1 BGP FORGOTTEN BUT USEFUL FEATURES Piotr Wojciechowski (CCIE #25543)
2 ABOUT ME Senior Network Engineer MSO at VeriFone Inc. Previously Network Solutions Architect at one of top polish IT integrators CCIE #25543 (Routing & Switching) Blogger Administrator of CCIE.PL board The biggest Cisco community in Europe Over 6800 users 3 admin, 7 moderators 58 polish CCIEs as members, 20 of them actively posting About 150 new topics per month About 1000 posts per month English section available!
5 WHY WE SHOULD VERIFY ORIGIN AS? Prefix hijacking any AS can advertise any prefix in BGP Human mistake Malicious How we can hijack prefix? Advertise someone else s prefix Advertise more specific of someone else s prefix
6 WHY WE SHOULD VERIFY ORIGIN AS? Has it happened before? Pakistan Telecom blocks YouTube In February 2008, Pakistan Telecom inadvertently brought down the entire YouTube site worldwide for two hours as it was attempting to restrict local access to the site. When Pakistan Telecom tried to filter access to YouTube, it sent new routing information via BGP to PCCW, an ISP in Hong Kong that propagated the false routing information across the Internet. Source: NetworkWorld: Six worst Internet routing attacks
7 WHY WE SHOULD VERIFY ORIGIN AS? Has it happened before? Northrop Grumman hit by spammers In May 2003, a group of spammers hijacked an unused block of IP address space owned by Northrop Grumman and began sending out massive amounts of unwanted messages. It took two months for the military contractor to reclaim ownership of its IP addresses and get the rogue routing announcements blocked across the Internet. In the meantime, Northrop Grumman's IP addresses ended up on high-profile spam blacklists Source: NetworkWorld: Six worst Internet routing attacks
8 WHY WE SHOULD VERIFY ORIGIN AS? Has it happened before? Biggest-ever BGP threat unveiled In August 2008, two security researchers demonstrated at DEFCON how an attacker could eavesdrop or change a company's unencrypted data by exploiting BGP. The attacker would reroute all of the company's traffic through their own network and then send it to its destination without the owner's knowledge. Source: NetworkWorld: Six worst Internet routing attacks
9 ORIGIN AS VALIDATION The network administrator must set up a Resource Public Key Infrastructure (RPKI) server The RPKI server handles the actual authentication of public key certificates. Image source: Juniper documentation
10 ORIGIN AS VALIDATION Router can handle the actual authentication of public key certificates but it s very resource (CPU) intensive and not preferred way of deployment. Image source: Juniper documentation
11 ORIGIN AS VALIDATION The server is set up so that certain prefixes or prefix ranges are allowed to originate from certain autonomous systems. Router establishes connection to RPKI server and downloads a list of prefixes and permitted origin AS numbers from one or more router/rpki servers using the RPKI-Router protocol (RTR) Image source: Juniper documentation
12 ORIGIN AS VALIDATION Components Image source: Juniper documentation
13 ORIGIN AS VALIDATION Route origin authorization (ROA) ROA is a digitally signed object distributed through the RPKI infrastructure Indicates the address prefix holder s explicit authorization that an AS can rightfully originate a prefix Is not directly used in route validation Cache servers exports ROA as RV records to the routers
14 ORIGIN AS VALIDATION Route Validation (RV) record: It s (prefix, maximum length, origin AS) triple. It matches any route whose prefix matches RV prefix, whose prefix length does not exceed maximum length given by RV record, and whose origin AS equals the origin AS given in the RV record. If maximum length not present then AS is only allowed to advertise exact prefix specified in RV
15 ORIGIN AS VALIDATION Example RV ( /24, /26, AS100) Which of following prefixes are authorized to be announced? / / / /26 Answer: All of them!
16 ORIGIN AS VALIDATION Example RV ( /24, /25, AS100) Which of following prefixes are authorized to be announced? / / / /26 Answer: Last one is not valid!
