BGP troubleshooting: route origin
0 likes22 views
The document details a BGP troubleshooting webinar organized by GLC Networks, led by expert Achmad Mardiansyah, covering key topics such as BGP attributes, routing tables, and practical exercises. It includes an introduction to GLC and the trainer's background, alongside prerequisites for attendees regarding network knowledge. The agenda also discusses routing protocols and the BGP best path selection process with comprehensive explanations of attributes and routing adjustments.
BGP troubleshooting: route origin
- 1. www.glcnetworks.com BGP troubleshooting: route origin GLC WEBINAR, 8 Dec 2022, 19:30 GMT+7 Achmad Mardiansyah [email protected] GLC Networks, Indonesia
- 2. www.glcnetworks.com Agenda ā Introduction ā Review prerequisite knowledge ā BGP ā BGP attribute, origin ā Live practice ā Q & A 2
- 4. www.glcnetworks.com What is GLC? ā Garda Lintas Cakrawala (www.glcnetworks.com) ā Based in Bandung, Indonesia ā Areas: Training, IT Consulting ā Certified partner for: Mikrotik, Ubiquity, Linux foundation ā Product: GLC radius manager ā Regular event 4
- 5. www.glcnetworks.com Trainer Introduction ā Name: Achmad Mardiansyah ā Base: bandung, Indonesia ā Linux user since 1999, mikrotik user since 2007, UBNT 2011 ā Mikrotik Certified Trainer (MTCNA/RE/WE/UME/INE/TCE/IPv6) ā Mikrotik/Linux Certified Consultant ā Website contributor: achmadjournal.com, mikrotik.tips, asysadmin.tips ā More info: http://au.linkedin.com/in/achmadmardiansyah 5
- 6. www.glcnetworks.com Past experience ā 2020-2022 (Congo DRC, PNG, Malaysia): network support, radius/billing integration ā 2019, Congo (DRC): build a wireless ISP from ground-up ā 2018, Malaysia: network revamp, develop billing solution and integration, setup dynamic routing ā 2017, Libya (north africa): remote wireless migration for a new Wireless ISP ā 2016, United Kingdom: workshop for wireless ISP, migrating a bridged to routed network ā 2015, Kalimantan, wireless support ā See our website for more details 6
- 7. www.glcnetworks.com Please introduce yourself ā Your name ā Your company/university? ā Your networking experience? ā Your mikrotik experience? ā Your expectation from this course? 7
- 8. www.glcnetworks.com Prerequisite This presentation some prerequisite knowledge ā We assume you already know: ā TCP/IP ā Mikrotik ā Routing protocol ā Routed protocol 8
- 10. www.glcnetworks.com 7 OSI layer & protocol ā OSI layer Is a conceptual model from ISO (International Standard Organization) for project OSI (Open System Interconnection) ā When you send a message with a courier, you need to add more info to get your message arrived at the destination (This process is called encapsulation) ā What is protocol ā Is a set of rules for communication ā Available on each layer ā Communication consist of series encapsulation ā SDU: service data unit (before PDU) ā PDU: protocol data unit (after header is added) 10
- 11. www.glcnetworks.com Layered model (TCP/IP vs ISO) and encapsulation 11 / datagram
- 12. www.glcnetworks.com Did you notice? ā There is a big overhead on encapsulation process ā More encapsulation means less payload? 12
- 13. www.glcnetworks.com Router and Routing 13 ā Router is a network device that is used to forward packets, based on layer 3 information (layer 3 header) ā Routing is the process of selecting a path for traffic in a network, or between or across multiple networks Physical router Router icon
