IP and ARP on HIPPI
obsoleted by
- rfc-2834 — ARP and IP Broadcast over HIPPI-800
Extracted elements (30)
Camp-on is required on connection attempts so that a rejection unambiguously signals an error (bad I-field or offline Destination) rather than a temporary busy condition; without Camp-on, a rejection is ambiguous and Sources should not treat it as an error.
Start_D2_on_Burst_Boundary is forbidden (shall be zero) so that HIPPI packets can traverse intermediate media (e.g. other LAN types between HIPPI LANs) that may alter burst boundaries; this flag is reserved for device-control protocols that need burst boundaries to separate command and data areas.
The 68-burst per-connection limit exists to ensure fair-share access among multiple Sources contending for a single Destination; without such a limit, the Source sending the most data per connection would capture the greatest share of bandwidth.
The MTU of 65280 octets was chosen because it allows the IP packet to fit in one 64K-byte buffer with up to 256 octets of overhead; at the time of writing, actual overhead was 40 octets, leaving 216 octets for future expansion.
ULAs are optional on HIPPI-SC LANs because HIPPI-SC switches do not use them for routing; however they are encouraged because they simplify gateway devices that replace HIPPI headers with MAC headers of other LANs and may be required by future HIPPI-based LANs.
D1_Area_Size should be sent as 3, but Destinations shall accept any HIPPI-FP-legal value (3–127 for 32-bit HIPPI, 3–255 for 64-bit); this preserves forward compatibility with implementations using a larger D1_Area.
Destinations should ignore overflow conditions where a Source adds fill bytes sufficient to overflow the destination input buffer, and should verify only that at least the number of bytes indicated by the IP header actually arrived.
HIPPI nodes may use Path MTU Discovery (RFC 1191) without modification to detect MTU restrictions on paths between HIPPI-SC LANs and other networks; gateways between HIPPI-SC LANs and other network types should implement RFC 1191.
Support for IEEE 802.2 XID, TEST, and Type 2 PDUs is not required on HIPPI; Destinations that receive these PDUs may either ignore them or respond correctly per IEEE 802.2, ensuring compatibility with generic 802-aware upper layers.
A Source shall make a best effort to ensure connection durations do not exceed 68 HIPPI bursts; a Source shall not make consecutive connection requests without Camp-on to the same Destination while requests are being rejected, to prevent circumventing fair-share switch arbitration.
All ARP requests shall be sent with I-field bit 28 (Double_Wide/W) set to zero, requesting a 32-bit connection; HIPPI-LE and Internet ARP messages should be sent together as a single HIPPI packet.
ARP packets shall be transmitted with hardware type code ar$hrd=1 (Ethernet) and shall be accepted if received with hardware type codes of either 1 or 6 (IEEE 802 networks).
Nodes shall accept both piggybacked and non-piggybacked forms of HIPPI-LE address resolution messages; each recipient of an ARP request or reply may use information in the packet to augment its address mapping tables even if it is neither the target nor the requester.
Once initialized, a Destination may reject connection requests only if the I-field was received with incorrect parity or contains invalid contents (e.g. unsupported W bit, locally administered bit set); transient conditions such as temporary buffer shortages must never cause rejected connections.
The IEEE 802.2 LLC header shall have SSAP=170 decimal, DSAP=170 decimal, and CTL=3 (Unnumbered Information); the SNAP Organization Code shall be zero and EtherType set per Assigned Numbers (IP=2048, ARP=2054, RARP=32821).
The length of a HIPPI packet including trailing fill shall be a multiple of 8 octets as required by HIPPI-LE; D2_Size shall contain the number of octets in the IEEE 802.2 LLC Type 1 PDU (not including fill) and shall not exceed 65,288 decimal.
The MTU for HIPPI-SC LANs is 65280 decimal octets; this is the maximum IP packet size including IP header but excluding lower-layer framing overhead.
