[dhcwg] Proposed resolution to DNA Issue 10: Strong vs. Weak hints
Bernard Aboba <aboba@internaut.com> Wed, 28 January 2004 11:26 UTC
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Date: Mon, 26 Jan 2004 12:45:35 -0800
From: Bernard Aboba <aboba@internaut.com>
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Subject: [dhcwg] Proposed resolution to DNA Issue 10: Strong vs. Weak hints
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The DNA issues list is available at: http://www.drizzle.com/~aboba/DNA/dnaissues.html The text of DNA issue 10 is enclosed below. The proposed resolution is as follows: Change Appendix A to the following: "Appendix A - Hints In order to assist in IPv4 network attachment detection, information associated with each network may be retained by the host. Based on IP and link-layer information, the host may be able to make an educated guess as to whether it has moved between subnets, or remained on the same subnet. If the host is likely to have moved between subnets, it may be possible to make an educated guess as to which subnet it has moved to. Since an educated guess is not the same as certainty, prior to concluding that the host remains on the same subnet, a reachability test MUST always be performed. IPv4 ICMP Router Discovery messages [RFC1256] provide information relating to prefix(es) available on the link. A host may use this information to conclude that an advertised prefix is available; however it cannot conclude the converse -- that prefixes not advertised are unavailable. For networks running over PPP [RFC1661], IP parameters negotiated in IPCP provide direct information on whether a previously obtained address remains valid on the link. On IEEE 802 [IEEE802] wired networks, hints include link-layer discovery traffic as well as information exchanged as part of IEEE 802.1X authentication [IEEE8021X]. Link-layer discovery traffic includes Link Layer Discovery Protocol (LLDP) [IEEE8021AB] traffic as well as network identification information passed in the EAP-Request/Identity or within an EAP method exchange, as defined in EAP [RFC2284bis]. For example, LLDP advertisements can provide information on VLANs supported by the device. When used with IEEE 802.1X authentication [IEEE8021X], the EAP-Request/Identity exchange may contain the name of the authenticator, also providing information on the potential network. Similarly, during the EAP method exchange the authenticator may supply information that may be helpful in identifying the network to which the device is attached. However, as noted in [RFC3580], it is possible for the VLANID defined in [IEEE8021Q] to be assigned dynamically, so this static information may not prove definitive. In IEEE 802.11 [IEEE80211] stations provide information in Beacon and/or Probe Response messages, such as the SSID, BSSID, and capabilities, as well as information on whether the station is operating in Infrastructure or Adhoc mode. As described in [RFC3580], it is possible to assign a Station to a VLAN dynamically, based on the results of IEEE 802.1X [IEEE8021X] authentication. This implies that a single SSID may offer access to multiple VLANs, and in practice most large WLAN deployments offer access to multiple subnets. Thus, associating to the same SSID is a necessary, but not necessarily a sufficient condition, for remaining within the same subnet: while a Station associating to the same SSID may not necessarily remain within the same subnet, a Station associating to a different SSID is likely to have changed subnets. Since the SSID is a non-unique identifier, and SSIDs such as "default", "linksys" and "tsunami" are advertised by default in various products, detection of these "default SSIDs" is not sufficient for a host to conclude that it has remained on the same subnet. It is recommended that before detecting a match to a "default SSID" that the BSSID also be checked before concluding that the host remains on the same subnet. In order to provide additional guidance on the subnets to which a given AP offers access, additional subnet-related Information Elements (IEs) have been proposed for addition to the IEEE 802.11 Beacon and Probe Response messages. As noted earlier, VLANs may be determined dynamically so that these information elements may not be reliable." ----------------------------------------------------------------- Issue 10: Strong vs. Weak hints Submitter: Bernard Aboba Submitter email address: aboba@internaut.com Date first submitted: November 10, 2003 Reference: Document: DNAv4-04 Comment type: T Priority: S Section: Appendix A Rationale/Explanation of issue: The distinction between "strong" and "weak" hints is not entirely clear to me. I think that the distinction does not affect protocol operation -- it's just affects the likelihood of success. For example, if there is any chance that a hint is not definitive, then the host needs to do a check anyway (such as a reachability test or a DHCPREQUEST). So behavior doesn't really change based on hint strength. The specification should say this. It's unclear now. _______________________________________________ dhcwg mailing list dhcwg@ietf.org https://www1.ietf.org/mailman/listinfo/dhcwg
- [dhcwg] Proposed resolution to DNA Issue 10: Stro… Bernard Aboba