On 2012-05-16, Russell Garrison <russell.garri...@gmail.com> wrote:
>> On Wed, May 16, 2012 at 9:40 AM, Indunil Jayasooriya
>> <induni...@gmail.com> wrote:
>
>>> If yes, How to ping external internet host when that link is DOWN? I find
>>> it difficult?
>>>
>>> I tried it with below commands
>>>
>>>
>>> ping -I WAN1_if_ip www.google.lk
>>>
>>> ping -I WAN2_if_ip www.google.lk
>>>
>>>
>>> Some times it works? some times it does NOT?
>>>
>>> Could you pls explain why?

Route lookups are based on the *destination* address not the source
address, you could add a route for a certain destination via a
certain interface to send packets out that way.

> I have been asked by management a few times about why some pings fail
> when you ping things like google servers and core routers at the ISP.

Management might need to set the TOS bits.

ping -T i_am_management_my_packets_are_important_dammit www.google.com

If they are really important they can use -i0.0001 -e to be sure
people pay attention. Needs root but they are probably logged
in like that already, right? :)

> The short answer I give is that things like that are too busy being
> the Internet to respond to all the ping traffic that doesn't do
> anything to enable them to be the Internet. Best advice is to consult
> your routing tables or contact your ISP and have your ifstated ping
> the far-end of your internet connection. Those systems are typically
> less busy and have a higher expectation of answering all pings while
> up.

"far-end of your internet connection" tends to be a router, which are
usually one of the worst things to be pinging, something like a
local web or ntp server might be a better idea.

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