Re[2]: [LARTC] script to perform dead gateway detection

Re[2]: [LARTC] script to perform dead gateway detection

[Denis Fedorishenko]

Hello Daniel,

Thursday, March 11, 2004, 4:55:15 AM, you wrote:

Maybe better just to use
ping -t 2 anyhost

:)

DC> How about iptables -A OUTPUT --destination ${GATEWAY_1} -j TTL --set-ttl
DC> 2 (or 1, I'm not sure if the ttl dec is done at all with output chains)

DC> So, after the next hop, if the IP address isn't GATEWAY_1, then the
DC> packet is dead in the water.

DC> Ming-Ching Tiew wrote:
>> I am also having some difficulty in doing dead gateway
>> detection using a shell script :-
>> 
>> Basically I am using ping -c 1 ${GATEWAY_1}  If it times
>> out, I supposed it got into error, so it is probably time for me to
>> change route.
>> 
>> However, even if the ping comes back, it does not mean the
>> GATEWAY is alive as my nexthop; this is because I figured
>> that the packet could have made a U-turn via the one of the alive
>> links to come back to answer the ping request, ie the gateway is
>> alive for a packet on the external network, but the gateway 
>> is still down from inside point of view, and this can happen
>> due to a faulty connection between by second link IP and the
>> second link gateway !
>> 
>> Without patching the kernel to do dead gateway detection,
>> how do I find out if a particular gateway is dead as my
>> NEXTHOP ?
>> 
>> 
>> 
>> 
>> 
>> 
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DC> _______________________________________________
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-- 
Best regards,
 Denis                            mailto:nuclearcat@nuclearcat.com

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