CSCI-1680 Network Layer: Inter-domain Routing

CSCI-1680Network Layer:Inter-domain Routing – Policy and Security Theophilus Benson Based partly on lecture notes by Jennifer Rexford, Rob Sherwood, David Mazières, Phil Levis, John Jannotti

Today • BGP Recap • BGP + IGP • iBGP, Scaling iBGP • Using BGP to take down the internet • BGP Security • Hijacking prefixes  making money • Solution: S-BGP • BPG Issues • ISP issues versus end-user issues • Solution: Overlays, CDNs

Recall BGP Tier 1 ISP Tier 1 ISP Default free, Has information on every prefix $$ $$ $$ Default: provider Tier 2 $$ $$ Tier 2 Regional Tier 2 $$ Tier 3 (local) Tier 3 (local)

Recall BGP Tier 1 ISP Tier 1 ISP “Best Route” is not The shortest route Default free, Has information on every prefix $$ $$ $$ Default: provider Tier 2 $$ $$ Tier 2 Regional Tier 2 $$ Tier 3 (local) Tier 3 (local)

Recall BGP: Realistic Example Tier 1 ISP Tier 2 Tier 2 $$ $$ Tier 2 $10 $$ Tier 2 $$ Tier 2 Regional $20 $$ Tier 3 (local) Tier 3 (local)

Zooming ISPD ISPC D is provider for B Peering ISPB Regional ISPA 10.10/16 ISPA 10.10/16

Zooming-in! ISPZ ISPD Who should ISPB send routes to? Who should ISPB use to get to Alice? Everyone? No one? Friends? Enemies? ISPC D is provider for B Peering Import Policies: (Who to use for transit?) Export Policies: (Who to send routes to?) ISPB Regional 10.10/16 ISPA • Provider  Customer • All routes so as to provide transit service • Customer  Provider • Only customer routes • Peer  Peer • Only customer routes ISPA 10.10/16

Zooming-in! ISPZ ISPD 10.10/16 ISPB ISPA Who should ISPB send routes to? Who should ISPB use to get to Alice? Everyone? No one? Friends? Enemies? ISPC 10.10/16 ISPB ISPA D is provider for B Peering Import Policies: (Who to use for transit?) Export Policies: (Who to send routes to?) ISPB Regional • Provider  Customer • All routes so as to provide transit service • Customer  Provider • Only customer routes • Peer  Peer • Only customer routes ISPA 10.10/16

Zooming-in! ISPZ ISPD 10.10/16 ISPZ Who should ISPB send routes to? Who should ISPB use to get to Alice? Everyone? No one? Friends? Enemies? ISPC D is provider for B Peering Import Policies: (Who to use for transit?) Export Policies: (Who to send routes to?) ISPB Regional • Provider  Customer • All routes so as to provide transit service • Customer  Provider • Only customer routes • Peer  Peer • Only customer routes customer > peer > provider • Customer route: charge $$  • Peer route: free • Provider route: pay $$  ISPA 10.10/16

Zooming-in! ISPZ ISPD Who should ISPB send routes to? Who should ISPB use to get to Alice? Everyone? No one? Friends? Enemies? 10.10/16 ISPD ISPZ ISPC 10.10/16 ISPC ISPZ D is provider for B Peering Import Policies: (Who to use for transit?) Export Policies: (Who to send routes to?) ISPB Regional • Provider  Customer • All routes so as to provide transit service • Customer  Provider • Only customer routes • Peer  Peer • Only customer routes customer > peer > provider • Customer route: charge $$  • Peer route: free • Provider route: pay $$  ISPA 10.10/16

Zooming-in! ISPZ ISPD Who should ISPB send routes to? Who should ISPB use to get to Alice? Everyone? No one? Friends? Enemies? ISPC D is provider for B Peering Import Policies: (Who to use for transit?) Export Policies: (Who to send routes to?) ISPB Regional • Provider  Customer • All routes so as to provide transit service • Customer  Provider • Only customer routes • Peer  Peer • Only customer routes customer > peer > provider • Customer route: charge $$  • Peer route: free • Provider route: pay $$  ISPB ISPC ISPZ 10.10/16 ISPA 10.10/16

Valley Free Routing Z is provider for D ISPZ ISPD Z is provider for C ISPC D  B  C  Z -1 +1 +1 D is provider for B C is provider for B D  Z +1 ISPB Regional B is provider for A A  B  C  Z +1 +1 +1 ISPA 10.10/16