The ULP-id field in the HIPPI-FP header shall contain 4 to identify IP/ARP payloads; D1_Data_Set_Present shall be set; Start_D2_on_Burst_Boundary shall be zero.
When a node receives an AR_S_Response message whose Destination_IEEE_Address matches its own ULA, it shall take the new switch address from Destination_Switch_Address and shall invalidate its ARP tables to force rediscovery using the new address.
A HIPPI packet consists of an 8-octet HIPPI-FP header, a 24-octet HIPPI-LE header (D1_Area), an 8-octet IEEE 802.2 LLC/SNAP header, and an IP or ARP payload (D2_Area), with trailing fill octets to align the total length to a multiple of 8 octets.
Destination_Address_Type and Source_Address_Type (4 bits each) encode the switch address format: 0=Unspecified, 1=HIPPI-SC Source Route (24 bits), 2=HIPPI-SC Address (12 bits); values 3–11 are reserved and 12–15 are locally assigned.
Each node on a HIPPI-SC LAN should be assigned a 48-bit Universal LAN MAC Address (ULA); the ULA occupies bits 47–0 of the HIPPI-LE address fields in IEEE 802.1A canonical bit order, with the U/L bit (L) and I/G bit (G) carried in the least significant bits of octet 0.
HIPPI-LE Message_Type (4 bits) defines: 0=Data PDU, 1=AR_Request, 2=AR_Response, 3=AR_S_Request (self address discovery), 4=AR_S_Response; values 5–11 are reserved by ANSI X3T9.3, and 12–15 are locally assigned.
The RFC notes security considerations but provides no protocol-level authentication or access-control mechanisms; HIPPI is a physically local, high-speed interface and security is presumed to rely on physical access control to the switch and cable plant rather than cryptographic means.
Channel data rate discovery: a 64-bit Source attempts connection with W=1 and Camp-on; if rejected, retries with W=0; if 32-bit succeeds, Source marks Destination as 32-bit-only; if 32-bit is also rejected, Destination/path is considered down. The Double_Wide field in HIPPI-LE provides a hint for the return path.
Self-address discovery: (1) transmit AR_S_Request to multicast address FE0h; (2) if AR_S_Request arrives back, extract own switch address from received I-field using bit 25 to distinguish logical-address from source-route mode; (3) if AR_S_Response arrives with own ULA in Destination_IEEE_Address, supersede any I-field-derived address with the agent-supplied Destination_Switch_Address.
The HIPPI ARP/RARP message uses the standard ARP format with ar$hrd=1 (16 bits), ar$pro=2048 (16 bits), ar$hln=6 (8 bits), ar$pln=4 (8 bits), ar$op (16 bits), plus 48-bit ULA and 32-bit IP address fields for both requester and target; the HIPPI-LE header carries the corresponding Switch Addresses in parallel.
The HIPPI-FP header (8 octets / 2 32-bit words) contains: ULP-id (8 bits, shall be 4), D1_Data_Set_Present (1 bit), Start_D2_on_Burst_Boundary (1 bit, shall be 0), Reserved (11 bits), D1_Area_Size (8 bits, should be 3), D2_Offset (3 bits), and D2_Size (32 bits, max 65,288 decimal).
The HIPPI-LE header (24 octets / words 2–7) contains: FC (3 bits), Double_Wide (1 bit), Message_Type (4 bits), Destination_Switch_Address (24 bits), Destination_Address_Type (4 bits), Source_Address_Type (4 bits), Source_Switch_Address (24 bits), Reserved (16 bits), Destination_IEEE_Address (48 bits), LE_Locally_Administered (16 bits), and Source_IEEE_Address (48 bits).
The I-Field (32 bits) in logical address mode contains: Locally Administered (bit 31), Reserved (bits 30–29), Double_Wide (bit 28), Direction (bit 27), Path Selection (bits 26–25), Camp-on (bit 24), Source Address (bits 23–12, unused in logical mode), and Destination Address (bits 11–0) holding the 12-bit Switch Address.