Crafting Confederations An overview of the Confederation POP Approach to Network Architecture Dan Golding NetRail, Inc. Miguel Dimayuga Earthlink, Inc.

The Old Way… Conventional Network Routing Architectures…. Full Mesh iBGP or Route Reflectors A fully meshed Network via ATM PVCs.

It’s not adapted to the New Optical Network! POS is here in force, ATM’s value in the core is receding. It is far more fragile, and far less agile than newer methods of Inter-domain Routing. The Old Way was prone to user-error. The E- Commerce Revolution demands a New Way! What’s Wrong With The Old Way?

A Better Way Emphasizes Large Scale, IP Based, Fiber Ring Networks Optimized for Service Provider Needs Utilizes cutting edge routing technologies to provide far greater fault tolerance and usable traffic engineering. Implemented via advanced BGP techniques: Communities and Confederations.

How the Old worked… (Full Mesh iBGP) Every router must be fully meshed with all others. Works well in small systems Grows exponentially Eventually consumes all CPU, memory, and engineering resources. Full iBGP Mesh Exponential growth!

How the Old Way worked… (Route Reflectors) Scaled Well Well suited to fully meshed ATM Networks – Star Topology. but... Not Survivable in a Fiber Ring Network. Peer Isolation with BGP Route Reflection Peers RR Server Peers RR Client

How the Old Way worked… (Filtering) List of IP Prefixes and/or AS numbers set on all border routers to other ISPs. Only the access-list contents would be advertised. Worked well when most customers were single- homed and didn’t run BGP. Changes were VERY manpower intensive. With multi-homed e-commerce shops, no longer feasible.

How the New Way works… (Confederations) Routers peer with neighbors Highly Survivable Very Scalable Easily Configured Aids Troubleshooting Peers Routers Peer with Neighbors BGP Confederations

BGP allows three types of peer relationships: –iBGP (Full iBGP mesh) –eBGP (External Peering or Transit) –Confederation eBGP (its an iBGP with an eBGP look!) Confederation eBGP is like regular eBGP, except –Next Hop, Local Preference and MEDs are preserved –Confederation elements in the AS-PATH are not counted for route selection purposes Confederation Overview

Confederation Overview Confederations allow groups of routers to form “sub- autonomous systems” to eliminate scaling problems with full mesh iBGP All Routers within a sub-AS must be fully meshed (or optionally in a route reflector cluster configuration) Confederations are most advantageous when there are few routers per sub-AS. There is no reason to limit the number of sub-AS’s you have – nothing is gained.

Confederation Overview Most confederation designs start out with only two or three sub-ASes. This offers few advantages over full mesh iBGP in a ring network topology. The more sub-ASes you add, the greater the advantage The final result: One sub-AS per POP The upper limit on this is 1000 sub-AS’s per RFC

The Advantages of a Confederation of POPs The routers within each POP need only peer with each other, utilizing iBGP Neighboring POPs are peered with via POP border routers speaking confederation eBGP Next Hop, Local Pref and MEDs are preserved More survivable than Route Reflectors Far more scalable than full iBGP mesh

How to Make It Work Thoughtful use of sub-AS numbers Local Preference Hierarchy Useful and Descriptive Community Strings Meaningful MEDs Use of various policies – via access lists, community lists, etc – as building blocks Use of Peer Groups whenever implementation allows.

Sub-AS Assignment Sub-AS’s become useful tools for debugging – show ip bgp, show route Suggested assignment is geographical Always remember to keep room for expansion! Put plenty of extra sub-AS’s in your configs – don’t count on adding them later!

Southeast Northeast Northcentral Southcentral Western Canadian Latin/South American European Asian Reserved Geographical Region as sub-AS

Sample Community Assignments

Communities are “tags” or “post-it notes” attached to routes to help identify them. –There can be more than one community attached to a route. Communities are recommended to be set at the ingress point. –Communities need be applied only once –administrative burden and complexity is greatly reduced. When routes egress, filtering can be based on one or more community strings. Sample Communities – Regional, by Peer, Customer, Internal, Peer, Transit Community Strings are the Key

Communities Set at Ingress AS701 AS4355 transit router bgp 4355 network /16 route-map make-green network /24 route-map make-red /16i /24i /8i /8i router bgp 4355 neighbor a.a.a.a remote-as 701 neighbor a.a.a.a route-map make-blue in /8701 i /8701 i

Communities Used to Filter on Egress AS701 AS3703 AS4355 transit customer /16i /24i /8i /8i / i / i / i router bgp 4355 neighbor b.b.b.b remote-as 3703 neighbor b.b.b.b route-map blue-green out /8701 i /8701 i

Customer Routes4006:65150 Private Peering4006:65140 Transit4006:65130 Public Peering4006:65120 Internal Routes (OPN-visible)4006:65110 Internal Routes (Global-visible)4006:65100 Community Categories – Route Type

Other Peoples Networks (OPNs) To expand our national coverage, Mindspring utilized third party networks’ dialup facilities. These networks are what we term as OPNs. Prefixes for Core Services which we want restricted to MindSpring customers and not visible to the rest of the world (e.g. news, radius, smtp) are announced to our OPNs alone. –This has the added advantage of protecting against abuse of our services by non-customers. With communities, we can tag routes for export to OPNs alone.

