[HECnet] Re: An example of non-optimal setup

Is there KMC-11 code for HDLC? The DUP-11 to my memory would not get in the way of HDLC. If you want to talk to a cisco sync interface, put the DECnet packet in a cisco HDLC frame. You can turn off all the keep alive/rarp humbo jumbo that goes on between two cisco boxes. The FCS is 16 bit CRC for slow links and 32 bit for "fast" links. -P cisco Serial Line Encapsulation ------------------------------- cisco's default encapsulation on synchronous serial lines uses HDLC framing, with packet contents defined as follows: The first ("address") octet is set to 0x0F for unicast packets and 0x8F for broadcast packets. Broadcast just means that the higher-level protocol thought this was a broadcast packet; cisco doesn't support multidrop HDLC at this time. The second ("control") octet is always 0. The next two octets are a 16-bit protocol code, sent

These codes are usually Ethernet type codes. cisco has added some codes to support packet types that don't appear on Ethernets. The current list of codes is as follows: TYPE_PUP 0x0200 PUP TYPE_XNS 0x0600 XNS TYPE_IP10MB 0x0800 IP TYPE_CHAOS 0x0804 Chaos TYPE_IEEE_SPANNING 0x4242 DSAP/SSAP for IEEE bridge

TYPE_DECNET 0x6003 DECnet phase IV TYPE_BRIDGE 0x6558 Bridged Ethernet/802.3 packet TYPE_APOLLO 0x8019 Apollo domain TYPE_REVERSE_ARP 0x8035 cisco SLARP (not real reverse

TYPE_DEC_SPANNING 0x8038 DEC bridge spanning tree protocol TYPE_ETHERTALK 0x809b Apple EtherTalk TYPE_AARP 0x80f3 Appletalk ARP TYPE_NOVELL1 0x8137 Novell IPX TYPE_CLNS 0xFEFE ISO CLNP/ISO ES-IS DSAP/SSAP This list is shared between serial and Ethernet encapsulations. Not all these codes will necessarily appear on serial lines. This list will probably be extended as cisco adds support for more protocols. Bytes after this are higher-level protocol data. These normally look the same as they'd look on Ethernet. Bridging packets include Ethernet/802.3 MAC headers; no other packets do. Packets with type 8035 (reverse ARP) don't contain reverse ARP data as they would on an Ethernet. Instead, they carry a protocol cisco refers to as SLARP. SLARP has two functions: dynamic IP address determination and serial line keepalive. The serial line model supported by SLARP assumes that each serial line is a separate IP subnet, and that one end of the line is host number 1, while the other end is host number 2. The SLARP address resolution protocol allows system A to request that system B tell system A system B's IP address, along with the IP netmask to be used on the network. It does this by sending a SLARP address resolution request packet, to which system B responds with a SLARP address resolution reply packet. System A then attempts to determine its own IP address based on the address of system B. If the host portion of system B's address is 1, system A will use 2 for the host portion of its own IP address. Conversely, if system B's IP host number is 2, system A will use IP host number 1. If system B replies with any IP host number other than 1 or 2, system A assumes that system B is unable to provide it with an

For the SLARP keepalive protocol, each system sends the other a keepalive packet at a user-configurable interval. The default interval is

Both systems must use the same interval to ensure reliable operation. Each system assigns sequence numbers to the keepalive packets it sends, starting with zero, independent of the other system. These sequence numbers are included in the keepalive packets sent to the other system. Also included in each keepalive packet is the sequence number of the last keepalive packet _received_ from the other system, as assigned by the other system. This number is called the returned sequence number. Each system keeps track of the last returned sequence number it has received. Immediately before sending a keepalive packet, it compares the sequence number of the packet it is about to send with the

If the two differ by 3 or more, it considers the line to have failed, and will route no further higher-level data across it until an acceptable keepalive response is received. There is interaction between the SLARP address resolution protocol and the SLARP keepalive protocol. When one end of a serial line receives a SLARP address resolution request packet, it assumes that the other end has restarted its serial interface and reset its keepalive sequence numbers. In addition to responding to the address resolution request, it will act as if the other end had sent it a keepalive packet with a sequence number of zero, and a returned sequence number the same as the returned sequence number of the last real keepalive packet it received

The following is a C definition for the SLARP packet. The "long" and

types are 32-bit numbers, high octet sent first. The "ushort" type is a 16-bit number, high octet sent first. struct slarp { long code; /* SLARP packet type code */ union sl { /* followed by one of: */ struct { /* Address resolution functions

ulong address; /* Address of system sending this

ulong mask; /* IP subnet mask for this line

ushort unused; /* Unused: contents undefined */ } add; /* -- or -- */ struct { /* Keepalive probing functions */ ulong mysequence; /* Outgoing sequence number */ ulong yoursequence; /* Returned sequence number */ ushort reliability; /* Reserved: set to FFFF */ } chk; } t; }; Note that the data storage for t.add is overlayed on the data storage for t.chk. The whole SLARP packet consists of a 32-bit type code, followed by two 32-bit quantities and one 16-bit quantity. The overall length of the SLARP packet is 14 octets. The "code" field is used to identify the packet's SLARP type. Legal values for the "code" field are as

SLARP_REQUEST 0 Address resolution request SLARP_REPLY 1 Address resolution reply SLARP_LINECHECK 2 Line keepalive For address resolution request packets, the "address" and "mask" fields are set to zero, and the contents of the "unused" field field are undefined. For address resolution reply packets, the "address" field contains the IP address of the _replying_ system, and the "mask" field contains the IP subnet mask to be used. The contents of the "unused"

For keepalive packets, the "mysequence" field contains the sequence number of the packet and the "yoursequence" field contains the returned sequence number, which is the sequence number of the last keepalive packet the sending system has gotten from the receiving system. The "reliability" field is reserved for future use, and _must_ be

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