icmp packets on em larger than 1472 [SEC=UNCLASSIFIED]

[Kevin Oberman]

> Date: Thu, 11 Nov 2010 13:01:26 +0800
> From: "Wilkinson, Alex" <alex.wilkinson at dsto.defence.gov.au>
> Sender: owner-freebsd-stable at freebsd.org
> 
> 
>     0n Wed, Nov 10, 2010 at 04:21:12AM -0800, Kirill Yelizarov wrote: 
> 
>     >All my em cards running 8.1 stable don't reply to icmp echo requests packets larger than 1472 bytes.
>     >
>     >On stable 7.2 the same hardware works as expected:
>     ># ping -s 1500 192.168.64.99
>     >PING 192.168.64.99 (192.168.64.99): 1500 data bytes
>     >1508 bytes from 192.168.64.99: icmp_seq=0 ttl=63 time=1.249 ms
>     >1508 bytes from 192.168.64.99: icmp_seq=1 ttl=63 time=1.158 ms
>     >
>     >Here is the dump on em interface
>     >15:06:31.452043 IP 192.168.66.65 > *****: ICMP echo request, id 28729, seq 5, length 1480
>     >15:06:31.452047 IP 192.168.66.65 > ****: icmp
>     >15:06:31.452069 IP **** > 192.168.66.65: ICMP echo reply, id 28729, seq 5, length 1480
>     >15:06:31.452071 IP *** > 192.168.66.65: icmp
>     > 
>     >Same ping from same source (it's a 8.1 stable with fxp interface) to em card running 8.1 stable
>     >#pciconf -lv
>     >em0 at pci0:3:4:0:	class=0x020000 card=0x10798086 chip=0x10798086 rev=0x03 hdr=0x00
>     >    vendor     = 'Intel Corporation'
>     >    device     = 'Dual Port Gigabit Ethernet Controller (82546EB)'
>     >    class      = network
>     >    subclass   = ethernet
>     >
>     ># ping -s 1472 192.168.64.200
>     >PING 192.168.64.200 (192.168.64.200): 1472 data bytes
>     >1480 bytes from 192.168.64.200: icmp_seq=0 ttl=63 time=0.848 ms
>     >^C
>     >
>     ># ping -s 1473 192.168.64.200
>     >PING 192.168.64.200 (192.168.64.200): 1473 data bytes
>     >^C
>     >--- 192.168.64.200 ping statistics ---
>     >4 packets transmitted, 0 packets received, 100.0% packet loss
> 
> works fine for me:
> 
> FreeBSD 8.1-STABLE #0 r213395
> 
> em0 at pci0:0:25:0:class=0x020000 card=0x3035103c chip=0x10de8086 rev=0x02 hdr=0x00
>     vendor     = 'Intel Corporation'
>     device     = 'Intel Gigabit network connection (82567LM-3 )'
>     class      = network
>     subclass   = ethernet
> 
> #ping -s 1473 host
> PING host(192.168.1.1): 1473 data bytes
> 1481 bytes from 192.168.1.1: icmp_seq=0 ttl=253 time=31.506 ms
> 1481 bytes from 192.168.1.1: icmp_seq=1 ttl=253 time=31.493 ms
> 1481 bytes from 192.168.1.1: icmp_seq=2 ttl=253 time=31.550 ms
> ^C

The reason the '-s 1500' worked was that the packets were fragmented. If
I add the '-D' option, '-s 1473' fails on v7 and v8. Are the V8 systems
where you see if failing without the '-D' on the same network segment?
If not, it is likely that an intervening device is refusing to fragment
the packet. (Some routers deliberately don't fragment ICMP Echos Request
packets.) 
-- 
R. Kevin Oberman, Network Engineer
Energy Sciences Network (ESnet)
Ernest O. Lawrence Berkeley National Laboratory (Berkeley Lab)
E-mail: oberman at es.net			Phone: +1 510 486-8634
Key fingerprint:059B 2DDF 031C 9BA3 14A4  EADA 927D EBB3 987B 3751