A Day in the Life of an Address. Bill Fenner AT&T Labs - Research IETF Routing Area Director

Transcription

1 A Day in the Life of an Address Bill Fenner AT&T Labs - Research fenner@research.att.com IETF Routing Area Director 1

2 Overview Addressing Routing Policy Data 2

3 Overview Addressing Routing Policy Data 3

4 Addressing IANA assigns big blocks to regional registries Regional/National/Local registries assign blocks to ISPs (or customers but don t guarantee routability) ISPs assign blocks to customers IANA RIR RIR ISP ISP ISP customer customer customer customer customer 4 This is the post-cidr world There may be several levels of *IR and several levels of *SP Although a customer can get space directly from an *IR, they must then convince the *SP to route it.

5 Aggregation This address assignment policy is designed to facilitate aggregation ISPs just advertise their large blocks in the routing table Scales by ISP (or, in the extreme, geographic location), not by customer Provider-independent addresses are not aggregable. 5 These benefits are partly theoretical - an ISP in Australia still sees many diverse routes for the ARIN aggregates (Note: this is usually not protocol-level aggregation)

6 Routability Customer gets address from ISP A; ISP A will guarantee to route it. Customer gets address from RIR; RIR does not guarantee that anyone will route it. Customer can likely find someone to pay to route anything. 6 e.g., ISP B routes space from ISP A (multihoming); ISP A routes space from RIR (for multihoming, big customer, etc.)

7 Except... Addresses assigned before this policy went into place (e.g., 13/8, 17/8, 18/8,...) more importantly, 192.x.x, class Bs - thousands of /16s and /24s Multihoming / Hole Punching 7 Multihoming: advertise specific through each provider; primary provider advertises both aggregate and specific Multihomed customers can get address from RIR or from one of the ISPs

8 Changing Service Provider Pay ISP A to be allowed to continue to use address space (for a while) Multihome to ISP B during transition Turn off ISP A after all users / services transition 8 The biggest downside to this allocation strategy is that it adds overhead to changing providers. Alternative: get provider-independent space; solve routability problem

9 Special Purpose Addresses 127/8 - localhost 10/8, /12, /16 - private use /16 - link local /24 - documentation /24 - f-root anycast address /24-6to4 anycast address 9 These are samples; there are more anycast is interesting: advertised from multiple places, reach the closest; has to be a big enough prefix to be routable f-root anycast was not explicitly assigned as anycast - just a routable block (sub-note: how to attest 6to4?)

10 Overview Addressing Routing Policy Data 10

11 Routing AS A advertises to AS B what prefixes are reachable through AS A. BGP carries a list of ASes that the advertisement has crossed for loop prevention. Set of rules for route selection 11 Path Vector Rules: - LOCAL_PREF, preference from preconfigured policy information - Discard my AS / AS Path Length / Origin - MED from same neighbor AS

12 Aggregation Combine several customer routes into one provider route Generally implemented by dropping the customer routes and advertising a static provider route 12

13 Overview Addressing Routing Policy Data 13

14 Policy Anything I can do to the route using BGP How does BGP select routes? I ll tune that. Used to implement contracts, business preferences, some traffic engineering Purely local to an AS LOCAL_PREF, preference from preconfigured policy information Discard my AS / AS Path Length / Origin MED from same neighbor AS Providers traditionally reluctant to be limited in what they do 14

15 Publishing Policy Internet Routing Registry / Routing Policy Specification Language Not expressive enough Incomplete participation Out of date data from those who do participate 15

16 Implementing Policy Inbound Route length filters, e.g., don t accept anything longer than a /19 in CIDRallocated space Policy based filters, e.g., don t accept any routes that came through AS X from AS B. Inbound policy 16

17 Implementing Policy Outbound Communities AS-path editing 17 Outbound policy / (communities delegates expression to the peer) Basically, anything that you can do to a route as it passes through your AS is called expressing policy. Extreme resistance to enumerating these things for fear of leaving something out. Barrier to describing policy and to designing a new routing protocol.

18 Remote Policy With agreement, Communities, MED, etc. cause remote enforcement of local policy Without agreement, or more than one AS away (in general), it s only possible to influence, not enforce, policy. Local policy trumps all others. The further away you are, the less influence you have over the policy applied to a route. 18

19 Global Policy? 19 The policy of the system is the composition of the policy of every AS on the path... -> instability, wedgies, etc.

20 Overview Addressing Routing Policy Data 20

21 Growth Allocated Addresses Routed Addresses AS Paths Data from Geoff Huston s bgp.potaroo.net 21

22 Allocated Addresses 17% 8% 6% 32% 29% IETF Reserved Multicast IANA Pool RIR Pool Advertised Assigned but not Advertised 8% 22 Green is what s in the BGP tables Orange could be there tomorrow (and much probably corresponds to Bellovin s cleanup) Red and Purple are available

23 IANA Allocations 10s of M addresses just passed 1.4B addresses 23

24 IANA Projection exponential fit for data since 1998 September 2018 = IANA pool exhausted 24

25 Routed Prefixes 25

26 Advertised Address Space 26 main point: growth continues, k prefixes covering 1.4B addresses

27 AS-Path Length 27 main point: network diameter is not necessarily growing - network is becoming meshier

28 Questions? 28

29 29

30 Policy requires Agreement AS3 would like AS1 to use Path 1 rather than Path 2 to forward traffic to /24 Controlling advertisements - breaks backup link MED - AS1 may not pay attention AS Path prepend - doesn t always work RFC1998 Communities AS1 s Local Preference trumps AS3 s policy, no matter what it is! AS /24 AS 4 AS /24 AS 2 30

31 More Policy Examples AS3 would like to send traffic to /24 Local Preference Controlling advertised routing information AS1 would not like to transit AS3, ever Controlling advertised routing information AS3 would not like to be transit NO_EXPORT, other community based systems AS /24 AS 4 AS /24 AS 2 31