Segment Routing. Anoop Ghanwani, Dell Saurav Das, ONF. Dell Networking Meetup May 21, 2015

Transcription

1 noop Ghanwani, ell Saurav as, ON May 21, 2015

2 genda What is segment routing? SR applications SR data plane SR control plane MPLS & IPv6 segment routing examples hallenges with SR SR standardization 2

3 What is segment routing? djacency source routing paradigm segment is an instruction Node djacency Service Node S Service source route is constructed using a sequence of instructions 3

4 Segment routing applications Traffic engineering and load balancing Protection Network programmability OM techniques I compaction 4

5 Traffic engineering and load balancing Use non shortest paths Improve network utilization Large flow optimization Pin flows to a specific path Instead of depending on MP void nodes or links To meet policy requirements 5

6 Protection Link Node Network Path X X 6

7 Network programmability menable to SN control With IGP Program a specific path Program a set of services Touch only edge devices Without IGP ontroller can program I Only programmed at startup SN ontroller S 7

8 OM techniques Inject packets to a specific path from anywhere in the network Inject OM packet here to test path Path Monitoring System 8

9 I compaction No need to maintain entire I in hardware in core devices Size of I = O(# routers) IPv4/IPv6 Size of I = O(# prefixes) MPLS Size of LI = O(# LSPs) 9

10 Why not just use MPLS? MPLS T adds complexity xplicit signaling for every LSP Requires a separate signaling protocol RSVP T epending on number of LSPs, LI can be very large Segment routing piggybacks on the IGP ewer protocols to manage oesn t require explicit per path signaling Instead, handled in the data path 10

11 What about IP source routing? Source routing is specified both for IPv4 and IPv6 Not widely used Security ttacker can easily gain information about the topology an conduct various data plane attacks SI support lacking Variable length headers Not widely used, so why support it? IPv6 SR extensions will address some of the shortcomings 11

12 Segment routing data plane MPLS IPv6 Why not IPv4? nhancements to IPv4 are discouraged by the IT 12

13 MPLS segment routing data plane Works with existing MPLS data plane No change to label syntax or semantics Push & forward, swap & forward, pop & lookup, pop & forward Label stack comprises the sequence of segments Label can represent Node (global) djacency (local) Service (local) 13

14 IPv6 segment routing data plane IPv6 Spec R 2460 Proposed segment routing header Next Hdr Hdr xt Len Routing Type Reserved Segments Left Next Hdr Hdr xt Len Routing Type Segments Left irst Segment lags HM Key I ddress [1] (.. ddress [n]) Segment List [0] (.. Segment List [n]) Routing header appears only once in the packet Node will examine header only if IP is self changes at each segment termination Policy List [0] (.. Policy List [3]) (optional) HM (256 bits) (optional) 14

15 IPv6 segment routing data plane (2) Segments Left ecremented after each completed segment ctive segment omputed from irst Segment and Segments Left lags lean up P Protected 2 reserved bits Policy element type HM Key I Used for security Next Hdr Hdr xt Len Routing Type Segments Left irst Segment lags HM Key I Segment List [0] Segment List [1] Segment List [2] Segment List [3] 15

16 s compared to IPv6 source routing llows the option of removing entire SRH when not needed Indication that protection is in use Policy elements Policy elements are IPv6 addresses or example, use a different IPS at the tunnel ingress & preserve original Security 16

17 Segment routing control plane 4 ways SN controller to setup I/LI for segment routing IS IS and OSP extensions GP LS extensions Prefix Segment I (Prefix SI) djacency Segment I (dj SI) 17

18 MPLS segment routing Label assignment and LI setup Label ction Type Swap to 100 & orward on Node (Global) Swap to 101 & orward on Node (Global) 102 Pop & lookup Node (Global) Swap to & orward on Node (Global) 104 Swap to 104 & orward on Node (Global) 105 Swap to 105 &orward on or Node (Global) 1020 Pop & orward on dj(local) Global labels are unique in the IGP domain 1021 Pop & orward on dj(local) 1022 Pop & orward on dj(local) 18

19 MPLS segment routing Strict & loose routing using node SI

20 MPLS segment routing Strict & loose routing using node SI with PHP Penultimate hop pop (PHP) reduces the label stack in many cases, especially with strict routing

21 MPLS segment routing Using node SI and adjacency SI Label ction Type 100 Swap to 100 & orward on Node (Global) 101 Swap to 101 & orward on Node (Global) 102 Pop & lookup Node (Global) Swap to & orward on Node (Global) 104 Swap to 104 & orward on Node (Global) 105 Swap to 105 &orward on or Node (Global) 1020 Pop & orward on dj(local) 1021 Pop & orward on dj(local) 1022 Pop & orward on dj(local) 21

22 IPv6 segment routing Strict & loose routing Plain old IP routing here because IP!= self IP Hdr IP SRH *,,, X IP Hdr IP SRH,*,, X IP Hdr IP SRH,,*, X IP Hdr IP X ata ata ata ata IP Hdr IP X ata IP Hdr IP X ata IP Hdr IP SRH *, X ata IP Hdr IP SRH *, X ata IP Hdr IP SRH *, X ata IP Hdr IP X ata * Indicates active segment 22

23 hallenges with segment routing Header size Packets have variable length headers, potentially large Makes bandwidth provisioning a little harder Packet entropy for hashing using LG/MP ntropy label for MPLS ccessing entropy for IPv6 epth of label stack for MPLS Typical support is only 3 4 labels New hardware for IPv6 ven the existing SRH is not common Multicast is not supported 23

24 Segment routing standardization in the IT SPRING WG Source Packet Routing In NetworkinG Problem statement, use cases, architecture OSP, IS IS WGs IGP extensions IR WG GP LS extensions IPv6 maintenance WG New segment routing header SRH Security 24

25 Implementations Open Networking oundation SPRING OPN project SR IPv6 on Linux routing.org/ 25

26 Summary Segment routing is a method for encoding a sequence of instructions llows very precise control over routing in the network Minimizes control plane complexity powerful complement to SN 26

27 Thank You 27