Bgp (1)

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  • Bgp (1)

    1. 1. Border Gateway Protocol (BGP4)
    2. 2. Border Gateway Protocol (BGP) • Routing/Forwarding basics • Building blocks • Exercises • BGP protocol basics • Exercises • BGP path attributes • Best path computation • Exercises
    3. 3. Border Gateway Protocol (BGP)... • Typical BGP topologies • Routing Policy • Exercises • Redundancy/Load sharing • Best current practices
    4. 4. Routing/Forwarding Basics
    5. 5. IP route lookup:Longest match routing R2 R3 R1 R4 All 10/8 except 10.1/16 10.1/16 Packet: Destination IP address: 10.1.1.1 10/8 -> R3 10.1/16 -> R4 20/8 -> R5 30/8 -> R6 ….. R2’s IP routing table
    6. 6. IP route lookup: Longest match routing R2 R3 R1 R4 All 10/8 except 10.1/16 10.1/16 10/8 -> R3 10.1/16 -> R4 20/8 -> R5 ….. R2’s IP routing table 10.1.1.1 & FF.0.0.0 is equal to 10.0.0.0 & FF.0.0.0 Match! Packet: Destination IP address: 10.1.1.1
    7. 7. IP route lookup: Longest match routing R2 R3 R1 R4 All 10/8 except 10.1/16 10.1/16 10/8 -> R3 10.1/16 -> R4 20/8 -> R5 ….. R2’s IP routing table 10.1.1.1 & FF.FF.0.0 is equal to 10.1.0.0 & FF.FF.0.0 Match as well! Packet: Destination IP address: 10.1.1.1
    8. 8. IP route lookup: Longest match routing R2 R3 R1 R4 All 10/8 except 10.1/16 10.1/16 10/8 -> R3 10.1/16 -> R4 20/8 -> R5 ….. R2’s IP routing table 10.1.1.1 & FF.0.0.0 is equal to 20.0.0.0 & FF.0.0.0 Does not match! Packet: Destination IP address: 10.1.1.1
    9. 9. IP route lookup: Longest match routing R2 R3 R1 R4 All 10/8 except 10.1/16 10.1/16 10/8 -> R3 10.1/16 -> R4 20/8 -> R5 ….. R2’s IP routing table Packet: Destination IP address: 10.1.1.1 Longest match, 16 bit netmask
    10. 10. IP route lookup: Longest match routing • default is 0.0.0.0/0 • can handle it using the normal longest match algorithm • matches everything. Always the shortest match.
    11. 11. Forwarding • Uses the routing table built by routing protocols • Performs the lookup to find next-hop and outgoing interface • Switches the packet with new encapsulation as per the outgoing interface
    12. 12. Building Blocks • Autonomous System (AS) • Types of Routes • IGP/EGP • DMZ • Policy • Egress • Ingress
    13. 13. Autonomous System (AS) • Collection of networks with same policy • Single routing protocol • Usually under single administrative control • IGP to provide internal connectivity AS 100
    14. 14. Autonomous System(AS)... • Identified by ‘AS number’ • Public & Private AS numbers • Examples: – Service provider – Multi-homed customers – Anyone needing policy discrimination
    15. 15. Routing flow and packet flow For networks in AS1 and AS2 to communicate: AS1 must announce routes to AS2 AS2 must accept routes from AS1 AS2 must announce routes to AS1 AS1 must accept routes from AS2 accept announce announc e acceptAS 1 AS2 packet flow packet flow Routing flow egress ingress
    16. 16. Egress Traffic • Packets exiting the network • Based on – Route availability (what others send you) – Route acceptance (what you accept from others) – Policy and tuning (what you do with routes from others) – Peering and transit agreements
    17. 17. Ingress Traffic • Packets entering your network • Ingress traffic depends on: – What information you send and to who – Based on your addressing and ASes – Based on others’ policy (what they accept from you and what they do with it)
