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ASR9000/XR: Understanding SNMP and troubleshooting

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Introduction

In this document we'll be discussing the SNMP architecture as it is implemented in IOS-XR. As you can read in the IOS to XR migration guide (A starting point), some of the high level differences between IOS and XR are already being highlighted.

As IOS-XR is a highly distributed operating system and is using hardware forwarding, the way that SNMP retrieves counts and responds to requests is a bit different then what you might be used to and in this article we deep dive into the architecture of stats collection, how it operates and what show commands you can use to verify the performance of your SNMP in regards to IOS-XR and specifically for the ASR9000 (though this article also applies to CRS and GSR running IOS-XR).

XR routers are highly distributed. Increasing capacity by distribution and replication does come at a cost. In any scaled design where replication or multiplication of the processing devices is used, a critical additional component is the design is the inter process communication path between the processing components

 

The nature for this article originated from the fact that some of our customers have seen SNMP timeouts in XR 4.2.3 and has raised a lot of questions in regards to caching, stats collection and the way SNMP operates. Hopefully with this technote we can clear up some of the confusion.

 

SNMP architecture in IOS-XR

This section describes the symptoms of the problem and the main issue the document resolves.

 

SNMP Packet flow inside the system

Depending on your configuration SNMP packets can be received in band or out of band (as per MPP definitions, see article on LPTS and MPP for more info) and after intial reception and punting to the control plane (RSP), they are handed over to NETIO. NETIO is sort of an IP INPUT process in IOS that deals with process level switching.

IF the SNMP requests are "for me" they are handed over to the SNMP-D process for evaluation of the request and dispatch to the next layer of processing.

 

Screen Shot 2013-03-25 at 1.36.54 PM.png

XR SNMP Specifics

 

  • Informs supported as of 4.1 (Inform proxy not supported)
  • Full AES Encryption support in 4.1 (V3 related)
  • Full IPv6 support  In 4.2 (snmp engine transport)
  • VRF-aware support in 3.3  (snmp engine, some MIBs already available)
  • Across Cisco capability files not well supprtoed, ASR9K MIB guide developed to improve situation
  • Event/expression MIB support for extendibility as in IOS
  • Warm standby on snmp agent
  • Management plane protection (mpp) / snmp overload control to limit impact of snmp on device
  • Standards based MIB support (IETF & IEEE)

ENTITY-MIB

IF-MIB

IP MIBs support

Routing MIBs support (BGP, OSPF, ISIS, etc)

MPLS, Pseudowire, VPLS MIBs support

IEEE 802x (LAG, CFM, OAM)

 

SNMP performance improvements

  • Asynchronous request processing / multithreading (4.2)
  • Bulk processing (dedicated processing path for bulking) (4.2)
  • Data Collection Manager – bulk MIB data collection and file push (4.2.0 & 4.2.1)
  • Additional IPv6 / VRF aware MIB support (4.2 and after)
  • Additional improvements with Async IPC and SysDB Backend infra (4.1)
  • Overload Control Integration (4.0)

SNMP request processing blocked during critical event periods (i.e. OSPF convergence)

Debugability:

  • Additional PDU performance monitoring support (4.2)
  • MIB guide update (4.2)

 

Caching

Caching is an integral part of IOS XR SNMP processing allowing it to perform at best performance while maintaining the most accurate stats possible.

There are various levels of caching and some of them are configurable, some of them are not. The reason why we cache is also to alleviate the hardware from the burden of getting continuous requests, especially in WALK scenarios retrieving many requests for eg interface stats counters.

 

There is a process called STATS-D which is a proc running on the linecard that periodically scrapes statistics of the linecards hardware and updates the interface counters and MIB stats.

This means that if you poll within the stats-D update time, you'd realistically see the same counter being returned twice.

Show interface commands (depending on release) will force a direct update read from hardware to get the most accurate reading, but the IF-MIB stats are cached.

Screen Shot 2013-03-25 at 1.23.01 PM.png

 

1.The SNMP UDP transport receives sends a SNMP GetRequest-PDU, GetNextRequest-PDU or GetBulk-PDU to the SNMPD.
 