Field Peering4006:65020 Exchange Point Peer4006:65010 Northeast Region Peering (DC)4006:65030 Southeast Region Peering (Atlanta)4006:65040 Northcentral Region Peering (Chicago)4006:65050 West Peering Region (Palo Alto)4006:65060 Southcentral Region Peering (Dallas)4006:65070 Community Categories – Route Ingress Location

Community Categories – Specials No Export to any external BGP peer No-Export Do Not Advertise to any peer (Well Known) No-Advertise Always Prefer (proposed Well Known) Prefer-Me (65535:65519) Always Avoid (proposed Well Known) Avoid-Me (65535:65504)

Also add a community string for the origin AS If the route comes from UUNet, then add 4006:701 If the route comes from Sprint, then add 4006:1239 Community Categories – Origin AS

router bgp 4355 neighbor b.b.b.b remote-as 4006 neighbor b.b.b.b route-map setlocpref90 in router bgp 4355 neighbor c.c.c.c remote-as 701 neighbor c.c.c.c route-map setlocpref60 in Local Preference AS4006 AS3703 AS4355 peering customer / i / i /24i router bgp 4355 neighbor a.a.a.a remote-as 3703 neighbor a.a.a.a route-map setlocpref100 in / i AS / i transit / i

The higher the Local Preference, the more desirable the route. Customers ALWAYS come first – we never want to send their traffic to a peer, regardless of AS- Path padding Private Peering is always more desirable than Public Peering Transit is less desirable than private peering for economic reasons Local Preference Hierarchy

Always Preferred250 Customer Routes100 Customer Backup Routes90 Private Peering80 Less Preferred Private Peering (congested)70 Paid Transit 60 Less Preferred Paid Transit (congested)50 Public Peering (ATM NAPs)40 Less Preferred Public Peering (FDDI NAPs)30 Never Preferred1 Local Preference Hierarchy

Peer Types Local sub-AS Peer (within a POP) Confederation Peers (other POPs or sub-ASes) Transit Peers (we buy transit from them) Public/Private Peering Customer Peers

Local sub-AS Peers All peers within a POP are members of this group. The update source for these BGP sessions will be the loopback address of the router. Communities must be recognized. Option to use full-mesh or route-reflectors. For Each Local Sub-AS Peer neighbor remote-as neighbor description otherlocalroutername neighbor update-source loopback0 neighbor send-community neighbor version 4

Update-Source Loopback Address The routers will use loopback address as the source of the bgp packets. –Only one session needs to be created even with multiple paths between routers. Peering between loopback addresses increase the stability of the bgp sessions since loopback addresses don’t go down / / / / / /32

All peers that are POP border routers are members of this group. The update source for these BGP sessions will be the facing interface of the router. Inbound Soft Reconfiguration is not necessary. –Outbound soft reconfiguration can be done at the remote end Communities must be recognized. Filtering is done on egress, MEDs are set on ingress. Confederation Peers

Soft Reconfiguration “clear ip bgp” drops the TCP session. Soft reconfiguration is much friendlier. “clear ip bgp soft out” issues withdrawals for all advertised routes, recomputes and then resends the routes (low cpu) “clear ip bgp soft in” reevaluates routes received from its peers stored in memory. (high memory requirements)

Peer-Group neighbor internal peer-group neighbor internal version 4 neighbor internal send-community For Each Peer neighbor remote-as neighbor description remotesitename neighbor route-map -recv- in neighbor route-map -send- out neighbor peer-group internal route-map -recv- permit 10 set metric + route-map -send- permit 10 match community Confederation Peer Configuration

Confederation Peer Routes Don’t Send: No Advertise Send: Customer, Peer, Transit, Internal

Additive MEDs Why –Allows a tiebreaker based on optimum routing –Allows an alternate method to de-prefer routes in case of transit/peering congestion Possible Values – –Mileage –delay in ms –fixed value per hop Supported by - –Cisco IOS –Feature Request in JUNOS, Riverstone, Foundry IronWare

Additive MEDs in Confederations /16120(65000) /160 (originated here) /16700 ( ) /16720 ( ) /16740 ( ) /16760 ( )

The update source for these BGP sessions will be the facing interface address of the router. Soft Reconfiguration should be used. Communities must be recognized. Send out only customer and internal routes. Apply an import ACL to the routes that prevents reception of martian routes, and assigns proper communities and local preference. Allows prepending certain subsets of routes with additional AS numbers. Transit Peers

neighbor send-community neighbor version 4 neighbor next-hop-self neighbor soft-reconfiguration inbound neighbor distribute-list martians in neighbor remote-as neighbor route-map -recv- in neighbor route-map -send- out neighbor description transitprovidername route map -send- deny 10 match community 4 route map -send- permit 20 match community 1 set as-path prepend route-map -recv- permit 10 set local-preference 60 set metric 0 (if you don’t want to listen to others meds) Set community 4006:30 additive Set community 4006:20 additive Set community 4006:500 additive Set community 4006: additive Transit Peer Config

