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yee379_137296's avatar
yee379_137296
Icon for Nimbostratus rankNimbostratus
Nov 07, 2013

snmp mac address and if index query

i normally query for all arp entries using the 

RFC1213-MIB
mib and 
ipNetToMediaPhysAddress
or 
ipNetToPhysicalPhysAddress
oid; the typical output is something like:

IP-MIB::ipNetToPhysicalPhysAddress.13.ipv4."172.18.x.y" = STRING: 0:d0:ff:ee:fc:a
IP-MIB::ipNetToPhysicalPhysAddress.14.ipv4."127.2.0.1" = STRING: 0:23:e9:6e:97:0
IP-MIB::ipNetToPhysicalPhysAddress.17.ipv4."127.1.1.2" = STRING: 0:1:23:45:67:0
IP-MIB::ipNetToPhysicalPhysAddress.17.ipv4."127.1.1.3" = STRING: 0:1:23:45:67:1
IP-MIB::ipNetToPhysicalPhysAddress.17.ipv4."127.1.1.4" = STRING: 0:1:23:45:67:2
IP-MIB::ipNetToPhysicalPhysAddress.17.ipv4."127.1.1.5" = STRING: 0:1:23:45:67:3
IP-MIB::ipNetToPhysicalPhysAddress.19.ipv4."a.b.c.d" = STRING: 0:0:c:7:ac:97

(first an last ip's redacted)

the number before the ipv4 bit usually corresponds to the ifIndex of the interface that the arp was seen on. however, on our ltm box:

IF-MIB::ifIndex.80 = INTEGER: 80
IF-MIB::ifIndex.736 = INTEGER: 736
IF-MIB::ifIndex.752 = INTEGER: 752
IF-MIB::ifIndex.768 = INTEGER: 768
IF-MIB::ifIndex.784 = INTEGER: 784
IF-MIB::ifIndex.800 = INTEGER: 800
IF-MIB::ifIndex.816 = INTEGER: 816
IF-MIB::ifIndex.832 = INTEGER: 832
IF-MIB::ifIndex.848 = INTEGER: 848
IF-MIB::ifIndex.864 = INTEGER: 864
IF-MIB::ifIndex.880 = INTEGER: 880
IF-MIB::ifIndex.896 = INTEGER: 896
IF-MIB::ifIndex.912 = INTEGER: 912
IF-MIB::ifIndex.928 = INTEGER: 928

(as you can see the index's don't match).

how can i match the ifIndex value from 

ipNetToPhysicalPhysAddress
to a real physical description like that presented with 
sysInterfaceName
?

arp
mac_address
management
snmp

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  • VernonWells's avatar
    VernonWells
    Icon for Employee rankEmployee
    Dec 17, 2013

    The ipNetToPhysicalPhysAddress indices match the ifIndex scheme used in the ipv6IfTable. To get the textual representation of the interface names, use ipv6IfDescr. For example:

     

    snmpwalk -c public -v 2c localhost ipNetToPhysicalPhysAddress IP-MIB::ipNetToPhysicalPhysAddress.2.ipv4."192.168.10.17" = STRING: 24:77:3:87:b8:68 IP-MIB::ipNetToPhysicalPhysAddress.8.ipv4."127.1.1.2" = STRING: 0:1:23:45:67:0 IP-MIB::ipNetToPhysicalPhysAddress.8.ipv4."127.1.1.3" = STRING: 0:1:23:45:67:1 IP-MIB::ipNetToPhysicalPhysAddress.16.ipv4."10.11.113.22" = STRING: 0:c:29:c3:86:f1

     

    snmpwalk -c public -v 2c localhost ipv6IfDescr IPV6-MIB::ipv6IfDescr.1 = STRING: lo IPV6-MIB::ipv6IfDescr.2 = STRING: eth0 IPV6-MIB::ipv6IfDescr.3 = STRING: eth1 IPV6-MIB::ipv6IfDescr.4 = STRING: eth2 IPV6-MIB::ipv6IfDescr.5 = STRING: eth3 IPV6-MIB::ipv6IfDescr.8 = STRING: tmm0 IPV6-MIB::ipv6IfDescr.16 = STRING: external

     

    eth0 is the mgmt interface. tmm0 is an internal interface used by TMOS. external is the name of a VLAN (and the only defined VLAN) on this system.