How to get Peering Z is provider for D ISPZ ISPD Z is provider for C D  Z  C +1 -1 ISPC D is provider for B • All users in network D want to go to something in network C: • Network C could be Google • Network C could be Netflix • ISP D can try and Peer with C C is provider for B ISPB Regional B is provider for A ISPA 10.10/16

How to get Peering Z is provider for D ISPZ ISPD Z is provider for C D  Z  C Valley free: +1 -1 ISPC D is provider for B • All users in network D want to go to something in network C: • Network C could be Google • Network C could be Netflix • ISP D can try and Peer with C • Path: D  C • Valley free: 0 • Why is this good for D? or C? • Neither has to pay Z anymore C is provider for B ISPB Regional B is provider for A ISPA 10.10/16

BGP State • BGP speaker conceptually maintains 3 sets of state • Adj-RIB-In • “Adjacent Routing Information Base, Incoming” • Unprocessed routes learned from other BGP speakers • Loc-RIB • Contains routes from Adj-RIB-In selected by policy • First hop of route must be reachable by IGP or static route • Adj-RIB-Out • Subset of Loc-RIB to be advertised to peer speakers

M How does router-X learns to the route to 10.20/8 or 10.20/16?? If don’t have routes Send to M ISPD • Stub Ass (e.g. ISP A, D) • Border router clear choice for default route • Inject into IGP: “any unknown route to border router” • Inject specific prefixes in IGP • E.g., Provider injects routes to customer prefix • For Large networks • Too many prefixes for IGP • Run internal version of BGP, iBGP • All routers learn mappings: Prefix -> Border Router • Use IGP to learn how to get to Border Router Who to send unknown to? Y or W? Y Z X W ISP-B ISPA

Two types of BGP sessions eBGP 128.112.0.0/16 Next Hop = 192.0.2.1 128.112.0.0/16 AS23 iBGP 192.0.2.1 AT&T Sprint AS23 Forwarding Table destination next hop 192.0.2.0/30 10.10.10.10 Forwarding Table + destination next hop BGP (iBGP) 128.112.0.0/16 10.10.10.10 destination next hop 192.0.2.0/30 10.10.10.10 128.112.0.0/16 192.0.2.1

Two types of BGP sessions eBGP session is a BGP session between two routers in different ASes iBGP session is a BGP session between internal routers of an AS. iBGP eBGP AT&T Sprint

Scaling iBGP • Every Router runs iBGP • All-to-All iBGP peering • Doesn’t scale • N*(N-1) connections

Scaling iBGPRoute reflectors • Every Router runs iBGP • Selective peering • Scales • N*K connections

“Shutting off” the Internet • Starting from Jan 27th, 2011, Egypt was disconnected from the Internet • 2769/2903 networks withdrawn from BGP (95%)! Source: RIPEStat - http://stat.ripe.net/egypt/

Egypt Incident Source: BGPMon (http://bgpmon.net/blog/?p=480)

BGP Security Goals • Confidential message exchange between neighbors • Validity of routing information • Origin, Path, Policy • Correspondence to the data path

Origin: IP Address Ownership and Hijacking • IP address block assignment • Regional Internet Registries (ARIN, RIPE, APNIC) • Who can advertise a prefix with BGP? • By the AS who owns the prefix • … or, by its upstream provider(s) in its behalf • However, what’s to stop someone else? • Prefix hijacking: another AS originates the prefix • BGP does not verify that the AS is authorized • Registries of prefix ownership are inaccurate

4 3 5 2 6 7 1 Prefix Hijacking: full or partial control • Consequences for the affected ASes • Blackhole: data traffic is discarded • Snooping: data traffic is inspected, and then redirected • Impersonation: data traffic is sent to bogus destinations 12.34.0.0/16 12.34.0.0/16

Hijacking is Hard to Debug • Real origin AS doesn’t see the problem • Picks its own route • Might not even learn the bogus route • May not cause loss of connectivity • E.g., if the bogus AS snoops and redirects • … may only cause performance degradation • Or, loss of connectivity is isolated • E.g., only for sources in parts of the Internet • Diagnosing prefix hijacking • Analyzing updates from many vantage points • Launching traceroute from many vantage points

4 3 5 2 6 7 1 Sub-Prefix HijackingFull control over sub-prefix • Originating a more-specific prefix • Every AS picks the bogus route for that prefix • Traffic follows the longest matching prefix 12.34.0.0/16 12.34.158.0/24

How to Hijack a Prefix • The hijacking AS has • Router with eBGP session(s) • Configured to originate the prefix • Getting access to the router • Network operator makes configuration mistake • Disgruntled operator launches an attack • Outsider breaks in to the router and reconfigures • Getting other ASes to believe bogus route • Neighbor ASes not filtering the routes • … e.g., by allowing only expected prefixes • But, specifying filters on peering links is hard