17 ORIGIN AS VALIDATION When prefix is received from an ebgp peer it is examined against import policy and marked: VALID prefix and AS pair are found in the database INVALID prefix is found but either corresponding AS or prefix length does not match database UNKNOWN prefix is not in database Prefix marked as INVALID is withdrawn from routing table and not advertised to peers. VALID prefix is preferred over UNKNOWN it affects BGP path selection
18 ORIGIN AS VALIDATION Prefix validation marking done only for ebgp updates Validation state is carried across ibgp mesh in an opaque extended community (non-transitive)
19 ORIGIN AS VALIDATION Available on: Cisco IOS 15.2(4)S or later platforms ME3600, ME3800, 7200-NPE- G2, 7201 IOS XE 3.10S or later platforms ASR1000-RP1, ASR1000- RP2, ASR-1001, ASR1002-X, ISR4451-X, CSR100V Juniper JunOS 12.2 or later (cache server required)
20 ORIGIN AS VALIDATION References PLNOG10: Alex Band (RIPE), Resource Certification (RPKI) NANOG49: Pradosh Mohapatra (Cisco Systems), BGP Prefix Origin Validation
21 BGP MULTIPATH
22 BGP MULTIPATH BGP Multipath allows to configure BGP to install multiple paths in the RIB for multipath load sharing. Load balancing is performed by CEF in per-packet basis (not recommended) or per-session basis (source and destination pair) Can be deployed also in MPLS network as well as with Route Reflectors
23 BGP MULTIPATH Deployment with Route Reflectors: When multiple ibgp paths are installed in a routing table, a route reflector will advertise only one path. If router is behind a route reflector, all routers that are connected to multihomed sites will not be advertised unless a different route distinguisher is configured for each VRF.
24 BGP MULTIPATH The BGP best-path algorithm considers the paths as equal-cost paths if the following attributes are identical: Weight Local preference AS_path Origin code Multi-exit discriminator (MED) IGP cost to the BGP next hop
25 BGP MULTIPATH Available on most platforms, this is not a new feature! Router(config)# router bgp Router(config- router)# address- family ipv4 vrf RED Router(config- router- af)# maximum- paths eibgp 6 Router(config- router- af)# end
26 BGP ADDITIONAL PATHS
27 BGP ADDITIONAL PATHS Default BGP behavior BGP routers and Route Reflectors propagate only their best paths over their sessions. Implicit Withdrawal Rule (The advertisement of a prefix replaces the previous announcement of that prefix). This approach can achieve better scaling, but at the cost of path diversity. This leads to path hiding that can prevent efficient use of BGP Multipath, prevent hitless planned maintenance and lead to sub-optimal routing.
28 BGP ADDITIONAL PATHS Multiple information of prefix p and x PE knows only one path (best) Image source: Cisco documentation
29 BGP ADDITIONAL PATHS BGP Additional Paths feature Path identifier (ID) is added to each path in the NLRI Path ID s are unique to a peering sessions and are generated for each network Path ID us used to prevent a route announcement from implicitly withdrawing the previous one It allows advertisement of more paths in addition to best path. Multiple paths to same prefix can exist in BGP table
30 BGP ADDITIONAL PATHS BGP Additional Paths feature Capability must me negotiated between peer routers Administrator have to configure router to send, receive or both capabilities Neighbors that have negotiated the capability will be grouped together in an update group and in a separate update group from those peers that have not negotiated the capability
31 BGP ADDITIONAL PATHS There are 3 path selection policies that are not mutually exclusive Best 2 or Best 3 best and 2 nd best path are advertised, best, 2 nd best and 3 rd best are advertised All all path with unique next hops are eligible for selection Group-best calculates the group-best for group of prefixes. Refer to documentation for details.
