Tag Archives: Cisco

Avoid Cisco FIB/TCAM exhaustion on full BGP table feed

The number of IPv4 prefixes in the global BGP table is approaching the limit of many Cisco products, such as 7600/6500 RSP720/Sup720 and some ASR1000, which may hold a maximum of ~500K routes in their FIB (the Forwarding Information Base, where only best paths are stored).

These routers can usually handle a bigger load of prefixes, they can also be used to receive the full BGP table from many upstream providers concurrently, but they can’t manage more than 500/512K entries in their RIB or FIB.

Routing protocols to FIB

Read more …

Cluster fencing using SNMP fence_ifmib and Cisco switch

Fencing is a vital component in a virtualization cluster; when a cluster member fails it must be inhibited to access shared resources such as network disks or SAN, so that any virtual machine still running on it could be restarted on other members, being sure that no data will be corrupted because of simultaneous access.

Many methods exist to fence failed cluster members, mostly based on powering them off or on disconnecting their network cards; here I would like to show how to use network fencing on a Linux cluster environment (Cman based), using the fence_ifmib against a Cisco managed switch.

The logic behind this mechanism is very simple: once a node has been marked as dead the agent uses the SNMP SET method to tell the managed switch to shut the ports down.

Read more …

Graphing near realtime PPPoE/PPPoA link speed using SNMP Traffic Grapher (STG to its friends)

Sometimes it happens to me that, for troubleshooting reasons, I need to graph PPPoE or PPPoA connections speed from the NAS/BRAS side. These links are terminated on Cisco routers, where other hundreds of CPEs are connected; connections are from dialin users and I can’t have static graphs, mostly because I don’t need endusers monitoring on a fulltime basis and it would only be a huge waste of resources.

In this case a little program helps me: STG, SNMPTrafficGrapher.

STG - SNMPTrafficGrapher

STG – SNMPTrafficGrapher

It’s a small Windows utility that uses SNMP to get counters data and put them on a graph, like MRTG does. It’s easy and fast to deploy (run it, set SNMP OID and it’s ready), does not use many resources and can give you graphs updated every second.


From the View / Settings menu you just have to set the device’s IP address and SNMP community, and then to select OID and polling frequency.

As said, users have dialin connections which go up and down and there is no way to predict their SNMP interface’s index; to obtain the right OID we can use the show snmp mib ifmib ifindex command.

Initially we get the actual Virtual-Access interface for the user we need to monitor:

Router#sh users | include MyUserName
  Vi1.195      MyUserName	   PPPoATM      -

Then we get it’s SNMP index:

Router#show snmp mib ifmib ifindex Virtual-Access 1.195
Interface = Virtual-Access1.195, Ifindex = 257

And finally we can use it to configure STG:

STG setup

Geen OID = (ifInOctets.257)
Blue OID = (ifOutOctets.257)

Where 257 is the dynamic SNMP ifIndex of our user’s Virtual-Access interface.


STG homepage: http://leonidvm.chat.ru/

Zabbix: monitoring HSRP on Cisco devices

On the basis of my previous post Cisco HSRP monitoring using SNMP I decided to extend the Zabbix lightweight dynamic template for SNMP routers by adding a new template, which uses part of the configuration already seen in order to monitor Cisco HSRP status. Here it is: Template_Cisco_HSRPGroup.

What we need is to have a trigger fired when a device changes its HSRP state on the LAN side; with the right configuration it may help to understand when something goes wrong on the WAN side.

As seen on the Cisco HSRP monitoring using SNMP post we need two parameters: SNMP interface ID and HSRP group. We already have the first, because each monitored host has the macro used by the Template_Lightweight_Dynamic_SNMPv2_Router: {$LAN_IF_IDX}. We just have to add a new macro to the host, {$HSRP_GROUP}, where we’ll put the HSRP group number used in the router’s configuration, and use it in the new template’s items:

Description: HSRP Group {$HSRP_GROUP} state
SNMP community: public
Key: cHsrpGrpStandbyState

Description: HSRP Group {$HSRP_GROUP} active IP
SNMP community: public
Key: cHsrpGrpActiveRouter

Description: HSRP Group {$HSRP_GROUP} standby IP
SNMP community: public
Key: cHsrpGrpStandbyRouter

At this point we add 3 more macros to tell Zabbix which values we expect to find for the HSRP group state, active IP and standby IP: {$HSRP_GROUP_EXPECTED_STATE}, {$HSRP_GROUP_EXPECTED_ACTIVE_IP} and {$HSRP_GROUP_EXPECTED_STANDBY_IP}.

Here are the host macros used by Template_Lightweight_Dynamic_SNMPv2_Router and by the new Template_Cisco_HSRPGroup:

Simple triggers will notice unexpected behaviour:

Name: Unexpected HSRP group state
Expression: {Template_Cisco_HSRPGroup:cHsrpGrpStandbyState.last(0)}#{$HSRP_GROUP_EXPECTED_STATE}
Severity: High

Name: Unexpected HSRP active router
Expression: {Template_Cisco_HSRPGroup:cHsrpGrpActiveRouter.str("{$HSRP_GROUP_EXPECTED_ACTIVE_IP}")}=0
Severity: High


Here you can find the XML Template: Template_Cisco_HSRPGroup.zip

Cisco HSRP monitoring using SNMP

Cisco HSRP MIB is defined in CISCO-HSRP-MIB and CISCO-HSRP-EXT-MIB; for a basic SNMP monitoring the first MIB is more than enough.

The most important table in order to get HSRP status information is cHsrpGrpTable, where we can find as many cHsrpGrpEntry objects as HSRP groups configured in the router. Each cHsrpGrpEntry object represents the HSRP configuration and status for a given HSRP group number on a given interface; it has, so, a double index: SNMP interface ID and HSRP group number.

Here is an example of a snmpwalk over a router:

root@NMS:~# snmpwalk -v 2c -c public .
iso. = STRING: "cisco"
iso. = Gauge32: 255
iso. = INTEGER: 1
iso. = Gauge32: 0
iso. = INTEGER: 2
iso. = Gauge32: 0
iso. = Gauge32: 0
iso. = Gauge32: 3000
iso. = Gauge32: 10000
iso. = IpAddress:
iso. = INTEGER: 1
iso. = IpAddress:
iso. = IpAddress:
iso. = INTEGER: 6
iso. = Hex-STRING: 00 00 0C 07 AC 0A
iso. = INTEGER: 1

The first highlighted value is the SNMP interface ID: you can get the SNMP ID for a given interface using the show snmp mib ifmib ifindex command:

CiscoRouter#show snmp mib ifmib ifindex FastEthernet 0/1
Interface = GigabitEthernet0/1, Ifindex = 2.

The second highlighted value is the HSRP group, the one you use while configuring HSRP:

interface FastEthernet0/1
 standby 10 ip
 standby 10 priority 255

In order to monitor the HSRP group state you just have to grab the cHsrpGrpStandbyState parameter (OID iso., which can have one of the following values:

1: initial
2: learn
3: listen
4: speak
5: standby
6: active

In my previous example the router was in the active state.


Cisco.com: Hot Standby Router Protocol Features and Functionality



Wikipedia: HSRP