OSPF and loopback interface

fusebox

Im sort of beginning to understand why they have RID and thus a loopback interface. My question is can you ping from that loopback address to another device?? ie: so that the loopback is the source of the ping?

Not sure if this is helpful in anyway, just curious.

hc2ab

fusebox wrote:

My question is can you ping from that loopback address to another device?? ie: so that the loopback is the source of the ping?

Techniquely it is possible. The definition of loopback interface is a device which provides limited function without using underlying layers.

Now the question becomes what you mean by loopback interface. Loopback device don't necessary mean it is network loopback device. Even if it is, it can be in L3, L2, or even L1(hardware loop back by using connector?).

But in short in window or linux you can ping yourself without even having a NIC. Or have multiple loopback pinging each other. So it's possible.

viper75

fusebox wrote:

Im sort of beginning to understand why they have RID and thus a loopback interface. My question is can you ping from that loopback address to another device?? ie: so that the loopback is the source of the ping?

Not sure if this is helpful in anyway, just curious.

From my understanding you can not ping an OSPF loopback address.

tunerX

You can ping a loopback interface address.

You can set the source address by doing an extended ping.

If you just type ping then enter you can access the ping functions like size and count. When it gets to the part about extended options just type y and you will be able to change the source address.

Another thing. If you make some of your interfaces unnumbered with a loopback interface address then any pings from that router over the unnumbered interface will have the loopback interface address as its source.

3620_2#show ip interface brief loopback 1
Interface IP-Address OK? Method Status Protocol
Loopback1 172.25.25.1 YES NVRAM up up

3620_2#ping
Protocol [ip]:
Target IP address: 192.168.1.1
Repeat count [5]:
Datagram size [100]:
Timeout in seconds [2]:
Extended commands [n]: y
Source address or interface: 172.25.25.1
Type of service [0]:
Set DF bit in IP header? [no]:
Validate reply data? [no]:
Data pattern [0xABCD]:
Loose, Strict, Record, Timestamp, Verbose[none]:
Sweep range of sizes [n]:
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.168.1.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 1/2/4 ms
3620_2#