Pakistan Youtube incident • Youtube’s has prefix 208.65.152.0/22 • Pakistan’s government order Youtubeblocked • Pakistan Telecom (AS 17557) announces 208.65.153.0/24 in the wrong direction (outwards!) • Longest prefix match caused worldwide outage • http://www.youtube.com/watch?v=IzLPKuAOe50

Cool Bit Coin attack using Prefix-Hijacking

Bit Coin Incident • Bit Coin Primer • You donate resources on your computer to ‘mine’ (create) bit coins • Your computer connects to a server • Servers tells it how to mine • Server rewards you for mining • Transaction fees for using coins • subsidies for new coins • Hacker steal Bit Coins • Hacker Hijacks a prefix • Pretends to be the bit coin-server • Collects bit coins you mine • Doesn’t give miners any rewards

4 3 5 2 6 7 1 12.34.0.0/16 12.34.158.0/24 Bit-coin Miners Legitimate Bit-Coin Server hacker

Avoiding Spam Detection with Prefix Hijacking • People create a whitelist of acceptable addresses for Mail servers • Only accept mail from address in that whitelist • Spammers steal unused IP space to hide • Announce very short prefixes (e.g., /8). Why? • For a short amount of time • Hijack route == announce a route you don’t own • Send lots of spam!! • Stop Hijack == Withdraw Route • Interesting talk: https://www.usenix.org/conference/lisa-07/homeless-vikings-bgp-prefix-hijacking-and-spam-wars

Attacks on BGP Paths • Remove an AS from the path • E.g., 701 3715 88 -> 701 88 • Why? • Attract sources that would normally avoid AS 3715 • Make path through you look more attractive • Make AS 88 look like it is closer to the core • Can fool loop detection! • May be hard to tell whether this is a lie • 88 could indeed connect directly to 701!

Attacks on BGP Paths • Adding ASesto the path • E.g., 701 88 -> 701 3715 88 • Why? • Trigger loop detection in AS 3715 • This would block unwanted traffic from AS 3715! • Make your AS look more connected • Who can tell this is a lie? • AS 3715 could, if it could see the route • AS 88 could, but would it really care?

Attacks on BGP Paths • Adding ASesat the end of the path • E.g., 701 88 into 701 88 3 • Why? • Evade detection for a bogus route (if added AS is legitimate owner of a prefix) • Hard to tell that the path is bogus! 701 3 18.0.0.0/8 88 18.0.0.0/8

Data Plane Attacks (Forwarding Attacks) • Routers/ASes can advertise one route, but not necessarily follow it! • May drop packets • Or a fraction of packets • What if you just slow down some traffic? • Can send packets in a different direction • Impersonation attack • Snooping attack • How to detect? • Congestion or an attack? • Can let ping/traceroute packets go through • End-to-end checks? • Harder to pull off, as you need control of a router

Proposed Solution: S-BGP • Based on a public key infrastructure • Address attestations • Claims the right to originate a prefix • Signed and distributed out of band • Checked through delegation chain from ICANN • Route attestations • Attribute in BGP update message • Signed by each AS as route along path • S-BGP can avoid • Prefix hijacking • Addition, removal, or reordering of intermediate ASes

BGP Issues BGP issues from ISP’s perspective BGP issues user’s perspective Network Outages Large latency Low Bandwidth • Prefix Hijacking • Internet outage • Route table overflow • Internet outage • Convergence issues • Temporary outage

Alice  Eve: 50 milliseconds Alice  Bob: 10 milliseconds Bob  Eve: 20 milliseconds Eve Alice Bob

Alice  Eve: 50 milliseconds Alice  Bob: 10 milliseconds Bob  Eve: 20 milliseconds Why not send traffic through Bob? Eve Alice Bob

Alice  Eve: 50 milliseconds Alice  Bob: 10 milliseconds Bob  Eve: 20 milliseconds • Why not send traffic through Bob? • Internet uses destination based routing .. • For Alice  Eve to go through Bob • Packets must use Bob as the destination Eve Alice Bob

IP tunnels: IP-in-IP Encapsulation 20.0.0.1 Alice-> Eve • Alice/Bob/Eve runs special software that perform • IP Encapsulate/decapsulation Alice-> Eve Bob->Eve Alice-> Eve Bob->Eve Eve Alice Bob Alive->Bob

CSCI-1680 Network Layer: Inter-domain Routing – Policy and Security