IP Switching

1. IP Switching 國立中正大學 資訊工程研究所 黃仁竑 副教授

2. IP Switching • Problem with classical IP over ATM • IP over ATM preserves ATM protocol stack as well as TCP/IP protocol stack • IP routing protocol running at IP layer • ATM signalling running at ATM control plan • Do we have other choices • Discard ATM signalling/routing • Ipsilon IP switching, Cisco Tag switching • Incorporating IP routing with ATM routing • Ascend IP Navigator, IBM ARIS • Issues of IP switching • Switching and routing • Flow classification • QoS support • Multicast support 中正資工/黃仁竑

3. Ipsilon IP Switching • Run IP over ATM hardware IP AAL ATM IP Ipsilon MAC ATM Switch ATM Switch 中正資工/黃仁竑

4. Protocols • IFMP • When downstream node identifies a flow, send flow identifier to the upstream node which indicates which VPI/VCI should be used for the flow. • GSMP • For the IP switch controller to communicate with ATM switch 中正資工/黃仁竑

5. Flow Classification • What is a flow • A sequence of IP packets that belong to the same IP service • “extended IP conversation” • Flow characterization • Same source-destination pair • Same protocol type (TCP/UDP) • Same type of service (port number) • Flow label in IPv6 • Cut-through • Long duration flows can be optimized by cut-through switching in the ATM hardware. • The rest of the traffic continues to receive the default treatment hop-by-hop store-and-forward routing. • Homogeneous Ipsilon IP switches • Recognize flow locally, but if all with the same criteria, an end-to-end ATM switching path will be built 中正資工/黃仁竑

6. Flow Type • A host-pair flow type (flow type 2) • For traffic flowing between the same source and destination IP addresses. • A port-pair flow type (flow type 1) • For traffic flowing between the same source and destination TCP/UDP ports on the same source and destination IP addresses. • The port-pair flow type allows quality of service differentiation among flows between the same pair of hosts and also supports simple flow-based firewall security features. 中正資工/黃仁竑

7. IFMP Note: When flow is identified and VC is set up, no LL/SNAP encapsulation is required. 中正資工/黃仁竑

8. GSMP • Five types of message • Configuration: discover the capabilities of the ATM switch • Connection management: establish/remove connections across switch • Port management: reset, bring up, take down, and loopback switch ports • Events: asynchronously alter the control significant events • Statistics 中正資工/黃仁竑

9. IP Switching Operations IP Switch IP Switch Controller ATM Switch Upstream Node Downstream Node   Connectionless packets are forwarded over default ATM VCs and IP switch controller makes a flow classification on each packet 中正資工/黃仁竑

10. IP Switching Operations IP Switch IP Switch Controller  ATM Switch Upstream Node Downstream Node   IP switch controller sends a message to the up-stream node to use a new VC for a selected flow.  Traffic for the selected flow begins to flow on the new VC 中正資工/黃仁竑

11. IP Switching Operations IP Switch IP Switch Controller  ATM Switch Upstream Node Downstream Node   Downstream node will also request a new VC for the flow  IP switch begins to send traffic on that flow to the downstream node on the new VC 中正資工/黃仁竑

12. IP Switching Operations IP Switch IP Switch Controller ATM Switch Upstream Node Downstream Node  Incoming labeled flow switched through to outgoing labeled flow where “cut-through” operation completed for flow-oriented traffic. 中正資工/黃仁竑

13. Miscellaneous Issues • Multicast • Support IP multicasting without any modification to IGMP • Can utilize Switch’s multicast functionality • Identify multicast flow based on source-based (point-to-multipoint) tree • QOS • Basically, lack of QOS since no “real” VC is set up. May cooperate with RSVP in the future • It’s up to ATM switch • Robustness • Each IFMP redirection is associated with a timer • New IFMP redirection must be sent before timeout if the flow continues 中正資工/黃仁竑

14. Tag Switching • A new technique, developed by Cisco, for high-performance packet forwarding that assigns "tags" to multiprotocol frames for transport across packet or cell-based networks. • Based on the concept of "label swapping," in which units of data carry a short, fixed length label that tells switching nodes how to process the data. 中正資工/黃仁竑

15. Tag Switching Internetwork 中正資工/黃仁竑

17. Tag Switching Internetwork • Tag edge routers: • located at the boundaries of an Internet, tag edge routers perform value-added network layer services and apply tags to packets. • Tag switches: • switch tagged packets or cells based on the tags. Tag switches may also support full Layer 3 routing or Layer 2 switching, in addition to tag switching. • Tag distribution protocol (TDP): • in conjunction with standard network layer routing protocols, TDP is used to distribute tag information between devices in a tag switched Internet. 中正資工/黃仁竑

