30 Jul
2016
30 Jul
'16
3:17 a.m.
[Apologies for the repost: I meant to have a useful Subject:
header and accidentally omitted that earlier.]
[Forgive the top-posting: I include the full text of what I'd
written several weeks ago below for refresher and reference.]
To recap, I've set up IPENCAP tunnels to AMPRNet networks on a
Ubiquiti EdgeRouter Lite running OpenBSD: there is one gif(4)
interface per tunnel and routes are kept in a dedicated routing
table (like Linux, OpenBSD supports multiple routing domains on a
single system); firewall rules are used to go from one routing
domain to another.
The biggest piece missing was a daemon to handle receiving 44net
RIP packets and use that data to maintain tunnels and routes. I
thought about porting one, but decided of write my own instead.
It has been running for a few weeks now on my node and while it's
still not quite "done" it seems to work well enough that I decided
it was time to cast a somewhat a wider net and push it up to
GitHub for comment from others.
A couple of quick notes on implementation:
1. The program maintains a copy of the AMPRNet routing table in
a modified PATRICIA trie (really a compressed radix tree).
Routes are expired after receiving a RIP packet.
2. A similar table of tunnels is maintained.
3. Tunnel interfaces are reference counted and garbage collected.
A bitmap indicating which tunnels are in use is
maintained.
4. The program is completely self-contained in the sense that I
do not fork/exec external commands to e.g. configure tunnels
or manipulate routes. That is all done via ioctls or writing
messages to a routing socket.
There is more to do; I'm sure there are a few bugs. I'd also like
to query the system state at startup to initialize the routing and
tunnel tables. Exporting and/or parsing an encap file would be
nice. Logging and error checking can, I'm sure, be improved.
It's about 1200 lines of non-comment code, compiles down to a 28K
MIPS64 executable (stripped). The code is at
https://github.com/dancrossnyc/44ripd
Please have a look and let me know what you think!
- Dan C.
On Fri, Jun 17, 2016 at 5:46 PM, Dan Cross <crossd(a)gmail.com> wrote:
On Tue, Jun 14, 2016 at 12:51 PM, Dan Cross
<crossd(a)gmail.com> wrote:
I'm trying to set up an AMPRNet gateway
at home and am running into
some problems. Has anyone successfully configured a BSD-based gateway
that would be willing to give me some pointers?
[snip]
It seems like what I want to do is configure a gif(4) interface
for tunnel traffic, but my attempts at doing so all seem to fail,
and documentation for setting up an IPENCAP tunnel is related to
setting up IPsec gateways; my attempts at transliterating from the
examples for e.g. Linux and Cisco et al have failed.
If someone has gone down this road before and has a working
setup, that would be tremendously helpful. If someone could send
me output from 'ifconfig -a' and/or 'netstat -rn -f inet' and
possibly some 'tcpdump' output, I could probably muddle through the
rest. If there are any caveats in setting up a 'pf' based firewall,
that would be helpful as well. If not, I suppose my next step will
be to reinstall RouterOS on the ERL, try and get everything configured,
and then see if I can replicate under BSD.
Folks,
I just wanted to do a quick followup to this for the archives.
I am now successfully transferring traffic between my 44net subnet
(44.44.107.0/24) and the rest of the world using my OpenBSD-based
router.
A quick recap of my setup:
1. I have a Comcast business class circuit.
2. I have a dedicated static IP address to use as an endpoint for
44net traffic.
3. My comcast router is just a router; no NATing, no firewalling.
4. My (non-comcast) edge router is a Ubiquiti EdgeRouter Lite
running OpenBSD 5.9. It has three ethernet interfaces:
a. cnmac0 is the external interface connected to Comcast's network
b. cnmac1 connects to my internal network
c. cnmac2 is my internal gateway to 44.44.107.0/24.
On OpenBSD, tunneling interfaces for IPENCAP are provided by
'gif' pseudo-devices. Unlike Linux, it appears that one creates a
separate 'gif' interface for each tunnel, but one seems able to
create an arbitrary number of such interfaces: I created a thousand
as a test. I'm sure there is a limit but it seems sufficiently
high that practically routing AMPRNet traffic won't run up against
it. (Again, if someone knows of a different way to configure a
single 'gif' interface so that it could support multiple tunnels,
I'd be happy to know about it). In other words, don't worry about
scalability because you are creating a separate 'gif' interface for
each tunnel to another AMPRNet site.
