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Frequently Asked Questions (FAQs)
- QWhat version of SNMP is available on my Cisco IOS image?
- AAll software releases to date have included SNMPv1. In addition, releases prior to Cisco IOS 11.2F(6.0) (including all releases of 11.2 and 11.2P) supported the SNMPv2 Party-based protocol. Releases from Cisco IOS 11.2F(6.0) onwards have SNMPv2C support (SNMPv2, RFCs 1441-1452, was replaced by SNMPv2C, RFCs 1901-1908 in these releases).
- QIs the OSPF link-state database available to a MIB query?
- AYes, and so is the IP routing table (IpRoutingTable).
- QHow can I obtain route redistribution parameters via SNMP requests for various protocols (RIP, OSPF, and so forth)?
- AYou cannot at this time. You can find a list of all presently supported at:
- QDoes Cisco implement 64-bit counters, especially for the IF-MIB? If not, when is 64-bit counter support expected?
- ACisco does not support 64-bit counters yet though when they exceed the 64-bit limit they will roll over. This is being worked on now.
- QWhat version of SNMP is required for 64-bit counter support?
- ASNMPv2C is required for Counter64.
- QDoes the Cisco IOS support subinterfaces in the IfTable?
- AGeneric support for sublayers in the IfTable has been present since Cisco IOS 11.1(1). For any given media type, it is up to the groups which support that media to determine the following:
- If sublayers are appropriate (with direction from IETF)
- How to support those sublayers
- QWhat is the minimum Cisco IOS version I should be running to see subinterfaces in SNMP tables?
- ACisco IOS 11.1.
- QAre the SNMP counters IfInOctets and IfOutOctets the same as the show interface in/out counters?
- QDo the ifInOctets and ifOutOctets counters include framing overhead (PPP, HDLC)?
- QOn an ATM interface, do the counters include the cell header?
- AATM counters do not include ATM overhead (cell headers and AAL5 padding).
- QA customer has a Cisco 7507 running Cisco IOS 126.96.36.199. He tries to do snmpwalk on mib2, and all the interfaces return a value except the ATM interface; it does not return any value. He is also having problems with HP OpenView retrieving information for this interface. For example:
ifDescr.1: ATM0/0 ifAdminStatus.1: up ifOperStatus.1: up ifInOctets.1: is not returned ifInUcastPkts.1: is not returned
Is this a bug?
- AThis has been fixed in Cisco IOS 11.1(5.0.2) via CSCdi63762. Keep in mind, in Cisco IOS 11.1 and later, sparse tables have been implemented, specifically in the ifmib, as well as other areas. Thus, there are valid situations where ifInOctets.1 would not be returned.
- QSome IfTable columns do not show up for certain interface types. Why? Is this a bug?
- AThis is not a bug IfTable based on RFC 1573 is designed specifically so that some columns in a given row will not be instantiated based on IfType. Please read the RFC compliance statement for further clarification for which columns to expect for different media groups. An example of this would be ATM, which is a fixed length packet. As such, rows in the IfTable etc. would be based on IfFixedLengthGroup.
- QIn which release is SNMPv2C support available?
- ACisco IOS 11.3 will be the first shipping release with SNMPv2C support.
- QP-SNMP CPU usage spikes to 90 percent (or higher). Is this a bug?
- ANo, this is not a bug. It is not unusual for IP-SNMP to take up 90 percent of the CPU on the router when the router is lightly loaded with other tasks. IP SNMP runs at a low priority and a CPU usage of 90 percent or higher means the router has the bandwidth to spend more time on SNMP. It might also mean that the router was responding to frequent polls from an NMS application, which could be a very bad thing.
- QIs there a way to tell the router to load a specific configuration file via TFTP from a specific host?
- AYes there is. Please refer to the following location for details: ftp://ftpeng.cisco.com/pub/mibs/app_notes/configset.
Alternately, you may use the following UNIX SNMP script written by Matt Birkner, CCIE 3719, who is also a technical editor for this book. The seed file for this script needs to be in ASCII file format with one IP address per line and in the same directory as the script.
