when i try the host who are using NAT, seems the TOS bits will lose.


Tracing route to 10.39.32.1 over a maximum of 30 hops



  1    <1 ms    <1 ms    <1 ms  mudd-edge-1-vlan236-5.net.columbia.edu [128.59.51.1] 

  2    <1 ms    <1 ms    <1 ms  10.39.32.1 



Trace complete.




: bart.cs.columbia.edu ;ping -P 0x06 10.39.32.1
10.39.32.1 is alive
: bart.cs.columbia.edu ;

: bart.cs.columbia.edu ;tcpdump -n -v -v
14:21:10.945846 128.59.19.191 > 10.39.32.1: icmp: echo request (DF) [tos 0x6,ECT(0)]  (ttl 255, id 60189, len 84)
14:21:10.946133 10.39.32.1 > 128.59.19.191: icmp: echo reply (DF) (ttl 254, id 60189, len 84)

lost its TOS bits
//---------------------------------------------------

: bart.cs.columbia.edu ;ping -P 0x06 128.59.51.1
128.59.51.1 is alive
: bart.cs.columbia.edu ;


: bart.cs.columbia.edu ;tcpdump -n -v -v
14:23:53.564603 128.59.19.191 > 128.59.51.1: icmp: echo request (DF) [tos 0x6,ECT(0)]  (ttl 255, id 51310, len 84)
14:23:53.564946 128.59.51.1 > 128.59.19.191: icmp: echo reply (DF) [tos 0x6,ECT(0)]  (ttl 255, id 51310, len 84)

while the node before NAT node still keep TOS bits