• Status: Solved
  • Priority: Medium
  • Security: Public
  • Views: 755
  • Last Modified:

TTL decrements by more than 1 for a single hop

I have a host I ping and its TTL is 241 yet directly connected off that router is anohter router and its TTL is 113. How is the TTL being dropped by 128 when just one hop involved?
0
murphymail
Asked:
murphymail
1 Solution
 
Death_RatCommented:
You have to remember that there are many factors involved here, cable quality, settings for both routers, and even the brand. Even if you have the same of every thing, it could still give you those results because you are still going through multiple hops.
0
 
MysidiaCommented:
Most like there's more than one hop, you just can't see it.   It could be a GRE tunnel, or your path from A to the "next hop" could be through a MPLS  LSP,
which can have some interesting treatment of TTLs.

The path in-between could even be different in a way that's invisible in a traceroute, and i.e. can be invisible hops.

Also, one of the routers on one of the paths could have a 'MAXIMUM TTL'
i.e. if it receives a TTL greater than 200, reduce to 200.
 
Perhaps now would also be a good time to remind you, that there's no rule that a router can only decrement a TTL by one.

The TTL is actually a timer.   If a router holds a packet in buffers  3 seconds before sending it,  the router may decrement the TTL by 3.

See RFC 1812   5.3.1  Time To Live (TTL) page 84.
https://www.arin.net/knowledge/rfc/rfc1812.txt


It's normally not a big issue, since many routers only ever opt to
decrement by 1 nowadays,   and it shold be rare that a router ever
holds onto a packet for longer than a fraction of a second, let-alone
a whole second.





0
 
murphymailAuthor Commented:
I found that the fartest router was using a 128 TTL thatn the ADtran (255) so when factoring in that each router used a different TTL to start and that is what I was seeing on my PING the results made sense. Thanks
0

Featured Post

VIDEO: THE CONCERTO CLOUD FOR HEALTHCARE

Modern healthcare requires a modern cloud. View this brief video to understand how the Concerto Cloud for Healthcare can help your organization.

Tackle projects and never again get stuck behind a technical roadblock.
Join Now