2.The SNMP Engine parses the PDU and dispatches the individual variable bindings. IF-MIB objects are dispatched to mibd_interface process & IF-MIB DLL callbacks get invoked.
 
3.If the request is a getnext, the IF-MIB’s cache of variable bindings is checked to see if there is a cache hit. If so, the value is returned to the engine and the response PDU is sent. ***look-ahead cache

 

4.If no cache hit, the IF-MIB passes a message to the statsd_manager process to get the information for the interface (and the next 99 interfaces for the cache in the getnext case). IPC = LWM The sysdb direct EDM connection invokes the EDM for statsd.
5.The statsd_manager gets the interface data from its cache and returns the statsd bags for the interfaces to IF-MIB.

 

Visualizing caching differently:

 

Screen Shot 2013-03-25 at 1.30.28 PM.png

 

Two caching mechanisms:

  1. Statsd caching
  2. Lookahead caching

1: Statsd caching:

Used for interface related statistics (IF-MIB, IF-EXTENSON-MIB, etc.)

Statsd caching is configurable (via CLI).

2: Lookahead caching:

Conceptually a varbind cache.

Not configurable.

Not all MIBs leverage/use this cache.

Statsd cache:

– Use command “snmp-server ifmib stats cache”* to enable it.
– This is a periodic cache which gets refreshed every 30 seconds for all interfaces.
– Statsd cache maintenance is done irrespective of this command. The command only dictates from where to fetch the stats.
– Without the above command stats are actually fetched from the linecard, real-time counters. (Default behavior).
• Involves more number of processes and hence more CPU utilization and latency. Additional tax for real-time counters.

 

System maintains look ahead cache:

– Stats fetched for next 100 rows (interfaces) in bulk and cached.

***Data for up to 500 interfaces kept in cache 

– Cache is maintained for a max of 20 seconds.
– Oldest used blocked is reused to maintain a new set of cache.
– There is no **** to enable/disable this cache.
– Provides good performance improvement if used along with statsd cache.

 

Parallel vs Serialized processing

The following picture tries to explain what the serialized processing means:

When an SNMP request is being received they are handled in a sequential manner. If one request currently in progress is "slow", subsequent requests are waiting to be handled and may time out.

The NMS station may resend its SNMP request building up the request queue potentially causing more trouble.

Now the good news is in 431 we have the ability to detect duplicate requests and throw them out of the queue making sure we're dealing only with "NEW" requests.

 

Screen Shot 2013-03-25 at 12.59.33 PM.png

 

Enhancements in XR 4.1

 

Screen Shot 2013-03-25 at 1.15.33 PM.png

 

Enhancements in XR 4.2

 

Screen Shot 2013-03-25 at 1.15.42 PM.png

 

Example (performance) trace point logging

 

Screen Shot 2013-03-25 at 1.15.58 PM.png

 

 

SNMP process architecture

  • All management interfaces (SNMP, XML, CLI) utilize the same core processing architecture [sysdb].
  • The SNMP processing architecture serializes PDU processing (pre-4.2).
  • Request PDUs for all pollers effect the response rate seen for a single poller.
  • The SNMP per-OID polling rate is very MIB specific (each MIB’s underlying data model dictates the performance of MIB’s OID access)
  • MIB request processing commonly involves the GSP IPC mechanism, sysDB (data store) and statsd in some cases.
  • In band and out of band SNMP requests are treated the same within SNMP.
  •      (In band means that the SNMP request can be received on an interface that is also transporting customer/user traffic. Out of band interfaces, such as the MGMT interfaces on the RSP are dedicated for management and carry management traffic only).
  • The current SNMP architecture has an SNMP daemon enqueue requests and separate MIB daemons process requests (requests are enqueued from transport layer receive fairly quickly)
  • There are multiple MIB-specific caching mechanisms in place to improve performance which also complicate the polling rate calculations.
  • There is no queue size limit for SNMP requests (grows with memory).

 

XR processes referenced

 

StatsD is a process that collects statistics from various places (eg hardware) and updates tables on the LC shared memory.

