Sending Hop Limited UDP packets

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Ashoka! - 10 Apr 2007 09:22 GMT

Is there a way to send a UDP packet with a specific TTL however it
must be a unicast address instead of multicast address. Any ideas?

regards
Usman Ismail

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Knute Johnson - 10 Apr 2007 17:15 GMT

> Is there a way to send a UDP packet with a specific TTL however it
> must be a unicast address instead of multicast address. Any ideas?
>
> regards
> Usman Ismail

I think you would have to write your own DatagramSocketImpl. But I'm
curious as to why you would want a TTL on a unicast UDP packet. Do you
not want it to get to it's address?

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Knute Johnson
email s/nospam/knute/

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Gordon Beaton - 10 Apr 2007 17:22 GMT

> I think you would have to write your own DatagramSocketImpl. But I'm
> curious as to why you would want a TTL on a unicast UDP packet. Do
> you not want it to get to it's address?

It's one way of implementing traceroute, but I can't think of any
other uses.

/gordon

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Esmond Pitt - 11 Apr 2007 10:09 GMT

> Is there a way to send a UDP packet with a specific TTL however it
> must be a unicast address instead of multicast address. Any ideas?

Use a MulticastSocket so you get the setTimeToLive() API and just send
to a unicast address.

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Gordon Beaton - 11 Apr 2007 10:23 GMT

> Use a MulticastSocket so you get the setTimeToLive() API and just
> send to a unicast address.

Does that actually work?

I was going to make the same suggestion earlier, but tested first and
couldn't see (with Wireshark) that the setting had any effect on
unicast packets. The documentation seems to confirm this:

"Set the default time-to-live for *multicast* packets sent [...]"

/gordon

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Esmond Pitt - 12 Apr 2007 01:21 GMT

>>Use a MulticastSocket so you get the setTimeToLive() API and just
>>send to a unicast address.
>
> Does that actually work?

oops, err, hmm, maybe not ... on investigation it turns out that there
are both IP_TTL and IP_MULTICAST_TTL, and
MulticastSocket.setTimeToLive() sets the latter, and the OP wants the
former ...

so you can't do it in Java.

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Ashoka! - 26 Apr 2007 12:41 GMT

I am trying to implement the tailgating algorithm to measure internet
bandwidth.

On Apr 12, 5:21 am, Esmond Pitt <esmond.p...@nospam.bigpond.com>
wrote:

> >>Use a MulticastSocket so you get the setTimeToLive() API and just
> >>send to a unicast address.
[quoted text clipped - 7 lines]
>
> so you can't do it in Java.

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Sending Hop Limited UDP packets

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