Copyright © 2005 Juniper Networks, Inc. Proprietary and Confidential www.juniper.net

4-1

Ethernet Switching and Virtual LANs

© 2008 Juniper Networks, Inc. All rights reserved. 2

Overview of Ethernet

Ethernet defined:•Family of LAN specifications, standardized in IEEE

802.3 Examples include:• 10Base-T (802.3i)—10 Mbps• 100Base-TX (802.3u)—100 Mbps• 1000Base-T (802.3ab)—1000 Mbps

•Uses data link layer technology to create LANs• Shared medium—a single broadcast and collision

domain• Uniquely identifies all nodes on the LAN with 48-bit MAC

address•Uses CSMA/CD to avoid and manage frame

collisions

© 2008 Juniper Networks, Inc. All rights reserved. 3

Ethernet LANs (1 of 2)

Characteristics:•Shared medium•Single collision domain•Nodes can transmit

simultaneously

Problems:1. Traffic is seen by everyone 2. Collisions can occur3. Unwanted resource consumption

Sharedmedium

Collisiondomain

Nodes can transmit

simultaneously

© 2008 Juniper Networks, Inc. All rights reserved. 4

Ethernet LANs (2 of 2)

As the network grows, the likelihood of collisions increases•As collisions increase, overall LAN efficiency

decreases

© 2008 Juniper Networks, Inc. All rights reserved. 5

Overview of Bridging

Bridging: •Is defined in the IEEE 802.1D-2004 standard•Segments a single collision domain•Isolates the physical layer•Learns and maintains a forwarding table (bridge

table)•Performs intelligent forwarding decisions based on

the bridge table

© 2008 Juniper Networks, Inc. All rights reserved. 6

Bridging: How Does it Work?

Transparent bridging builds and maintains bridge tables using the following mechanisms:•Learning:

• Learns MAC address and associated port•Forwarding:

• Forwards packets out proper egress interface towards destination

•Flooding: • Replicates packets out other ports for unknown destination

MAC addresses; also used when passing multicast and broadcast traffic

•Filtering: • Limits traffic to its associated network segment

•Aging: • Ensures bridge table entries are current

© 2008 Juniper Networks, Inc. All rights reserved. 7

MAC Address Learning

MAC Address Table

0140.5501.1111

0140.5501.2222

ge-0/0/0

ge-0/0/0: 0140.5501.1111ge-0/0/0: 0140.5501.2222ge-0/0/1: 0140.5501.3333ge-0/0/1: 0140.5501.4444

Pre TypeDA SA FCSData

B2

ge-0/0/1

A1

A2

B1

0140.5501.3333

0140.5501.4444 = Hub

Source MAC addresses are learned for all incoming Ethernet frames

Each MAC address is associated with the frame’s incoming interface

© 2008 Juniper Networks, Inc. All rights reserved. 8

Forwarding: Known Unicast Frames (1 of 2)

MAC Address Table

ge-0/0/0: 0140.5501.1111

ge-0/0/0: 0140.5501.2222

ge-0/0/1: 0140.5501.3333

ge-0/0/1: 0140.5501.4444

0140.5501.1111

0140.5501.2222

ge-0/0/0

B2

ge-0/0/1

A1

A2

B1

0140.5501.3333

0140.5501.4444 = Hub

A1 sends a frame to

B2

Switch checks forwarding

table

Switch forwards frame from A1 to

B2

A2 receives and

discards the frame from A1

© 2008 Juniper Networks, Inc. All rights reserved. 9

Forwarding: Known Unicast Frames (2 of 2)

MAC Address Table

ge-0/0/0: 0140.5501.1111

ge-0/0/0: 0140.5501.2222

ge-0/0/1: 0140.5501.3333

ge-0/0/1: 0140.5501.4444

0140.5501.1111

0140.5501.2222

ge-0/0/0

B2

ge-0/0/1

A1

A2

B1

0140.5501.3333

0140.5501.4444 = Hub

A1 sends a frame to

A2

Switch checks forwarding

table

Switch filters frame from A1 to

A2

A2 processes the frame from

A1

© 2008 Juniper Networks, Inc. All rights reserved. 10

Flooding: Broadcast, Multicast, or Unknown Unicast Frames

0140.5501.1111

MAC Address Table

0140.5501.2222

ge-0/0/0

ge-0/0/0: 0140.5501.1111

ge-0/0/0: 0140.5501.2222

ge-0/0/1: 0140.5501.3333

ge-0/0/1: 0140.5501.4444

B2

ge-0/0/1

A1

A2

B1

0140.5501.3333

0140.5501.4444 = Hub

Switch floods frame out all ports associated with the LAN

(except the port on which it was received)

