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

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Ip switching

IP Switching

國立中正大學

資訊工程研究所

黃仁竑 副教授


Ip switching1

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


Ipsilon ip switching

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


Protocols

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


Flow classification

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


Flow type

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


Ip switching

IFMP

Note: When flow is identified and VC is set

up, no LL/SNAP encapsulation is required.

中正資工/黃仁竑


Ip switching

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


Ip switching operations

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


Ip switching operations1

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


Ip switching operations2

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


Ip switching operations3

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


Miscellaneous issues

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


Tag switching

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


Tag switching internetwork

Tag Switching Internetwork

中正資工/黃仁竑


Tag switching internetwork1

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


Tag switching operations

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


Tag switching operations1

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


Tag switch components

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


Forwarding component

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


    Control component

    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


    Destination based routing module

    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


    Downstream tag allocation

    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


    Downstream tag allocation on demand

    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


    Upstream tag allocation

    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


    Hierarchy of routing knowledge module

    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


    Explicit routes module

    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


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