Download IP Switching

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
 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
2
Ipsilon IP Switching

Run IP over ATM hardware
IP
MAC
AAL
ATM
IP
ATM
Switch
Ipsilon
ATM
Switch
中正資工/黃仁竑
3
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
4
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-byhop 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
5
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
6
IFMP
Note: When flow is identified and VC is set
up, no LL/SNAP encapsulation is required.
中正資工/黃仁竑
7
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
8
IP Switching Operations
IP Switch
IP Switch
Controller
Upstream
Node

ATM
Switch
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
9
IP Switching Operations
IP Switch
IP Switch
Controller

Upstream
Node

ATM
Switch
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
10
IP Switching Operations
IP Switch
IP Switch
Controller
Upstream
Node
ATM
Switch


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
11
IP Switching Operations
IP Switch
IP Switch
Controller
Upstream
Node
ATM
Switch
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
12
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
13
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
14
Tag Switching Internetwork
中正資工/黃仁竑
15
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
17
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
18
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
19
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
20
Forwarding component

Tag Information Base (TIB) - each entry consists of :



Forwarding algorithm





Incoming tag
One or more sub-entries (outgoing tag, outgoing interface,
outgoing MAC address)
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
21
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
22
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
23
Downstream Tag Allocation
A
B
C
For each route in its FIB the switch allocates (C)
a tag, creates an entry in its Tag Information
Base (TIB)
Ru
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
Incoming : 1
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
Outgoing : 1
(B)
140.123.108
<1>
Rd
(A)
24
Downstream Tag Allocation on Demand
A
B
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
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
中正資工/黃仁竑
(C)
Outgoing : 1
Ru
(A)
Request
140.123.108
140.123.108
<1>
(B)
Rd
Incoming : 1
25
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
binding
B
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
Outgoing : 1
(A)
Ru
140.123.108
<1>
(B)
Rd
Incoming : 1
26
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
27
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
28