Friday, October 25, 2013

Are the snmp index values for Mpls Tunnels persistent? And how to decode the index values.

A customer was reporting that the mplsTunnelDown SNMP Trap shows a tunnel index, but that the correlating mplsTunnelUp SNMP Trap shows a different tunnel index. We wanted to know if the indexes were persistent.

It looks like this can possibly happen if mpls has to rebuild the lsps (i.e. due to a crash), but not when there is a link flap.

user@PE-router-RE0# run show snmp mib walk mplsTunnelName.29702 
mplsTunnelName.29702.1.2870018049.2870018050 = router-to-MX-1

user@PE-router-RE0# run restart routing 
Routing protocols process signalled but still running, waiting 8 seconds more
Routing protocols process started, pid 1707

user@PE-router-RE0# run show snmp mib walk mplsTunnelName     |  Match router
mplsTunnelName.26096.1.2870018049.2870018050 = router-to-MX-1

user@PE-router-RE0# run show snmp mib walk mplsTunnelName.29702    

user@PE-router-RE0# run show snmp mib walk mplsTunnelName | match router 
mplsTunnelName.26096.1.2870018049.2870018050 = router-to-MX-1

When I flapped a link on the lsp, the tunnel index stayed the same. So something has to happen where rpd has to rebuild the lsps.

The second part is how can you decipher the snmp OID index value.

user@PE-router-RE0> show mpls lsp ingress name router-to-MX-1 
Ingress LSP: 6 sessions
To              From            State Rt P     ActivePath       LSPname      Up     0 *                      router-to-MX-1
Total 1 displayed, Up 1, Down 0

user@PE-router-RE0> show snmp mib get mplsTunnelName.26096.1.2870018049.2870018050    
mplsTunnelName.26096.1.2870018049.2870018050 = router-to-MX-1

2870018049 as an integer and convert to hex to get 0xAB110001.

Split it into 4 octets:
AB = 171
11 = 17
00 = 0
01 = 1

Which is 

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