IPC is an inter process call or communication that is used by processes to talk to each other to request data or send commands.

GSP is group services protocol, which is a process in IOS-XR that allows for one process to communicate with multiple "nodes" at the same time (like a sort of multicast way that the RSP can use to talk to multiple linecards, for instance to update a FIB route).

 

 

SNMP tracepoints

 

“show snmp trace requests” is a sliding window of logs indicating the above information about PDU processing

 

Screen Shot 2013-03-25 at 1.06.58 PM.png

 

XR MIB implementation specifics

Implementations of specific MIBs packaged as individual DLLs. Each MIBd process “houses” a group of MIB DLLs
Grouped according to the “type” of MIB—interface, entity, route, infra, at runtime, grouping is determined via a config file in XR source control
MIB DLLs handle the specifics of mapping MIB defined data model to XR data model. MIB DLLs map MIB namespace to XR data owner access
APIs (sysdb EDM is most common)
Look-ahead Caching—Any support for look-ahead cacheing is done within the MIB DLL. (No generic support for all MIBs)
Non-look-ahead cacheing—Some features may support access to cached managed data. These are accessed via separate data access point (ie. separate sysdb EDM path)

 

Screen Shot 2013-03-25 at 3.01.03 PM.png

Troubleshooting commands and what they do

 

The following show and debug commands are very powerful to verify and track SNMP.

 

show snmp

Global agent counters—incoming,   outgoing (request and trap), & error PDUs

Technique:

- Periodically collect output to determine overall PDU response rate and identify error rate.

show snmp   trace requests

Log of   high level PDU   processing tracepoints—Rx, Proc Start, Tx   time

Technique:

Periodically collect this log. Decode and use the data to determine the   following per-PDU   data:

1.Source   IPs of   pollers
2.Queue   lengths of per-source IP PDU queues
3.Types   of request PDUs   being used
4.Timestamp   when PDUs   are enqueued   into the queues for the source IPs
5.Duration   of the PDU enqueued   & waiting to be processed
6.Processing   time of PDUs   from pollers
 

show snmp mib   access

Per-OID   counters indicating the number of times an operation was done on that OID, ie.   GET, GETN,   SET.

Technique:

Periodically collecting & diff will   indicate what was polled during the time periods.

show snmp mib   access time

 

Per-OID timestamp of the last operation on the OID.

Technique:

Periodically collecting &   diff will indicate if any polling on the OID   was done in the time period.

debug snmp   request

(careful!!!)

Enable   to log every OID   being processed by every PDU to syslog.   Need to enable “debug snmp packet” as well to identify source of PDUs.

NOTE: Disable “logging trap debug” if “snmp trap syslog” is configured!!!

debug snmp   packet

(careful!!!)

Enable to log same data as “sh snmp   trace requests” to syslog.

NOTE: Disable “logging trap debug” if “snmp trap syslog” is configured!!!

 

 

Show commands that are new to XR 4.2 onwards

 

show snmp mib   statistics

Per-OID statistics summarizing   transaction times within the mibd level—count + min/max/avg .

Technique:

Collect to determine if specific MIB   objects are averaging high processing times and/or large variance (low min,   high avg & max).

show snmp   queue rx

Indicates   the min/max/avg   queue sizes for the PDU receive and pending queues. Real-time and 5min views.

show snmp   queue trap

Indicates the min/max/avg queue sizes for the internal trap PDU   queue

(config)# snmp   logging thresh oid

show snmp   trace slow oid

Allows   configuring a duration threshold for logging per-OID transactions exceeding   the time threshold.

This   is measured within the mibd process beginning with the call to the   MIB specific handler for the OID and ending with the response from the same.

(config)# snmp   logging thresh pdu

show snmp   trace slow pdu

 

Allows   configuring a duration threshold for logging per-PDU transactions exceeding   the time threshold. When logging all   OIDs within the PDU are also logged to this buffer.

This   is measured within the snmpd process beginning with the dequeue   of the PDU from the receive queue and ending when all the OIDs in the PDU   have been processed and the response is ready to be sent.

