what is the exact purpose of loopback lo0,ni0 and ni1

[Karthik_2]

# netstat -in
Name Mtu Network Address Ipkts Ierrs Opkts Oerrs Coll
ni0* 0 none none 0 0 0 0 0
ni1* 0 none none 0 0 0 0 0
lo0 4608 127 127.0.0.1 73206890 0 73205714 0 0
lan1* 4352 none none 22995298 0 3100390 0 0
lan0 1500 172.24.10.0 172.24.10.8 26148065 173 20002233 6033 1317024

[melvyn burnard]

If I remember correctly, ni0 and ni1 are used for SLIP connections.

[Volker Borowski]

Loopback is used to have a tcp/ip stack available even without a network card.

Since it is always UP, it is an essential testing device.

Volker

[Karthik_2]

If it is a emulation of TCP/IP stack even without a lan card .Am I right it assuming the traffic through lo0 does not play any part in network collison.Is this traffic going to have any impact on the network or local lan card as such.

[Volker Borowski]

Hi Karthik,

as far as I remember, it is even more:
It detects traffic directed to locally attached nics and redirects this traffic to the loopback interface.

# netstat -r (output adjusted)
Routing tables
Dest/Netmask Gateway Use Interface Pmtu
localhost localhost 23454340 lo0 4136
xxxhp10 xxxhp10 337977 lan0 4136
yyyyyy xxxgw02_bac 0 lan0 1500
192.168.249.0 xxxhp10 0 lan0 1500

You can see, that although the traffic form xxxhp10 <-> xxxhp10 is assigned to lan0 (ether) the Pmtu is adjusted to the size of lo0, because it is adjusted to the size of the route actually used (see "man netstat" on this).

But I am not so sure on this...
(Although I saw exactly the same behavior, when I unhooked the machine from the hub)

Volker