A1 sends broadcast frame

on to LAN (DA:

FFFF.FFFF.FFFF)

© 2008 Juniper Networks, Inc. All rights reserved. 11

Viewing the MAC Address Table

Use the show ethernet-switching table command to view MAC address table entries

user@switch> show ethernet-switching table Ethernet-switching table: 6 entries, 3 learned VLAN MAC address Type Age Interfaces blue * Flood - All-members blue 00:19:e2:50:7c:0b Learn 48 ge-0/0/10.0 orange * Flood - All-members orange 00:19:e2:50:3f:ee Learn 42 ge-0/0/13.0 purple * Flood - All-members purple 00:19:e2:50:77:b1 Learn 38 ge-0/0/16.0

Entries are organized based on associated

VLAN

Each VLAN maintains an entry used for

flooding

© 2008 Juniper Networks, Inc. All rights reserved. 12

Clearing the MAC Address Table

Use the clear ethernet-switching table command to clear MAC address table contentsuser@switch> clear ethernet-switching table ?

Possible completions: <[Enter]> Execute this command interface Clear MAC table for specified interface | Pipe through a command

Clear all entries in table or only the entries for a

specific interface

© 2008 Juniper Networks, Inc. All rights reserved. 13

Overview of VLANs

VLANs:•Segment a single broadcast domain into multiple

broadcast domains•Allow for grouping users based on business needs,

regardless of physical location

VLAN Orange

VLAN Orange

VLA

N O

ran

ge VLAN Blue

VLAN Blue

VLA

N B

lue

© 2008 Juniper Networks, Inc. All rights reserved. 14

Default and Management VLANs

All network ports belong to the default VLAN in the factory-default configuration

The mgmt VLAN allows redundant management connections to the vme interface (EX 4200 switches only)

user@switch> show vlans default Name Tag Interfacesdefault ge-0/0/0.0*, ge-0/0/1.0*, ge-0/0/2.0, ge-0/0/3.0, ge-0/0/4.0, ge-0/0/5.0*, ge-0/0/6.0, ge-0/0/7.0, ge-0/0/8.0, ge-0/0/9.0, ge-0/0/10.0*, ge-0/0/11.0*, ge-0/0/12.0*, ge-0/0/13.0*, ge-0/0/14.0*, ge-0/0/15.0*, ge-0/0/16.0*, ge-0/0/17.0*, ge-0/0/18.0*, ge-0/0/19.0, ge-0/1/0.0, ge-0/1/1.0, ge-0/1/2.0, ge-0/1/3.0

user@switch> show vlans mgmt Name Tag Interfacesmgmt me0.0*

© 2008 Juniper Networks, Inc. All rights reserved. 15

Switch Port Modes

Switch ports operate in either access or trunk mode•Access mode:

• Connects to network devices (desktop, IP phones, printers, and so forth)

• Typically transmit untagged Ethernet frames for a single VLAN; the exception is when the voice VLAN feature is being used

• Default mode for all ports•Trunk mode:

• Connects to other switches or a router• Typically transmits tagged Ethernet frames for multiple

VLANs; the exception is when the native VLAN option is configured or control traffic is sent

• Must be explicitly configured

© 2008 Juniper Networks, Inc. All rights reserved. 16

802.1Q—Ethernet Frame

4-byte tag inserted into Ethernet frame (max 1522 bytes)•Tag Protocol Identifier (TPID): 16 bits, default

0x8100•Priority: 3 bits, 802.1p•Canonical Format Indicator (CFI): 1 bit, default 0•Unique VLAN identifier (VID): 12 bits