Don’t Send: No Exports, No Advertise Peers or Transit Send: Customers, Internal Transit Peer Config

De-prefer routes for congested outbound –Set Local Pref normally for routes with AS-Path Length=1 or 2 –Set Local Pref Lower for all other routes –Effect: Only most direct routes flow through that connection. Others flow through other transit, if available OPN’s and sending OPN routes –Send special routes – usually for servers and services – only to your own network, and OPNs –Have a special community list or policy specifying the routes. Transit Tricks

The update source for these BGP sessions will be the facing interface address of the router. Soft Reconfiguration should be used. Communities must be recognized. Send out only customer and internal routes. Apply an import ACL to the routes that prevents reception of martian routes, and assigns proper communities and local preference. Option to use local preference to prefer unconditionally all or only some routes coming from a free peer. Private/Public Peers

Peer Configuration neighbor free-peering peer-group neighbor free-peering send-community neighbor free-peering version 4 neighbor free-peering next-hop-self neighbor free-peering-full soft-reconfiguration inbound neighbor free-peering-full distribute-list martians in neighbor free-peering route-map -in in neighbor free-peering route-map cust-routes out route map cust-routes deny 5 match community-list 4 route-map cust-routes permit 10 match community-list 1 route-map -in permit 10 set local-preference 80 set community 4006:30 additive set community 4006:20 additive set community 4006:700 additive set community 4006: additive Per-Peer neighbor remote-as neighbor peer-group free-peering neighbor description Peer Name

Don’t Send: No Exports, No Advertise Peers or Transit Send: Customers, Internal Free Peering Routes

The update source for these BGP sessions will be the facing interface address of the router. Soft Reconfiguration should be used. Communities must be recognized. This includes communities sent from customers. Send out selected routes, based on customer request. Apply an import ACL to the routes that prevents reception of martian routes, and assign proper communities and local preference. The import filter must also accept only specific customer routes. –We recommend using Rtconfig to query RADB and generate the ACLs. Customer Peers

Full Routes –Customer, Peers, Internals, Transit. –AKA “A Full View” Customer Routes –Customer and Internal Routes. –Good for weaker routers (Cisco) –AKA “A Partial View” Default Route –Send only a default route /0, pointed to the router interface –Limited utility What Type of Routes Can We Send?

Special Considerations for Customers Carefully Filter routes – the farther downstream you get, the less clueful (generally) Filtering can be based on AS or Prefix The generally accepted practice is to filter by IP Access List at ingress (use radb tools if possible) Customers do not have to advertise the same routes everywhere – peers do!

Customer Configuration – Full Routes bgp { group { type external; description ; peer-as ; neighbor ; import -in; } policy-options { policy-statement -in { term term1 { from policy ; then { local-preference 100; nexthop self; community + customer; community + field community + ATL; community + ; } policy-statement atl-myco { from { route-filter /24 exact accept; route-filter /16 exact accept; } then reject

bgp { group { type external; description ; peer-as ; neighbor ; import -in; export custroutes; } policy-options { policy-statement -in { term term1 { from policy ; then { local-preference 100; nexthop self; community + customer; community + field; community + ATL; community + ; } Customer Configuration – Partial Routes policy-statement atl-myco { from { route-filter /24 exact accept; route-filter /16 exact accept; } then reject policy-statement custroutes { term term1 { from community [no-export no-advertise]; then reject; } term term2 { from community [internal customer custback]; then accept; }

Cisco – neighbor a.b.c.d default-originate Juniper - A little more complex... bgp { group { type external; description ; peer-as ; neighbor ; import -in; export default-originate; } routing-options { static { route /0 { nexthop ; no-install; } Default Route Only policy-statement default-originate { from route-filter /0; then { nexthop self; accept; }

Question and Answer Confederations General BGP Questions

The New Way gives us… Less complexity More stability More flexibility for traffic management Greater Survivability Lower Engineering and Administrative costs. Increased Uptime A Scalable, Next Generation IP Network

RFC 1771 A Border Gateway Protocol 4 (BGP-4) RFC 1965 Autonomous System Confederations for BGP RFC 1930 Guidelines for creation, selection, and registration of an Autonomous System (AS) RFC 1997 BGP Community Attributes Nussbacher, Rudnev, and Hares, Global BGP Community Values, Internet Draft, 12/99 Halabi, Bassam; Internet Routing Architectures Freedman, Avi, Lecture Notes: January 1999 NANOG Conference Session: “BGP 102” Bibliography

In Tribute to the Memory of... MindSpring Enterprises, Inc. Brandon Ross, Netrail Avi Freedman, Akamai Khalid Raza, Cisco Very Special Thanks to…