Cabletron Systems DMS-100 Limitations associated with protocols, Routing information protocol

Chapter 1: Introduction to the EIU 37

The Ethernet address in the LIUINV table has the format of the Nortel SuperNode family range of addresses: X000075Fxxxxx, where X is hexadecimal notation and x is a variable. For more information on MAC addresses, refer to “Appendix I: Obtaining a MAC address”.

Diagnostics for the EIU test only the Ethernet interface card (EIC) and the Ethernet interface paddle board (EIP). These diagnostics do not test the AUI cable. The AUI cable attaches to the paddle board and to a connector in the bulkhead. An extension of the AUI then runs from the bulkhead to the MAU.

Diagnostics also test the MAU. EIU diagnostics test the EIU’s connectivity to the AUI and the MAU up to the HUB.

Lastly, the record start command cannot be initiated during a telnet session on the connected device.

Limitations associated with protocols

Trailers are not supported. Trailers are the field on the data packet in which the system places the “headers”, which normally precede the data, after the data. Trailers can be negotiated between cooperating systems in an attempt to improve efficiency.

In the DMS-core, the protocol stack runs in the SuperNode IP (SNIP) scheduler class. This includes the IP receive processes and timer functions for TCP. In all other nodes, the protocol stack runs in CP class. The initial allocation for SNIP class is 3 percent and an interface is provided that allows an application to modify this value.

The following sections describe specific limitations associated with protocols.

Routing information protocol

The size of the dynamic routing table is limited to 436 entries. This limitation is imposed by the current implementation of and the current number of buffer management system (BMS) buffers reserved for routing information protocol (RIP) broadcasts. If the routing table overflows the routes at the end of the RIP, the system ignores the messages. This situation can lead to unpredictable routing behavior, such that routes may appear and disappear every 30 s. There is no warning log to notify the operating company that this errant behavior is occurring.

RIP Version 1.0 does not support variable-length subnetting. This limitation means that all subnets that use RIP to exchange routing information must use the same number of bits in their IP address to identify their subnet. If a subnet does not adhere to this rule, unpredictable and intermittent loss-of- connectivity behavior may be experienced on the EIU. RIP-II, which supports variable-length subnetting, is not implemented on the EIU.

DMS-100 Family EIU User Guide TELECOM12