Netmanias 기술문서: IP망장애복구기술[1] Router Architecture

IP망장애복구기술[1] Router Architecture
2009년2월13일
NMC Consulting Group(tech@netmanias.com)

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Router Hardware Architecture: Core router reference model –Single RP
Route Learning & AdvertisingRoute Download to ingress FIBsCustomer Traffic ForwardingABCBackbone급Router의architecture를살펴보면…Data Plane (Forwarding Plane)-Line card는, 자싞에게download되어있는local FIB 정보만을가지고traffic forwarding을수행한다.Control Plane -Route Processor(RP) Board가Control Plane 기능을담당한다.-OS with OSPF/IS-IS/BGP + PIM + SNMP + RADIUS/DIAMETER/COPS + etc.-RP가Neighbor router들과Routing Protocol Message를교홖하여Routing 정보를파악하면Control Plane 상에서RIB(Routing Information Base)가구축됨.-RIB가각Line card의FIB(Forwarding Information Base)에반영된다. (예, download됨)Route ProcessingRIBControl PlaneDatal PlaneI/OI/OI/OLine CardFIBLine CardFIBLine CardFIBSwitching Fabric

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Router Hardware Architecture: Core router reference model –Dual RP
Route Learning & AdvertisingRoute Download to ingress FIBsCustomer Traffic ForwardingABCControl Plane-RP는Router Control Plane의중추기능요소이므로, 장애발생에대비하여Backup RP를둬이중화한다.-Primary RP와Backup RP는, RIB를포함한주요state들에대해지속적혹은주기적으로sync.를맞춖다.-Primary RP에장애가감지되면Backup RP가대싞동작하는데, seamless switchover가되려면두RP 갂의각종state 정보의일치가중요(얼마나sync가잘맞는지는구현기술에따라다르다.)Primary RPRIBControl PlaneDatal PlaneI/OI/OI/OLine CardFIBLine CardFIBLine CardFIBSwitching FabricBackup RPRIB’Health checkRIB pollingRIB pollingPrimary RP의RIB와Backup RP의RIB 갂의Sync 맞추기를위한주기적Update. RIB정보이외의기타시스템의존적인데이터들다수포함.Primary RP의변화를항상Backup RP에게Sync맞추는것은구현이어려운것으로알려져있어, 이같은polling 방식이사용된다.Health checkPrimary RIB에문제가발생하면바로Backup하기위해주기적으로상태를확인(예, Hello message 방식or Hardware적으로지원되는watch-dog timer)

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Functional Architecture of a RouterOSPFRIBControl PlaneFIBLine CardMFIBIS-ISMRIBRouting Protocol ManagerPIM-SMBGMPUnicast Routing ProtocolMulticast Routing ProtocolRouting Protocol Manager각Routing Protocol Suite는여러Routing Protocol이동시에동작하더라도, 이들정보를취합하여하나의RIB/MRIB를구성할수있어야하므로, Protocol-independent하면서중앙집중적인Software entity가필요한데, 이를가리켜“Routing Protocol Manager”라고칭하기로한다. (표준용어는아니고본문서에서그렇게쓰자는얘기)유명한Routing Protocol Suite인ZebOS의NSM(Network Service Module) 또는그와유사한Software Module을지칭함.이같은process가Interface Up/Down 정보반영, RIB/MRIB 취합관리, Static Route Info, Inter-protocol re-distribution 정책등을담당한다.RIBRouting Information Base. 하나의Router의각인터페이스별로서로다른Routing Protocol을구동할수있으며, RIB는이들여러Protocol 정보를통합하여구축된다.특정Destination Network 정보에대해OSPF의{Nexthop, Cost} 정보와IS-IS의{Nexthop, Cost} 정보가다르다면, 각Protocol에대해설정된“선호도”(Preference)값에따라RIB에적용할정보가결정된다.MRIBMulticast Routing Information Base. MRIB는RIB로부터추춗되는, multicast topology table로서, multicast router 갂의연결로이루어지는topology 정보를담는다.PIM의경우PIM protocol 자체적으로topology를파악하는방법은없고, unicastRIB로부터구해짂다. PIM-SM에서MRIB는Join/Prune 메시지를어디로보낼지를결정하기위해이용된다.BGMP와같이자체적으로Multicast topology를파악하는방법이있는경우, multicast routing protocol의연동에의해MRIB가구축될수있다.TIBTree Information Base. 수싞된Join/Prune 메시지및Local host들로부터수싞한IGMP 메시지를총괄하여구축된Multicast distribution tree 이다.BGMPBorder Gateway Multicast ProtocolFIBForwarding Information Base. RIB의내용이Data plane에반영된것.MFIBMulticast Forwarding Information Base. TIB가data plane에반영된것임.FIBMFIBPDU 교홖PDU 교홖TIB※ Conceptual Architecture 이므로Vendor마다다를수있다.


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Simplified Functional Architecture
RIBControl PlaneFIBLine CardMFIBIS-ISPIM-SMPDU 교홖PDU 교홖IS-IS 동작에의해RIB가구성된다.RIB가변경되었는지PIM process가polling하여읽어갂다.또는RIB가변경되면PIM Process에통보된다.(MRIB가별도로존재하지않고, PIM-SM 이RIB를직접참조한다.)TIB변경된(M)RIB를참조하여RPF update(Reverse Path Forwarding 경로갱싞) 수행함.TIB도따라서update됨.123TIB가갱싞됨에따라line card 내의MFIB도update됨.4

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