manello@BI1.SIMPACT.COM ("MIKE ANELLO") (10/25/89)
I have a question about running IP over 802.5.
RFC 1042 says that the largest frame field of the routing control bytes
for source routing are as follows:
Postel & Reynolds [Page 8]
RFC 1042 IP and ARP on IEEE 802 Networks February 1988
The RIF consists of a two-octet Routing Control (RC) field
followed by 0 to 8 two-octet Route-Designator (RD) fields. The
RC for all-routes broadcast frames is formatted as follows:
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| B | LTH |D| LF | r |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Note that each tick mark represents one bit position.
LF - Largest Frame: 3 bits
The LF bits specify the maximum MTU supported by all
bridges along a specific route. All multi-ring broadcast
frames should be transmitted with a value at least as
large as the supported MTU. The values used are:
LF (binary) MAC MTU IP MTU
000 552 508
001 1064 1020
010 2088 2044
011 4136 4092
100 8232 8188
All other values are reserved for future use.
The TMS380 Adapter CHipset User's Guide Supplement uses the following:
page 7-4
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| B | LTH |D| LF | r |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
LF (4 bits)
0000 reserved
0001 upto 516 octets in the information field
0010 reserved
0011 upto 1500 octets in the info field
0100 reserved
0101 upto 2052 octets in the info field
0110 reserved
0111 upto 4472 octets in the info field
1000 reserved
1001 upto 8191 octets in the info field
1010 - 1110 reserved
1111 initial value of broadcast frames
Does anyone know which values should be used for the LF bits and what
IP MTU should be used?
Is there a standard for 4-Mb Token Ring and 16-Mb Token RIng?
Mike Anello
Simpact Associates
manello@simpact.com