Using virtual interface with dhcpd v3.0.5

[Randall C Grimshaw]

> > >This morning we copied the conf and lease files and started the
> > >server on the new machine.  It was processing DHCPDISCOVER requests
> > >on our eth1 interface, but not on the virtual eth1:1 interface.
> > >Both interfaces were processing DHCPREQUESTs.
> > >
> > >Any thoughts on what we need to do to get this working again?
> > >
> > >Also, can I put "eth1 eth1:1" on the startup command line, or is
> > >"eth1" sufficient?
> >
> > You can't use virtual interfaces with DHCP. Think about it, when a
> > broadcast packet comes in, how you you figure which interface it
> > should have been destined for ?

> Actually you can, *if* your dhcpd is compiled with USE_SOCKETS and
> you configure it to listen to a specific interface/IP address instead
> of all broadcast traffic. It assumes all your requests are coming in
> via DHCP relay agents (thus no broadcast handling needed). Obviously
> this is not a general purpose DHCP installation, and you need to know
> what you're doing...


Virtual interfaces can make sense in the context of 802.1q vlan truncking.... but note as wriiten earlier - there is always a base interface.

so for a startup like
DHCPDARGS="eth1.192 eth1.154 eth1.452 eth1.453 eth1.454 eth1.455 eth1.456 eth1.
457 eth1.460"

you also have a network something like
eth1.192  Link encap:Ethernet  HWaddr 00:11:22:33:44:55 
          inet addr:x.x.x.x.0  Bcast:x.x.x.x.255  Mask:255.255.252.0
          inet6 addr: xxxx:xxxx:xxxx:xxxx:xxxx:xxxx/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:17976870 errors:0 dropped:0 overruns:0 frame:0
          TX packets:17032019 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0 
          RX bytes:4006985054 (3.7 GiB)  TX bytes:3260831688 (3.0 GiB)

eth1.192:0 Link encap:Ethernet  HWaddr 00:11:22:33:44:55  
          inet addr:x.x.x.x.1  Bcast:x.x.x.x.255  Mask:255.255.252.0
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1

eth1.192:1 Link encap:Ethernet  HWaddr 00:11:22:33:44:55  
          inet addr:x.x.x.x.1  Bcast:x.x.x.x.255  Mask:255.255.255.0
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1

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Randall Grimshaw
rgrimsha at syr.edu