[tsvwg] NQB claim of DSCP-

[Sebastian Moeller <[e-mail]>]

Dear All,

https://datatracker.ietf.org/doc/html/draft-ietf-tsvwg-nqb-23#name-security-considerations

    • For application traffic that originates outside of the Wi-Fi network, and thus is transmitted by the Access Point, the choice of DSCP 45 does create a potential for abuse by non-compliant applications. But, opportunities exist in the network components upstream of the Wi-Fi Access Point to police the usage of the NQB DSCP and potentially re-mark traffic that is considered non-compliant, as is recommended in Section 4.4.1. Furthermore, it is a common practice for residential ISPs to re-mark the Diffserv field to zero on all traffic destined to their customers' networks, and any change to this practice done to enable the NQB DSCP to pass through could be done alongside the implementation of the recommendations in Section 4.4.1.


This section proposes the theory that ISPs commonly violate IETF recommendations and re-mark the Diffserv field to zero.

Fortunately that is an hypothesis that is open to relative easy testing at least on systems offering freebsd's traceroute utility:

The -D option will show differences in the header of the transmitted packet and the header returned as part of the TTL exceeded response and helpfully even shows just the changed bits.
The -t 180 option will set the TOS bitfield to decimal 180 or 0xB4 which corresponds to DSCP decimal 45 and Not-ECT in the ECN bitfield
In this example my router was set to forward port 2224 to an internal host to not have this trace end at my firewall:



user@123-1234567 script % traceroute -aD -e -p 2224 -t 180 77.10.144.227 
traceroute to 77.10.144.227 (77.10.144.227), 64 hops max, 40 byte packets
 1  [AS0] 192.168.250.1 (192.168.250.1)  1.469 ms
vhtslen id  off tlprsum srcip   dstip   spt dpt len sum
45b42800fb82000001110000c0a8fa664d0a90e3fb8208b000146296000000000000000000000000
____________________2492________________________________________________________

 2  [AS680] xr-physik1-zgpz.net.gwdg.de (134.76.241.254)  1.174 ms
vhtslen id  off tlprsum srcip   dstip   spt dpt len sum
45b42800fb83000002110000c0a8fa664d0a90e3fb8308b000146295000000000000000000000000
________________01__2491________________________________

 3  [AS680] 134.76.250.59 (134.76.250.59)  1.471 ms
vhtslen id  off tlprsum srcip   dstip   spt dpt len sum
45b42800fb84000003110000c0a8fa664d0a90e3fb8408b000146294000000000000000000000000
________________01__2490________________________________

 4  [AS680] fw-perimeter-gwdg-bb-xr-int.net.gwdg.de (134.76.131.51)  1.356 ms
vhtslen id  off tlprsum srcip   dstip   spt dpt len sum
45b42800fb85000004110000c0a8fa664d0a90e3fb8508b000146293000000000000000000000000
________________01__248f________________________________________________________

 5  [AS680] xr-fmz1-ext-bb-fw-perimeter.net.gwdg.de (134.76.131.37)  1.927 ms
vhtslen id  off tlprsum srcip   dstip   spt dpt len sum
45b42800fb86000005110000c0a8fa664d0a90e3fb8608b000146292000000000000000000000000
________________01__248e________________________________

 6  [AS680] ae0-1624.cr-gfmz1.as207592.net (195.12.38.74)  1.854 ms
vhtslen id  off tlprsum srcip   dstip   spt dpt len sum
45b42800fb87000006110000c0a8fa664d0a90e3fb8708b000146291000000000000000000000000
________________01__248d________________________________

 7  [AS680] cr-fra2-be18-1180.x-win.dfn.de (188.1.238.181)  5.765 ms
vhtslen id  off tlprsum srcip   dstip   spt dpt len sum
45b42800fb88000007110000c0a8fa664d0a90e3fb8808b000146290000000000000000000000000
________________01__248c________________________________________________________00000000000000000000000000000000000000000000000000000000

 8  [AS680] cr-fra2-be18-1180.x-win.dfn.de (188.1.238.181)  5.544 ms
vhtslen id  off tlprsum srcip   dstip   spt dpt len sum
45b42800fb89000008110000c0a8fa664d0a90e3fb8908b00014628f000000000000000000000000
________________01__248b________________________________________________________00000000000000000000000000000000000000000000000000000000

 9  [AS6805] ae64-0.0001.prrx.13.fra.de.net.telefonica.de (212.23.106.20)  11.321 ms
vhtslen id  off tlprsum srcip   dstip   spt dpt len sum
45b42800fb8a000009110000c0a8fa664d0a90e3fb8a08b00014628e000000000000000000000000
________________01__248a________________________________

10  [AS6805] ae3-0.0002.corx.02.fra.de.net.telefonica.de (62.53.0.208)  42.210 ms
vhtslen id  off tlprsum srcip   dstip   spt dpt len sum
45b42800fb8b00000a110000c0a8fa664d0a90e3fb8b08b00014628d000000000000000000000000
________________01__2489________________________________________________________000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000002000fdcd000801010027e101

11  [AS6805] ae10-0.0001.corx.06.ham.de.net.telefonica.de (62.53.0.48)  12.880 ms
vhtslen id  off tlprsum srcip   dstip   spt dpt len sum
45b42800fb8c00000b110000c0a8fa664d0a90e3fb8c08b00014628c000000000000000000000000
________________01__2488________________________________________________________0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000020006dce0008010100277101

12  [AS6805] bundle-ether9.0003.corx.01.ham.de.net.telefonica.de (62.53.0.34)  14.325 ms
vhtslen id  off tlprsum srcip   dstip   spt dpt len sum
45b42800fb8d00000c110000c0a8fa664d0a90e3fb8d08b00014628b000000000000000000000000
________________03__2287________________________________________________________0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000020001e13000801010fe2b101

13  [AS6805] bundle-ether2.0001.cord.01.ham.de.net.telefonica.de (62.53.14.231)  13.602 ms
vhtslen id  off tlprsum srcip   dstip   spt dpt len sum
45b42800fb8e00000d110000c0a8fa664d0a90e3fb8e08b00014628a000000000000000000000000
________________04__2186________________________________________________________000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000002000fe14000801010fe0d101

14  [AS6805] dynamic-077-010-144-227.77.10.pool.telefonica.de (77.10.144.227)  22.576 ms
vhtslen id  off tlprsum srcip   dstip   spt dpt len sum
45b42800fb8f00000e110000c0a8fa664d0a90e3fb8f08b000146289000000000000000000000000
________________01__2485________________________________________________________

15  [AS6805] dynamic-077-010-144-227.77.10.pool.telefonica.de (77.10.144.227)  23.264 ms
vhtslen id  off tlprsum srcip   dstip   spt dpt len sum
45b42800fb9000000f110000c0a8fa664d0a90e3fb9008b000146288000000000000000000000000
________________01__2484________________________________________________________


We can easily see that my ISP (O2/Telefonica) does not remark DSCP decimal 45 (they do remap  tos 192 (CS6) and tos 224 (CS7), but I assume that these DSCPs are used in the O2 network itself; all in all this looks like the expected behaviour, of letting DSCPs that do not interfere with local use traverse unchanged). This makes me wonder whether the hypothesis should be removed from the draft or sufficiently quantified. I am open to the possibility that most other ISPs will remark DSCPs, but I would do mike to see actual data showing such remarking executed by the residential ISP, please.