What APT does Assumption PI (or equivalent) prefixes of edge sites - PowerPoint PPT Presentation

What APT does � Assumption � PI (or equivalent) prefixes of edge sites are not routed globally APT: A Practical Transit Mapping � Packets are tunneled from ITRs to ETRs � APT Service � Provide PI prefixes to ETRs mapping � Adapt to failures and recoveries H3 Dan Jen, Michael Meisel, P3 Dan Massey, Lan Wang, Beichuan Zhang, Lixia Zhang P1 N2 L3 H2 L1 Routing Research Group H1 routable address space IETF69 L2 N3 L4 P2 H4 Three Types of Nodes in Transit Recall the questions Space (no change to edges!) Q1: How to get mapping info � Standard routers (routers, blue) Q1.1 How to inject the mapping info into the system � Tunnel routers (TRs, oragen) Q1.2 Where to distribute, who holds the mapping info Q1.3 Where/who makes selection decision from multiple (Pi � Hi) � Default mappers (mappers, green) Q2: How to detect failure Q3: How to handle failure Q3.1: Which nodes to inform Q3.2: How to handle in-flight packets Q3.3: which party holds the temporary failure info, and how to promptly remove it when failure recovered? mappers TRs Owner of holder of user of mapping info mapping info mapping info

Default Mappers Tunnel Routers (TRs) � These are a new device � Design goals for TRs: minimal changes, stay simple � Encapsulate outgoing packets (ITR mode) � Store all edge prefix to transit-space (GRA) address mappings � Decapsulate incoming packets (ETR mode) � Cache only mapping entries that are currently in use � Each edge prefix maps to a non-empty set of GRA addresses � No mapping entry? Tunnel packet to mapper's anycast address � Mapper (1) forwards the packet, and (2)responds with a � Each GRA address has a priority mapping entry containing one GRA address for the edge prefix � Same priority? Use the shortest path � At least one per AS � Use multiple for robustness, load sharing, shorter data path � Use anycase to reach nearest mapper � Mappers tell ITRs which mapping entries to use Standard Routers (“Routers”) Default Mapping Example � These are the rest of the existing routers edge prefix GRA address 1.1.1.0/24 a.b.c.d � (roughtly) no changes required to support APT X 2.2.0.0/16 a.b.c.e X 3.3.3.7 X X X X M edge Space GRA Space

Mapping Not in Cache Use the Default Mapper edge prefix GRA address 1.1.1.0/24 a.b.c.d X X 2.2.0.0/16 a.b.c.e X X X X X X Mapping Cache Miss! 3.3.3.7 X X X X M M 3.3.3.7 edge prefix is Multihomed Default Mapper Selects a Mapping edge prefix GRA address Priority edge prefix GRA address Priority ... ... ... ... ... ... X X X X a.b.c.f 10 a.b.c.f 10 3.3.3.0/24 3.3.3.0/24 p.q.r.s 20 p.q.r.s 20 ... ... ... ... ... ... X X X X X X X X M M 3.3.3.7 a.b.c.f 3.3.3.7

Default Mapper Responds with Mapping Added to Cache Mapping and Delivers Packet edge prefix GRA address 1.1.1.0/24 a.b.c.d X X 2.2.0.0/16 a.b.c.e X X 3.3.3.0/24 a.b.d.f X X X X a.b.c.f 3.3.3.7 a.b.c.f 3.3.3.7 X X X X ICMP Mapping Response M M Packet Decapsulated and Delivered Next Packet edge prefix GRA address edge prefix GRA address 1.1.1.0/24 a.b.c.d 1.1.1.0/24 a.b.c.d X X 2.2.0.0/16 a.b.c.e 2.2.0.0/16 a.b.c.e X X 3.3.3.0/24 a.b.d.f 3.3.3.0/24 a.b.d.f 3.3.3.7 3.3.3.7 X X X X X X X X M M

Mapping Already in Cache Packet Encapsulated edge prefix GRA address edge prefix GRA address 1.1.1.0/24 a.b.c.d 1.1.1.0/24 a.b.c.d X X 2.2.0.0/16 a.b.c.e 2.2.0.0/16 a.b.c.e X X 3.3.3.0/24 a.b.d.f 3.3.3.0/24 a.b.d.f X X X X 3.3.3.7 3.3.3.7 a.b.c.f X X X X M M Handling Temporary Failures Packet Delivered Three situations require failover to alternate ETR � addresses X A transit space prefix is unroutable via BGP 1. X A single transit space address becomes unreachable 2. A link between an ETR and user space fails 3. Basic approach: � X X Temporarily invadidate the corresponding mapping entries � Do not change the mapping table a.b.c.f 3.3.3.7 X X � Additional info at default mappers � M Reverse mapping table: ETR to all PI-prefixes reachable thru it � Time Till Retry (TTR) for each mapping entry �

