Junos OS

Hi expert,

i just wana know why juniper have logical interface concept  as while configuring devices for ip we always put in logical interface is there any specific reason why not we use physical interfaces as we use in cisco so wana know about the concept of having every thing logical in junos as compare to cisco.............there must be a reason for this so pls tell me the reason don't say it junos architecure becoz without reason not  cpncept created so i hope someone come with nice explaination over it

Hello Praveen, 

Logical units allow greater flexibility, as the name suggests it allows us to to subdidivde a physical interface into multiple logical units.

Each logical unit can have its own properties with appropriate encapsulations configured. As an example, when  vlan-tagging or flexible ethernet-services vlan-tagging enabled you can assign individual logical units to a specific vlan and configure the logical units with their own specific properties.

Here is an example : 

ge-0/3/2 {
    vlan-tagging;
    encapsulation flexible-ethernet-services;
    unit 1 {
        vlan-id 1;
        family inet {
            mtu 1500;
            address 10.1.1.1/30;
        }
    }
    unit 2 {
        vlan-id 2;
        family inet {
            mtu 1000;
            address 10.1.2.1/30;        
        }
    }
    unit 513 {
        encapsulation vlan-vpls;
        vlan-id 513;
        family vpls;
    }
    unit 514 {
        encapsulation vlan-ccc;
        vlan-id 514;
        family ccc;
    }
}

# run show interfaces ge-0/3/2 
Physical interface: ge-0/3/2, Enabled, Physical link is Up
  Interface index: 155, SNMP ifIndex: 507
  Link-level type: Flexible-Ethernet, MTU: 1518, Speed: 1000mbps, BPDU Error: None, MAC-REWRITE Error: None, Loopback: Disabled, Source filtering: Disabled, Flow control: Enabled, Auto-negotiation: Enabled, Remote fault: Online
  Device flags   : Present Running
  Interface flags: SNMP-Traps Internal: 0x4000
  CoS queues     : 4 supported, 4 maximum usable queues
  Schedulers     : 256
  Current address: 00:1b:c0:89:2c:5f, Hardware address: 00:1b:c0:89:2c:5f
  Last flapped   : 2012-09-26 19:45:55 UTC (2w3d 15:29 ago)
  Input rate     : 0 bps (0 pps)
  Output rate    : 0 bps (0 pps)
  Ingress rate at Packet Forwarding Engine      : 0 bps (0 pps)
  Ingress drop rate at Packet Forwarding Engine : 0 bps (0 pps)
  Active alarms  : None
  Active defects : None
  Interface transmit statistics: Disabled

  Logical interface ge-0/3/2.1 (Index 120) (SNMP ifIndex 568) 
    Flags: SNMP-Traps 0x4000 VLAN-Tag [ 0x8100.1 ]  Encapsulation: ENET2
    Input packets : 0 
    Output packets: 1
    Protocol inet, MTU: 1500
      Flags: Sendbcast-pkt-to-re, User-MTU
      Addresses, Flags: Is-Preferred Is-Primary
        Destination: 10.1.1.0/30, Local: 10.1.1.1, Broadcast: 10.1.1.3

  Logical interface ge-0/3/2.2 (Index 121) (SNMP ifIndex 569) 
    Flags: SNMP-Traps 0x4000 VLAN-Tag [ 0x8100.2 ]  Encapsulation: ENET2
    Input packets : 0 
    Output packets: 2
    Protocol inet, MTU: 1000
      Flags: Sendbcast-pkt-to-re, User-MTU
      Addresses, Flags: Is-Preferred Is-Primary
        Destination: 10.1.2.0/30, Local: 10.1.2.1, Broadcast: 10.1.2.3

  Logical interface ge-0/3/2.513 (Index 122) (SNMP ifIndex 570) 
    Flags: SNMP-Traps 0x4000 VLAN-Tag [ 0x8100.513 ]  Encapsulation: VLAN-VPLS
    Input packets : 0 
    Output packets: 0
    Protocol vpls, MTU: 1518
      Flags: Is-Primary

  Logical interface ge-0/3/2.514 (Index 123) (SNMP ifIndex 574) 
    Flags: SNMP-Traps 0x4000 VLAN-Tag [ 0x8100.514 ]  Encapsulation: VLAN-CCC
    Input packets : 0 
    Output packets: 0
    Protocol ccc, MTU: 1518
      Flags: Is-Primary

 Disclaimer : The above snippet is just an emaple to help demonstrate topic discussed here. 

