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TTL in the PING Command Query

Hi all

I have a question for you good people.....

We are currently in the process of migrating floors in a large building onto a new network infrastructure. So currently we have two LAN/WAN cores - the legacy and the new, with the legacy to be decommisioned at the end. As part of this we are re-IPing all workstations that are migrated. So what we will have midway is half the building on the legacy network and half on the new. Communication between the two is via the (private) MPLS core we have.

Now, all floors thus far have migrated beautifully with no problems, however, now we have a floor where we have some servers (they should be in the data centre but that's another story!), and users map/connect to a drive on one of these servers. The servers have yet to be migrated, however, the users that map to that drive on those servers have. Post-migration they can still connect to the drive, however, it is dead slow, painful even and they are not happy.

When we were troubleshooting we noticed that if we ping a migrated workstation (workstation A) from another workstation (workstation B) which is elsewhere in the network, i.e. from a different site, that the TTL on the ping is reduced to about 120. The strange thing is that if we ping the local LAN switch that workstation A connects to from B, we get a TTL of 246. Now, basic networking knowledge tells me that the TTL is essentially a value that get decremented by each router the packet travels through to stop the packet from endlessly travelling around the network. When we traceroute from the workstation B to A we see that it takes the route we expect, nothing out the ordinary. It travels through approximately 8 devices/hops. So why in the name of beelzebubs middle toe would the traceroute show 9 hops from workstation B to A, yet the TTL on the ping from B to A sees the TTL decremented from 255 to 120? And why would the TTL from workstation B to the LAN switch that connects A only be decremented by 8, i.e. the number of hops that the traceroute shows? Why do we lose a value of 126 on the TTL from B to A?

Confusion ensues.

I would most appreciate you advuce in this matter. It's probably something silly and I've embarrased myself yet again.

Thank you.

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2 REPLIES
Hall of Fame Super Silver

TTL in the PING Command Query

Hello Devlin,

>> The strange thing is that if we ping the local LAN switch that workstation A connects to from B, we get a TTL of 246

this is the good news what you see is caused by host A that builds the answer in its own way decrementing from 128 instead of decrementing from 255.

Actually the TTL in ping reply reflects some local settings on the device that answers.

This is not an issue and it is not related to the problem the users have in accessing the mapped drives on the servers.

Hope to help

Giuseppe

TTL in the PING Command Query

Hi Giuseppe

Thank you for your fast reply. Glad to know this is due to the host and the way it replies and not a network problem.

Cheers!

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