Re: TTL modification while routing IP packets

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From: Steve Riley [MSFT] (steriley_at_microsoft.com)
Date: 01/13/05 

Date: Thu, 13 Jan 2005 15:23:01 -0800

It's ok, Herb, this way we know you're human, like (most of) the rest of
us :)

Long time ago 30 was a de facto TTL used in a lot of devices. We set the
default TTL in Windows NT 3.51 to 32. Starting with NT 4.0 we increased the
default TTL to 128, which is still where it is today.

You can change the default, if you wish, with the "DefaultTTL : REG_DWORD"
key in the "Tcpip\Parameters" branch. The range can be from 1 to 255. Of
course, this applies only to packets that the computer generates. RRAS follows
its normal decrement-whatever-the-current-is-by-1 behavior when forwarding
packets.

Steve Riley
steriley@microsoft.com

> "Steve Riley [MSFT]" <steriley@microsoft.com> wrote in message
> news:49038632412067451211383@news.microsoft.com...
>
>> Don't confuse IP packet TTLs with DNS record TTLs, they're different.
>> The OP is asking about Windows RRAS routing functionality for IP
>> packet TTLs.
>>
> Excuse me.
>
> For some (strange) reason, I though the question
> was about DNS.
>> Jakub, there's no facility in Windows that will let you do this. RRAS
>> does what any router should: it decremets the TTL by one when it
>> forwards a
>>
> packet
>
>> across an interface. You can't change or alter this behavior. Why do
>> you need this functionality?
>>
> Aren't the modern default VERY high anyway?
>
>> Steve Riley
>> steriley@microsoft.com
>>> "Jakub Lida" <shibbsd@o2.pl> wrote in message
>>> news:cs638e$8tn$1@srv.cyf-kr.edu.pl...
>>>> Hello,
>>>>
>>>> Is it possible to modify the TTL of packets that are being
>>>> forwarded by a Windows 2000/2003 router? I mean re-setting TTL for
>>>> them or ensuring that it is not lower/higher than a specified value
>>>> (as it is possible for example in OpenBSD's pf filter with a "scrub
>>>> all reassemble tcp min-ttl 2").
>>>>
>>> Anything is "possible" but the is no built in facility for that and
>>> it seems rather silly since the OWNER (authoritative servers) for
>>> the zone decides the correct TTL for his own records.
>>>
>>> Their are settings on MS DNS Server and Client DNS cache that sets a
>>> MAXIMUM however (I believe).
>>>
>>> The clients default to 1 day max rather than the actual value of the
>>> TTL (if it is greater.)
>>>
>>>> Thank you very much for your help!
>>>>
>>>> Kuba <shibbsd@o2.pl>
>>>> Krakow, PL

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