Enhanced Resource Handling Procedures

If the peer and the local LSR do support the Overload Protection Capability it means that the LSR signals the overload state for the FEC type that caused the resource exhaustion as part of the enhanced resource handling mechanism.

To verify if the local router has received or sent the overload status TLV, perform the following:

-[show router ldp session detail]
show router ldp session 192.168.1.1 detail 
-------------------------------------------------------------------------------
Session with Peer 192.168.1.1:0, Local 192.168.1.110:0
-------------------------------------------------------------------------------
Adjacency Type         : Both           State                  : Established
Up Time                : 0d 00:05:48    
Max PDU Length         : 4096           KA/Hold Time Remaining : 24
Link Adjacencies       : 1              Targeted Adjacencies   : 1
Local Address          : 192.168.1.110  Peer Address           : 192.168.1.1
Local TCP Port         : 51063          Peer TCP Port          : 646
Local KA Timeout       : 30             Peer KA Timeout        : 45
Mesg Sent              : 442            Mesg Recv              : 2984
FECs Sent              : 16             FECs Recv              : 2559
Addrs Sent             : 17             Addrs Recv             : 1054
GR State               : Capable        Label Distribution     : DU
Nbr Liveness Time      : 0              Max Recovery Time      : 0
Number of Restart      : 0              Last Restart Time      : Never
P2MP                   : Capable        MP MBB                 : Capable
Dynamic Capability     : Not Capable    LSR Overload           : Capable
Advertise              : Address/Servi* BFD Operational Status : inService
Addr FEC OverLoad Sent : Yes            Addr FEC OverLoad Recv : No     <---- 
// this LSR sent overLoad for unicast FEC type to peer
Mcast FEC Overload Sent: No             Mcast FEC Overload Recv: No
Serv FEC Overload Sent : No             Serv FEC Overload Recv : No
-------------------------------------------------------------------------------

show router ldp session 192.168.1.110 detail 
-------------------------------------------------------------------------------
Session with Peer 192.168.1.110:0, Local 192.168.1.1:0
-------------------------------------------------------------------------------
Adjacency Type         : Both           State                  : Established
Up Time                : 0d 00:08:23    
Max PDU Length         : 4096           KA/Hold Time Remaining : 21
Link Adjacencies       : 1              Targeted Adjacencies   : 1
Local Address          : 192.168.1.1    Peer Address           : 192.168.1.110
Local TCP Port         : 646            Peer TCP Port          : 51063
Local KA Timeout       : 45             Peer KA Timeout        : 30
Mesg Sent              : 3020           Mesg Recv              : 480
FECs Sent              : 2867           FECs Recv              : 16
Addrs Sent             : 1054           Addrs Recv             : 17
GR State               : Capable        Label Distribution     : DU
Nbr Liveness Time      : 0              Max Recovery Time      : 0
Number of Restart      : 0              Last Restart Time      : Never
P2MP                   : Capable        MP MBB                 : Capable
Dynamic Capability     : Not Capable    LSR Overload           : Capable
Advertise              : Address/Servi* BFD Operational Status : inService
Addr FEC OverLoad Sent : No             Addr FEC OverLoad Recv : Yes     <---- 
// this LSR received overLoad for unicast FEC type from peer
Mcast FEC Overload Sent: No             Mcast FEC Overload Recv: No
Serv FEC Overload Sent : No             Serv FEC Overload Recv : No
===============================================================================

A trap is also generated:

70002 2013/07/17 16:06:59.46 PST MINOR: LDP #2008 Base LDP Session State Change
"Session state is operational. Overload Notification message is sent to/from peer 
  192.168.1.1:0 with overload state true for fec type prefixes"

Besides interfaces and targeted peer, locally originated FECs may also be put into overload. These are the following:

- unicast fec-originate pop

- multicast local static p2mp-fec type=1 [on leaf LSR]

- multicast local Dynamic p2mp-fec type=3 [on leaf LSR]

The user can check if only remote and, or local FECs have been set in overload by the resource enhanced resource exhaustion mechanism using the following command:

- [tools dump router ldp instance]

The relevant part of the output is described below:

  Num Entities OLoad (FEC: Address Prefix  ):  Sent: 7           Rcvd: 0   <----- 
// # of session in OvLd for fec-type=unicast
  Num Entities OLoad (FEC: PWE3            ):  Sent: 0           Rcvd: 0   <----- 
// # of session in OvLd for fec-type=service
  Num Entities OLoad (FEC: GENPWE3         ):  Sent: 0           Rcvd: 0   <----- 
// # of session in OvLd for fec-type=service
  Num Entities OLoad (FEC: P2MP            ):  Sent: 0           Rcvd: 0   <----- 
// # of session in OvLd for fec-type=MulticastP2mp
  Num Entities OLoad (FEC: MP2MP UP        ):  Sent: 0           Rcvd: 0   <----- 
// # of session in OvLd for fec-type=MulticastMP2mp
  Num Entities OLoad (FEC: MP2MP DOWN      ):  Sent: 0           Rcvd: 0   <----- 
// # of session in OvLd for fec-type=MulticastMP2mp
  Num Active Adjacencies:    9
  Num Interfaces:            6           Num Active Interfaces: 6
  Num OLoad Interfaces:      0      <----- // link LDP interfaces in resource 
 exhaustion
 should be zero when Overload Protection Capability is supported
  Num Targ Sessions:         72          Num Active Targ Sess:  67
  Num OLoad Targ Sessions:   0      <----- // T-LDP peers in resource exhaustion
 should be zero if Overload Protection Capability is supported
  Num Addr FECs Rcvd:        8667        Num Addr FECs Sent:    91
  Num Addr Fecs OLoad:       1                                    <----- 
// # of local/remote unicast Fecs in Overload
  Num Svc FECs Rcvd:         3111        Num Svc FECs Sent:     0
  Num Svc FECs OLoad:        0                                    <----- 
// # of local/remote service   Fecs in Overload
  Num mcast FECs Rcvd:       0           Num Mcast FECs Sent:   0
  Num mcast FECs OLoad:      0                                    <----- 
// # of local/remote multicast Fecs in Overload
  Num MAC Flush Rcvd:        0           Num MAC Flush Sent:    0

When at least one local FEC has been set in overload the following trap occurs:

69999 2013/07/17 16:06:59.21 PST MINOR: LDP #2002 Base LDP Resources Exhausted
 "Instance state changed - vRtrID: 1, administrative state: inService, operational
 state: inService"

After the user has detected that at least one overload status TLV has been sent or received by the LSR, he/she must protect the router by applying one or more of the following to free resources up:

Identify the source for the [unicast/multicast/service] FEC flooding. This is most likely the LSRs which session received the overload status TLV.
Configure the appropriate [import/export] policies and delete the excess [unicast/multicast/service] FECs from the FEC type in overload.

Next, the user has to manually attempt to clear the overload state on the affected sessions and for the affected FEC types and allow the router to clear the overload status TLV to its peers.

Note:

Because of the dynamic nature of FEC distribution and resolution by LSR nodes, one cannot predict exactly which sessions and which FECs are cleared after performing the following commands if the LSR activates overload again.

One of the following commands can be used depending if the user wants to clear all sessions in one step or one session at a time:

- [clear router ldp resource-failures]

Clears the overload state for the affected sessions and FEC types.
Clear the overload state for the local FECs.

- [clear router ldp session a.b.c.d overload fec-type {services | prefixes | multicast}]

Clears the overload state for the specified session and FEC type.
Clears the overload state for the local FECs.