Code change:
Key updates MUST be initiated before usage limits on packet protection keys are exceeded.  For the cipher suites mentioned in <del> this document, the limits in Section 5.5 of TLS13 apply.  Other cipher suites MUST define usage limits in order to be used with QUIC. </del> <ins> this document, the limits in Section 5.5 of TLS13 apply.  TLS13 does not specify a limit for AEAD_AES_128_CCM, but the analysis in ccm- bounds shows that a limit of 2^23 packets can be used to obtain the same confidentiality protection as the limits specified in TLS. The usage limits defined in TLS 1.3 exist for protection against attacks on confidentiality and apply to successful applications of AEAD protection.  The integrity protections in authenticated encryption also depend on limiting the number of attempts to forge packets.  TLS achieves this by closing connections after any record fails an authentication check.  In comparison, QUIC ignores any packet that cannot be authenticated, allowing multiple forgery attempts. Endpoints MUST count the number of received packets that fail authentication for each set of keys.  If the number of packets that fail authentication with the same key exceeds a limit that is specific to the AEAD in use, the endpoint MUST stop using those keys. Endpoints MUST initiate a key update before reaching this limit.  If a key update is not possible, the endpoint MUST immediately close the connection.  Applying a limit reduces the probability that an attacker is able to successfully forge a packet; see AEBounds and ROBUST. Due to the way that header protection protects the Key Phase, packets that are discarded are likely to have an even distribution of both Key Phase values.  This means that packets that fail authentication will often use the packet protection keys from the next key phase.  It is therefore necessary to also track the number of packets that fail authentication with the next set of packet protection keys.  To avoid exhaustion of both sets of keys, it might be necessary to initiate two key updates in succession. For AEAD_AES_128_GCM, AEAD_AES_256_GCM, and AEAD_CHACHA20_POLY1305, the limit on the number of packets that fail authentication is 2^36. Note that the analysis in AEBounds supports a higher limit for the AEAD_AES_128_GCM and AEAD_AES_256_GCM, but this specification recommends a lower limit.  For AEAD_AES_128_CCM, the limit on the number of packets that fail authentication is 2^23.5; see ccm-bounds. These limits were originally calculated using assumptions about the limits on TLS record size.  The maximum size of a TLS record is 2^14 bytes.  In comparison, QUIC packets can be up to 2^16 bytes.  However, it is expected that QUIC packets will generally be smaller than TLS records.  Where packets might be larger than 2^14 bytes in length, smaller limits might be needed. Any TLS cipher suite that is specified for use with QUIC MUST define limits on the use of the associated AEAD function that preserves margins for confidentiality and integrity.  That is, limits MUST be specified for the number of packets that can be authenticated and for the number packets that can fail authentication.  Providing a reference to any analysis upon which values are based - and any assumptions used in that analysis - allows limits to be adapted to varying usage conditions. </ins> 6.7.

Related discussion:
text: I would point out that that volume of unproductive traffic is probably a good reason to use something other than a key update to deal with the sender. A reminder that the underlying analysis assumes that packets are all 2^14 in size, which is the record size in TLS. This is ~10 times larger than typical MTU on the Internet and many QUIC packets might be smaller than that, so - at least for AES-GCM - recommending a 2^36 limit is more conservative than necessary. However, if we were to allow for different limits, we'd have to address the question of packet size, as a 2^16 byte packet will be used by some deployments. For ChaCha20+Poly1305, the only value that matters is the number of packets, so we avoid that question. Quoting from Felix's email for reference (with permission):
NAME Can I request that you review this analysis for correctness? I know that you had reservations about the claims here.
Another (simplier?) option could be to just update keys much more often. I've done performance tests with msquic on the effect of updating the key ~once per round trip. There was no noticeable effect on performance. In fact, more often than not, the key update perf tests happen to perform slightly better (within noise tolerance) than without key update. I'm not suggesting we advocate once a round trip or anything near that; more like every 2^20 packets (or 2^30 bytes?) sent or received (including failed decryptions). As I understand it, this is an ultra conservative number as far as protecting from any kind of attacks, and should be free as far as any performance impact on the connection. This also has the added benefit of exercising the key update scenario more often, which should hopefully improve interoperability of the feature.
I support a change like this, but I am not qualified to say what the thresholds should be. There certainly isn't a reason to push it to very high limits. This change would not break interoperability, so it's a good one. Banning CCM might break interoperability for someone, but I'm not too concerned, particularly if we can update all the browsers to not offer it.