atalk-proxy#

atalk-proxy listens for AppleTalk DDP (Datagram Delivery Protocol) and AARP (AppleTalk Address Resolution Protocol) traffic on two ethernet interfaces and proxies packets between them.

There are other solutions for this such as multitalk but this one has a few features I needed:

• It does not require kernel or libpcap support for AppleTalk, as is the situation on OpenBSD. Packets are found by looking for specific bytes in the header.

• It drops privileges after opening listening sockets using pledge, when running on OpenBSD.

• Bare AARP packets that appear on the wire without a Logical-Link Control header are given an LLC encapsulation before proxying.

• AARP replies that are sent out from the local side (-t) are inspected and the MAC address of the sender is replaced with the MAC of the egress (-e) interface. This works as a "proxy ARP" solution so other network devices know to send traffic to the device running the proxy to reach devices on the proxy's other interface, which is likely needed on Wi-Fi networks.

Installation#

$ git clone https://github.com/jcs/atalk-proxy
$ cd atalk-proxy
$ make

atalk-proxy was written on OpenBSD and also tested on Linux.

Usage#

When using an emulated Macintosh Plus in pce on my laptop, configured with an emulated DaynaPort SCSI ethernet device, and configured to use EtherTalk for AppleTalk traffic, it sends packets out through a tap interface on my laptop.

I then run atalk-proxy to proxy traffic between that tap0 interface and my laptop's wireless iwx0 interface. That usage for me looks like:

$ doas ./atalk-proxy -e iwx0 -t tap0

This enables the emulated device to communicate with other devices on my network using AppleTalk.

The -d flag can be used to print debugging information where each forwarded packet is described.

$ doas ./atalk-proxy -d -e iwx0 -t tap0
[12:47:35.599] [iwx0] listening on egress using outbound MAC 00:d4:9e:x:x:x
[12:47:35.599] [tap0] listening on tap
[12:47:45.386] [tap0] [ 50] AARP: is there a 65512.1? [-> iwx0]
[12:47:45.741] [tap0] [ 50] AARP: is there a 65512.1? [-> iwx0]
[12:47:46.072] [tap0] [ 50] AARP: is there a 65512.1? [-> iwx0]
[12:47:46.402] [tap0] [ 50] AARP: is there a 65512.1? [-> iwx0]
[12:47:46.734] [tap0] [ 50] AARP: is there a 65512.1? [-> iwx0]
[12:47:47.063] [tap0] [ 50] AARP: is there a 65512.1? [-> iwx0]
[12:47:47.420] [tap0] [ 50] AARP: is there a 65512.1? [-> iwx0]
[12:47:47.735] [tap0] [ 50] AARP: is there a 65512.1? [-> iwx0]
[12:47:48.067] [tap0] [ 50] AARP: is there a 65512.1? [-> iwx0]
[12:47:48.396] [tap0] [ 50] AARP: is there a 65512.1? [-> iwx0]
[12:47:48.750] [tap0] [ 42] ZIP: GetNetInfo [-> iwx0]
[12:47:49.566] [tap0] [ 42] ZIP: GetNetInfo [-> iwx0]
[12:47:50.404] [tap0] [ 42] ZIP: GetNetInfo [-> iwx0]
[12:47:51.270] [tap0] [ 67] NBP: lookup: "nanomac:Macintosh Plus@*" [-> iwx0]
[12:47:52.324] [tap0] [ 67] NBP: lookup: "nanomac:Macintosh Plus@*" [-> iwx0]
[12:47:53.231] [tap0] [ 67] NBP: lookup: "nanomac:Macintosh Plus@*" [-> iwx0]
[12:47:57.418] [tap0] [ 56] NBP: lookup: "=:AFPServer@*" [-> iwx0]
[12:47:57.580] [iwx0] [ 42] AARP: who has 57344.0? tell 256.12 [-> tap0]
[12:47:57.610] [tap0] [ 50] AARP: 65512.12 is at 00:80:19:c0:c0:c0: replacing MAC in outbound AARP reply [-> iwx0]
[12:47:57.612] [iwx0] [ 57] NBP: reply[1]: "fs:AFPServer@*" [-> tap0]
[12:47:58.593] [tap0] [621] echo from 65512.1 to 65280.224 [-> iwx0]
[12:47:58.596] [iwx0] [621] echo from 65280.224 to 65512.1 [-> tap0]
[12:47:58.622] [tap0] [ 43] transaction protocol [-> iwx0]
[12:47:58.628] [iwx0] [470] transaction protocol [-> tap0]
[12:47:59.134] [tap0] [ 56] NBP: lookup: "=:AFPServer@*" [-> iwx0]
[12:47:59.443] [iwx0] [ 57] NBP: reply[1]: "fs:AFPServer@*" [-> tap0]
[12:48:00.337] [tap0] [ 43] transaction protocol [-> iwx0]

Caveats#

atalk-proxy only proxies AppleTalk and AARP traffic and does not proxy IP or ARP traffic. Use kernel-level NAT if you also need IP traffic proxied.

On Linux you may need to enable the ALLMULTI flag on the egress Wi-Fi interface:

$ sudo ip link set wlan0 allmulticast on