- 14. www.glcnetworks.com Typical connection (physical) 14 R2 R1 R3 ā Router connects layer 2 segments ā Router works on layer 3, connecting L2 segments ā Meaning, each layer 2 segment has network ID
- 15. www.glcnetworks.com Typical connection (logical) and routing table 15 Routing table: ā A table at router that is used to forward packet ā Available on every devices (router and host) ā Entry is executed sequentially 192.168.0.0/26 R1 192.168.0.1/26 192.168.0.3/26 192.168.0.2/26 R3 R2 192.168.1.0/24 192.168.2.0/24 192.168.3.0/24 192.168.3.3/24 192.168.3.9/24 192.168.2.9/24 192.168.2.2/24 192.168.1.1/24 192.168.1.9/24 destination gateway 192.168.0.0/26 direct 192.168.1.0/24 direct 192.168.2.0/24 192.168.0.2 192.168.3.0/24 192.168.0.3 192.168.16.3/32 192.168.0.2 0.0.0.0/0 (default gw) 192.168.0.3
- 16. www.glcnetworks.com Forwarding packets using routing table 16 ā It works like a firewall: match and action ā When a packet arrived, routing table is used to forward packets ā You should think in binary to understand how it works destination gateway 192.168.16.3/32 11000000 10101000 00001000 00000011 192.168.0.2 192.168.0.0/26 11000000 10101000 00000000 00 direct 192.168.1.0/24 11000000 10101000 00000001 direct 192.168.2.0/24 11000000 10101000 00000010 192.168.0.2 192.168.3.0/24 11000000 10101000 00000011 192.168.0.3 0.0.0.0/0 (no match) 192.168.0.3
- 17. www.glcnetworks.com A packet arrived at R1ā¦ (example) 17 Destination IP address of the packet is 192.168.2.6, which gateway do we use? A: 192.168.2.6 = (11000000 10101000 00000010 00000110) destination gateway 192.168.16.3/32 11000000 10101000 00001000 00000011 192.168.0.2 192.168.0.0/26 11000000 10101000 00000000 00 direct 192.168.1.0/24 11000000 10101000 00000001 direct 192.168.2.0/24 11000000 10101000 00000010 192.168.0.2 192.168.3.0/24 11000000 10101000 00000011 192.168.0.3 0.0.0.0/0 192.168.0.3
- 18. www.glcnetworks.com Where routing table lookup happens? 18
- 19. www.glcnetworks.com How routing works & Administrative distance (analogy) 19 19 CITY 1 100 km CITY 2 120 km CITY 2 90 km CITY 3 500 km CITY 4 250 km 10.10.10.0/24 192.168.0.1 10 10.10.20.0/24 192.168.0.2 12 10.10.20.0/24 192.168.0.3 9 10.10.30.0/24 192.168.0.3 50 10.10.40.0/24 192.168.0.4 25
- 20. www.glcnetworks.com Administrative distance 20 ā Distance is considered when prefix length is same ā Lowest distance wins ā Administrative distance policy is depends on vendor ā Table on the right shows an example of administrative distance on cisco router
- 21. www.glcnetworks.com Static routing 21 ā Entries on routing table is created manually ā Admin must manage routing table in all routers ā Admin have full control 192.168.0.0/26 R1 192.168.0.1/26 192.168.0.3/26 192.168.0.2/26 R3 R2 192.168.1.0/24 192.168.2.0/24 192.168.3.0/24 192.168.3.3/24 192.168.3.9/24 192.168.2.9/24 192.168.2.2/24 192.168.1.1/24 192.168.1.9/24 destination gateway 192.168.0.0/26 direct 192.168.1.0/24 direct 192.168.2.0/24 192.168.0.2 192.168.3.0/24 192.168.0.3 192.168.16.3/32 192.168.0.2 0.0.0.0/0 192.168.0.3