 

Troubleshooting PDU performance issues

 

Some MIBs dont have accelerated processing or dont have caching and because in certain releases SNMP is processed serially, it could happen that you'll see timeouts on OID requests that are normally operating perfectly fine. An example of a slow MIB is the SONET MIB. Because this mib needs to talk from the SNMP process all the way down to the SPA of the SIP-700 linecard (on the ASR9000), the response may not be provided in a timely manner. At the same time new requests for other OID's may be in the holding or pending queue causing timeouts and retries.

Retries to an already under performing MIB may exacerbate the overal issue.

 

The vast majority of PDU performance issues are related to a poller polling a specific MIB which is slow to process its OIDs.

This causes all other pollers to see some of their PDUs slowed due to queueing delays (waiting on slow MIB)

Troubleshooting Goal:

     Identify the slow MIB/MIBs being polled

Workarounds

Use SNMP View Access Control to block access to the slow MIB tables / objects

snmp-server view MyPollView <slow MIB OID> excluded

Use ACLs to permit only “known” NMS devices/applications . In this case “known” is referring to content of requests issued from the app

 

 

Determining Internal Timeout of a MIBd

snmpd will timeout a mibd process if it has not received a response to a request for an OID/s within 10s by default.

Once in timeout state, snmpd will continue processing requests BUT it will mark the mibd as unavailable until it responds to the timed-out request.

 

  • Getnext operations to any OIDs for MIBs in the timed out mibd will skip to the lexi-next OID owned by a different mibd process.
  • Get/Set operations to any OIDs for MIBs in the timed out mibd will be responded to with a PDU error-code of “resourceUnavailable”.

Troubleshooting

(in addition to normal “slow OID” techniques):

If able to catch mibd in the state:
run attach_process –p <PID of mibd process> -i 5 –S
May be possible to identify the MIB being polled via examining “show snmp lib group agent ipc” for “request timeout” to get the timestamp for when
the mibd timeout is detected.
Using the timeout timestamp, “sh snmp mib access time” may still have an OID timestamp correlating to 10s prior.
 
 

 

Examples and Recommendations

For the purpose of clarification the following is an example of an snmp table. The columns (vertical) represent the instance or entity, and the rows represent the objects. In this case we have 3 instances 1, 2 and 3, and each instance has 3 objects, ifName, ifInOctets and ifMtu.

 

 

ifIndex

ifName

ifInOctets

ifMtu

1

Ethernet1/0

1234

1500

2

POS2/0

512

500

3

Serial3/0

235

600

 

 

The customers current snmp design is using snmpwalk. Snmpwalk works by performing a sequence of get-nexts, but on a column by column  basis if the column object is specified as the starting point.

 

An example of a column walk specifying the ifDescr from IF-MIB

[no-sense-1 68] ~ > snmpwalk -c public 10.66.70.87   IF-MIB::ifDescr

IF-MIB::ifDescr.1 = STRING: Loopback0

IF-MIB::ifDescr.2 = STRING: Bundle-POS1

IF-MIB::ifDescr.3 = STRING: Bundle-Ether1

IF-MIB::ifDescr.4 = STRING: TenGigE1/2/0/0

IF-MIB::ifDescr.5 = STRING: TenGigE1/2/0/1

IF-MIB::ifDescr.6 = STRING: SONET0/2/0/0

IF-MIB::ifDescr.7 = STRING: SONET0/2/0/1

IF-MIB::ifDescr.8 = STRING: SONET0/2/0/2

IF-MIB::ifDescr.9 = STRING: SONET0/2/0/3

IF-MIB::ifDescr.10 = STRING: SONET0/2/0/4

<cut>

 

Snmpwalk can also be used to get a single object only, for instance, the object IF-MIB::ifDescr.9. It does not support the ability to specify any more than 1 object in its request. The example below shows two objects being requested, but only the first returned.