    18. 18. Types of Routes • Static Routes – configured manually • Connected Routes – created automatically when an interface is ‘up’ • Interior Routes – Routes within an AS • Exterior Routes – Routes exterior to AS
    19. 19. What Is an IGP? • Interior Gateway Protocol • Within an Autonomous System • Carries information about internal prefixes • Examples—OSPF, ISIS, EIGRP…
    20. 20. What Is an EGP? • Exterior Gateway Protocol • Used to convey routing information between ASes • De-coupled from the IGP • Current EGP is BGP4
    21. 21. Why Do We Need an EGP? • Scaling to large network – Hierarchy – Limit scope of failure • Define administrative boundary • Policy – Control reachability to prefixes
    22. 22. • Interior – Automatic discovery – Generally trust your IGP routers – Routes go to all IGP routers • Exterior Specifically configured peers Connecting with outside networks Set administrative boundaries Interior vs. Exterior Routing Protocols
    23. 23. Hierarchy of Routing Protocols Local NAP FDDI Other ISP’s BGP4 BGP4/Static BGP4 / OSPF Customers BGP4
    24. 24. AS 100 AS 101 AS 102 DMZ Network AA BB CC DD EE • Shared network between ASes Demilitarized Zone (DMZ)
    25. 25. Addressing - ISP • Need to reserve address space for its network. • Need to allocate address blocks to its customers. • Need to take “growth” into consideration • Upstream link address is allocated by upstream provider
    26. 26. BGP Basics • Terminology • Protocol Basics • Messages • General Operation • Peering relationships (EBGP/IBGP) • Originating routes
    27. 27. Terminology • Neighbor – Configured BGP peer • NLRI/Prefix – NLRI - network layer reachability information – Reachability information for a IP address & mask • Router-ID – Highest IP address configured on the router • Route/Path – NLRI advertised by a neighbor
    28. 28. Protocol Basics • Routing protocol used between ASes –if you aren’t connected to multiple ASes, you don’t need BGP :) • Runs over TCP • Path vector protocol AS 100 AS 101 AS 102 EE BB DD AA CC Peering
    29. 29. BGP Basics ... • Each AS originates a set of NLRI • NLRI is exchanged between BGP peers • Can have multiple paths for a given prefix • Picks the best path and installs in the IP forwarding table • Policies applied (through attributes) influences BGP path selection
    30. 30. AS 100 AS 101 AS 102 AA CC BGP speakers are called peers BGP Peers eBGP TCP/IP Peer Connection Peers in different AS’s are called External Peers Note: eBGP Peers normally should be directly connected. EE BB DD 220.220.8.0/24 220.220.16.0/24 220.220.32.0/24
    31. 31. AS 100 AS 101 AA CC BGP speakers are called peers BGP Peers iBGP TCP/IP Peer Connection Peers in the same AS are called Internal Peers AS 102 EE BB DD Note: iBGP Peers don’t have to be directly connected. 220.220.8.0/24 220.220.16.0/24 220.220.32.0/24
    32. 32. AS 100 AS 101 AA CC BGP Peers AS 102 DD 220.220.8.0/24 220.220.16.0/24 220.220.32.0/24 EE BB BGP Peers exchange Update messages containing Network Layer Reachability Information (NLRI) BGP Update Messages