Situation 1: GRA Prefix Unroutable Situation 1: GRA Prefix Unroutable � ITRs forward packets with unroutable destinations Dan to their default mapper Michael X � Default mappers use mapping priorities to pick a X routable GRA destination address ETR2 X X � And reply to ITR with a new mapping entry of a short TTL X X ETR1 ETR1 prefix ITR1 unreachable! 3.3.3.7 M1 M2 Situation 2: Single GRA address Situation 2 Example Failure � Handling packets in-the-fly: minimizing losses Dan � In the ETR domain: Forwards packets destined to ETR to its Michael default mapper X X � At the ETR’s mapper: Tries to find an alternate GRA ETR2 destination address to tunnel packet to Lixia X X � Informing the sender: 2 options Router X 1. The involved router sends an ICMP destination-unreachable X ETR1 Down! msg to sending ITR, which in turn forwards to its mapper ITR1 2. (with a wellknown mapper address definition) ETR domain's 3.3.3.7 mapper sends the ICMP msg to ITR's mapper; the ITR mapper informs the ITR � In either case: ITR’s mapper temporarily avoids M1 M2 corresponding mapping entries � Set the TTR in the reverse mapping table

Situation 2 Example Situation 3 Example Dan Dan Michael Michael X X X X ETR2 ETR2 Lixia Lixia X X X X Router X X X X ETR1 ETR1 Down! ITR1 ITR1 3.3.3.7 3.3.3.7 M1 M2 M1 M2 Situation 3: Border Link Failure Distributing Mappings Between ASes Handling packets in-the-fly: minimize losses � APT has two distinct parts � At the ETR: Forwards the data packet to its default mapper � Data forwarding � At the ETR’s default mapper: Tries to find an alternate GRA � Mapping info distribution to mappers � destination address to tunnel packet to � The latter can take any new distribution protocol Informing the sending AS: 2 options once we have one � ETR sends an ICMP Border Link Failure msg to ITR 1. � e.g. NERD, or CONS ETR's mapper sends the ICMP msg to ITR's mapper; the 2. � The current option: APT floods mapping info by mapper informs ITR piggybacking on BGP announcements In either case: ITR’s mapper invalidates mapping � entry by setting its TTR for the particular edge prefix mapping entry

Distributing Mappings Between ASes In Defense of piggybacking on BGP � Define a new BGP transitive attribute � Mapping updates far less problematic than BGP routing updates � mapping entry: edge prefix to GRA address mapping � An edge network sends signed mapping to all its � It only matters where mapping messages go, not what path provider they take � Only require processing at APT nodes � A provider network floods their customers’ mappings to other provider networks via BGP � No path exploration for mapping messages � this GRA address may not have any relation with the prefix � Eases incremental deployment being announced � All APT nodes (ITRs and mappers) listen � Default mappers store all incoming mappings � ITRs just invalidate cache entries that match incoming mappings Security and Robustness for ICMP Security and Robustness Packets � Wins � Mapping messages � Transit space is not directly addressable from user space � Only used within an AS, � Mapping announcements are only accepted from configured � drop them at AS boundaries if any trying to cross borders BGP peers � Border Link Failure messages � Issues � Can only be sent by GRA routers � ICMP packets are unreliable and can be spoofed � Signature field allows easy addition of cryptographic security � Mappings can be misconfigured

Incremental Deployment Regular Mapping Refresh � The user address space will not be affected � Newly added default mappers will need to get the full mapping table � Some edge prefixes will simply not have mappings � Allows stale mappings to expire � Packets destined for unmapped addresses are sent via the current infrastructure � Each provider re-announces its customers’ � TRs keep negative cache entries mappings on a regular basis � Daily? Weekly? � New default mappers boostrapping from other mappers (near) Future Work � Finish an incremental deployment design � Borrow ideas from other work (e.g. IvIP) � Understanding TR cache size using real-world data Questions? � Help us get real data !!! � Reliable key distribution/discovery bgpng@cs.ucla.edu � Edge network keys � Provider keys � Securing ICMP msgs