identified or selected, as appropriate, for a route which has failed, and several substitute routes are provided. This combination can also be described as an array of alternative routes or an array of substitute routes. The usefulness of several substitute routes will be explained in more detail by reference to FIG. 4 .
  • This figure shows autonomous systems AS- 1 to AS- 7 . Suppose the link between autonomous systems AS- 1 and AS- 4 , shown as a dashed line, has failed.
  • a second route is available, namely via the autonomous system AS- 3 , over which traffic can be forwarded to the autonomous system AS- 7 .
  • the two different routes via the autonomous systems AS- 2 and AS- 3 , can be selected depending on the autonomous system to which the traffic is to be transmitted, for example AS- 5 , AS- 6 and AS- 7 , and depending on the routing strategy of the destination network concerned.
  • the provision of several substitute routes can in this way contribute to taking into account the routing strategy in routing the traffic along a substitute route.

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EP03004532A EP1453250A1 (de) 2003-02-28 2003-02-28 Verfahren zur schnellen Reaktion auf Linkausfälle zwischen verschiedenen Routing-Domänen
PCT/EP2004/001171 WO2004077759A1 (de) 2003-02-28 2004-02-09 Verfahren zur schnellen reaktion auf linkausfälle zwischen verschiedenen routing-domänen

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KR101100244B1 (ko) 2011-12-28
EP1597877A1 (de) 2005-11-23
US7961598B2 (en) 2011-06-14
CN1759573A (zh) 2006-04-12
EP1453250A1 (de) 2004-09-01
DE502004001480D1 (de) 2006-10-26
US20090185484A1 (en) 2009-07-23
EP1597877B1 (de) 2006-09-13
KR20050103274A (ko) 2005-10-28
CN100581127C (zh) 2010-01-13
PL381187A1 (pl) 2007-04-30

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