Strange FreeBSD behavior when trying to forward beetween ipsec
crypted gif's. May be a problem with ICMP unreach packets at all
Tom Judge
tom at tomjudge.com
Thu Sep 16 15:08:55 UTC 2010
On 09/16/2010 09:00 AM, Vladimir Grigorov wrote:
> Greetings all.
>
>
> I have strange problems related to passage icmp need-frag packets, and, as result, all packets with packets length greater than output gif MTU.
>
> Network diagram:
>
> [HostA] -- (mtu 1500) --- [FW1] --- ipsec gif mtu 1280 <-gif1 -- [FW2] - gif0 -> ipsec gif mtu 6100 - [FW3] -(mtu 1500) - [HostB]
>
> All FW's - Freebsd hosts
> HostA - freebsd host
> HostB - Cisco 3750e switch in L3 mode
>
> HostA can reach HostB and vice versa. Ping with length above 1280 works fine (pmtu = 1280). Ping with len=1281 without df bit also work fine. But ping with mtu 1281 fails.
>
> Question: Why FW2 does not send ICMP need-fragment-but-DF-set message to HostB ?
>
If you take a look at icmp_error() in sys/netinet/ip_icmp.c you will see
that icmp errors are not sent for packets that have been previously been
decrypted by IPSec. I have a feeling that this is because
icmp_reflect() will not use the correct output path but I may be and
most probably am wrong. Bjoern (CC'd) can probably shed more light on
it.
I am willing to spend some time on the fix for this if someone could
give me a gentle nudge in the right direction.
> I try to permit icmp from all interfaces on FW2, explicit send unreachable packet for all ip packets from defined source ip - nothing happens. I see increased packets counts related my source ip, but cant see responce icmps with unreachable code
>
> uname -a
> FreeBSD fw2-mru.astrum-nival.com 8.0-RELEASE-p3 FreeBSD 8.0-RELEASE-p3 #3: Thu Jul 1 18:24:35 MSD 2010 root at fw2-mru.astrum-nival.com:/usr/obj/usr/src/sys/gw amd64
>
> ifconfig gif0
> gif0: flags=8051<UP,POINTOPOINT,RUNNING,MULTICAST> metric 0 mtu 6100
> tunnel inet 217.69.143.28 --> 217.69.143.57
> inet 10.192.224.5 --> 10.192.224.6 netmask 0xfffffffc
> options=1<ACCEPT_REV_ETHIP_VER>
>
> ifconfig gif1
> gif1: flags=8051<UP,POINTOPOINT,RUNNING,MULTICAST> metric 0 mtu 1280
> tunnel inet 217.69.143.28 --> 88.212.205.166
> inet 10.160.192.6 --> 10.160.192.5 netmask 0xfffffffc
> options=1<ACCEPT_REV_ETHIP_VER>
>
> netstat -nr | grep 192.168.224
>
> 192.168.224.0/22 10.192.224.6 UG1 0 36031303 gif0
>
> netstat -nr | grep 192.168.160.
> 192.168.160.0/24 10.160.192.5 UG1 0 10969867 gif1
>
> # ipfw show
> 00006 10 6505 allow icmp from any to 192.168.225.1 via gif0
> 00100 10524445 1225052712 allow ip from any to any via lo0
> 00200 0 0 deny ip from any to 127.0.0.0/8
> 00300 0 0 deny ip from 127.0.0.0/8 to any
> 00305 2054 433651 allow icmp from any to any via gif0 icmptypes 3,11
> 00306 0 0 allow icmp from any to 192.168.225.1 via gif0
> 00310 6960 575159 nat 220 ip from table(10) to any via vlan220
> 00315 1198 70832 deny ip from not me to 192.168.66.0/23 out xmit vlan220
> 00320 6512 1611912 nat 220 ip from 192.168.66.0/23 to 192.168.13.199 in recv vlan220
> 00400 114560294 8963623578 nat 123 ip from 192.168.196.0/24 to any out via vlan506
> 00402 36831424 2199804860 nat 123 ip from 192.168.193.0/24 to any out via vlan506
> 00403 153380 9265905 nat 123 ip from 192.168.197.0/24 to any out via vlan506
> 00500 0 0 nat 123 ip from any to 195.211.130.9 in via vlan506
> 00501 147593882 174870597871 nat 123 ip from any to 195.211.130.9 in via vlan500
> 01100 0 0 allow tcp from table(21) to table(23) dst-port 29000
> 01110 0 0 deny tcp from table(22) to table(23) dst-port 29000
> 01120 3 144 deny tcp from table(20) to table(23) dst-port 29000
> 65530 589120438508 133855063718386 allow ip from any to any
> 65535 0 0 deny ip from any to any
>
> try to ping from cisco:
>
> c3750e.gldn#ping 192.168.160.248 source 192.168.225.1 repea 5 size 1281 df
>
> Type escape sequence to abort.
