question about "ip rsvp bandwidth" on the interface

[aljoush12]

Hello Experts, 

Do we need to enable "ip rsvp bandwidth" on the interfaces for MPLS-TE? This is for the ASR920 platform. I have seen some examples of people using "ip rsvp bandwidth" on the MPLS interface without specifying the amount of bandwidth. My understanding is we need to enable "ip rsvp bandwidth" only when we want to reserve bandwidth for MPLS-TE tunnels on an interface. Can you please clarify if we need to enable "IP rsvp bandwidth" for the MPLS-TE on ASR920? I appreciate your response. 

Thank you 

[MHM Cisco World]

The interface have BW and there is rsvp BW 

If you dont specify the BW in ip rsvp command it inherit it value from real BW of interface.

MHM

[aljoush12]

Hi MHM, 

Thank you for your response. Just to confirm we don't need to enable "IP rsvp bandwidth" on the interface for MPLS-TE if we don't want to reserve the bandwidth for tunnels. 

Thank you

[MHM Cisco World]

If you use dynamic path then you need ot if you use explicit path then no need.

MHM

[aljoush12]

Hi MHM, 

Thank you for your response. Can you please explain why we need to enable "ip rsvp bandwidth" on the interface for the dynamic path? If you can refer to me a document, that would be great. I have tested in the lab with and without "IP rsvp bandwidth" on the interface and I have used dynamic path. I saw the same result. 

Thank you

[MHM Cisco World]

Can i see topolgy you use in lab

And you config 

MHM

[Harold Ritter]

Hi @aljoush12 ,

"ip rsvp bandwidth" is required to enable RSVP on an interface. This is required for MPLS TE either you want to use dynamic or explicit path.

https://www.cisco.com/en/US/docs/ios-xml/ios/qos_rsvp/configuration/15-2mt/config-rsvp.html#GUID-13441DBE-6FD4-43BF-B865-624933EE480C

Regards,

[aljoush12]

Hi Harold and MHM, 

Thank you for your response. I did a quick test. So looks like it if we enable "mpls traffic-eng tunnels" on the interface, it automatically enables rsvp on the interface. If we enable "ip rsvp bandwidth" and don't specify bandwidth, rsvp will use 75% of the interface bandwidth for reservations. 

interface GigabitEthernet0/0/22

 mtu 9190

 ip address x.x.x.x 255.255.255.252

 ip ospf network point-to-point

 ip ospf 1 area 0

 mpls traffic-eng tunnels

 bfd interval 300 min_rx 300 multiplier 3

end

#show ip rsvp interface gigabitEthernet 0/0/22

interface    rsvp       allocated  i/f max  flow max sub max  VRF            

Gi0/0/22     ena        0          0        0        0   

interface GigabitEthernet0/0/22

 mtu 9190

 ip address x.x.x.x 255.255.255.252

 ip ospf network point-to-point

 ip ospf 1 area 0

 mpls traffic-eng tunnels

 bfd interval 300 min_rx 300 multiplier 3

 ip rsvp bandwidth

end

#show ip rsvp interface gigabitEthernet 0/0/22       

interface    rsvp       allocated  i/f max  flow max sub max  VRF            

Gi0/0/22     ena        0          750M     750M     0   

[Harold Ritter]

Hi @aljoush12 ,

I stand corrected. "ip rsvp bandwidth" is not required if you do not need to allocate bandwidth. 

Regards,

[MHM Cisco World]

Now in TE tunnel specify tunnel BW to be for example 500

Abd config one path BW 300 and other 200 and check the dynamic path 

Then change BW to he one path 200 and other 300 

See if TE change the path depend on BW you config.

MHM