    33. 33. Configuring BGP Peers interface Serial 0 ip address 222.222.10.2 255.255.255.252 router bgp 100 network 220.220.8.0 mask 255.255.255.0 neighbor 222.222.10.1 remote-as 101neighbor 222.222.10.1 remote-as 101 interface Serial 0 ip address 222.222.10.1 255.255.255.252 router bgp 101 network 220.220.16.0 mask 255.255.255.0 neighbor 222.222.10.2 remote-as 100neighbor 222.222.10.2 remote-as 100 eBGP TCP Connection • BGP Peering sessions are established using the BGP “neighbor” configuration command 222.222.10.0/30 BB CC DDAA AS 100 AS 101 .2220.220.8.0/24 220.220.16.0/24.2 .1 .2 .1.1 – External (eBGP) is configured when AS numbers are different
    34. 34. – Internal (iBGP) is configured when AS numbers are same AS 100 AS 101 Configuring BGP Peers 222.222.10.0/30 .2 interface Serial 1 ip address 220.220.16.2 255.255.255.252 router bgp 101 network 220.220.16.0 mask 255.255.255.0 neighbor 220.220.16.1 remote-as 101neighbor 220.220.16.1 remote-as 101 BB interface Serial 1 ip address 222.220.16.1 255.255.255.252 router bgp 101 network 220.220.16.0 mask 255.255.255.0 neighbor 220.220.16.2 remote-as 101neighbor 220.220.16.2 remote-as 101 CC iBGP TCP Connection • BGP Peering sessions are established using the BGP “neighbor” configuration command DD220.220.8.0/24 220.220.16.0/24AA .2 .1 .2 .1.1 – External (eBGP) is configured when AS numbers are different
    35. 35. Configuring BGP Peers • Each iBGP speaker must peer with every other iBGP speaker in the AS iBGP TCP/IP Peer Connection AS 100 AA BB CC
    36. 36. Configuring BGP Peers • Loopback interface are normally used as peer connection end-points AS 100 215.10.7.1 215.10.7.2 215.10.7.3 AA BB CC iBGP TCP/IP Peer Connection
    37. 37. iBGP TCP/IP Peer Connection Configuring BGP Peers AS 100 AA 215.10.7.1 215.10.7.2 215.10.7.3 CC BB interface loopback 0 ip address 215.10.7.1 255.255.255.255 router bgp 100 network 220.220.1.0 neighbor 215.10.7.2 remote-as 100 neighbor 215.10.7.2 update-source loopback0neighbor 215.10.7.2 update-source loopback0 neighbor 215.10.7.3 remote-as 100 neighbor 215.10.7.3 update-source loopback0neighbor 215.10.7.3 update-source loopback0 AA
    38. 38. Configuring BGP Peers AS 100 AA 215.10.7.1 215.10.7.2 215.10.7.3 CC AA interface loopback 0 ip address 215.10.7.2 255.255.255.255 router bgp 100 network 220.220.5.0 neighbor 215.10.7.1 remote-as 100 neighbor 215.10.7.1 update-source loopback0neighbor 215.10.7.1 update-source loopback0 neighbor 215.10.7.3 remote-as 100 neighbor 215.10.7.3 update-source loopback0neighbor 215.10.7.3 update-source loopback0 BB iBGP TCP/IP Peer Connection
    39. 39. Configuring BGP Peers AS 100 AA 215.10.7.1 215.10.7.2 215.10.7.3 AA BB interface loopback 0 ip address 215.10.7.3 255.255.255.255 router bgp 100 network 220.220.1.0 neighbor 215.10.7.1 remote-as 100 neighbor 215.10.7.1 update-source loopback0neighbor 215.10.7.1 update-source loopback0 neighbor 215.10.7.2 remote-as 100 neighbor 215.10.7.2 update-source loopback0neighbor 215.10.7.2 update-source loopback0 CC iBGP TCP/IP Peer Connection
    40. 40. BGP Updates — NLRI • Network Layer Reachability Information • Used to advertise feasible routes • Composed of: – Network Prefix – Mask Length
    41. 41. BGP Updates — Attributes • Used to convey information associated with NLRI – AS path – Next hop – Local preference – Multi-Exit Discriminator (MED) – Community – Origin – Aggregator