- 22. www.glcnetworks.com Dynamic routing 22 ā Router will talk to each other with routing protocol (RIP, OSPF, BGP) ā Entries on routing table is created automatically ā Admin must have a good knowledge about routing protocol 192.168.0.0/26 R1 192.168.0.1/26 192.168.0.3/26 192.168.0.2/26 R3 R2 192.168.1.0/24 192.168.2.0/24 192.168.3.0/24 192.168.3.3/24 192.168.3.9/24 192.168.2.9/24 192.168.2.2/24 192.168.1.1/24 192.168.1.9/24 destination gateway 192.168.0.0/26 direct 192.168.1.0/24 direct 192.168.2.0/24 192.168.0.2 192.168.3.0/24 192.168.0.3 192.168.16.3/32 192.168.0.2 0.0.0.0/0 192.168.0.3
- 23. www.glcnetworks.com Routing metric ā is value used by a router to make routing decisions. It depends on routing protocols ā OSPF: accumulated cost ā RIP: hop count ā IS-IS: cost ā EIGRP: bandwidth, load, delay, reliability and MTU ā BGP: AS-Path, Next-hop, Origin, Local preference, Atomic aggregate, Multi Exit Discriminator (MED) 23
- 24. www.glcnetworks.com Asymmetric routing 24 ā Currently, routing is done one-way only ā Forwarding process on router is based on destination IP address ā There is no guarantee incoming path is similar to outgoing path ā We can only control outgoing forwarding R1 192.168.0.1/26 192.168.0.3/26 R3 R2 192.168.1.0/24 192.168.2.0/24 192.168.3.0/24 192.168.3.3/24 192.168.3.9/24 192.168.2.9/24 192.168.2.2/24 192.168.1.1/24 192.168.1.9/24
- 26. www.glcnetworks.com ā Dynamic routing protocol, Path-vector ā Connecting AS numbers ā Each router need to create BGP-peer ā Only receive and send routing prefix to peer ā At Layer 5 (session): use for BGP peer session ā At Layer 4 (transport): TCP port 179 ā Used by all routers in the internet ā Routes contents: ā Full routes: all prefix in the internet ā Partial routes: specific prefix Need to consider: ā Requires knowledge to operate ā More complex (compared to RIP), lots of options What is BGP? 26
- 27. www.glcnetworks.com ā A collection of Routers & Networks ā Under one administration (organisation, company, etc) ā Defined by AS number, given by IANA via RIR (APNIC, LACNIC, AFRINIC, ARIN, RIPE-NCC) ā We run BGP between AS ā Inside AS we run IGP (Interior gateway protocol): RIP, OSPF, IS-IS, EIGRP, etc Autonomous number (AS), IGP, BGP AS1 AS4 AS3 AS2 R1 27
- 28. www.glcnetworks.com HOW BGP works? BGP steps ā Each router must have router-id and AS number ā Each router must create BGP peer ā Setup BGP filter: ā Inbound filter ā Outbound filter ā Exchange routing tables between routers ā Send keep alive periodically 28
- 29. www.glcnetworks.com BGP attributes BGP metrics are called path attributes. Classifications: ā Well-known (all router must support) ā Mandatory (must exist, in every update) ā AS-Path ā Next-hop ā Origin ā Discretionary (not always exist) ā Local preference ā Atomic aggregate ā Optional (some routers do not support) ā Transitive (If not recognized, marked as partial and still propagated to neighbor) ā Community ā Aggregator ā Non-Transitive (If not recognized, discard) ā Multi Exit Discriminator (MED) 29
- 30. www.glcnetworks.com BGP best path selection algorithm 1. Router is ignoring received path if the route is not valid. Route is valid if: a. NEXT_HOP of the route is valid and reachable b. AS_PATH received from external peers does not contain the local AS c. route is not rejected by routing filters 2. The first path received is automatically considered 'best path'. Any further received paths are compared to first received to determine if the new path is better. 