Hey Phil,
At some point over night on 30th September (i.e. the night going into 1st October), we saw a number of Spectrum (Charter) customers stop handling fragmented UDP packets. This has manifested itself in such that the phones of affected customers are no longer receiving UDP SIP INVITE packets which exceed whatever their WAN side MTU is. We've so far had 6 customers report the issue - we can see that the last call on 30th September worked and the first and subsequent calls on 1st October failed.
Is anyone aware of an update to CPE devices pushed out that night which may have broken their ability to handle IP fragmentation?
I don't know anything specific to this case, but you'd serve your best interest to send small enough packets that do not need fragmentation, particularly in the backbone. Even devices often considered SP quality, such as ASR9k, fragment in the linecard CPU, giving very poor service quality compared to sending two packets not fragmented. While we can say this should just work, the reality is, it's not very reliably true and I would not build product or business on the assumption that it works well. -- ++ytti