Hi Joe, Thanks for your response. Please see my response with [Xiaohu] inline.
From: Joe Touch [mailto:[email protected]] Sent: Tuesday, May 24, 2016 12:31 AM To: Xuxiaohu; Fred Baker (fred); Wassim Haddad Cc: [email protected] Subject: Re: [Int-area] Call for adoption of draft-xu-intarea-ip-in-udp-03 On 5/22/2016 7:44 PM, Xuxiaohu wrote: Hi Joe,, As for the four things that you have pointed out (see below), We know of at least four things that tunnels need that IP-in-UDP ignores: - stronger checksums [Xiaohu] it said in the draft that " For IPv4 UDP encapsulation, this field is RECOMMENDED to be set to zero for performance or implementation reasons because the IPv4 header includes a checksum and use of the UDP checksum is optional with IPv4. For IPv6 UDP encapsulation, the IPv6 header does not include a checksum, so this field MUST contain a UDP checksum that MUST be used as specified in [RFC0768<https://tools.ietf.org/html/rfc0768>] and [RFC2460<https://tools.ietf.org/html/rfc2460>] unless one of the exceptions that allows use of UDP zero-checksum mode (as specified in [RFC6935<https://tools.ietf.org/html/rfc6935>]) applies." In other words, the stronger checksum (i.e., non-zero checksum of UDP) is strongly recommended especially for IPv6 UDP case. Furthermore, as stated in RFC6935, "Tunnel protocols that encapsulate IP will generally be safe for deployment, because all IPv4 and IPv6 packets include at least one checksum at either the network or transport layer." This statement is just applied to the IP-in-UDP case. - fragmentation support [Xiaohu] It said in the draft that " Ingress AFBRs MUST NOT fragment I-IP packets (i.e., UDP encapsulated IP packets), and when the outer IP header is IPv4, ingress AFBRs MUST set the DF bit in the outer IPv4 header. It is strongly RECOMMENDED that I-IP transit core be configured to carry an MTU at least large enough to accommodate the added encapsulation headers. Meanwhile, it is strongly RECOMMENDED that Path MTU Discovery [RFC1191<https://tools.ietf.org/html/rfc1191>] [RFC1981<https://tools.ietf.org/html/rfc1981>] is used to prevent or minimize fragmentation. Once an ingress AFBR needs to perform fragmentation on an E-IP packet before encapsulating, it MUST use the same source UDP port for all fragmented packets so as to ensures these fragmented packets are Xu, et al. Expires August 3, 2016 [Page 5] ________________________________ <https://tools.ietf.org/html/draft-xu-intarea-ip-in-udp-03#page-6> Internet-Draft Encapsulating IP in UDP January 2016 always forwarded on the same path. In a word, IP-in-UDP is just applicable in those Softwire network environments where fragmentation on the tunnel layer is not needed." In other words, fragmentation on I-IP packets (i.e., UDP encapsulated IP packets) must be avoided. fragmentation on E-IP packets should be avoided by some means (e.g., I-IP transit core is configured to carry an MTU at least large enough to accommodate the added encapsulation headers or Path MTU discovery is enabled on the UDP tunnels). Fragmentation on E-IP packets is possible only when the E-IP packets are IPv4 packets and the DF bit is not set. - signalling support (e.g., to test whether a tunnel is up or to measure MTUs) [Xiaohu] It said in the draft that "it is strongly RECOMMENDED that Path MTU Discovery [RFC1191<https://tools.ietf.org/html/rfc1191>] [RFC1981<https://tools.ietf.org/html/rfc1981>] is used to prevent or minimize fragmentation." - support for robust ID fields (related to fragmentation, e.g., to overcome the limits of IPv4 ID as per RFC 6864) in other words, the PMTUD signaling is recommended to be supported. [Xiaohu] Is it enough to add a sentence like "to overcome the limits of IPv4 ID as per RFC 6864 when performing fragmentation on E-IP IPv4 packets, the specifications as described in RFC6864 MUST be followed."? Best regards, Xiaohu I'm wondering whether those issues are specific to IP-in-UDP or not. In other words, are those issue also applicable to other X-in-UDP approaches (where X could be LISP, TRILL, VXLAN, VXLAN-GPE, GENEVE, GUE, NSH or MPLS)? That set of issues applies to all IP-in-(xlist), where xlist includes IP again. The issue is what IP expects and what the tunnel exports. The other items I pointed out are specific to transport-in-UDP or this specific approach. Joe
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