32 BGP ADDITIONAL PATHS router bgp 1 address- family ipv4 unicast bgp additional- paths select all neighbor additional- paths send receive neighbor advertise additional- paths all
33 BGP ADDITIONAL PATHS router bgp 1 neighbor remote- as 1! address- family ipv4 unicast bgp additional- paths send receive bgp additional- paths select all best 3 group- best neighbor activate neighbor route- map add_path1 out neighbor advertise additional- paths best 2 exit- address- family! route- map add_path1 permit 10 match additional- paths advertise- set best 2 set metric 780 route- map add_path1 permit 20
36 BGP DYNAMIC NEIGHBORS BGP Dynamic Neighbors feature allows BGP peering to a group of remote neighbors that are defined by a range of IP addresses. Each range can be configured as a subnet IP address. Another router initiates TCP session Dynamic BGP neighbor inherits configuration from peer-group, it does not require any additional configuration Available only for IPv4 BGP peering
37 BGP DYNAMIC NEIGHBORS In larger BGP networks implementing BGP dynamic neighbors can reduce the amount and complexity of CLI configuration It also saves CPU and memory usage Number of allowed dynamic neighbors can be defined in configuration Up to 5 optional AS number for listen range can be defined
38 BGP DYNAMIC NEIGHBORS Configuration router bgp bgp log- neighbor- changes bgp listen limit 200 bgp listen range /16 peer- group group172 bgp listen range /16 peer- group group192 neighbor group172 peer- group neighbor group172 remote- as neighbor group192 peer- group neighbor group192 remote- as alternate- as neighbor remote- as address- family ipv4 unicast neighbor group172 activate neighbor group192 activate neighbor activate
41 BGP SLOW PEER BGP Update Group BGP update generation uses the concept of update groups to optimize performance An update group is a collection of peers with the identical outbound policy Group policy is used to format messages that are then transmitted to the members of the group with every update
42 BGP SLOW PEER BGP Update Group Each update group is allocated a quota of formatted messages that it keeps in its cache to maintain fairness in resource utilization Messages are added to the cache when they are formatted by the group, and they are removed when they are transmitted to all the members of the group.
43 BGP SLOW PEER BGP Slow Peer A slow peer is a peer that cannot keep up with the rate at which the Cisco IOS software is generating update messages There is packet loss or high traffic on the link to the peer The throughput of the BGP TCP connection is very low The peer has a heavy CPU load and cannot service the TCP connection at the required frequency When a slow peer is present in an update group, the number of formatted updates pending transmission builds up
44 BGP SLOW PEER BGP Slow Peer The rest of the members of the group that are faster than the slow peer and have completed transmission of the formatted messages will not have anything new to send, even though there may be newly modified BGP networks waiting to be advertised or withdrawn
45 BGP SLOW PEER When peer is not Slow Peer Events that cause large churn in the BGP can cause a brief spike in the rate of update generation. A peer that temporarily falls behind during such events, but quickly recovers after the event, is not considered a slow peer. Temporary Slowness Does Not Constitute a Slow Peer In order for a peer for be marked as slow, it must be incapable of keeping up with the average rate of generated updates over a longer period
46 BGP SLOW PEER BGP Slow Peer Detection It relies on the timestamp on the update messages in an update group. Update messages are timestamped when they are formatted. When BGP slow peer detection is configured, the timestamp of the oldest message in a peers queue is compared to the current time to determine if the peer is lagging more than the configured slow peer time threshold. Peer can be marked also statically
47 BGP SLOW PEER What to do with Slow Peer The slow peer is moved from its normal update group to a slow update group The normal update group will continue to function without being slowed down Peer can be kept in slow update group until manually cleared or router can dynamically move it back to its regular update group as conditions improve
48 BGP SLOW PEER Static Slow Peer router bgp 5 address- family ipv4 neighbor slow- peer split- update- group static
49 BGP SLOW PEER Dynamic Slow Peer router bgp 13 no bgp default route- target filter no bgp enforce- first- as bgp log- neighbor- changes neighbor remote- as 13 address- family ipv4 neighbor slow- peer split- update- group dynamic
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