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eduardomora473
Beginner

CEF recursive lookup

I am verifying the routing in a network and i see in the cef table that the field of interface appears as <recursive> so i am not really sure if this is a problem and the router are performing recursive lookups for each packet. The router are receiving the hole internet table from its peers. The output is something like this:

 

show ip cef

Prefix                                    Next Hop                  Interface
------------------- ------------------- ------------------
0.0.0.0/0                              drop                       default handler
0.0.0.0/32                          broadcast
1.0.0.0/24                      10.10.10.10/32            <recursive>
1.0.4.0/22                      10.10.10.10/32            <recursive>
1.0.4.0/24                      10.10.10.10/32            <recursive>
1.0.5.0/24                      10.10.10.10/32            <recursive>
1.0.6.0/24                      10.10.10.10/32             <recursive>
1.0.7.0/24                      10.10.10.10/32             <recursive>
1.0.64.0/18                    10.10.10.10/32             <recursive>
1.0.128.0/17                  10.10.10.10/32             <recursive>
1.0.128.0/18                  10.10.10.10/32            <recursive>
1.0.128.0/19                  10.10.10.10/32            <recursive>

 

 

Is this an issue? The router is performing recursive lookups for each packet? If this is a problem how can i solve it?

 

Thanks in advance

1 ACCEPTED SOLUTION

Accepted Solutions

Hi @eduardomora473 ,

 

It is hard to say without knowing your network and design. Unless you use some form of traffic engineering that changes the traffic flow, MPLS should normally not add delay. 

 

Regards,

Harold Ritter
Sr Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México
Paseo de la Reforma 222
Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México

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3 REPLIES 3
Harold Ritter
Cisco Employee

Hi @eduardomora473 ,

 

There is absolutely nothing wrong with CEF recursive entries. CEF resolves the recursive entry as soon as it becomes aware of the path and updates it if there is any change in the network. This is not done on a per packet basis.

 

Regards,

Harold Ritter
Sr Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México
Paseo de la Reforma 222
Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México

Thanks @Harold Ritter  I am asking because I notice that in the network the latency has augmented significantly after MPLS was configured, and I think that could be that the routers has a wrong configuration or there is a process that should not be made. The network has several routers running MPLS and borders connecting to ISPs. Do you know what could cause a grow in the latency after configure MPLS?

Hi @eduardomora473 ,

 

It is hard to say without knowing your network and design. Unless you use some form of traffic engineering that changes the traffic flow, MPLS should normally not add delay. 

 

Regards,

Harold Ritter
Sr Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México
Paseo de la Reforma 222
Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México

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