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Re: ping packet loss when size gt 1500

Chris Davies on 17/10/10 23:08, wrote:
Adam Hardy <adam.ant@cyberspaceroad.com> wrote:
Thanks for all the info. I guess it tells me there's nothing definitely

MTU is a per-link value, and the smallest MTU determines the MTU
for all hops that the packet travels between client and server. If
something between the client and server eats the ICMP messages that say
"you're sending packets that are too large - my MTU's only XYZ" then
you will see this kind of problem, and there's definitely something
wrong. Misconfigured firewalls are typical culprits in such instances.

You should not have to reduce your MTU to reach a particular server.

I tried lowering the MTU to 1400 but it made no difference.

Are you saying the same sort of thing as camaleon who responded earlier, quote:

>>>It can be a black hole router.

Most firewalls block pings that send packets bigger than normal (32-64
bytes) to avoid "ping of death" and "blocking icmp fragment".<<<

I'm running a windows app to monitor it called 'ping plotter' which charts the ping responses and flags up the packet loss, and one server out there in particular loses 15% of pings:

It's on hop 5 of my 23 hop traceroute to mktgw1.ibllc.com (well it was last night - it's gone now).

When I try


I get "Packet filtered" errors. But when I ping past it to my target mktgw1.ibllc.com I don't get the filter error.

When I try

ping -s 1500

I also get packet filtered errors, whereas mktgw1.ibllc.com will just eat the packets.

Is this a different issue completely? Certainly smells different, but suspicious.


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