Introduction to RSVP

(Rene Molenaar) #6

Hi Taylor,

I never tried it on Linux (never had to) and even on Cisco devices I don’t see it very often :slight_smile:

Rene

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(system) #7

Hi Rene…thanks for taking time to put this wonderful post together. I’ve got a question. I did not see anywhere in the article you mentioning WFQ or CBWFQ…isn’t WFQ or CBWFQ a prerequisite for RSVP since the flows reservations are based on their QoS weightings?

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(system) #8

Hi Rene,

Your article is really good about RSVP. I have done my own implementation of RSVP into Linux and it works pretty well (I have the same result in R2 and R3 as you when I replace R1 and R4 by my Linux code). However, when I try to use the reservation done it never works. I have two big data flows going through R2 and R3, one matching the RSVP reservation and the other not. But it’s always the flow that I start first which is prioritary even when the reservation is present.
I guess I’m missing a configuration point, but I didn’t see which one (And I have the exact same configuration for R2 and R3 than you have).

Do you have any idea/lead to point me out?

Regards,
Mandu

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(Rene Molenaar) #9

Hi Mandu,

Glad to hear that it is useful to you. It’s hard to tell why the second data flow isn’t working…I’d have to lab it up and try it…

Rene

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(Rene Molenaar) #10

Hi Sam,

Good comment, RSVP does require WFQ to actually give priority by assigning a low weight. In this tutorial I only focused on RSVP itself and its reservations but this is important to know.

Rene

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(seafarmer11@gmail.com) #11

Great article again so clear… Thnx to you !

As long as I read about that, we are able to implement QoS (DSCP or COS) mechanism for MPLS within EXP bits right instead of RSVP. How is the current MPLS network designs with QoS nowadays? RSVP is first precedence for MPLS ?

Deniz

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(Rene Molenaar) #12

Hi Deniz,

Intserv (RSVP) isn’t used much to give packets a certain treatment, we use Diffserv (DSCP, COS, MPLS EXP bits) for this. The problem with Intserv is that it’s not scalable.

In MPLS environments however, RSVP can be used for traffic engineering.

Rene

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(Mario R) #13

I’m not familiar with this protocol but I’ve heard of RSVP-TE. It is used in my job. Do you cover it in this article or is it in another. I could not find it by searching.

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(Rene Molenaar) #14

Hi Mario,

RSVP TE is used in MPLS VPN networks, I do have examples for MPLS but I don’t have any RSVP TE examples (yet). I’ll create something and will add it here:

Rene

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(Abhishek D) #15

Hi Rene

But the concept of RSVP that you explained here is same in MPLS-TE also right ?

Thanks
Abhishek

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(Rene Molenaar) #16

That’s right.

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(Y W) #17

Hello Rene
I have a question. This configuration sample showed reserve BW between R1 and R4 for telnet traffic, but what if I want to reserve BW for telnet traffic passing though R1 to R4, like I have a host A connecting on R1, and host B connecting on R4, and I’d like to RSVP 64k BW for telnet traffic from A to B which the traffic will passing through R1 and R4, and what if it’s multiple hosts to multiple hosts traffic I want to RSVP? Can you give me an example for that kind of cases?

Thanks a lot.

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(Lazaros Agapides) #18

Hello Y W

In order to understand how RSVP would work with hosts, you can replace R1 and R4 in the topology with two PCs. PCs can also be RSVP hosts and can request or deliver specific levels of QoS. You can even replace them with switches and have several PCs connected to each switch. A PC could still function as an RSVP host and request the bandwidth necessary from end to end.

I hope this has been helpful!

Laz

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(DJAN M) #19

Hello Rene,
I hope u r doing well!
I want to know what in this command line:

R4(config)#ip rsvp reservation-host 192.168.34.4 192.168.12.1 tcp 23 0 ff rate 64 32

The double ff means please?

BR,
Ulrich

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(Rene Molenaar) #20

Hello Ulrich,

I’m doing good, hope you as well!

The “ff” is about the reservation style. There are three options:

• Fixed Filter (ff) is single reservation.
• Shared Explicit (se) is shared reservation, limited scope.
• Wild Card Filter (wf) is shared reservation, unlimited scope.

The fixed filter reservation means that we want to use a reservation for one specific source.

Rene

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(Nguyen Cao V) #21

Hi,
If i have 10 Mbps leased-line connect HQ and Branch and i set up InterSrv or DiffSrv between my 2 edge router . QoS for high priority for a service , example http

1- Qos by DiffSrv : When no congestion on Leased-line ( traffic < 10 Mbps), Qos no affect ? or http traffic going to high priority only when have congestion ?

2- QoS by InterSrv : If i config 2 Mbps for RSVP, allway have only 2 Mbps for http traffic , if over 2 Mbps, it drop . Others traffic can using 8 Mbps ?

Thank .

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(Lazaros Agapides) #22

Hello Nguyen

Your explanation seems to be correct. You have understood the concept correctly.

Laz

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(Timothy R) #23

Hello Rene,

I have a question on rather Integrated Services (RSVP) can be used in MPLS to identify Real Time Protocol (RTP) traffic like voice or video to give it preference over other traffic. I read your explanation on Resource Reservation, and Admission Control. I’m not understanding how RSVP is used to give RTP traffic that is sensitive to packet loss, jitter, and latency priority over other traffic. Could you explain how this can be done?

Thanks
Tim

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(Lazaros Agapides) #24

Hello Timothy

RSVP is used in Cisco Unified Communications architecture in a feature called Call Admission Control (CAC) makes a bandwidth reservation using RSVP along the full length of the path between the two communicating endpoints. Look at the following diagram that comes from Cisco documentation (the link to this document is shown further below).
image
There is a SIP session that is initiated between two user agents (UAs). These can be phones, gateways, conference bridges etc, anything that will terminate a SIP session. The SIP session begins with INVITE, SESSION PROGRESS, and PRACK OK messages between the two devices. Once that is done, the SIP UA1 initiates an RSVP reservation to UA2. This process involves all RSVP enabled routers between the two devices. Once that has successfully been established, the SIP session continues with an exchange of UPDATE messages, and then the phone rings.

So RSVP takes place chronologically between the initialization of the SIP session and the beginning of the actual telephony communication starting with the ringing of the phone.

This whole mechanisms is a subset of a broader concept of CAC which is fundamental for Cisco’s implementation of IP telephony. You can find out more information about this specific portion of CAC at the following link:


Also, a very elegant explanation of RSVP and how it works can be found in the same document at this location:

I hope this has been helpful!

Laz

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(Timothy R) #25

Laz,
Thanks for the detailed explanation. It makes since. The documents are also helpful also. I’m going over them now to get a better understanding of RSVP.

Thanks
Tim

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