On AMPRNet, the UCSD gateway *will not* pass traffic for an
IP address that does not have a corresponding entry in the AMPR.ORG
domain. Also, 44.0.0.1 does not respond to 'ping' from 44/8 IP's.
Caveat emptor as one tries to test: make sure you have DNS entries
for your addresses and try pinging something other than 44.0.0.1
or you'll suffer contusions banging your head against a desk trying
to figure out why nothing appears to work....
Once I had a tunnel up to UCSD, I found that I could ping my
44.44.107.1 machine from a host on my internal network, but not
from arbitrary machines. This was interesting; it turns out that
hosts on my internal network get NAT'ed to another IP address on
the small subnet I got from Comcast (through another, completely
separate router -- not comcast's router but another ERL). What was
happening was that as I ping'ed 44.44.107.1 from e.g. my laptop,
ICMP echo request packets got NAT'ed to this other address and
routed over to amprgw.sysnet.ucsd.edu and tunneled back to the
external interface of my AMPRNet gateway. The gateway accepted the
encapsulated ICMP echo requests (I have a PF rule that explicitly
allows ping) and forwarded them across the tunnel interface where
they were unencapsulated; the IP stack saw that the result was
addressed to an IP address on a local interface (i.e., they were
for the router) and generated an ICMP echo response packet with a
*source* address of 44.44.107.1 and a *destination* address of the
external address of my other router (that is, the address the ICMP
echo request was NAT'ed to). This matched the network route for
my local Comcats subnet and so my AMPRNet router realized it could
pass the packet back to my other router directly. It did so and
the other router happily took the packet, matched it back through
the NAT back to the original requesting machine (my laptop) and
forwarded it: hence, I got my ping responses back. But note that
the response was not going through the tunnel back to UCSD: it was
being routed directly through the external interface.
Now consider what happens when I tried to ping 44.44.107.1 from
a different machine on some other network. The ICMP echo request
packet gets routed through the UCSD gateway and tunneled back to
my gateway as before, but since responses don't go through back
through the tunnel, the response packet matches the default route
of my gateway and get's forwarded to comcast's router. Comcast
would look at it, see that 44.44.107.1 wasn't on one of it's known
networks that it would route floor, and discard the response. Oops.
The solution was to set up a separate routing table in a different
routing domain specifically for AMPRNet traffic, and tie the two
together using firewall rules. In the AMPRNet routing table, I
could set my default route to point to the UCSD gateway, so any
traffic sent from one of my 44.44.107.0/24 addresses that doesn't
match a route to a known tunnel gets forwarded through
amprgw.sysnet.ucsd.edu. With that in place, I could ping my gateway
from random machines. This must seem obvious to a lot of folks
here, but it took me a little while to figure out what was going
on. Things are working now, however.
So far I have encountered two other caveats: I decided to
configure two tunnel interfaces statically at boot time: 'gif0'
goes to the UCSD tunnel, and 'gif1' sets up a tunnel to N1URO for
his 44.88 net. Under OpenBSD, I assumed that the natural way to
do this would be to add /etc/hostname.gif0 and /etc/hostname.gif1
files and this does in fact create the tunnels at boot time. However,
traffic going out from my gateway doesn't seem to get sent through
the tunnels; I did not bother to track down exactly why, but I
believe it has to do with some kind of implicit ordering dependency
when initializing PF. When I set up the separate routing domain,
it struck me that the language accepted by /etc/netstart in an
/etc/hostname.if file was not sufficiently rich to set up tunnels
in a routing domain, so I capitulated and just set up the static
interfaces from /etc/rc.local; imperfect but it works.
The second caveat is that I seem to have tickled a kernel error
trying to set up an alias of a second IP address on my 44.44.107.1
NIC; I get a kernel panic due to an assertion failure. It looks a
bug to me, but I haven't had the bandwidth to track it down. In
the meanwhile, simply don't add aliases to interfaces in non-default
routing domains.
I'll try to go through my notes and type up something for the
wiki.
The next step is to write a modified version of rip44d for BSD.
I may take a stab at that this weekend if I can get some time. As
near as I can tell, the wire format of the protocol is strictly
RIPv2; the difference is what the gateway does with the data in the
RIP packet (it sets up tunnels in addition to maintaining routes).
Anyway, I hope this can be of some small help to someone else
who wants to run an OpenBSD-based gateway!