#!/bin/ksh # # Start of code clear print - " This code takes the seed file in the current directory & will TFTP the config" print - " Used by permission, Copyright 1998, Matt Birkner " print - " Usage ./change_config <seed filename>" for ROUTER in cat $1.seed do ( print "Now connecting to router $ROUTER" /tools/snmpset $ROUTER <SNMP Read/Write Community String> .188.8.131.52.184.108.40.206.1.50.<TFTP Server IP address> s <Config File Name> sleep 2 /tools/snmpset $ROUTER <SNMP Read/Write Community String> .220.127.116.11.18.104.22.168.1.54.0 i 1 ) print - " $ROUTER config written..Going to next." done
<TFTP Server IP address> is the IP address of your TFTP server
<Config File Name> is the name of file that you will use to modify the Cisco router.
The following sample configuration will shut off DNS in the router, set the routers time to follow GMT and cause the syslog to be time stamped. Alternately, this example could contain an entire router configuration or customized OSPF settings.
An example of the contents of <Config File Name> is as follows:
no ip domain-lookup clock timezone GMT 0 clock summer-time GMT recurring service timestamps log datetime localtime show-timezone ! end
- QIs there an SNMP MIB to grab arp table information? We need both the IP and MAC address in the same table.
- AYes, IPNETTOMEDIATABLE in MIB-II (RFC 1213).
- QA customer activated Silicon Switching and now MIB values for interface statistics are only updated every 10 seconds. SNMP GETs for MIB values show no change if polled more often (in this case, 8 seconds). Is this is a bug?
- AThis is expected (not a bug). Part of the tradeoff for allowing the box to dedicate more resources to actually switching traffic is to poll less often for interface statistics. show interface should present the same behavior.
- QA customer is seeing two coldstart traps out of the router. Is this a bug?
- AThis behavior is not a bug. See bug report CSCdi54387. A coldstart trap is normally the first trap (and the first packet) to be sent to a trap destination. So the router needs to arp for the trap destination. Cisco devices drop the trap if an arp has to be sent out. Therefore, many customers were not seeing the coldstart trap before the fix, which was to send it twice. This is RFC compliant, as the network can also duplicate the coldstart traps.
- QWhat is the EXACT information contained in an SNMP trap, and where is it documented?
- AFor the list of objects on traps, check out: ftp://ftpeng.cisco.com/pub/mibs/traps. Note that the information at this site only specifies what should be contained within a trap. It does not mean that the trap has been implemented in the agent code yet.
- QIs there a tool for extracting MIBs from an RFC?
- AYes, try premosy <rfc> mib, where rfc is the text document from which mib is to be extracted.
- QI would like to capture SNMP traps on my workstation. What tool can I use for this?
- AOn SunOS machines, use /usr/local/bin/tcpdump. On Solaris, use /sw/current/solaris2bin/traprcv. On Windows, use MGSOFT MIB Master, located at http://www.mg-soft.com.
- QHow are the MIB variables locIfInbitsSec and locIfOutbitsSec and calculated? Are the packet and frame header/trailer bytes included in the calculations?
- AThose variables are an exponentially decayed five minute average of the amount of all traffic that comes in and goes out of the interface. Exponentially decayed five minute average means that the most recent sample is weighted more heavily than the oldest sample. The current sample period is 10 seconds.
- QDo the SNMP accounting tables contain addresses of access list violators?
- AYou can get the access list number violated by packets sourced from one address to another. See the IP accounting MIB in the MIB document found at: ftp://ftp/pub/MIBs/v1/OLD-Cisco-IP-MIB.my.
- QWhat is the minimum and maximum length of the snmp-server location and snmp-server contact fields?
- AOne (1) character is the minimum length and 233 characters is the maximum (limited by the length of a single command line in the parser).
- QIs there a way to get the serial number of a router using SNMP?
- AThe serial number of the router is not retrievable by default. You can retrieve only the serial number of the CPU (if it exists). You can, however, use the snmp-server chassis-id config command to set the SNMP MIB variable chassis ID. In this way, you could have the serial number of a remote router.
- QHow can I get SNMP information on total collisions per-interface on a Catalyst 5000?
- AHere is the MIB for the Workgroup products, including the 5000, Cisco-STACK-MIB.my, found on CCO. This MIB and RFC1213 (MIB-II) are the only MIBs supported on the Catalyst 5000. There is nothing that references collisions except for the MIB variable PORTADDITIONALSTATUS, which indicates that more than one collision has occurred on the interface when the variable has a value of two.
