10 • ICMP '6/'$&6$GPLQLVWUDWRUVª5HIHUHQ H*XLGH66 ,QWURGX WLRQIntroductionWhen networking problems or undesirable conditions occur, the ICMP protocol is used for communicatingcontrol or error information plus testing. The statistics listed on the DACS ICMP window (see figure 22) com-prise those contained in RFC 792—Internet Control Message Protocol (ICMP). Implementation of the ICMPgroup is mandatory for all TCP/IP networks. RFC 1312—ICMP Group of MIB-II Variables—provides thedefinitions of these variables. It is important to remember that any RFC can be superseded by a newer.)LJXUH,&03ZLQGRZClick on ICMP under the Configuration Menu to monitor DACS ICMP statistics.Block ICMP redirects (boxBLockIcmpRedirects)The two options for “Block ICMP Redirects” either allow the reception of ICMP Redirect messages [allowre-directs(0)] or block the reception of ICMP Redirect messages [stopredirects(1)]. The recommended configura-tion is to block the ICMP redirect messages because in some instances they could alter the routing table withundesirable effects, which is considered a breach of security.ICMP Receive/Send Messages windowThe ICMP window displays the ICMP message counters. ICMP messages are displayed in the window as col-umns comprising two types of messages:• Messages received by the DACS (InMibVariable)• Messages sent by the DACS (OutMibVariable)The numbers following the parameters can be a good source of what is happening on the network to point outpotential problems. Both gateways (routers) and hosts can send ICMP messages.Total Received (icmpInMsgs)The total number of ICMP messages which the 3092 Multiplexer has received. Note that this counter includesall those counted by icmpInErrors (see “w/Errors (icmpInErrors, icmpOutErrors)” on page 67).