 

[no-sense-1 69] ~ > snmpwalk -c public 10.66.70.87 IF-MIB::ifDescr.9

IF-MIB::ifDescr.9 = STRING: SONET0/2/0/3

[12:18 - 0.31]

 

[no-sense-1 70] ~ > snmpwalk -c public 10.66.70.87 IF-MIB::ifDescr.9 IF-MIB::ifDescr.10

IF-MIB::ifDescr.9 = STRING: SONET0/2/0/3

[12:18 - 0.36]

 

For efficiency row traversal is preferred, with multiple objects requested in a single snmp transaction. This reduces unnecessary overhead on the XR system. For this reason snmpwalk is not recommended.

 

 

Examples of row traversal

The customer is currently requesting via snmpwalk the following IF-MIB objects

ifDescr

ifHCInOctets

ifHCOutOctets

ifHCInUcastPkts

ifHCOutUcastPkts

ifInNUcastPkts

ifOutNUcastPkts

ifInOctets

ifOutOctets

ifInUcastPkts

ifOutUcastPkts

 

 

The preferred method is to specify all the objects required from an instance/entity in a single command such as get-next or bulk-get. An example follows using snmpbulkget

 

 

[no-sense-1 115] ~ > snmpbulkget -v 2c -c public 10.66.70.87 IF-MIB::ifDescr IF-MIB::ifHCInOctets IF-MIB::ifHCOutOctets IF-MIB::ifHCInUcastPkts IF-MIB::ifHCOutUcastPkts IF-MIB::ifInNUcastPkts IF-MIB::ifOutNUcastPkts IF-MIB::ifInOctets IF-MIB::ifOutOctets IF-MIB::ifInUcastPkts IF-MIB::ifOutUcastPkts

IF-MIB::ifDescr.1 = STRING: Loopback0

IF-MIB::ifHCInOctets.2 = Counter64: 0

IF-MIB::ifHCOutOctets.2 = Counter64: 7116596

IF-MIB::ifHCInUcastPkts.2 = Counter64: 0

IF-MIB::ifHCOutUcastPkts.2 = Counter64: 99611

IF-MIB::ifInDiscards.2 = Counter32: 0

IF-MIB::ifOutDiscards.2 = Counter32: 0

IF-MIB::ifInOctets.2 = Counter32: 0

IF-MIB::ifOutOctets.2 = Counter32: 7116596

IF-MIB::ifInUcastPkts.2 = Counter32: 0

IF-MIB::ifOutUcastPkts.2 = Counter32: 99611

IF-MIB::ifDescr.2 = STRING: Bundle-POS1

IF-MIB::ifHCInOctets.3 = Counter64: 38796828

IF-MIB::ifHCOutOctets.3 = Counter64: 66076323

IF-MIB::ifHCInUcastPkts.3 = Counter64: 331833

IF-MIB::ifHCOutUcastPkts.3 = Counter64: 402546

IF-MIB::ifInDiscards.3 = Counter32: 0

IF-MIB::ifOutDiscards.3 = Counter32: 0

IF-MIB::ifInOctets.3 = Counter32: 38796828

IF-MIB::ifOutOctets.3 = Counter32: 66076323

IF-MIB::ifInUcastPkts.3 = Counter32: 331833

IF-MIB::ifOutUcastPkts.3 = Counter32: 402546

IF-MIB::ifDescr.3 = STRING: Bundle-Ether1

<snip>

 

Note above that all the objects in a row for all instances (columns) are obtained with one command. The same can be done with a get-next, however the added overhead of including the instance must be used for each instance present.

 

[no-sense-1 120] ~ > snmpgetnext -v 2c -c public 10.66.70.87 IF-MIB::ifDescr.1 IF-MIB::ifHCInOctets.1 IF-MIB::ifHCOutOctets.1 IF-MIB::ifHCInUcastPkts.1 IF-MIB::ifHCOutUcastPkts.1 IF-MIB::ifInNUcastPkts.1 IF-MIB::ifInOctets.1 IF-MIB::ifOutOctets.1 IF-MIB::ifInUcastPkts.1 IF-MIB::ifOutUcastPkts.1

 

IF-MIB::ifDescr.2 = STRING: Bundle-POS1

IF-MIB::ifHCInOctets.2 = Counter64: 0

IF-MIB::ifHCOutOctets.2 = Counter64: 7116596

IF-MIB::ifHCInUcastPkts.2 = Counter64: 0

IF-MIB::ifHCOutUcastPkts.2 = Counter64: 99611

IF-MIB::ifInDiscards.2 = Counter32: 0

IF-MIB::ifInOctets.2 = Counter32: 0

IF-MIB::ifOutOctets.2 = Counter32: 7116596

IF-MIB::ifInUcastPkts.2 = Counter32: 0

IF-MIB::ifOutUcastPkts.2 = Counter32: 99611

[13:03 - 0.35]

 

Although the examples are specific to IF-MIB, the same concept is relevant to all MIBs.