    42. 42. • Sequence of ASes a route has traversed • Loop detection • Apply policy AS 100 AS 300 AS 200 AS 500 AS 400 170.10.0.0/16 180.10.0.0/16 150.10.0.0/16 Network Path 180.10.0.0/16 300 200 100 170.10.0.0/16 300 200 150.10.0.0/16 300 400 Network Path 180.10.0.0/16 300 200 100 170.10.0.0/16 300 200 AS-Path Attribute
    43. 43. 160.10.0.0/16 150.10.0.0/16 192.10.1.0/30 .2 AS 100 AS 200 Network Next-Hop Path 160.10.0.0/16 192.20.2.1 100 CC Next Hop Attribute .1 BGP Update Messages BB AA .1 .2 192.20.2.0/30 AS 300 EE DD • Next hop to reach a network • Usually a local network is the next hop in eBGP session 140.10.0.0/16
    44. 44. • Next hop to reach a network • Usually a local network is the next hop in eBGP session 160.10.0.0/16 150.10.0.0/16 192.10.1.0/30 .2 AS 100 AS 200 CC Next Hop Attribute .1 BB AA .1 .2 192.20.2.0/30 BGP Update Messages EE DD • Next Hop updated between eBGP Peers AS 300 140.10.0.0/16 Network Next-Hop Path 150.10.0.0/16 192.10.1.1 200 160.10.0.0/16 192.10.1.1192.10.1.1 200 100
    45. 45. • Next hop not changed between iBGP peers 160.10.0.0/16 150.10.0.0/16 192.10.1.0/30 .2 AS 100 AS 200 Network Next-Hop Path 150.10.0.0/16 192.10.1.1 200 160.10.0.0/16 192.10.1.1192.10.1.1 200 100 CC Next Hop Attribute .1 BB AA .1 .2 192.20.2.0/30 BGP Update Messages DD EE AS 300 140.10.0.0/16
    46. 46. Next Hop Attribute (more) • IGP should carry route to next hops • Recursive route look-up • Unlinks BGP from actual physical topology • Allows IGP to make intelligent forwarding decision
    47. 47. BGP Updates — Withdrawn Routes • Used to “withdraw” network reachability • Each Withdrawn Route is composed of: – Network Prefix – Mask Length
    48. 48. BGP Updates — Withdrawn Routes AS 321 AS 123 192.168.10.0/24 192.192.25.0/24 .1 .2 x Connectivity lost BGP Update Message Withdraw Routes 192.192.25.0/24 Withdraw Routes 192.192.25.0/24 Network Next-Hop Path 150.10.0.0/16 192.168.10.2 321 200 192.192.25.0/24 192.168.10.2 321
    49. 49. BGP Routing Information Base BGP RIB D 10.1.2.0/24 D 160.10.1.0/24 D 160.10.3.0/24 R 153.22.0.0/16 S 192.1.1.0/24 Network Next-Hop Path router bgp 100 network 160.10.0.0 255.255.0.0 no auto-summary Route Table *>i160.10.1.0/24 192.20.2.2 i *>i160.10.3.0/24 192.20.2.2 i BGP ‘network’ commands are normally used to populate the BGP RIB with routes from the Route Table
    50. 50. BGP Routing Information Base BGP RIB router bgp 100 network 160.10.0.0 255.255.0.0 aggregate-address 160.10.0.0 255.255.0.0 summary-only no auto-summary Route Table Network Next-Hop Path D 10.1.2.0/24 D 160.10.1.0/24 D 160.10.3.0/24 R 153.22.0.0/16 S 192.1.1.0/24 *> 160.10.0.0/16 0.0.0.0 i*> 160.10.0.0/16 0.0.0.0 i * i 192.20.2.2 i* i 192.20.2.2 i s> 160.10.1.0/24 192.20.2.2 i s> 160.10.3.0/24 192.20.2.2 i BGP ‘aggregate-address’ commands may be used to install summary routes in the BGP RIB
    51. 51. BGP ‘redistribute’ commands can also be used to populate the BGP RIB with routes from the Route Table BGP Routing Information Base BGP RIB Network Next-Hop Path router bgp 100 network 160.10.0.0 255.255.0.0 redistribute static route-map foo no auto-summary access-list 1 permit 192.1.0.0 0.0.255.255 route-map foo permit 10 match ip address 1 Route Table D 10.1.2.0/24 D 160.10.1.0/24 D 160.10.3.0/24 R 153.22.0.0/16 S 192.1.1.0/24 *> 160.10.0.0/16 0.0.0.0 i * i 192.20.2.2 i s> 160.10.1.0/24 192.20.2.2 i s> 160.10.3.0/24 192.20.2.2 i *> 192.1.1.0/24 192.20.2.2 ?*> 192.1.1.0/24 192.20.2.2 ?