TPIDTPIDPriorityPriority CFICFI VIDVID

DestinationMAC Data FCSSource

MACType/

LengthTAG

© 2008 Juniper Networks, Inc. All rights reserved. 17

802.1Q—Trunk Links

A trunk is a single Ethernet link that can carry traffic for multiple VLANs

VLAN Orange

VLAN Orange

VLA

N O

ran

ge

VLAN Blue

VLAN Blue

VLA

N B

lue

VLAN Orange

VLAN Orange

VLA

N O

ran

ge

VLAN Blue

VLAN Blue

VLA

N B

lue

© 2008 Juniper Networks, Inc. All rights reserved. 18

[edit]user@switch# show interfaces …ge-0/0/13 { unit 0 { family ethernet-switching { port-mode access; vlan { members orange; } } }}…[edit]user@switch# show vlans …orange { vlan-id 101;}

VLAN Configuration Example

VLAN Blue

VLAN Purple

VLAN Orange

VLAN Defined

VLAN Referenced

Port-Based Assignment

© 2008 Juniper Networks, Inc. All rights reserved. 19

user@switch> show vlans Name Tag Interfacesblue 100 ge-0/0/10.0*default ge-0/0/0.0, ge-0/0/5.0*orange 101 ge-0/0/13.0*purple 102 ge-0/0/16.0*mgmt me0.0*

user@switch> show vlans orange detail VLAN: orange, 802.1Q Tag: 101, Admin state: EnabledNumber of interfaces: 1 (Active = 1) Untagged interfaces: ge-0/0/13.0*

Monitoring VLAN Assignments

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802.1Q Trunk Configuration Example

[edit]user@switch# show interfaces ...ge-0/0/18 { unit 0 { family ethernet-switching { port-mode trunk; vlan { members [ orange blue ]; } } }}

[edit]user@switch# show vlans blue { vlan-id 100;}orange { vlan-id 101;}

Single physical link carries traffic for multiple VLANs

© 2008 Juniper Networks, Inc. All rights reserved. 21

Interface belongs to

both VLANs

Monitoring 802.1Q Trunks

user@switch> show vlans orange detail VLAN: orange, 802.1Q Tag: 101, Admin state: EnabledNumber of interfaces: 2 (Active = 2) Untagged interfaces: ge-0/0/13.0* Tagged interfaces: ge-0/0/18.0*

user@switch> show ethernet-switching interfaces Interface State VLAN members Blocking ge-0/0/10.0 up blue unblockedge-0/0/13.0 up orange unblockedge-0/0/18.0 up blue unblocked orange unblockedme0.0 up mgmt unblocked

Interface is 802.1Q trunk for

both VLANs

© 2008 Juniper Networks, Inc. All rights reserved. 22

Routed VLAN Interface

Logical Layer 3 VLAN interface used for inter-VLAN routing

VLAN Blue

VLAN Purple

VLAN Orange

© 2008 Juniper Networks, Inc. All rights reserved. 23

RVI Configuration Example

[edit]user@switch# show interfaces ge-0/0/13 { unit 0 { family ethernet-switching { port-mode access; vlan { members orange; } } }}…vlan { unit 101 { family inet { address 10.1.2.1/24; } }}…

[edit]user@switch# show vlans blue { vlan-id 100; l3-interface vlan.100;}orange { vlan-id 101; l3-interface vlan.101;}purple { vlan-id 102; l3-interface vlan.102;}

This example facilitates routing through all interfaces associated with the blue, orange, and purple VLANs

© 2008 Juniper Networks, Inc. All rights reserved. 24

user@switch> show interfaces terse vlan Interface Admin Link Proto Local Remotevlan up up vlan.100 up up inet 10.1.1.1/24 vlan.101 up up inet 10.1.2.1/24 vlan.102 up up inet 10.1.3.1/24

user@switch> show vlans orange extensive VLAN: orange, Created at: Thu Apr 17 22:31:43 2008802.1Q Tag: 101, Internal index: 17, Admin state: Enabled, Origin: StaticProtocol: Port-based, Layer 3 interface: vlan.101 (UP)IP addresses: 10.1.2.1/24Number of interfaces: Tagged 1 (Active = 1), Untagged 1 (Active = 1) ge-0/0/18.0*, tagged, trunk ge-0/0/13.0*, untagged, access

Monitoring an RVI

RVI state and IP address details

At least one port must be active for RVI state to

be up