# ifconfig output explanation wanted



## l2f (Apr 16, 2014)

Dear,

I try to find the meaning of the ifconfig output:
`ifconfig fxp1`

```
fxp1: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu 1500
        options=48<VLAN_MTU,POLLING>
        ether 00:50:8b:07:ff:56
        inet 192.168.1.1 netmask 0xffffff00 broadcast 192.168.1.255
        media: Ethernet autoselect (100baseTX <full-duplex>)
        status: active
```

Especially the numbers: 
flags=*8843*<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu 1500
and 
options=*48*<VLAN_MTU,POLLING>

It will be great.

Regards,

l2f


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## ralphbsz (Apr 16, 2014)

The numbers are just hex numbers, showing the binary flag bits that are equivalent to the list of flags or options in the pointed brackets.  So "48" is two bits that correspond to VLAN_MTU and POLLING, and so on.  The list of flags has the same information.

The MTU (fundamentally biggest packet size), ethernet MAC (hardware address), IPv4 information, media, and status should be obvious, right?

I don't remember exactly what "metric" is used for, but for some reason I have stuck in my brain that it has to do with routing priority, if the same host can be reached via two different interfaces or something like that.


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## SirDice (Apr 16, 2014)

ralphbsz said:
			
		

> I don't remember exactly what "metric" is used for, but for some reason I have stuck in my brain that it has to do with routing priority, if the same host can be reached via two different interfaces or something like that.


Spot on. You remembered well. With a metric you can give each connection a certain "weight" and you can configure routing to use the least amount of "weight" to get from A to B. You can use this for example if you have 2 similar connections but one travels over an expensive leased-line and the other on a cheap DSL connection. With the metric you can have the routing prefer the cheap DSL connection over the expensive leased-line. Dynamic routing protocols like OSPF make use of this feature to find a preferred path.


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## l2f (Apr 16, 2014)

Dear,

Thank you a lot.

Regards,

l2f


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