> Sending 5, 1281-byte ICMP Echos to 192.168.160.248, timeout is 2 seconds:
> Packet sent with a source address of 192.168.225.1
> Packet sent with the DF bit set
> .....
> Success rate is 0 percent (0/5)
>
> tcpdump on gif0 (large mtu before small mtu gif)
>
> [root at fw2-mru ~]# tcpdump -i gif0 -vvv -n host 192.168.225.1
> tcpdump: listening on gif0, link-type NULL (BSD loopback), capture size 96 bytes
> 17:55:54.006210 IP (tos 0x0, ttl 254, id 805, offset 0, flags [DF], proto ICMP (1), length 1281)
> 192.168.225.1 > 192.168.160.248: ICMP echo request, id 161, seq 0, length 1261
> 17:55:56.013039 IP (tos 0x0, ttl 254, id 806, offset 0, flags [DF], proto ICMP (1), length 1281)
> 192.168.225.1 > 192.168.160.248: ICMP echo request, id 161, seq 1, length 1261
> 17:55:58.015870 IP (tos 0x0, ttl 254, id 807, offset 0, flags [DF], proto ICMP (1), length 1281)
> 192.168.225.1 > 192.168.160.248: ICMP echo request, id 161, seq 2, length 1261
> 17:56:00.020833 IP (tos 0x0, ttl 254, id 808, offset 0, flags [DF], proto ICMP (1), length 1281)
> 192.168.225.1 > 192.168.160.248: ICMP echo request, id 161, seq 3, length 1261
> 17:56:02.027756 IP (tos 0x0, ttl 254, id 809, offset 0, flags [DF], proto ICMP (1), length 1281)
> 192.168.225.1 > 192.168.160.248: ICMP echo request, id 161, seq 4, length 1261
> ^C
> 5 packets captured
> 99753 packets received by filter
> 0 packets dropped by kernel
>
> tcpdump on gif1 (small mtu on route to destination)
>
> (nothing)
>
> but if i omit df on cisco:
>
> [root at fw2-mru ~]# tcpdump -i gif1 -vvv -n host 192.168.225.1
> tcpdump: listening on gif1, link-type NULL (BSD loopback), capture size 96 bytes
> 17:59:03.083053 IP (tos 0x0, ttl 253, id 815, offset 0, flags [+], proto ICMP (1), length 1276)
> 192.168.225.1 > 192.168.160.248: ICMP echo request, id 163, seq 0, length 1256
> 17:59:03.083147 IP (tos 0x0, ttl 253, id 815, offset 1256, flags [none], proto ICMP (1), length 25)
> 192.168.225.1 > 192.168.160.248: icmp
> 17:59:03.090882 IP (tos 0x0, ttl 253, id 816, offset 0, flags [+], proto ICMP (1), length 1276)
> 192.168.225.1 > 192.168.160.248: ICMP echo request, id 163, seq 1, length 1256
> 17:59:03.090976 IP (tos 0x0, ttl 253, id 816, offset 1256, flags [none], proto ICMP (1), length 25)
> 192.168.225.1 > 192.168.160.248: icmp
> 17:59:03.097254 IP (tos 0x0, ttl 253, id 817, offset 0, flags [+], proto ICMP (1), length 1276)
> 192.168.225.1 > 192.168.160.248: ICMP echo request, id 163, seq 2, length 1256
> 17:59:03.097346 IP (tos 0x0, ttl 253, id 817, offset 1256, flags [none], proto ICMP (1), length 25)
> 192.168.225.1 > 192.168.160.248: icmp
> 17:59:03.105749 IP (tos 0x0, ttl 253, id 818, offset 0, flags [+], proto ICMP (1), length 1276)
> 192.168.225.1 > 192.168.160.248: ICMP echo request, id 163, seq 3, length 1256
> 17:59:03.105844 IP (tos 0x0, ttl 253, id 818, offset 1256, flags [none], proto ICMP (1), length 25)
> 192.168.225.1 > 192.168.160.248: icmp
> 17:59:03.115617 IP (tos 0x0, ttl 253, id 819, offset 0, flags [+], proto ICMP (1), length 1276)
> 192.168.225.1 > 192.168.160.248: ICMP echo request, id 163, seq 4, length 1256
> 17:59:03.115707 IP (tos 0x0, ttl 253, id 819, offset 1256, flags [none], proto ICMP (1), length 25)
> 192.168.225.1 > 192.168.160.248: icmp
>
> e.g. destination reachable, fragmentation work, routes symmetrical.
>
> any comments ?
>
>
>
Good Luck
Tom
--
TJU13-ARIN
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