    52. 52. BGP Routing Information Base BGP RIB IN Process Update Network Next-Hop Path 173.21.0.0/16 192.20.2.1 100 * 173.21.0.0/16 192.20.2.1 100 • BGP “in” process • receives path information from peers • results of BGP path selection placed in the BGP table • “best path” flagged (denoted by “>”) Update Network Next-Hop Path *>i160.10.1.0/24 192.20.2.2 i *>i160.10.3.0/24 192.20.2.2 i OUT Process >
    53. 53. BGP Routing Information Base OUT Process Network Next-Hop Path 160.10.1.0/24 192.20.2.2 200 160.10.3.0/24 192.20.2.2 200 173.21.0.0/16 192.20.2.2 200 100192.20.2.1192.20.2.1 BGP RIB > 173.21.0.0/16 192.20.2.1 100 Network Next-Hop Path *>i160.10.1.0/24 192.20.2.2 i *>i160.10.3.0/24 192.20.2.2 i * IN Process Update Update • BGP “out” process • builds update using info from RIB • may modify update based on config • Sends update to peers Next-Hop changed
    54. 54. BGP Routing Information Base BGP RIB D 10.1.2.0/24 D 160.10.1.0/24 D 160.10.3.0/24 R 153.22.0.0/16 S 192.1.1.0/24 Network Next-Hop Path *>i160.10.1.0/24 192.20.2.2 i *>i160.10.3.0/24 192.20.2.2 i *> 173.21.0.0/16 192.20.2.1 100 • Best paths installed in routing table if: B 173.21.0.0/16 Route Table • prefix and prefix length are unique • lowest “protocol distance”
    55. 55. The ‘Bible’ & other resources • Route-views.oregon-ix.net • Internet Routing Architectures – Bassam Halabi – pg. 168 BGP Decision Process Summary
    56. 56. Types of BGP Messages • OPEN – To negotiate and establish peering • UPDATE – To exchange routing information • KEEPALIVE – To maintain peering session • NOTIFICATION – To report errors (results in session reset)
    57. 57. Internal BGP Peering (IBGP) • BGP peer within the same AS • Not required to be directly connected • Maintain full IBGP mesh or use Route Reflection AS 100 AA EE BB DD
    58. 58. External BGP Peering (EBGP) AS 100 AS 101 CC BB AA • Between BGP speakers in different AS • Directly connected or peering address is reachable
    59. 59. An Example… Learns about 35.0.0.0/8 from F & D AS3561 B E C D F A AS200 AS101 AS21 AS675 35.0.0.0/8
    60. 60. Basic BGP commands Configuration commands router bgp <AS-number> neighbor <ip address> remote-as <as-number> Show commands show ip bgp summary show ip bgp neighbors
    61. 61. Originating routes... • Using network command or redistribution network <ipaddress> redistribute <protocol name> • Requires the route to be present in the routing table
    62. 62. Originating routes/Inserting prefixes into BGP • network command • network 198.10.4.0 mask 255.255.254.0 • ip route 198.10.0.0 255.255.254.0 serial 0 • matching route must exist in the routing table before network is announced! • Origin: IGP
    63. 63. Update message • Withdrawn routes • Path Attributes • Advertised routes
    64. 64. Stable IBGP peering • Unlinks IBGP peering from physical topology. • Carry loopback address in IGP router ospf <ID> passive-interface loopback0 • Unlink peering from physical topology router bgp <AS1> neighbor <x.x.x.x> remote-as <AS1> neighbor <x.x.x.x> update-source loopback0
    65. 65. BGP4 continued...
    66. 66. BGP Path Attributes: Why ? • Encoded as Type, Length & Value (TLV) • Transitive/Non-Transitive attributes • Some are mandatory • Used in path selection • To apply policy for steering traffic
    67. 67. BGP Path Attributes... • Origin • AS-path • Next-hop • Multi-Exit Discriminator (MED) • Local preference • BGP Community • Others...
