kern/76966: udp/520 reply packets when routed is not running
Emil Cazamir
emil.cazamir at galati.rdsnet.ro
Mon Feb 7 08:18:39 PST 2005
-----Original Message-----
From: David Malone [mailto:dwmalone at maths.tcd.ie]
Sent: 7 februarie 2005 14:09
To: Emil Cazamir
Cc: freebsd-bugs at FreeBSD.org
Subject: Re: kern/76966: udp/520 reply packets when routed is not running
> There is no problem with the netmask, there are several subnets sharing
the
> same wire. I lokked into few kernel config files and I didn't found
anything
> specific. I think that the cause of what's happening is somewhere in
> natd/libalias, all the machines which respond to [or forward] udp/520
> packets are running natd. I will make available kernel config files,
process
> listings, etc if it is required.
OK - that probably explains how the source address of the packet
was changed. I can suggest two things that might be useful. First,
if you could check with tcpdump -X that the payloads of the packets
look identical. Second, it might be worth posting your natd/libalias
config.
David.
----
I captured some packets at the same time on two machines: the gateway
[common for all subnets] and one freebsd box running natd. Tcpdump's
timestamp shows a 12 minutes difference, but I can assure you that they were
taken at the same time.
Gateway:
I changed the real IP addresses with 192.168.x.x, using the same netmask.
The subnets are: 192.168.0.126/26, 192.168.1.0/28 and 192.168.2.0/26. The
machine running routed is a linux box [don't know what distribution/kernel]
--->
[linux gateway]
17:57:31.528159 IP (tos 0x0, ttl 64, id 0, offset 0, flags [DF], length:
52) 192.168.0.126.520 > 192.168.0.127.520: [udp sum ok]
RIPv1, Request, length: 24
0x0000: 0101 0000 0000 0000 0000 0000 0000 0000
0x0010: 0000 0000 0000 0010
0x0000: 4500 0034 0000 4000 4011 2a34 51c4 367e E..4.. at .@.*4Q.6~
0x0010: 51c4 367f 0208 0208 0020 ea07 0101 0000 Q.6.............
0x0020: 0000 0000 0000 0000 0000 0000 0000 0000 ................
0x0030: 0000 0010 ....
17:57:31.528555 IP (tos 0x0, ttl 63, id 0, offset 0, flags [DF], length:
52) 192.168.0.126.520 > 192.168.0.127.520: [udp sum ok]
RIPv1, Request, length: 24
0x0000: 0101 0000 0000 0000 0000 0000 0000 0000
0x0010: 0000 0000 0000 0010
0x0000: 4500 0034 0000 4000 3f11 2b34 51c4 367e E..4.. at .?.+4Q.6~
0x0010: 51c4 367f 0208 0208 0020 ea07 0101 0000 Q.6.............
0x0020: 0000 0000 0000 0000 0000 0000 0000 0000 ................
0x0030: 0000 0010 ....
17:57:31.528712 IP (tos 0x0, ttl 63, id 0, offset 0, flags [DF], length:
52) 192.168.0.126.520 > 192.168.0.127.520: [udp sum ok]
RIPv1, Request, length: 24
0x0000: 0101 0000 0000 0000 0000 0000 0000 0000
0x0010: 0000 0000 0000 0010
0x0000: 4500 0034 0000 4000 3f11 2b34 51c4 367e E..4.. at .?.+4Q.6~
0x0010: 51c4 367f 0208 0208 0020 ea07 0101 0000 Q.6.............
0x0020: 0000 0000 0000 0000 0000 0000 0000 0000 ................
0x0030: 0000 0010 ....
17:57:31.528721 IP (tos 0x0, ttl 63, id 0, offset 0, flags [DF], length:
52) 192.168.0.126.520 > 192.168.0.127.520: [udp sum ok]
RIPv1, Request, length: 24
0x0000: 0101 0000 0000 0000 0000 0000 0000 0000
0x0010: 0000 0000 0000 0010
0x0000: 4500 0034 0000 4000 3f11 2b34 51c4 367e E..4.. at .?.+4Q.6~
0x0010: 51c4 367f 0208 0208 0020 ea07 0101 0000 Q.6.............
0x0020: 0000 0000 0000 0000 0000 0000 0000 0000 ................