 

Timeout and Retry Setting on NMS

Timeout recommenations:

  1. use dynamic timeout when available
  2. if dynamic timeout is not available, increase timeout if more management applications are simultaneously polling the SNMP agent on asr9k. Multiply the default timeout by the number of applications that are simultaneously polling the SNMP agent on asr9k.

 

Retry recommendations:

  1. use dynamic retry when available
  2. if dynamic retry is not available, establish number of retries based on testing

 

For more details refer to IOS XR SNMP Best Practices.

 

 

Special thanks to the XR SNMP dev team for some of the amazing content used in this article, most notably Timothy Swanson and Leon Zachary

 

 

 

Xander Thuijs CCIE #6775

Principal Engineer, ASR9000

Comments
eric.follos
Beginner

Hello Xander,

I have a problem where our NMS shows intermittent SNMP Poll failures with our 9ks. Issue occurs every couple hours or so, at seemingly irregular intervals. Polling to other IOS device types (6509, 3750, 7206) works ok. We are running XR 4.3.1.  

When I try to ping the server from a 9k with a series of 10k pings I don’t see any packet loss.

Tried to explore slow oid but we don’t always have slow requests coincide with the poll fail.

'show snmp trace request' shows pdu requests with the same src ip/port and occasionally same req_id.  After an SNMP poll fail if I run the command 'show snmp trace dupdrop' it reflects Dup Count increasing. Is there a way to disable on the 9k the ability to detect duplicate requests?

Regards,

Eric

xthuijs
Cisco Employee

hi eric,

yeah there are some perf issues in 431 that we have uncovered. although there are improvements in 431 over 423, we were not done there. So in 432 you'll see better results in especially in 434. we have put a lot of testing effort into the snmp operations and discovered/implemented many improvements. I dont know right off hand if we smu'd things in 431.

the issue you are running into is likely not network connectivity or anything but just the snmp processing inside that is the culprit.

you cant enable dupe request checking, that is one of the performance improvements, if we are alrady working on a request and getting the retry in, it would only excarbate the issue if we enqueue the same request again.

for sure enable the caching if not already, and try to stay current on the smu's pertaining to snmp.

when XR434 comes out in December consider that as a goto release if you're planning an upgrade.

regards

xander

davecs
Beginner

4.3.4 doesn't solve our snmp timeout issue.

here is the strange thing - we have 4 ASR's, a mix of 4.2.3 and 4.3.4, every 30 mins or so each ASR will stop responding to snmp queries.

and not at the same time, ie at *:15 and *:45 the first ASR will stop responding, then at *:20 and *:50 the second ASR will stop responding, I am querying both ASR's from multiple clients, just incase its a client issue and the same thing occurs on both clients.

its almost like there is some sort of 30 min garbage collection timer that blocks snmp queries to IFMIB but not say the hostname mib (tested).

also I havn't confirmed this, but the more interfaces the ASR has the longer the outage, eg the 4.3.4 ASR which has maybe 100 interfaces has an snmp outage for about 1 minute, whereas the the 4.2.3 ASR has 400 interfaces seems to have a few minutes of outage time...

btw - icmp/ping to each is working properly (i have a script which runs every second, first pings and then snmpget's, the ping always works, the snmpget stops every 30 mins or so)

xthuijs
Cisco Employee

thanks for that notification davecs, I did not expect that in 434 where we have put a lot of improvements in place.

the "outage time to number of interfaces" seems suspicious and a resurrection of a previous problem that I thought

was fixed.

