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NE5000E Fails to Implement Load Balancing of MPLS LSPs Due to the Incorrect Configuration on the Peer Device

Publication Date:  2013-09-03 Views:  35 Downloads:  0
Issue Description
The networking is as follows.

Each NE5000E has four links to NE40E-1 and NE40E-2 for load balancing, whereas each NE5000E has only one LSP to NE40E-1 (load balancing is not implemented) and has only one outbound interface configured. The following uses NE5000E-1 as an example.

//Only one outbound interface of the LSP is configured to NE40E-1.
<NE5000E-1>display  mpls  ldp  peer
 
 LDP Peer Information in Public network
 A '*' before a peer means the peer is being deleted.
------------------------------------------------------------------------------
PeerID                 TransportAddress   DiscoverySource
 ------------------------------------------------------------------------------
218.X.Y.115:0      218.X.Y.6      GigabitEthernet4/0/0  

//Four outbound interfaces of the LSP are configured to NE40E-2.

 218.X.Y.122:0      218.X.Y.122    GigabitEthernet5/0/2
                                                           GigabitEthernet5/0/3
                                                           GigabitEthernet4/0/3
                                                           GigabitEthernet4/0/2


Handling Process
1. On NE5000E-1, configurations of the four outbound interfaces to NE40E-1 are similar. The following uses interface GE4/0/0 as an example:
<NE5000E-1>dis cu interface  g4/0/0
#
interface GigabitEthernet4/0/0
description to_C7606-A
undo shutdown
ip address 218.X.Y.5 255.255.255.252
traffic-policy tuisong inbound  //Delivery policies on the interfaces are the same.
ospf cost 100   //OSPF cost is set to 100 for the interfaces.
mpls          //MPLS and MPLS LDP are enabled on the interfaces.
mpls mtu 1548
mpls ldp
#
 
Routes from NE5000E-1 to NE40E-1 work in load balancing mode.
<NE5000E-1>display  ip routing-table 218.X.Y.115
Route Flags: R - relay, D - download to fib
------------------------------------------------------------------------------
Routing Table : Public
Summary Count : 4
Destination/Mask    Proto  Pre  Cost       Flags NextHop         Interface
 
218.X.Y.115/32  O_ASE  150  20           D   218.X.Y.6   GigabitEthernet4/0/0
                             O_ASE  150  20           D   218.X.Y.14  GigabitEthernet5/0/0
                             O_ASE  150  20           D   218.X.Y.26  GigabitEthernet4/0/1
                             O_ASE  150  20           D   218.X.Y.18  GigabitEthernet5/0/1
 
The NE5000E-1 has only one LSP to NE40E-1. Load balancing is not implemented.
<NE5000E-1>dis mpls lsp include 218.X.Y.115 32
-------------------------------------------------------------------------------
                 LSP Information: LDP LSP
-------------------------------------------------------------------------------
FEC                In/Out Label  In/Out IF                      Vrf Name      
218.X.Y.115/32 NULL/3        -/GE4/0/0                                    
218.X.Y.115/32 1221/3        -/GE4/0/0                                     
<NE5000E-1-FZ1>
 
On NE5000E-1, the TCP transport address of NE40E-1 is a direct address, not a loopback address.
<NE5000E-1>display  ip routing-table 218.X.Y.6
Route Flags: R - relay, D - download to fib
------------------------------------------------------------------------------
Routing Table : Public
Summary Count : 1
Destination/Mask    Proto  Pre  Cost       Flags NextHop         Interface
 
  218.X.Y.4/30  Direct 0    0            D   218.X.Y.5   GigabitEthernet4/0/0
 
2. The NE40E-1 interface may have the TCP transport address of MPLS LDP configured as the interface address. Check configurations on the NE40E-1. The mpls ldp transport-address interface command has been configured on the NE40E-1 interface.
Root Cause
The mpls ldp transport-address interface command has been configured on the NE40E-1 interface.
Solution
To implement load balancing of LSPs, a loopback address must be configured as the LSR ID and each interface uses this loopback address as the TCP transport address. Delete the mpls ldp transport-address interface configuration on eight ports of NE40E-1 to rectify the fault.
Suggestions
1. When the MPLS LDP session is set up, the first Hello packet is a UDP packet sent to the multicast address 224.0.0.2. The source address is the IP address of the local interface and the destination port number is 646. The LSR ID is also identified in the packet. When the interface of NE40E-1 is enabled with MPLS LDP, it sends Hello packets to the remote interface. NE5000E receives the Hello packets with the same LSR ID from four interfaces. NE5000E determines that only one MPLS LDP session and one peer need to be set up. The peer address is the LSR ID.

2. Then an MPLS session, that is, TCP connection, needs to be set up. The transport address needs to be used in the TCP connection. If the interface address is used to set up a TCP connection, the source address is the interface address. If the interface address is not used to set up a TCP connection, the source address is the LSR ID. In this example, the preemption mode is used to set up TCP connections on the four links. The TCP connection using the interface address can be set up quickly. NE5000E retains this connection, and other TCP connections are not set up. In this case, only one interface can be used as the outbound interface of the LSP. If the LSR ID is used to establish a TCP connection, NE5000E retains this connection, and four interfaces can be used as outbound interfaces of the LSP through route iteration.

3. Generally, the loopback address is used as the LSR ID. Do not use the interface address to establish a TCP connection.

END