Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!ucbvax!VAX.FTP.COM!jbvb From: jbvb@VAX.FTP.COM (James Van Bokkelen) Newsgroups: comp.protocols.tcp-ip.ibmpc Subject: Re: Here's the Rub (with bridging FDDI or 802.5 to Ethernet) Message-ID: <8907201523.AA01883@vax.ftp.com> Date: 20 Jul 89 15:23:59 GMT References: <1679@brwa.inmos.co.uk> Sender: daemon@ucbvax.BERKELEY.EDU Organization: The Internet Lines: 35 Date: 17 Jul 89 12:35:59 GMT From: Robin Pickering >frame directed to the MAC address of the original station. The ARP reply >frame contains the MAC address of sender, in this case a server, "in a >field in the user data". The ARP packet contains a field which defines the Hardware address space. Implementations of ARP over 802.5 should not respond to requests for an address of type Ethernet (802.3) unless the address which they return is of the type used on Ethernet. The endian swapped 802.5 address clearly does not correspond to this address type and hence should not be returned for a request of this type. We're talking about RFC 1042 encapsulation, using 802.2 headers on the Ethernet here, not RFC 826. All RFC 1042 networks use the same ARP hardware type, 6, so no distinction can be made. Why not have the ARP implementation return the Ethernet ordered address to requests which have the Ethernet address type and the 802.5 address to requests which have the 802.5 address type (is there a type defined for anything other than Ethernet?). .... The reason that both 802.3 and 802.5 are using RFC 1042 format packets in this example is so that the bridge can exist at all. The bridge can't be intelligent enough to understand RFC 894 encapsulation on the ether side and convert it to RFC 1042 on the TR side and remain a bridge. It is presently postulated that at some time in the future most or all Ethernet TCP/IPs will have a configuration option to add support for RFC 1042 on 802.3, but the thing that Roger has discovered is that it won't buy us as much as had been hoped. James B. VanBokkelen 26 Princess St., Wakefield, MA 01880 FTP Software Inc. voice: (617) 246-0900 fax: (617) 246-0901