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Cisco Bug: CSCtd28031 - Incorrect mpls mtu when interface manager returns EAGAIN

Last Modified

Jan 08, 2017

Products (1)

  • Cisco Carrier Routing System

Known Affected Releases

3.6.2.BASE

Description (partial)

Symptom:

- Incorrect MTU for MPLS forwarding entries:

sho mpls forwarding interface tenGigE 0/0/5/0 detail
<snip>
16002  Pop         <prefix>     Te0/0/5/0    <next hop> 1273896609
     MAC/Encaps: 14/18, MTU: 1520   <=================

- Incorrect MPLS MTU on the interface:

sh im chains tenGigE 0/0/5/0
TenGigE0/0/5/0, nodeid:0x1 control chains:
--------------------------------------------

Interface  TenGigE0/0/5/0, ifh 0x01080080 (up, 4484)
  [pic:0x26404, intf_flags:0x2005]
  Protocol        Caps (state, mtu)
   <base>          qos_out (up, 4484)
                   ether (up, 4484)
   mpls            mpls (up, 0)  <============
   arp             arp (up, 4470)
   ipv4            ipv4 (up, 4470)
   ether_sock      ether_sock (up, 4470)

- Incorrect mtu in show mpls int location:

sh mpls interfaces location 0/0/CPU0
Tue Nov 10 12:29:17.354 MET gmt
Interface      IFH         MTU 
-------------- ---------- -----
<snip>
Te0/0/5/0      0x01080080  1520
<snip>

- Errors in the traces:

show mpls io trace location 0/0/CPU0
<snip>
Mar  6 09:12:45.530 mpls/io/ma/rare 0/0/CPU0 t1  ERR|INTF:501: 'mpls_io_mtu_updatecfg mtu-mtu_update' failed, intf='0x1080080', if name='Te0/0/5/0', rc='ifmgr' detected the 'try again' condition 'Try the operation again'

Mar  6 09:12:45.534 mpls/io/ma/rare 0/0/CPU0 t1  ERR|INTF:519: 'mpls_io_mtu_updateimWAck_cfg_keep_mtu_update' failed, intf='0x1080080', if name='Te0/0/5/0', rc='ifmgr' detected the 'warning' condition 'Incorrect state in the FSM'

Conditions:

In 3.6 and older releases, it's possible that IM would return EAGAIN for an MTU operation and the mpls code would not handle this correctly when an mpls mtu is configured.

This issue will not be hit in 3.7 onwards since IM no longer returns try-again for mtu operations.
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