- QHow can I tell if EIGRP is enabled on a interface via SNMP? Can I obtain EIGRP metrics through SNMP requests?
- AYou cannot at this time.
- QHow can I obtain route redistribution parameters via SNMP requests for various protocols (RIP, OSPF, etc.)?
- AYou cannot at this time.
- QA network management workstation is attempting to perform SNMP network management functions on remote LAN concentrators. Their SNMP traffic must pass through one or more routers for which they do not have the community string. Can they manage the remote devices without having the SNMP community string?
- AYes. You only need the community string for the device that you are actually managing. You also need to make sure that the routers along the way are not filtering the SNMP port.
- QWhat is the impact of SNMP management traffic on router performance?
- AAll SNMP queries sent to a router are prioritized as either low or medium priority, depending on the version of code run by the route processor. This means that processes with a higher priority than the SNMP process will be serviced before SNMP. So, regardless of SNMP polling intensity, routing processes will generally be processed before SNMP requests because route processes are high priority.
You can view the priorities of each of the routers processes by doing a show process and looking in the Q column (L = Low, M = Medium, H = High). The router processes H before M, and M before L. Here is an example:
CPU utilization for five seconds: 6%/1%; one minute: 7%; five minutes: 6% PID Q T PC Runtime (ms) Invoked uSecs Stacks TTY Process 3 L E 50AE2 18124 41610 435 736/1000 0 ARP Input 6 H E 67864 959264 2167473 442 1602/2000 0 IP Input 43 M E 9DBB0 940300 141179 6660 528/1000 0 IP SNMP
Be cautious with the amount and frequency of polling. Often, network management platforms request more information than you think. Your routers can become processor-bound as a result of excessive information being polled, sometimes driving the route processor CPU utilization to 99 percent (despite the SNMP priority). The rule of thumb is that a minimum amount of information should be polled as infrequently as possible. You can use an analyzer to determine the amount and frequency of information being polled from a particular router. To avoid extensive polling, the SNMP priority should generally be set to low. Do this with the hidden snmp-server priority command.
- QWhats the difference between SNMP and SNMPv2 configuration in Cisco IOS? Which version of Cisco IOS supports SNMPv2?
- AThese are two different SNMP versions. The SNMP packet format is different in each, but there is no difference in configuring them in Cisco IOS. SNMPv2 provides more flexibility and is actually an enhancement to SNMPv1. SNMPv2 is supported as of Cisco IOS 10.2. Cisco supports both versions of SNMP. Some NMS stations do not support SNMPv2 yet, so the SNMPv2 MIBs cause an error on the management platform (SNM, HPOV, NetView) when compiled.
- QWhat does Ciscos private MIB support?
- ACiscos private MIB supports DECnet (including DECnet routing and host tables), XNS, AppleTalk, VINES, NetWare, and additional system variables that highlight such information as average CPU utilization over selectable intervals. Cisco users can add private extensions to the MIB as required.
- QHow can I find out where and how to access other vendor MIB variables that are supported by Cisco Systems.
- AOther-vendor MIBs supported on Cisco products can be retrieved from CCO or via anonymous FTP. Cisco supports Novells IPX (2.5), NLSP, and RIPSAP (22.0) MIBs, among others.
- QI can issue an SNMP ping directly to the router asking it to ping all DLCI partners, and it is successful. What does this indicate?
- AThis confirms that the protocol is configured and the protocol-to-DLCI mapping is correct at both ends.
- QAre there SNMP variables that will provide an accurate status on the DLCIs?
- AYes, RFC1315, and the Frame Relay DTR MIB.
The SNMP variable for a circuits status is FRCIRCUITSTATE. Its ASN.1 OID form is 22.214.171.124.126.96.36.199.2.1.3. It resides in the FRCIRCUITTABLE; so to get the value (the actual status in this case), the index and the DLCI would be the first and second instance respectively. Through SNMP GET or GETNEXT requests, you should get the system internal circuit status. Valid values for it include the following:
- 1. invalid
- 2. active
- 3. inactive
For Cisco, you would see either 2 or 3.
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