    68. 68. AS-PATH • Updated by the sending router with its AS number • Contains the list of AS numbers the update traverses. • Used to detect routing loops – Each time the router receives an update, if it finds its AS number, it discards the update
    69. 69. • Sequence of ASes a route has traversed • Loop detection AS-Path AS 100 AS 300 AS 200 AS 500 AS 400 170.10.0.0/16 180.10.0.0/16 150.10.0.0/16 180.10.0.0/16 300 200 100 170.10.0.0/16 300 200 150.10.0.0/16 300 400 180.10.0.0/16 dropped
    70. 70. Next-Hop • Next hop router to reach a network • Advertising router/Third party in EBGP • Unmodified in IBGP 160.10.0.0/16 150.10.0.0/16 150.10.1.1 150.10.1.2 AS 100 AS 300 AS 200 150.10.0.0/16 150.10.1.1 160.10.0.0/16 150.10.1.1 AA BB 20Cisco Systems Confidential0799_04F7_c2
    71. 71. Third Party Next Hop 192.68.1.0/24 150.1.1.3150.1.1.3 150.1.1.1 150.1.1.2 192.68.1.0/24 150.1.1.3 AS 201 AS 200 CC AA BB • More efficient, but bad idea! peering
    72. 72. Next Hop... • IGP should carry route to next hops • Recursive route look-up • Unlinks BGP from actual physical topology • Allows IGP to make intelligent forwarding decision
    73. 73. Local Preference • Not for EBGP, mandatory for IBGP • Default value is 100 on Ciscos • Local to an AS • Used to prefer one exit over another • Path with highest local preference wins
    74. 74. Local Preference AS 400 AS 200 160.10.0.0/16 AS 100 AS 300 160.10.0.0/16 500 > 160.10.0.0/16 800 500 800 EE BB CC AA DD
    75. 75. Multi-Exit Discriminator • Non-transitive • Represented as a numeric value (0-0xffffffff) • Used to convey the relative preference of entry points • Comparable if paths are from the same AS • Path with lower MED wins • IGP metric can be conveyed as MED
    76. 76. Multi-Exit Discriminator (MED) AS 201 AS 200 192.68.1.0/24 CC AA BB 192.68.1.0/24 1000192.68.1.0/24 2000 preferred
    77. 77. Origin • Conveys the origin of the prefix • Three values: – IGP - Generated using “network” statement • ex: network 35.0.0.0 – EGP - Redistributed from EGP – Incomplete - Redistribute IGP • ex: redistribute ospf • IGP < EGP < INCOMPLETE
    78. 78. Communities • Transitive, Non-mandatory • Represented as a numeric value (0-0xffffffff) • Used to group destinations • Each destination could be member of multiple communities • Flexibility to scope a set of prefixes within or across AS for applying policy
    79. 79. Customer AS 201 Service Provider AS 200 192.68.1.0/24 CC AA BB Community:201:110 Community:201:120 DD Community Local Preference 201:110 110 201:120 120 Community...
    80. 80. Synchronization • C not running BGP (non-pervasive BGP) • A won’t advertise 35/8 to D until the IGP is in sync • Turn synchronization off! – Run pervasive BGP router bgp 1880 no sync 1880 209 690 B A C 35/8 D OSPF
    81. 81. BGP Route Selection (bestpath) Only one path as the bestpath ! • Route has to be synchronized Prefix in forwarding table • Next-hop has to be accessible Next-hop in forwarding table • Largest weight Local to the router • Largest local preference Spread within AS • Locally sourced Via redistribute or network statement
    82. 82. BGP Route Selection ... • Shortest AS-path length number of ASes in the AS-path attribute • Lowest origin IGP < EGP < INCOMPLETE • Lowest MED between paths from same AS • External over internal closest exit from a router • Closest next-hop Lower IGP metric, closer exit from as AS • Lowest router-id • Lowest IP address of neighbor
    83. 83. BGP Route Selection... AS 400 AS 200 AS 100 AS 300 BBAA DD AS 400’s Policy to reach AS100 AS 200 preferred path AS 300 backup Increase AS path attribute length by at least 1
    84. 84. Stub AS • Typically no need for BGP • Point default towards the ISP • ISP advertises the stub network to Internet • Policy confined within ISP policy
    85. 85. Stub AS AS 100 AS 101 BB AA Provider Customer
    86. 86. Multi-homed AS • Only border routers speak BGP • IBGP only between border routers • Exterior routes must be redistributed in a controlled fashion into IGP or use defaults
    87. 87. Multi-homed AS AS 100 AS 200 AS 300 DD CCBB AA provider provider customer
    88. 88. Service Provider Network • IBGP used to carry exterior routes • IGP keeps track of topology • Full IBGP mesh is required
    89. 89. Common Service Provider Network AS 100 AS 200 AS 400 AS 300 FF EE DD GG HH CCBB AA provider
    90. 90. Routing Policy • Why? – To steer traffic through preferred paths – Inbound/Outbound prefix filtering – To enforce Customer-ISP agreements • How ? – AS based route filtering - filter list – Prefix based route filtering - distribute list – BGP attribute modification - route maps
    91. 91. Distribute list - using IP access lists access-list 1 deny 10.0.0.0 access-list 1 permit any access-list 2 permit 20.0.0.0 … more access-lists as prefixes are added ... router bgp 100 neighbor 171.69.233.33 remote-as 33 neighbor 171.69.233.33 distribute-list 1 in neighbor 171.69.233.33 distribute-list 2 out
    92. 92. Filter list rules Regular Expressions • RE is a pattern to match against an input string • Used to match against AS-path attribute • ex: ^3561.*100.*1$ • Flexible enough to generate complex filter list rules
    93. 93. Filter list - using as-path access list ip as-path access-list 1 permit 3561 ip as-path access-list 2 deny 35 ip as-path access-list 2 permit .* router bgp 100 neighbor 171.69.233.33 remote-as 33 neighbor 171.69.233.33 filter-list 1 in neighbor 171.69.233.33 filter-list 2 out
    94. 94. Route Maps router bgp 300 neighbor 2.2.2.2 remote-as 100 neighbor 2.2.2.2 route-map SETCOMMUNITY out ! route-map SETCOMMUNITY permit 10 match ip address 1 match community 1 set community 300:100 ! access-list 1 permit 35.0.0.0 ip community-list 1 permit 100:200
    95. 95. Route-map match & set clauses Match Clauses Set Clauses• AS-path • Community • IP address • AS-path prepend • Community • Local-Preference • MED • Origin • Weight • Others...
