FreeBSD 6.3 gre and traceroute

Stephen Clark sclark46 at
Wed Nov 12 12:57:46 PST 2008

Julian Elischer wrote:
> Stephen Clark wrote:
>> Hi,
>> When I run traceroute thru a gre it doesn't seem to decrement the
>> ttl, so I get * * * for that hop. Can this be fixed?
>> Thanks,
>> Steve
> you will need to define the setup and question better.
> TTL is controlled by the IP stack which is unaware of which interface
> it came in on and doesn't care which interface it goes out on. That 
> includes GRE interfaces.. Is it freebsd at both ends?
> BTW * * * would come from an EXTRA decrement
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FreeBSD workstation<--> Freebsd FW "A" with gre over ipsec 
tunnel<---->FreeBSD FW "B" with gre over ipsec tunnel<---> linux workstation

$ sudo traceroute
traceroute to (, 64 hops max, 40 byte packets
  1 (  0.575 ms  0.423 ms  0.173 ms
  2  * * *
  3 (  47.972 ms  45.174 ms  49.968 ms

No response from the FreeBSD "B" box.

When I do a tcpdump on "B" of the gre interface I see UDP packets
with a TTL of 1 but no ICMP repsonse packets being sent back.

If I do the traceroute from the linux workstation I get
similar results - I don't see a response from the FreeBSD "A" box.


"They that give up essential liberty to obtain temporary safety,
deserve neither liberty nor safety."  (Ben Franklin)

"The course of history shows that as a government grows, liberty
decreases."  (Thomas Jefferson)

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