kernel network device interface/link encap

From: jeff sacksteder
Date: Tue Apr 12 2005 - 19:13:23 EST


I need an explanation of what exactly the 'link encap' field returned
by ifconfig means in relationship to an interface. Information about
how to change it and where it comes from would be a tremendous help.

This is apparently a kernel-level feature of a network interface that
can be viewed with ifconfig. How can it be changed?

The specific problem I am trying to work through is related to
openvpn over TUN devices. One end of the tunnel reports 'Link
Encap:point-to-point ' and the other says 'Link encap:UNSPEC'. There
seems to be no list specifically for discussion of tun devices, and I
have seen numerous unanswered postings about various configurations
that include the 'unspecified encapsulation' information. ifconfig
does no appear to be able manipulate the encapsulation attribute.

Exhibit A-

tun0 Link encap:Point-to-Point Protocol
inet addr:10.1.0.2 P-t-P:10.1.0.1 Mask:255.255.255.255
UP POINTOPOINT RUNNING NOARP MULTICAST MTU:1255 Metric:1
RX packets:0 errors:0 dropped:0 overruns:0 frame:0
TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:10
RX bytes:0 (0.0 b) TX bytes:0 (0.0 b)

Exhibit B-

tun0 Link encap:UNSPEC HWaddr
00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00
inet addr:10.1.0.1 P-t-P:10.1.0.2 Mask:255.255.255.255
UP POINTOPOINT RUNNING NOARP MULTICAST MTU:1255 Metric:1
RX packets:0 errors:0 dropped:0 overruns:0 frame:0
TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:10
RX bytes:0 (0.0 b) TX bytes:0 (0.0 b)
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