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Both the physical and logical interfaces have encapsulations. The default for both is<br />

Ethernet II (RFC 894).<br />

The physical interface shows the encapsulation in the Link-level type field, and the<br />

logical interface shows it in the Encapsulation field:<br />

Physical interface: fe-0/0/3, Enabled, Physical link is Up<br />

Interface index: 131, SNMP ifIndex: 82<br />

Link-level type: Ethernet, MTU: 1514, Speed: 100mbps, Loopback: Disabled,<br />

Logical interface fe-0/0/3.0 (Index 69) (SNMP ifIndex 87)<br />

Flags: SNMP-Traps Encapsulation: ENET2<br />

The JUNOS software supports IEEE 802.1Q VLAN tagging on Ethernet interfaces,<br />

which channelizes an Ethernet interface, allowing it to carry traffic from different<br />

Ethernet segments over the same physical link but keeping the traffic on separate logical<br />

interfaces. VLAN tagging works on an entire physical Ethernet interface, and you<br />

configure each logical interface to carry traffic from different Ethernet segments, as<br />

shown in this example:<br />

[edit interfaces fe-2/1/2]<br />

aviva@router1# set vlan-tagging<br />

aviva@router1# set unit 0 vlan-id 0<br />

aviva@router1# set unit 0 family inet address 10.10.1.0/24<br />

aviva@router1# set unit 1 vlan-id 1<br />

aviva@router1# set unit 1 family inet address 10.10.1.1/24<br />

aviva@router1# set unit 2 vlan-id 0<br />

aviva@router1# set unit 2 family inet address 10.10.1.2/24<br />

You see the VLAN configuration parameters in the logical portion of the show<br />

interfaces command output:<br />

aviva@router1# show interfaces fe-2/1/2.2<br />

Logical interface fe-2/1/2.2 (Index 75) (SNMP ifIndex 214)<br />

Flags: SNMP-Traps 16384 VLAN-Tag [ 0x8100.2 ] Encapsulation: ENET2<br />

Input packets : 0<br />

Output packets: 1<br />

Protocol inet, MTU: 1500<br />

Flags: None<br />

Addresses, Flags: Is-Preferred Is-Primary<br />

Destination: 10.10.1/24, Local: 10.10.1.2, Broadcast: 10.10.1.255<br />

7.14 Using VRRP on Ethernet Interfaces<br />

Problem<br />

You want to set up a router to be a backup default gateway to provide redundancy in<br />

case the primary default gateway router goes down.<br />

220 | Chapter 7: Router Interfaces<br />

This is the Title of the Book, eMatter Edition<br />

Copyright © 2008 O’Reilly & Associates, Inc. All rights reserved.

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