strange TTL problem

Answered Question
May 17th, 2012

                   Hi all,

I have a cisco airport 1040 attached to a SG300 switch.

The issue i found is strange;if i connect to the network using a wireless client, and perform a ping-test to the default gateway, i get a responce with a low TTL, when i ping my Router i do not have this, and when i ping my server(which is on a different vlan, i get another TTL again.

As far as i noticed, there is no impact to the network.

Ping-test to my server:

C:\Documents and Settings\menno hogenbirk>ping 192.168.5.2

Pingen naar 192.168.5.2 met 32 byte gegevens:

Antwoord van 192.168.5.2: bytes=32 tijd=2 ms TTL=127
Antwoord van 192.168.5.2: bytes=32 tijd=1 ms TTL=127
Antwoord van 192.168.5.2: bytes=32 tijd=1 ms TTL=127
Antwoord van 192.168.5.2: bytes=32 tijd=2 ms TTL=127

Ping-statistieken voor 192.168.5.2:
    Pakketten: verzonden = 4, ontvangen = 4, verloren = 0
    (0% verlies).De gemiddelde tijd voor het uitvoeren van één bewerking in mill
iseconden:
    Minimum = 1ms, Maximum = 2ms, Gemiddelde = 1ms

Ping-test to default-gateway:

C:\Documents and Settings\menno hogenbirk>ping 192.168.4.1

Pingen naar 192.168.4.1 met 32 byte gegevens:

Antwoord van 192.168.4.1: bytes=32 tijd=1 ms TTL=64
Antwoord van 192.168.4.1: bytes=32 tijd=1 ms TTL=64
Antwoord van 192.168.4.1: bytes=32 tijd=1 ms TTL=64
Antwoord van 192.168.4.1: bytes=32 tijd=1 ms TTL=64

Ping-statistieken voor 192.168.4.1:
    Pakketten: verzonden = 4, ontvangen = 4, verloren = 0
    (0% verlies).De gemiddelde tijd voor het uitvoeren van één bewerking in mill
iseconden:
    Minimum = 1ms, Maximum = 1ms, Gemiddelde = 1ms

Ping-test to router:

C:\Documents and Settings\menno hogenbirk>ping 192.168.1.1

Pingen naar 192.168.1.1 met 32 byte gegevens:

Antwoord van 192.168.1.1: bytes=32 tijd=2 ms TTL=254
Antwoord van 192.168.1.1: bytes=32 tijd=1 ms TTL=254
Antwoord van 192.168.1.1: bytes=32 tijd=1 ms TTL=254
Antwoord van 192.168.1.1: bytes=32 tijd=1 ms TTL=254

Ping-statistieken voor 192.168.1.1:
    Pakketten: verzonden = 4, ontvangen = 4, verloren = 0
    (0% verlies).De gemiddelde tijd voor het uitvoeren van één bewerking in mill
iseconden:
    Minimum = 1ms, Maximum = 2ms, Gemiddelde = 1ms

As you can see from the above the TTL to the router is the lowest.

While in my opinion i should have a lower TTL while pinging to my switch, since traffic has to traverse the switch to come to the router.

Please help.

I have this problem too.
0 votes
Correct Answer by Richard Burts about 1 year 11 months ago

To understand what is going on here we should start with the question of where and how the TTL is set. When you send a ping to some device you set the TTL on the ping request. The device sends a response and the responding device sets the TTL in the response. The TTL value that you see in your results is the TTL of the response coming to you. Various OS will set the TTL differently. Some, like the router will start with 255. Some like the server may start at 128. And some, like your default gateway may start at 64.

So the differences that you are seeing in TTL are no more than the differences in how various OS will set the TTL. It should have no impact on network performance and is not anything to be concerned about.

HTH

Rick

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Correct Answer
Richard Burts Mon, 05/21/2012 - 03:50

To understand what is going on here we should start with the question of where and how the TTL is set. When you send a ping to some device you set the TTL on the ping request. The device sends a response and the responding device sets the TTL in the response. The TTL value that you see in your results is the TTL of the response coming to you. Various OS will set the TTL differently. Some, like the router will start with 255. Some like the server may start at 128. And some, like your default gateway may start at 64.

So the differences that you are seeing in TTL are no more than the differences in how various OS will set the TTL. It should have no impact on network performance and is not anything to be concerned about.

HTH

Rick

Richard Burts Mon, 05/28/2012 - 07:24

I am glad that my response helped you to understand what is going on with the various TTL values. Thank you for using the rating system to mark this question as answered. It makes the forum more useful when people can read a question and can know that a correct answer was given. Your marking has contributed to this process.

HTH

Rick

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Posted May 17, 2012 at 2:32 AM
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