18. Tag Switching Operations • Step 1: Tag edge routers and tag switches use standard routing protocols to identify routes through the network. • Fully interoperable with non-tag switching routers. • Step 2: Tag routers and switches use the tables generated by the standard routing protocols to assign and distribute tag information via the TDP. • Step 3: Tag routers receive the TDP information and build a forwarding database which makes use of the tags. • Step 4: When a tag edge router receives a packet for forwarding across the tag network, it analyzes the network layer header selects a route for the packet from its routing tables, applies a tag, and forwards the packet to the next hop tag switch. 中正資工/黃仁竑

19. Tag Switching Operations • Step 5: The tag switch receives the tagged packet and switches the packet based solely on the tag, without re-analyzing the network layer header. • Step 6: The packet reaches the tag edge router at the egress point of the network, where the tag is stripped off and the packet delivered. 中正資工/黃仁竑

20. Tag Switch Components • Forwarding component • Uses the tag information carried by packets and the tag forwarding information maintained by a tag switch to perform packet forwarding • Control component • Creating tag bindings, and then distributing the tag binding information among tag switches 中正資工/黃仁竑

21. Forwarding component • Tag Information Base (TIB) - each entry consists of : • Incoming tag • One or more sub-entries (outgoing tag, outgoing interface, outgoing MAC address) • Forwarding algorithm • Based on the exact match algorithm • Independent of the tag’s forwarding granularity • Could be implemented with any MAC/link layer technology • Network layer independent • Carrying tag information • As part of the network layer header (IPv6) • As part of the MAC header (VCI/VPI in ATM) • Via a “shim” between the MAC and the network layer header 中正資工/黃仁竑

22. Control component • Organized as a collection of modules, each module is designed to support a particular routing function : • Destination-based routing • Hierarchy of routing knowledge • Resource reservation • Explicit routes • Multicast • New modules could be added to support new routing functions without impacting the forwarding component 中正資工/黃仁竑

23. Destination-Based Routing Module • Forwarding decision is based on the destination address carried in a packet and the information stored in the Forwarding Information Base (FIB) • A tag switch constructs its FIB by using the information receives from routing protocols (e.g., OSPF, BGP) • Three methods for tag allocation and Tag Information Base (TIB) management • downstream tag allocation • downstream tag allocation on demand • upstream tag allocation 中正資工/黃仁竑

24. Downstream Tag Allocation • For each route in its FIB the switch allocates a tag, creates an entry in its Tag Information Base (TIB) • Advertises binding between the incoming tag and the route to all of the adjacent switches : by either piggybacking the binding on top of the existing routing protocol, or by using a separate Tag Distribution Protocol (TDP) • When a switch receives tag binding information for a route, if the information was received from the next hop for that route, the switch places the tag into the outgoing tag of the TIB entry associated with the route 中正資工/黃仁竑

25. Downstream Tag Allocation on Demand • For each route in its FIB, the switch request (via TDP) the next hop for a tag binding for that route • When the next hop receives the request, it • allocates a tag • creates an entry in its TIB with the incoming tag set to the allocated tag • returns the binding to the requester • When the requester receives the tag binding information for a route from the next hop for that route, the requester places the tag into the outgoing tag of the TIB entry associated with the route 中正資工/黃仁竑

26. Upstream Tag Allocation • If a tag switch has one or more point-to-point interface, then for each route in its FIB whose next hop is reachable via one of these interfaces • The switch allocates a tag • Creates an entry in its TIB with the outgoing tag set to the allocated tag • Advertises to the next hop (via TDP) the binding • When the next hop receives the tag binding information, the switch places the tag into the incoming tag of the TIB entry associated with the route 中正資工/黃仁竑

27. Hierarchy of Routing Knowledge Module • Allows the de-coupling of interior and exterior routing • Between domains use tags with exterior routes (BGP tag) • Within a domain use tags associated with interior routes to BGP border routers of the domain (IGP tag + BGP tag) • Tag (label) stack • Reduces the routing load on non-border switches • Shortens routing convergence time 中正資工/黃仁竑

28. Explicit Routes Module • Overrides the hop-by-hop destination-based routing paths • Requires the ability to install tag bindings that are independent from the tags installed via the destination-based routing protocol • May be coupled with resource reservations • Possible applications : • Allows finer control over traffic distribution over multiple paths • Support forwarding in QoS-based routing 中正資工/黃仁竑