Re: RIPng advertisement hop count 1 (should be 255 per RFC)
On Thu, Jun 20, 2013 at 12:32:18PM -0700, Simon Dickhoven wrote:
Alright. After a lot of digging I got a working RIPng hopcount check.
See attached patch file.
Thanks for the patch and the thorough description.
...
2.1.1) In order to actually receive this additional information I had to
increase the control message buffer size by 13 (a number I arrived at
through trial and error and certainly a hack, rather than the correct
way of doing this... FIXME!!!).
#define CMSG_RX_SPACE CMSG_SPACE(sizeof(struct in6_pktinfo) + 13)
Proper way would be:
#define CMSG_RX_SPACE (CMSG_SPACE(sizeof(struct in6_pktinfo)) +
CMSG_SPACE(sizeof(int
3) Finally, I modified proto/rip/rip.c to take advantage of this new
functionality.
3.1) In the new_iface function I set my newly created socket flag.
#ifndef IPV6
rif-sock-ttl = 1;
rif-sock-flags = SKF_LADDR_RX;
#else
rif-sock-ttl = 255;
rif-sock-flags = (SKF_LADDR_RX | SKF_HLIM_RX);
#endif
...
3.2) Once that was done, the rip_rx function had access to the HLIM info
via the socket struct (s-ttl).
if (s-ttl 255) {
log( L_REMOTE %s: Discarding packet with HLIM = %d 255 from %I on
%s., p-name, s-ttl, s-faddr, i-iface ? i-iface-name : (dummy) );
return 1;
}
BTW, did you notice my comment to your first patch -
http://www.mail-archive.com/bird-users@atrey.karlin.mff.cuni.cz/msg02685.html ?
According to RFC 2080, TTL 255 should be used (and checked)
just for multicast response packets, not for unicast response packets.
But BIRD don't send RIP[ng] requests so it should not receive
any unicast responses and ignoring unsolicited responses with
spoofed source address is probably a good idea anyway.
For compatibility purposes, the TTL checking should be optional.
As far as I can tell, the only thing that could possible affect other
protocols is 2.1.1). Other than that, all my changes exclusively apply
to RIPng since that's the only code that sets the SKF_HLIM_RX flag. As
long as this flag is not set, all my modifications are disabled and the
code is functionally equivalent to what it was before.
Please feel free to use the above modifications and also to give me
feedback on it.
I will do some minor modifications and merge it.
PS: I saw that my Cisco router sets the class for RIPng advertisements
to 0xe0 though I couldn't find any RFCs that call for that. The current
BIRD code (or at least version 1.3.7 of the code) doesn't set the class
at all because it hasn't (/hadn't) been defined by an RFC.
Well, this is not specified in RIP RFC, but it is consistent with RFC 2474
4.2.2.2. We use 0xc0 for IPv4 and we should probably use the same value
for IPv6. BTW, it seems that Linux ignores these values by default for
local tx queue purposes, so we should probably set SO_PRIORITY too.
--
Elen sila lumenn' omentielvo
Ondrej 'SanTiago' Zajicek (email: santi...@crfreenet.org)
OpenPGP encrypted e-mails preferred (KeyID 0x11DEADC3, wwwkeys.pgp.net)
To err is human -- to blame it on a computer is even more so.
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Re: RIPng advertisement hop count 1 (should be 255 per RFC)
Alright. After a lot of digging I got a working RIPng hopcount check.
See attached patch file.
Here's what I did:
1) In order to reduce any deleterious effects of my subsequent
modifications I first introduced a new socket flag in lib/socket.h.
#define SKF_HLIM_RX 8 /* Report Hop Limit for RX packets */
2) I then modified sysdep/unix/io.c to do the following.
2.1) Based on the above flag, I added a setsockopt statement in the
sysio_register_cmsgs function that causes the IPv6 HLIM field to be
passed as ancillary data in the recvmsg call (which takes place in the
sk_read function).
if ((s-flags SKF_HLIM_RX)
setsockopt(s-fd, IPPROTO_IPV6, IPV6_RECVHOPLIMIT, ok, sizeof(ok))
0)
return IPV6_RECVHOPLIMIT;
2.1.1) In order to actually receive this additional information I had to
increase the control message buffer size by 13 (a number I arrived at
through trial and error and certainly a hack, rather than the correct
way of doing this... FIXME!!!).