Hope this helps. 

Hi Asrikumar

 thanks buddy i know this logical interfaces has flexibility and could be part of multiple logical addresses line inet and inet 6 but my point is why juniper comes with the idea to have mandatory to create logical interfaces and other vendors like cisco use logical in rarae cases like intervlan routing case but  juniper use logical interface concept  for all configration at interface level.....................

Hello ,

"why juniper comes with the idea to have mandatory to create logical interfaces and other vendors like cisco use logical in rarae cases like intervlan routing case but  juniper use logical interface concept  for all configration at interface level......................"

The interfaces are hierarchically represented as physical and logical.  Physical properties are and can be configured at the physical level and the logical properties are configured at the unit level. This directly relates to the forwarding lookup architecture of Juniper which would be certainly different for different vendors.

Thanks,

Aravind

@seabiscuit  hi friend as per your explaination one benefit is to asign diffrent vlan id and encapsulation on logical interfaces but i feel its more on flexible part  becoz this task we can done on physical interfaces as well...............

 what i feel about logical interfaces concept on juniper is they thing whenever we talk about logical thinks either its assigning Ip address,vlan or routing protocol it would be part  of logical interfaces becoz a logical interfaces can be part of multiple logical protocol family and firewall filters but still look  something appealing answer to have logical interfaces concept

1 is flexiblity what every one talks about................... 

In not sure if you can do things like this with physical interfaces. Here r1, r2, r3, r4 are all logical-systems inside a physical router.

[edit]
lab@router# show logical-systems

r1 {
    interfaces {
        ge-0/0/0 {
            unit 12 {
                vlan-id 12;
                family inet {
                    filter {
                        output test;
                    }
                    address 1.1.1.1/30;
                }
            }
            unit 14 {
                vlan-id 14;
                family inet {
                    address 3.3.3.1/30;
                }
            }
        }
    }
    protocols {
        ospf {
            area 0.0.0.0 {
                interface all;
            }
        }
    }
    policy-options {
        policy-statement lb {
            term lb {
                then {
                    load-balance per-packet;
                }
            }
        }
    }
    routing-options {
        forwarding-table {
            export lb;
        }
    }
    firewall {
        family inet {
            filter test {
                term test {
                    then count test;
                }
            }
        }
    }
}

r2 {
    interfaces {
        ge-0/0/0 {
            unit 23 {                   
                vlan-id 23;
                family inet {
                    address 2.2.2.1/30;
                }
            }
        }
        ge-0/1/0 {
            unit 12 {
                vlan-id 12;
                family inet {
                    filter {
                        input test;
                    }
                    address 1.1.1.2/30;
                }
            }
        }
    }
    protocols {
        ospf {
            area 0.0.0.0 {
                interface all;
            }
        }
    }
    firewall {
        family inet {
            filter test {
                term test {
                    then {
                        count test;
                        log;
                    }
                }
            }
        }
    }
}
r3 {
    interfaces {
        ge-0/1/0 {
            unit 23 {
                vlan-id 23;
                family inet {
                    address 2.2.2.2/30;
                }
            }
            unit 43 {
                vlan-id 43;
                family inet {
                    address 4.4.4.2/30;
                }
            }
        }                               
        lo0 {
            unit 3 {
                family inet {
                    address 100.100.100.1/32;
                }
            }
        }
    }
    protocols {
        ospf {
            area 0.0.0.0 {
                interface all;
            }
        }
    }
}
r4 {
    interfaces {
        ge-0/0/0 {
            unit 43 {
                vlan-id 43;
                family inet {
                    address 4.4.4.1/30;
                }
            }
        }
        ge-0/1/0 {
            unit 14 {
                vlan-id 14;
                family inet {
                    address 3.3.3.2/30;
                }
            }
        }
    }
    protocols {
        ospf {
            area 0.0.0.0 {
                interface all;
            }
        }
    }
}

Again as I mentioned previously Juniper`s forwarding architecutre looks at physical interface as a parent  interface (if you wii)l and all the logical interfaces as a child of the same.