Re: ping packet loss when size gt 1500

[Adam Hardy <adam.ant@cyberspaceroad.com>]

Chris Davies on 20/10/10 11:45, wrote:
> Adam Hardy <adam.ant@cyberspaceroad.com> wrote:
> > Chain FORWARD (policy ACCEPT)
> > target     prot opt source               destination
> > TCPMSS     tcp  --  anywhere             anywhere           tcp 
> > flags:SYN,RST/SYN TCPMSS set 1460
>
> So you're clamping TCPMSS at 1460? What if the MSS needs to be lower,
> i.e. your MTU has dropped? (I'm not sure how iptables handles this
> situation as I don't usually need to fiddle MSS and MTU.)
>
> Would you remove this rule and retest, please?
>
>
> > Chain OUTPUT (policy ACCEPT)
> > target     prot opt source               destination
> > DROP       icmp --  anywhere             anywhere           icmp 
> > destination-unreachable
> > DROP       icmp --  anywhere             anywhere           state INVALID

No, no I'm not deliberately doing that. It's the DLink modem that has this 
mini-firewall set up in its ROM. I can telnet in & drop the rules, but I have to 
remember to do it every power cycle.

What I need is a ping test or something that I can put in smokeping to alert me 
when I forget, e.g. this morning there was a power outage that took out the modem.

What do you mean by 'clamped'?

I dropped these firewall rules just now and "ping -s 1473 mktgw1.ibllc.com" 
loses all packets, so our thread pretty much only concerns the situation when 
this firewall is down.

My actual question is: what would fail to get through when that firewall was up? 
 For my testing purposes.

Regards
Adam