#define CMSG_RX_SPACE CMSG_SPACE(sizeof(struct in6_pktinfo) + 13)
2.1.2) For backward-compatibility with RFC 2292 I also included this:
#ifndef IPV6_RECVHOPLIMIT
#define IPV6_RECVHOPLIMIT IPV6_HOPLIMIT
#endif
2.2) Then I reworked the sysio_process_rx_cmsgs function to parse out
the HLIM info from the control message and set the TTL field in the
socket struct (s-ttl) (if and only if the SKF_HLIM_RX flag is set).
(see attached)
3) Finally, I modified proto/rip/rip.c to take advantage of this new
functionality.
3.1) In the new_iface function I set my newly created socket flag.
#ifndef IPV6
rif-sock-ttl = 1;
rif-sock-flags = SKF_LADDR_RX;
#else
rif-sock-ttl = 255;
rif-sock-flags = (SKF_LADDR_RX | SKF_HLIM_RX);
#endif
3.2) Once that was done, the rip_rx function had access to the HLIM info
via the socket struct (s-ttl).
if (s-ttl 255) {
log( L_REMOTE %s: Discarding packet with HLIM = %d 255 from %I on
%s., p-name, s-ttl, s-faddr, i-iface ? i-iface-name : (dummy) );
return 1;
}
As far as I can tell, the only thing that could possible affect other
protocols is 2.1.1). Other than that, all my changes exclusively apply
to RIPng since that's the only code that sets the SKF_HLIM_RX flag. As
long as this flag is not set, all my modifications are disabled and the
code is functionally equivalent to what it was before.
Please feel free to use the above modifications and also to give me
feedback on it.
I have tested these modifications with a Quagga (Vyatta) router and a
Cicso router. I used ip6tables on the Quagga (Vyatta) router to mangle
the HLIM in order to force a rejection of routing updates from it.
ip6tables -t mangle -A OUTPUT -p udp -m udp --sport 521 -j HL --hl-set 10
When I removed the mangle rule, routes were accepted. When I re-added
it, routes were rejected again and removed from the routing table.
Note: The above modifications were made to version 1.3.7 of the source
code so they may not apply to the latest code.
Thanks.
- Simon
PS: I saw that my Cisco router sets the class for RIPng advertisements
to 0xe0 though I couldn't find any RFCs that call for that. The current
BIRD code (or at least version 1.3.7 of the code) doesn't set the class
at all because it hasn't (/hadn't) been defined by an RFC.
On 06/18/2013 05:48 PM, Simon Dickhoven wrote:
Correction: The RFC does state explicitly that advertisements must be sent with
an HLIM of 255, as well as that receiving routers must check that the HLIM is
255.
So I guess my little patch makes BIRD half-compliant in that respect then :).
- Simon
On Jun 18, 2013, at 17:38, Simon Dickhoven simon.dickho...@tachyon.com
wrote:
Hi, again
If you were paying attention (unlike myself) you may have noticed that
the below fix doesn't actually make BIRD RFC-compliant.
Rather, it makes BIRD interoperate with other RFC-compliant RIPng routers.
After all, the RFC doesn't state that route advertisements must be sent
with an HLIM of 255 (though that's implied, of course), but rather that
routers must _check_ that the HLIM is 255 when they _receive_ routing
updates.
I tried getting that to work by checking s-ttl in the rip_rx function.
However, that always returns 255 (or, I suspect, whatever rif-sock-ttl
was set to in the new_iface function) regardless of the incoming
packet's HLIM.
I then tried using the sk_set_min_ttl function on the socket in the
new_iface function but got this error:
Kernel does not support IPv6 TTL security
(i.e. the socket protocol doesn't support that option). Since I'm on
Linux (Debian) this error comes from sysdep/linux/sysio.h.
Anyway, I am not familiar enough with the BIRD code to understand where
I can obtain the actual HLIM (TTL) of the incoming packet in order to
ensure that the HLIM (TTL) is 255.
I'll keep digging but if anybody has any suggestions or pointers to get
me moving in the right direction I'd appreciate it.
Thanks.