0x0030: 0000 0010 ....
17:57:31.528771 IP (tos 0x0, ttl 63, id 0, offset 0, flags [DF], length:
52) 192.168.1.83.520 > 192.168.0.127.520: [udp sum ok]
RIPv1, Request, length: 24
0x0000: 0101 0000 0000 0000 0000 0000 0000 0000
0x0010: 0000 0000 0000 0010
0x0000: 4500 0034 0000 4000 3f11 46c5 d45d 9853 E..4.. at .?.F..].S
0x0010: 51c4 367f 0208 0208 0020 0599 0101 0000 Q.6.............
0x0020: 0000 0000 0000 0000 0000 0000 0000 0000 ................
0x0030: 0000 0010 ....
17:57:31.528780 IP (tos 0x0, ttl 63, id 0, offset 0, flags [DF], length:
52) 192.168.2.33.520 > 192.168.0.127.520: [udp sum ok]
RIPv1, Request, length: 24
0x0000: 0101 0000 0000 0000 0000 0000 0000 0000
0x0010: 0000 0000 0000 0010
0x0000: 4500 0034 0000 4000 3f11 2b91 51c4 3621 E..4.. at .?.+.Q.6!
0x0010: 51c4 367f 0208 0208 0020 ea64 0101 0000 Q.6........d....
0x0020: 0000 0000 0000 0000 0000 0000 0000 0000 ................
0x0030: 0000 0010 ....
17:57:31.528806 IP (tos 0x0, ttl 63, id 0, offset 0, flags [DF], length:
52) 192.168.0.126.520 > 192.168.0.127.520: [udp sum ok]
RIPv1, Request, length: 24
0x0000: 0101 0000 0000 0000 0000 0000 0000 0000
0x0010: 0000 0000 0000 0010
0x0000: 4500 0034 0000 4000 3f11 2b34 51c4 367e E..4.. at .?.+4Q.6~
0x0010: 51c4 367f 0208 0208 0020 ea07 0101 0000 Q.6.............
0x0020: 0000 0000 0000 0000 0000 0000 0000 0000 ................
0x0030: 0000 0010 ....
17:57:31.529237 IP (tos 0x0, ttl 63, id 0, offset 0, flags [DF], length:
52) 192.168.0.126.520 > 192.168.0.127.520: [udp sum ok]
RIPv1, Request, length: 24
0x0000: 0101 0000 0000 0000 0000 0000 0000 0000
0x0010: 0000 0000 0000 0010
0x0000: 4500 0034 0000 4000 3f11 2b34 51c4 367e E..4.. at .?.+4Q.6~
0x0010: 51c4 367f 0208 0208 0020 ea07 0101 0000 Q.6.............
0x0020: 0000 0000 0000 0000 0000 0000 0000 0000 ................
0x0030: 0000 0010 ....
8 packets captured
8 packets received by filter
0 packets dropped by kernel
<--- Gateway
a Freebsd host in one subnet, running natd:
--->
[freebsd-4.10-box]:~# tcpdump -nXvvni rl0 -p udp and port 520
tcpdump: listening on rl0
17:45:48.504732 192.168.0.126.520 > 192.168.0.127.520: [udp sum ok]
RIPv1-req 24 (DF) (ttl 64, id 0, len 52)
0x0000 4500 0034 0000 4000 4011 2a34 51c4 367e E..4.. at .@.*4Q.6~
0x0010 51c4 367f 0208 0208 0020 ea07 0101 0000 Q.6.............
0x0020 0000 0000 0000 0000 0000 0000 0000 0000 ................
0x0030 0000 0010 ....
17:45:48.505114 192.168.2.33.520 > 192.168.0.127.520: [udp sum ok]
RIPv1-req 24 (DF) (ttl 63, id 0, len 52)
0x0000 4500 0034 0000 4000 3f11 2b91 51c4 3621 E..4.. at .?.+.Q.6!
0x0010 51c4 367f 0208 0208 0020 ea64 0101 0000 Q.6........d....
0x0020 0000 0000 0000 0000 0000 0000 0000 0000 ................
0x0030 0000 0010 ....
^C
670 packets received by filter
0 packets dropped by kernel
<---
Best regards,
Emil Cazamir
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