Date: Wed, 02 Jun 1999 09:51:55 +1000 From: Mark Summerfield <m.summerfield@ee.mu.oz.au> To: freebsd-net@freebsd.org Subject: Interface implementation and ARP under FreeBSD Message-ID: <199906012352.JAA15035@mullian.ee.mu.OZ.AU>
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Hi freebsd-net'ers,
I'm developing a driver for an experimental network interface. Currently
my development system is running FreeBSD 2.2.7. The system has an
Ethernet interface (xl0) and the experimental interface (exp0). I'm
having real trouble getting address resolution going for my interface.
I know that the BSD implementation of ARP is fairly "ethernet-centric",
but I also know that it does work for networks that have ethernet-like
addressing (e.g. FDDI).
Incoming packets are OK -- I can e.g. construct an ICMP packet addressed
to a host on the local ethernet, send it into the experimental interface,
and, with ipforwarding enabled, "see" (with tcpdump on another host) it
emerge from the Ethernet interface. This implies that the packet is
correctly received on exp0, passed up the IP stack, and routed out of
xl0 intact.
Sending IP packets out of the experimental interface is another matter.
If I configure exp0 with "inet 10.0.0.1 netmask 255.255.255.0" then
"ping 10.0.0.2" my output code calls arpresolve(), and I expect my output
function to be called again, by arprequest(), since the address is not
yet resolved.
Instead I get the message "arpresolve: can't allocate llinfo". I've
looked at the source, and consulted the bible (Wright and Stevens), and
I believe that what it's really telling me is that it can't infer the
route (i.e. interface exp0) to 10.0.0.2, and hence can't work out which
interface to send the ARP request on -- it's not an actual allocation
failure, nor is it one of the conditions explicitly trapped and reported
by arplookup(). I think I must have misconfigured something, either in
my interface initialisation, or via "ifconfig".
I *can* "ping 10.0.0.255" and generate broadcast echo-requests with a
correct source address of 10.0.0.1 on the experimental interface (since
arpresolve() automatically resolves packets with the M_BCAST flag set to
the ethernet broadcast address). The (duplex) experimental interface then
receives an echo-request and passes it up -- and the attempt to generate
a (unicast) echo-reply then results in the error above.
The relevant output of "netstat -r -n", "ifconfig xl0" and "ifconfig exp0"
is (note that tcpdump is running, so the PROMISC flag on xl0 is set):
Routing tables
Internet:
Destination Gateway Flags Refs Use Netif
default 128.250.79.129 UGSc 2 0 xl0
10/24 10.0.0.1 Uc 0 0 exp0
127.0.0.1 127.0.0.1 UH 0 0 lo0
128.250.79.128/25 link#3 UC 0 0
xl0: flags=8943<UP,BROADCAST,RUNNING,PROMISC,SIMPLEX,MULTICAST> mtu 1500
inet 128.250.79.184 netmask 0xffffff80 broadcast 128.250.79.255
ether 00:60:97:8a:37:b9
exp0: flags=3<UP,BROADCAST> mtu 9180
inet 10.0.0.1 netmask 0xffffff00 broadcast 10.0.0.255
lladdr 00:60:97:8a:37:b9
Note that my link-level addresses are Ethernet compatible (this was done
specifically to try to get ARP to work with a minimum of fuss). I have,
in fact, just used the address of the Ethernet interface on each host,
since the choice is essentially arbitrary and this makes identifying
the source of packets easy. The difference is that ifconfig reports
the Ethernet address as "ether" (since it's of type IFT_ETHER), and the
experimental LL address as "lladdr", since it's type IFT_OTHER.
Any hints as to what it is I'm doing wrong would be greatly appreciated.
Thanks,
Mark
----
Dr. Mark Summerfield
Australian Photonics Cooperative Research Centre
Photonics Research Laboratory
Dept. of Electrical and Electronic Engineering
The University of Melbourne
Parkville, 3052 AUSTRALIA
Phone: +61 3 9344 7419
Fax: +61 3 9344 6678
Email: m.summerfield@ieee.org
WWW: http://www.ee.mu.oz.au/staff/summer/index.htm
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