ip switching 國立中正大學資訊工程研究所黃仁竑副教授. 中正資工 / 黃仁竑...

IP Switching

國立中正大學資訊工程研究所黃仁竑副教授

中正資工/黃仁竑 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


Ipsilon IP Switching

Run IP over ATM hardware

IPAALATM

MACATM

Switch

IP

ATMSwitch

Ipsilon


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


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 hardw

are. 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


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.


IFMP

Note: When flow is identified and VC is set up, no LL/SNAP encapsulation is required.


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


IP Switching Operations

IP SwitchController

ATMSwitch

UpstreamNode

UpstreamNode

DownstreamNode

DownstreamNode

IP Switch

Connectionless packets are forwarded over default ATM VCs and IP switch controller makes a flow classification on each packet



IP SwitchController

ATMSwitch

UpstreamNode

UpstreamNode

DownstreamNode

DownstreamNode

IP Switch

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



IP SwitchController

ATMSwitch

UpstreamNode

UpstreamNode

DownstreamNode

DownstreamNode

IP Switch

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



IP SwitchController

ATMSwitch

UpstreamNode

UpstreamNode

DownstreamNode

DownstreamNode

IP Switch

Incoming labeled flow switched through to outgoing labeled flow where “cut-through” operation completed for flow-oriented traffic.


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 contin

ues


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.


Tag Switching Internetwork


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.


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.


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.


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


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


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


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


Downstream Tag Allocation

A For each route in its FIB the switch allocates a tag, creates an entry in its Tag Information Base (TIB)

B 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)

C 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

(A )

(C )

(B )

R u

R d

O u tg o in g : 1

In c o m in g : 1

1 4 0 .1 2 3 .1 0 8< 1 >


Downstream Tag Allocation on Demand

A For each route in its FIB, the switch request (via TDP) the next hop for a tag binding for that route

B 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

C 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

(B )

(C )

(A )R u

R d

R e q u e s t1 4 0 .1 2 3 .1 0 8

1 4 0 .1 2 3 .1 0 8< 1 >

In c o m in g : 1

O u tg o in g : 1


Upstream Tag Allocation

A 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 bindingB 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

(B )

(A )

R u

R d

1 4 0 .1 2 3 .1 0 8< 1 >

In c o m in g : 1

O u tg o in g : 1


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


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 multi

ple paths Support forwarding in QoS-based routing

ip switching 國立中正大學 資訊工程研究所 黃仁竑 副教授. 中正資工 / 黃仁竑...

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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. 中正資工 / 黃仁竑...