    96. 96. H H eth H H eth H H eth H H eth C31 C22C21 C32 ISP3 ISP2 Inbound route-map to set community Route-map Configuration Example neighbor <x.x.x.x> route-map AS100_IN in ! route-map AS100_IN permit 10 set community 100:200 neighbor <y.y.y.y> route-map AS200_IN in ! route-map AS200_IN permit 10 match community 1 set local-preference 200 ! ip community-list 1 permit 100:200
    97. 97. Load Sharing & Redundancy using BGP
    98. 98. Load-sharing - single path AS100 AS200 Router A: interface loopback 0 ip address 20.200.0.1 255.255.255.255 ! router bgp 100 neighbor 10.200.0.2 remote-as 200 neighbor 10.200.0.2 update-source loopback0 neighbor 10.200.0.2 ebgp-multi-hop 2 ! ip route 10.200.0.2 255.255.255.255 <DMZ-link1, link2> A Loopback 0 10.200.0.2 Loopback 0 20.200.0.1
    99. 99. 100 200 A Note:A still only advertises one “best” path to ibgp peers Router A: router bgp 100 neighbor 10.200.0.1 remote-as 200 neighbor 10.300.0.1 remote-as 200 maximum-paths 2 Load Sharing - Multiple paths from the same AS
    100. 100. Redundancy - Multi-homing •Reliable connection to Internet •3 common cases of multi-homing: - default from all providers - customer + default routes from all - full routes from all
    101. 101. Default from all providers • Low memory/CPU solution • Provider sends BGP default – provider is selected based on IGP metric • Inbound traffic decided by providers’ policy – Can influence using outbound policy, example: AS-path prepend
    102. 102. Default from all providers AS 400 Provider AS 200 Provider AS 300 EE BB CC AA DD
    103. 103. Customer + default from all providers • Medium memory and CPU solution • Granular routing for customer routes and default for the rest • Inbound traffic decided by providers’ policy – Can influence using outbound policy
    104. 104. Customer routes from all providers AS 400 Provider AS 200 Customer AS 100 160.10.0.0/16 Provider AS 300 EE BB CC AA DD C chooses shortest AS path
    105. 105. Full routes from all providers • More memory/CPU • Full granular routing • Usually transit ASes take full routes • Usually pervasive BGP
    106. 106. Full routes from all providers AS 400 AS 200 AS 100 AS 300 EE BB CC AA DD C chooses shortest AS path AS 500
    107. 107. Best Practices IGP in Backbone • IGP connects your backbone together, not your client’s routes • IGP must converge quickly • IGP should carry netmask information - OSPF, IS-IS, EIGRP
    108. 108. Best Practices... Connecting to a customer • Static routes – You control directly – No route flaps • Shared routing protocol or leaking – You must filter your customers info – Route flaps • BGP for multi-homed customers
    109. 109. Best Practices... Connecting to other ISPs • Use BGP4 • Advertise only what you serve • Take back as little as you can • Take the shortest exit
    110. 110. Best Practices... The Internet Exchange • Long distance connectivity is expensive • Connect to several providers at a single point
    111. 111. Q & A

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