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9 votes

Accurate TTL calculation

TTL is a hop counter, it's not a timing mechanism.
Teun Vink's user avatar
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5 votes

Is TCP's MSL value equivalent to IP's TTL value?

TCP MSL isn't a field carried in packets/segments. It's a time interval used by the TCP state-machine. The values and their uses are very different. IP TTL is mainly needed for loop prevention, ...
Jeff Wheeler's user avatar
  • 5,502
4 votes

Accurate TTL calculation

I previously thought that TTL is a counter of hopes to device. It largely is. Today I learned that this is not so, but is connected with the processing time of packets. The point of TTL was/is to ...
Peter Green's user avatar
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4 votes

Accurate TTL calculation

Initially, TTL was supposed to be decremented by the amount of seconds that a hop (router) required to process the packet, but at least by one (see RFC 791 3.1 Internet Header Format) (emphasis mine): ...
Zac67's user avatar
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3 votes

Confusion about TTL when pinging

Why does it start from 253 but not 255? And why doesnt it decrease at each router? (Why does it stays constant at 253?) It is not starting at 253, the reply is ending with 253. Different ping ...
Ron Maupin's user avatar
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3 votes
Accepted

Confusion about TTL when pinging

The displayed TTL is a value from the ping reply packet. The host sending that reply decides the initial TTL for that packet, and it's decremented once per hop en-route to you. Allow me to show an ...
Jeff Wheeler's user avatar
  • 5,502
3 votes
Accepted

Is TCP's MSL value equivalent to IP's TTL value?

No. IP TTL is actually only decreased by routers when receiving a packer, so is effectively a "hop count". (a packet is never in transit on a single equipment for as long as one second, so ...
JFL's user avatar
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3 votes

How traceroute add TTL field to UDP header?

The TTL field is within the IPv4 packet header. UDP doesn't have such a counter of its own. The TTL is decreased by each router the packet passes. Routers only operate on the packet header, not on the ...
Zac67's user avatar
  • 85.5k
3 votes

How traceroute add TTL field to UDP header?

UDP datagrams are carried in IP packets. The IP packet header will have that field: TTL for IPv4 or Hop Count for IPv6. UDP datagrams do not travel unencapsulated across a network (no IP addressing in ...
Ron Maupin's user avatar
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2 votes

How are TCP segments discarded after Maximum Segment Lifetime expires?

They don't. The MSL is an assumption. We assume that no segment takes more than 2 minutes to be delivered, and therefore it is safe to reuse a segment number if we wait for 2 minutes or more.
Quitting Due To Antisemitism's user avatar
2 votes

What TTL value should i use to make sure the packet never leaves the broadcast domain

Packets with TTL 0 will be dropped at the interface. Link-local protocols, like multicast (by default), use a TTL of 1 to be confined to the broadcast domain.
Ron Maupin's user avatar
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1 vote
Accepted

The TTL and packet drop

When a router receives a packet with a TTL of 1, the router can still process and accept it if its destined for itself, correct? Yes. Because for example, eBGP messages use a TTL of 1 by default and ...
Zac67's user avatar
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1 vote

RDP Dropping When TTL Changes From 127 to 63

Thanks for the help. I found what was causing the problem. I had recently enlarged my IP scope and in doing so inadvertently included my servers IP address in the new scope without a reservation. ...
Quinntessential's user avatar
1 vote

RDP Dropping When TTL Changes From 127 to 63

The returning ICMP Echo Reply TTL shows the pinged node's initial TTL minus the path decrements. When the TTL jumps like that it indicates different paths or even different end nodes. 64 as initial ...
Zac67's user avatar
  • 85.5k
1 vote

Do destination hosts decrement the TTL?

A proper IPv4 implementation should also look at the intention of RFC 791: The intention [of the TTL mechanism] is to cause undeliverable datagrams to be discarded, and to bound the maximum datagram ...
Angelos Vassiliou's user avatar
1 vote

Do destination hosts decrement the TTL?

As of RFC 791 (emphasis mine): The Time to Live is an indication of an upper bound on the lifetime of an internet datagram. It is set by the sender of the datagram and reduced at the points along ...
Zac67's user avatar
  • 85.5k
1 vote

What TTL value should i use to make sure the packet never leaves the broadcast domain

See RFC 791: If the time to live reaches zero before the internet datagram reaches its destination, the internet datagram is destroyed. Accordingly, a packet with TTL=0 can only be processed locally ...
Zac67's user avatar
  • 85.5k
1 vote

ipsrc multicast group

Multicast groups can only be used as destination addresses, not source addresses. If an application or device is using a multicast group as a source address, it is non-standard and incorrect. Sending ...
Ron Maupin's user avatar
  • 99.9k
1 vote
Accepted

IP packet expired by TTL generate an ICMP response in any case?

This means that if a TCP or UDP packet expire, the router send an ICMP reporting packet to the origin host? No and yes. TCP segments or UDP datagrams cannot carry a TTL value themselves. If the TTL ...
Zac67's user avatar
  • 85.5k
1 vote

How traceroute add TTL field to UDP header?

Commands and apps like traceroute take advantage of normal IP behavior. They play with TTL field in IPv4 (Hop Count in IPv6) by replacing it with 1, instead of default values of 32, 64, etc. First ...
MTG's user avatar
  • 211
1 vote

How to ensure packet was created within certain time?

No. The IP packet TTL effectively counts down the L3 or router hops the packet takes. Setting the TTL to a custom value n ensures that the packet cannot take more than n hops on its path. If it does ...
Zac67's user avatar
  • 85.5k
1 vote

Confusion about TTL when pinging

The traffic that passing between network interfaces must go through the Forwarding Engine. The Forwarding Engine is a component that directs packets to their destination. During the process of ...
Sagar Uragonda's user avatar

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