ttl expired packet counter

[kphelps]

Is there a counter for discards due to ttl expiration?  Does this roll up to a global error counter like ifInErrors or is it tracked separately?

[AFROJ AHMAD]

Hi,

TTL can be tracked or used differently depends , where it is been used.

for Example:

For DNS

TL in DNS means how much time will it take for your browser to reload the new DNS information.

So, if you visit a website that has a TTL of 6 hours, your browser will not need to check for any new information for up to 6 hours. Beyond that, your browser will be forced to look up the DNS data to get the most up-to-date information.

FOR IP Packet

Every IP packet that gets sent out has a TTL field which is set to a relatively high number (in the case of ping a TTL of 255). As the packet traverses the network, the TTL field gets decreased by one by each router it goes through; when the TTL drops to 0, the packet is discarded by the router. The IP spec says that the TTL should be set to 60 (though it's 255 for ping packets). The main purpose of this is so that a packet doesn't live forever on the network and will eventually die when it is deemed "lost." But for ping purposes, it provides additional information. The TTL can be used to determine approximately how many router hops the packet has gone through. If the TTL field varies in successive pings, it could indicate that the successive reply packets are going via different routes, which isn't a great thing.

Thanks-

Afroz

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