- Simon
On 06/14/2013 05:41 PM, Simon
Re: RIPng advertisement hop count 1 (should be 255 per RFC)
Hi, again
If you were paying attention (unlike myself) you may have noticed that
the below fix doesn't actually make BIRD RFC-compliant.
Rather, it makes BIRD interoperate with other RFC-compliant RIPng routers.
After all, the RFC doesn't state that route advertisements must be sent
with an HLIM of 255 (though that's implied, of course), but rather that
routers must _check_ that the HLIM is 255 when they _receive_ routing
updates.
I tried getting that to work by checking s-ttl in the rip_rx function.
However, that always returns 255 (or, I suspect, whatever rif-sock-ttl
was set to in the new_iface function) regardless of the incoming
packet's HLIM.
I then tried using the sk_set_min_ttl function on the socket in the
new_iface function but got this error:
Kernel does not support IPv6 TTL security
(i.e. the socket protocol doesn't support that option). Since I'm on
Linux (Debian) this error comes from sysdep/linux/sysio.h.
Anyway, I am not familiar enough with the BIRD code to understand where
I can obtain the actual HLIM (TTL) of the incoming packet in order to
ensure that the HLIM (TTL) is 255.
I'll keep digging but if anybody has any suggestions or pointers to get
me moving in the right direction I'd appreciate it.
Thanks.
- Simon
On 06/14/2013 05:41 PM, Simon Dickhoven wrote:
OK. I looked at proto/rip/rip.c a bit more and figured that I might as
well give it a shot and hack around a little bit. I ended up making this
tiny mod:
--- a/proto/rip/rip.c
+++ b/proto/rip/rip.c
@@ -706,7 +706,11 @@
rif-sock-dport = P_CF-port;
if (new)
{
+#ifndef IPV6
rif-sock-ttl = 1;
+#else
+ rif-sock-ttl = 255;
+#endif
rif-sock-tos = IP_PREC_INTERNET_CONTROL;
rif-sock-flags = SKF_LADDR_RX;
}
Subsequently, I did a full Debian package build based on
http://backports.debian.org/debian-backports/pool/main/b/bird/bird_1.3.7-1~bpo60+1.diff.gz
I added the above patch to the debian/patches dir and appended the patch
file name (I named it 011-ripng_hopcount.patch) to debian/patches/series.
The package built fine. I installed it on my test box and lo and behold:
Vyatta/Quagga is now happy and I'm seeing my IPv6 routes propagate via
RIPng.
Tcpdump reveals that RIP(v2) is still using a TTL of 1 and RIPng is
using an HLIM (IPv6 equivalent of TTL) of 255.
Thanks.
- Simon
On 06/14/2013 03:04 PM, Simon Dickhoven wrote:
Hi,
I just started experimenting with BIRD for an IPv6 deployment. I am
using Vyatta VC6.6R1 router VMs on either side of my BIRD VM (which runs
on a customized Debian Squeeze release with kernel 3.3.1). I installed
bird/bird6 1.3.7 from the squeeze-backports repository.
Here my setup.
Lab Net --- Vyatta --- BIRD on Debian --- Vyatta --- Stub Net
Anyway, I don't have any problems with my configs or anything like that.
My problem is that Vyatta's ripngd (part of Quagga) complains about an
RFC violation when it receives RIPng advertisements from BIRD:
Jun 14 21:43:40 vyatta ripngd[1682]: RIPng packet comes with non 255 hop
count 1 from fe80::20c:29ff:fef8:cbc5
I looked at the source code in rip.c and see this line:
rif-sock-ttl = 1;
which is the only reference I can find to TTL/Hop Count. So I'm guessing
this is the culprit. The latest source code (1.3.10) is identical in
this respect.
RFC 2080 states
[...]
As an additional check, periodic advertisements must have their hop
counts set to 255, and inbound, multicast packets sent from the RIPng
port (i.e. periodic advertisement or triggered update packets) must be
examined to ensure that the hop count is 255.
[...]
The use of the term must leads me to believe that this is not optional
and is therefore required for RFC-compliance.
There seems to be no such requirement for RIP (v1/v2) so simply changing
the source code to indiscriminately set the TTL to 255 is probably not
the right thing to do.
Have others encountered this problem and is there possibly a patch or
something for getting RFC-compliance and hence interoperability with
Vyatta/Quagga(ripngd)?
Thanks.
- Simon
