What do you consider acceptable packet / session modification for a network operator?

[Andrew via NANOG <nanog () lists nanog org>]

I’m doing a bit of research on how consumer-focused ISPs are modifying their user’s traffic, and I think you guys would 
have useful insight into legitimate reasons to touch user packets.

Almost all of these examples have been seen in the wild by at least one US ISP, so none of these are purely 
hypothetical.

So, how do you feel about where to draw the line for what is acceptable from an ISP?

Examples:

- Using different source IP ranges in CGNat for ‘web’ traffic vs ’non-web’ (i.e. port 80/443 vs all other ports) - this 
can break local IP discovery for peer-to-peer stuff if it relies on a ‘web’ port for an API endpoint

- Using any form of NAT / packet translation with IPv6 (not including nat64 / other v4 transition related)

- Dropping non-TCP/UDP/ICMP protocols (outside of CGNat) - such as ‘raw’ IPSec ESP / AH without UDP encapsulation, or 
SCTP

- TCP MSS - MSS Clamping all connections

- TCP MSS - MSS Clamping, but you instead (accidentally?) set MSS to your desired value even if it was lower before

- Other TCP options - Dropping syn packets with invalid/unknown options

- TCP connection interception - Network operator terminates TCP session from user and then establishes a new one with 
the original destination. All TCP options, sequence numbers, .. are lost in this translation

- Related to above - Network accepts TCP connection which it will intercept (sends SYN/ACK to user) before it confirms 
that the destination is reachable

- Dropping/resetting port 80 sessions that don't ‘look like’ HTTP

- Dropping/resetting port 443 sessions that don't ‘look like’ TLS

- Redirecting port 53 DNS queries to ISP’s own servers, regardless of destination IP

- HTTP header injection into port 80 HTTP traffic (i.e. for user tracking)

- HTTP content injection into port 80 HTTP traffic (i.e. replacing ads, adding dialogs, …) (and not blanket redirection 
for non-payment)

Thanks,

Andrew ‘apalrd’ Palardy
www.apalrd.net
https://www.youtube.com/c/apalrdsadventures
_______________________________________________
NANOG mailing list 
https://lists.nanog.org/archives/list/nanog () lists nanog org/message/JCNJISMBZQ3RBO5YJQKF6EU52T73A6B7/