3. Prefer the path with the highest WEIGHT. a. WEIGHT parameter is local to the router on which it is configured. A route without assigned WEIGHT have a default value of 0. 4. Prefer the path with the highest LOCAL_PREF. It is used only within an AS. a. A path without LOCAL_PREF attribute have a value of 100 by default. 5. Prefer the path with the shortest AS_PATH. (skipped if ignore-as-path-len set to yes) a. Each AS_SET counts as 1, regardless of the set size. The AS_CONFED_SEQUENCE and AS_CONFED_SET are not included in the AS_PATH length. 6. Prefer the path that was locally originated via aggregate or BGP network 7. Prefer the path with the lowest ORIGIN type. a. Interior Gateway Protocol (IGP) is lower than Exterior Gateway Protocol (EGP), and EGP is lower than INCOMPLETE, in other words IGP < EGP < INCOMPLETE 8. Prefer the path with the lowest multi-exit discriminator (MED). a. The router compare MED attribute only for paths that have the same neighboring (leftmost) AS. Paths without explicit MED value are treated as with MED of 0 9. Prefer eBGP over iBGP paths 10. Prefer the route that comes from the BGP router with the lowest router ID. If a route carries the ORIGINATOR_ID attribute, then the ORIGINATOR_ID is used instead of router ID. 11. Prefer the route with the shortest route reflection cluster list. Routes without a cluster list are considered to have a cluster list of length 0. 12. Prefer the path that comes from the lowest neighbor address 30
- 32. www.glcnetworks.com Topology 1 32 E4 R1 R2 R21 R22 R41 R42 E2 E4 E4 E4 E4 E2 E2 E2 E3 E3 E6 R3 R4 R23 R24 R43 R44 E2 E4 E4 E4 E4 E2 E2 E2 E3 E3 E6 R5 R6 R25 R26 R45 R46 E2 E4 E4 E4 E4 E2 E2 E2 E3 E3 E6 R7 R8 R27 R28 R47 R48 E2 E4 E4 E4 E2 E2 E2 E3 E3 E6 R9 R10 R29 R30 R49 R50 E2 E4 E4 E4 E4 E2 E2 E2 E3 E3 E6 SW86 192.168.86.0/24 E5 E5 E5 E5 E5 R86 E6 R61 R62 R63 R64 R65 R66 R67 R68 R69 R70 E3 E3 E3 E3 E2 E2 E2 E2 E3 E3 E3 E3 E2 E2 E2 E2 E3 E3 E3 E3 E2 E2 E2 E2 E3 E3 E3 E3 E2 E2 E2 E2 E3 E3 E3 E3 E2 E2 E2 E2 E6 E5 E6 E5 SW51 E2 E2 SW52 SW53 SW54 SW55 SW55 SW59 SW58 SW55 SW60 E2 pc79 pc80 E2 E3 E4 E2 E3 E2 E4 pc78 E2 E2 E3 E4 pc71 pc72 E2 E2 E3 E4 E3 E4 pc73 pc74 pc75 E2 pc76 E2 pc77 E2 E2 E3 E4 E2 E2 E3 E4 E2 E2 E3 E4 E2 E3 E4 E2 E3 E4 E6 E5 E6 E5 E6 E5
- 33. www.glcnetworks.com BGP attribute: Origin Options ā Interior Gateway Protocol (IGP) ā Assumes that the prefix came from an Interior Gateway Protocol ā Exterior Gateway Protocol (EGP) ā Prefix coming from EGP protocol (before BGP exist). Egp is old protocol ā INCOMPLETE ā BGP is unsure how the prefix was injected into routing table. Can be from: static route, redistribute Priority: ā IGP < EGP < INCOMPLETE 33
- 35. www.glcnetworks.com Interested? Just come to our training... ā Topics are arranged in systematic and logical way ā You will learn from experienced teacher ā Not only learn the materials, but also sharing experiences, best-practices, and networking 35
- 36. www.glcnetworks.com End of slides ā Thank you for your attention ā Please submit your feedback: http://bit.ly/glcfeedback ā Find our further event on our website : https://www.glcnetworks.com ā Like our facebook page: https://www.facebook.com/glcnetworks ā Slide: https://www.slideshare.net/glcnetworks/ ā Discord (bahasa indonesia): (https://discord.gg/6MZ3KUHHBX ) ā Recording (youtube): https://www.youtube.com/c/GLCNetworks ā Stay tune with our schedule 36