I may need to ask you to file a tac case to have this investigated in depth asap so we can identify the reasoning for this issue and address it if necessary.

regards

xander

davecs
Beginner

Yeah I logged a TAC case and they told me to use "snmp-server ifmib stats cache" (and a restart of snmpd) which worked straight away on 4.3.4, but didn't work at all on the other three ASR's running 4.2.3.

BUT I just had another look and my cacti graphs started looking gappy again, and log show snmp timeouts...

Something interesting, I also graph CPU, when I initially enabled stats cache (on 4.3.4) one of the four CPU basically went idle instead of peaks every 30 mins, now that the graph has returned to "gappy mode" that CPU is back to it's 30 min peaky behaviour.



xthuijs
Cisco Employee

davecs,

yup leveraging the cache is key for good snmp performance.

the 30 min spikes you see, needs to be correlated to something, it could be the snmp process, it could be something else periodic.

also it may help to increase the timeout on your snmp requests, especially when long mib walks are done.

considering you have a tac case open, perhaps we can drive it through that channel, and we can report back on thsi discussion when the situation is resolved for everyone's awareness. otherwise we may be duplicating efforts potentially.

regards

xander

davecs
Beginner

short answer = solarwinds topology mapping (occurs at a 30 min interval)

disable or change (ie max) the interval and it fixes the ifmib problems.

long answer = hopefully TAC/DE can work out what OID is causing snmp ifmib to hang

fjordan
Beginner

davecs,

We have this exact same problem; gaps in cacti graphs.

We opened a TAC case and found the policer was limiting the SNMP queries and dropping packets.

Do the following command for each location:

show lpts pifib hardware police location 0/0/CPU0

If you have drops listed for SNMP you are being policed by the default policy.

The default of 300pps on the SNMP LPTS policer was causing our drops.

We are considering increasing this from 300pps to a higher value.

Would be interested in if this is your problem as well.

You can email me off line at fmjordan@fsu.edu

Thanks, and hope this helped.

davecs
Beginner

interesting and good to know about this command.

but no there are 0 drops for anything in that list

i believe the problem to be that solarwinds is trying to grab routing tables from the ASR, and perhaps the ASR is blocking on this request...

Alexandr Gurbo
Beginner

Xander,

My question about the periodic MIB data collection and transfer feature is also known as bulk statistics on asr9k. More detail about Bulk Statistics Transfer Options.

Is it possible to download the data to the server that is located in the VRF?

xthuijs
Cisco Employee

hi there,

the destination location is in the form of a url, and in 41 we added the vrf capability to that in this way:

ftp://<ftp-server-ip>;<vrf-name>//<pie-path >

but this was specifically for the install add, so I am not sure if this is going to work also for the snmp bulk stat url. I haven't tried it myself though.

regards

xander

Alexandr Gurbo
Beginner

Xander,

Thank you for quick reply. I tried. For snmp bulk stat url doesn't work vrf-aware mechanism. May be in future IOS XR releases will be support vrf-aware feature.

Alexandr Gurbo
Beginner

Xander,

I found with you help that it works for tftp.

url primary tftp://192.168.x.x;Mgmt/

without filename after last slash. All other combinations doesn't work for tftp.

For ftp doesn't work in any my combinations. With anonymous ftp, with authenticated ftp user, with/without filename after last slash, with "ftp client vrf Mgmt username/password".

xthuijs
Cisco Employee

do you see the connection attempt going out when using FTP or there is nothing happening? Looking at the ddts that provided support for that ;<vrf> it tells me this is in the base infra that takes a url input, hence should also be applicable to this CLI in question.

With that a case/ddts is probably warranted.

Also see if it makes a difference using a mgmt interface on the RSP vs a fabric enabled interface on a linecard.

thanks for the testing btw!

cheers

xander

ajc
Rising star
Rising star

Hi Xander,

We have a brand new ASR9K and I was wondering if we should monitor this device in the same way we do with our 6500, 4900, 7500, etc. I mean, monitor the interfaces status, drop packets counters, etc; or we should consider another important variable based on the complexity added by this kind of device. Do you have any recommendations about this you could provide me?

thanks

Abraham

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